for Plant and Soil Science
Plant diseases, pests and weeds in Denmark 1986
103rd annual report Compiled by
The Research Centre for Plant Protection
Lyngby 1988
Plant diseases, p e sts a n d weeds in Denm ark 1986
103rd annual re p o rt Compiled by
The R esearch C en tre for Plant Protection
Lyngby 1988
C ontents Page
A. Institute of P lant Pathology, L y n g b y ... 4
I. Staff II. G en eral survey of plant pathology subjects 1986 ... 4
III. Advisory w o r k ... 14
1. D iseases in agricultural crops 1 9 8 6 ... 17
2. Pests in agricultural crops 1986 ... 21
3. D iseases in horticultural plants 1986 ... 27
4. Pests in horticultural plants 1986 ... 30
IV. B otany D e p a r tm e n t... 32
Experim ental w o r k ... 32
V. V irology D e p a r t m e n t ... 39
1. E xperim ental w o r k ... 39
2. N ew attacks of virus diseases 1986... 47
VI. Zoology D e p a r t m e n t ... 49
1. R outine e x a m in a tio n s...49
2. E xperim ental w o r k ...49
B. Pesticide R esearch Institute, Lyngby... 57
I. S t a f f . ... 57
II. G eneral s u r v e y ...58
III. A griculture...60
IV. F ruit grow ing...71
V. New pesticides tested in 19 8 6 ... 75
C. Plant P rotection Advisory D epartm ent, G o d th å b ... 78
D. Institute of W eed C ontrol, F lakkebjerg ... 80
I. Field of a c tiv ity ...80
II. A g ric u ltu re ... 81
1. Field experim ents concerning developm ent, testing and advisory w o r k ... 81
2. T esting of c o m p o u n d s ... 85
III. H o r tic u ltu r e ...88
IV. C ontrolled Environm ent E x p e rim e n ts ... 91
V. Forestry, w in d b r e a k s ...94
VI. W eed biology, distribution and spreading...101
E . Laboratory fo r Pesticide analysis...102
I. Field of activ ity ...102
II. Effect o f pesticides on m ic ro flo ra ... 102
III. R eg istratio n of pesticides in groundw ater... 103
IV. D egradation of pesticides etc. in s o il... 104
V. Fungicides and pesticides in plants... 104
VI. H erbicides in p la n ts ... 105
F. Publications 107
A. INSTITUTE OF PLANT PATHOLOGY I. STAFF
D irector o f Institute H. R ø n d e K ristensen Botany Department
H ead of D epartm ent: Ib G. D inesen (acting) Scientific staff:
M orgens H oum øller
V irulence analysis of barley and w heat powdery mildew (E rysiphe graminis) A rn e Jensen (from D ecem ber 1)
R etu rn ed from assignm ent as vegetable plant protection officer in Zambia H enrik A lbert Jørgensen (until N ovem ber 30)
D iagnostics of fungi; diseases of horticultural crops and ro o t rot of sugar b eet;
D utch elm disease; registration of scientific literature K aren Jørgensen
D iseases of sour cherries; bacterial diseases of glasshouse crops and fruit trees Lilian Kloster
Studies on the occurrence o f Polym yxa gram inis and P. betae, vectors for barley yellow m osaic virus and Rhizom ania.
Bent Løschenkohl (from F ebruary 1)
Fungal diseases in horticulture; horticultural nuclear stockplants; fungi in recirculating w atering systems; testing of resistance to potato wart disease;
testing o f resistance to po tato wart disease; testing o f disinfection com pounds;
w hite ro t in onion.
H ellfried Schulz
R o o t and foot rot of cereals; take-all decline; survey an d diagnosis o f fungal diseases in peas
Sten Stetter
Threshold values for leaf diseases o f cereals; developm ent o f E P ID A N - a com puter-based sytem for advice on disease control.
Kirsten Thinggaard
R oot diseases in greenhouse crops, especially Pythium and Phytophthora. T esting for races in B rem ia lactucae (lettuce downy mildew)
Boldt Welling
Diseases of cereals and grasses; storage fungi on grain Biotechnology Project
Project leader: Ib G . D inesen Scientific staff:
L one Buchwaldt Fungal toxins T ine Hoff
G ene transfer E lisabeth Johansen
G ene probes H enning Kaufholz
Tissue culture H elle Krogaard
Tissue culture G e rt B. Poulsen Tissue culture Virology Department
H ead of D epartm ent: H . R ø n d e K ristensen
Scientific staff:
Jens B egtrup
E lectron microscopy B ent Engsbro
V iruses of agricultural plants; production of healthy nuclear stocks of potatoes M orten H eide
Serological diagnosis m ethods Niels Paludan
V iruses o f vegetables and ornam ental plants (herbaceous); production o f healthy nuclear stocks
A rn e Thom sen
V iruses o f fruit trees, soft fruit and woody o rnam ental plants; production of healthy nuclear stocks
Zoology Department
H ead of D epartm ent: Jørgen Jakobsen Scientific staff:
P eter Esbjerg
Insect pherom ones and cutworm population dynamics Lars M onrad H ansen
Soil-borne pests on b eet and potatoes; grow er-based m onitoring o f p ests in cereals
Lise Stengaard H ansen
Biological and integrated control of pests on glasshouse crops Jørgen Jakobsen
Plant-parasitic nem atodes
Fritiof Lind
Pests on oil-seed rape; threshold values for pests in cereals; m ethods for testing insecticides
Jørgen R eitzel (until N ovem ber 30)
Aphid population dynamics, particularly on potato and cereal crops; mass production of parasitic and predatory species of insects and m ites used for biological control o f pests in glasshouses
Lise Sam søe-Petersen
M ethods for testing side effects of pesticides on beneficial arthropods Advisory service
Ghita C ordsen N ielsen
Pests and diseases o f agricultural plants Lars A. H obolth
Pests and diseases o f horticultural plants
II. GENERAL SURVEY O F PLANT PATHOLOGY SU B JEC TS 1986, H. RØNDE K R ISTEN SEN
In 1986 26 research w orkers and 30 laboratory attendants an d other staff m em bers w ere em ployed at the Institute o f Plant Pathology.
F urtherm ore, 8 students and 8 laboratory trainees as well as 1 person w orking under the G overnm ent Em ploym ent Scheme participated in th e work carried o u t by the institute.
B ent Løschenkohl was transferred (from the Pesticide R esearch Institute) to th e Botany D ep artm en t from F ebruary 1, and H enrik A lb ert Jørgensen left th e d epartm ent on N ovem ber 30 after working for 36 years with plant pathology.
S. S. A hsan from Pakistan spent 4 m onths working at the V irology D epartm ent.
Jørgen R eitzel left the Zoology D epartm ent after nearly 25 years, and F. L ind left the departm ent on D ecem ber 31.
M uham m ed R iaz Jam il from Pakistan visited the Zoology D e p artm en t for 2 months.
O ver the years, testing of sam ples from various trials for fungal diseases has been carried out at the Botany D epartm ent.
T he threshold investigations concerning leaf fungi in cereals were continued as well as the virulence m onitoring, which included exam ination o f the strain spectrum of barley and w heat mildew from different parts o f D enm ark.
Soil sam ples from fields with w inter barley and beet w ere analysed for the presence of Polym yxa gram inis and Polym yxa beta, respectively.
N um erous new D anish potato hybrids w ere tested for resistance against p o tato w art disease.
T he work on developm ent of a suitable system of forecasting attacks of Sclerotinia sclerotiorum in rape was continued, and in view of the m uch increased area w ith fodder peas, a survey of the distribution of fungal diseases in this crop was w orked out, and seed was tested for seed-borne fungi.
F u rth erm o re, num erous seed-borne isolates of Botrytis spp. w ere tested for fungicide resistance (M B C resistance).
In cultures o f greenhouse-grow n lettuce exam inations o f different strains of Brem ia lactacae w ere carried out, and guidance was given as to the choice of resistant varieties. Bacterial as well as fungal diseases in a num ber o f p o t plants have been included in the investigations carried out by the Botany D epartm ent, especially in connection with the establishm ent of healthy nuclear plants.
W ater from nurseries using recirculated nutrient solutions in soilless cultures was examined for content of root-pathogenic fungi (Phytophthora and Pythinum species).
In cooperation w ith the Botany D epartm ent the Zoology D epartm ent carried out registrations o f mildew, rust and aphids in a great num ber of spring barley fields;
this work was the basis for direct guidance about control m easures and for P lant Protection Bulletins.
Density d eterm ination in Ju n e/Ju ly of aphids in spring barley and w heat was carried out in o rd e r to determ ine the econom ic dam age threshold.
A s an aid in establishing the right tim e for haulm destruction in potato fields (to prevent late infection by potato viruses), aphid sam ples from yellow tray traps placed in different localities were analysed.
For many years, the Zoology D epartm ent has carried out routine exam inations for potato cyst nem atodes in soil sam ples; a great num ber o f these sam ples originated from the P lant Protection Service. Since Septem ber 1986, this Service has been carrying out these examinations in their own laboratories.
In rape, a survey was m ade of the m ost im portant pests by examining plant samples and insect catches in traps.
Besides, econom ic dam age thresholds and forecasting m ethods have b een developed at the Zoology D epartm ent.
Various investigations have also been carried out concerning the pea and bean weevil in peas as well as cutworm s in carrots.
A special research project aim ed at developm ent of standard m ethods of controlling the effect of pesticides on beneficial arthropods.
Also the flow er thrips, Frankliniella occidentalis, has been involved in trials with chemical as well as biological control.
A t the Virology D ep artm en t the work on the developm ent o f various diagnostic m ethods was continued w ith special em phasis on the m ethods o f dot im m unobinding and ELISA.
T he ISE M m ethod com bining the use of the electron m icroscopy with serology has been m uch used; during the year, about 3500 ISEM analyses w ere carried out.
A t present, 225 antisera are available at the D epartm ent, so th a t a quick diagnosis is often possible.
In the electrophoretic field, work is in progress regarding the analysis of viroids.
C urative work was carried out on a fairly large scale using h eat therapy as well as tissue culture.
In this connection, long-tim e storage in vitro took place using the following plant genera: Arabis, Begonia, Cam panula, Chrysanthemum, Dieffenbachia, D ipladenia, Euphorbia, H em erocallis, K alanchoe, Lavandula, Pelargonium, P en tas and Phlox.
T he E E C project (C O ST 87) with m icro-propagation of th e apple rootstock M M 26 was continued and extended to include M IX as a m odel plant.
A similar E E C project concerning m icro-propagation of Pelargonium in connection with the elim ination of pathogens was concluded after th ree years’ experiments.
A t the sam e time, a new project regarding m icro-propagation of forestry plants using Betula and Quercus as m odel plants was initiated.
A t the Virology D epartm ent, antiviral com ponents has been added to the grow th m edia used for the tissue culture experiments.
T o a lim ited extent, m onitoring o f virus diseases took place in cocksfoot, m aize, peas, wheat, barley and beet.
Special interest was attached to the examinations of w inter barley and b e e t fields for barley yellow mosaic and rhizomania. However, none of these diseases have been found in D enm ark so far.
In com m ercial orchards, surveys have been carried out concerning Prunus ringspot, cherry rasp leaf and little cherry.
F urtherm ore, re-testing of nuclear stocks of apples, p ears and cherries was initiated.
In Septem ber 1986, plum pox (Sharka) was recorded for the first tim e in D enm ark.
This finding resulted in a considerable am ount o f extra work for the Virology D epartm ent - especially in the field of diagnostics.
Advisory work
In 1986 the staff m em bers m ade altogether 77 journeys abroad visiting the following countries: Belgium , E ngland, Finland, France, G erm any, G reenland, Indonesia, Kenya, the N etherlands, Norway, Poland, Portugal, Sweden, Switzerland, Tanzania, the U nited States and Yugoslavia.
Among the subjects dealt with during these travels w ere po tato ringrot, virus yellows and rhizom ania o f beet, fruit tre e viruses, soil-borne viruses, diseases o f grasses, pathogenic Pythium species, viroids and their detection, resistance biology, integrated control of fungal diseases, biological control of fungi, biological control of thrips, pherom ones, pesticides and beneficial organisms, entom ology in the tropics, p o tato tissue culture, m eristem culture of woody plants and international cooperation ab o u t plant protection.
Several visitors from abroad visited the Institute of Plant Pathology. In 1986 visits by colleagues from the following countries were received: Belgium, B urm a, China, Czechoslovakia, Egypt, England, Finland, France, G erm any, Hungary, Ireland, Israel, Italy, the N etherlands, Norway, Pakistan, Scotland, Switzerland, Somalia, Spain, Sri L anka and Sweden.
Plant Health Control and Propagation of Healthy Plants
On May 21st th e P lant H ealth Council celebrated its 40th anniversary.
The council was set up by the Ministry of A griculture in 1946, the sam e year as the Plant P ro tectio n Service was established as a separate institution directly under the M inistry of Agriculture. Originally, the Council acted as a governing committee to the Service, but today the Council is an advisory body assisting the M inister o f A griculture and the Plant Protection Service in their efforts to control and prevent the introduction and spread of agents harm ful to plants, and giving advice on o th er questions o f plant health.
During the past forty years the Council has taken up num erous problem s and has had a g reat influence on D anish plant health legislation.
The Council has furtherm ore participated in international cooperation regarding the control o f harm ful organism s threatening plants.
Over the years the chairm an o f the Council has been a p erm an en t representative o f D enm ark in the council o f E uropean and M ed iterra n ean Plant Protection O rganization (E P P O ) and he has several tim es been a m em b er o f the executive com m ittee as well as several o ther com m ittees, such as th e editorial board, the phytosanitary panel, etc.
Since D enm ark joined the E E C , m em bers of the D anish P lant H ealth Council have participated in a large num ber of m eetings in B russels in connection w ith the p rep aratio n of the E E C Plant H ealth Directive, and for two periods, the form er vice-chairm an of the Council functioned as chairm an of the working group on plant health set up by the Council of M inisters.
A t present, the secretary of the D anish Plant H ealth C ouncil and the Council’s legal adviser are m em bers of the E E C standing com m ittee on plant health.
The P lant H ealth Council can be involved in all questions concerning plant health;
b ut the m ain concern of the Council is m atters relating to dangerous organisms, i.e. those u nder public control.
A t the m om ent, this category includes black rust o f w heat (the growing of all susceptible Berberis species is prohibited), mildew and rust o f barley (compulsory treatm ents o f fields with w inter barley), wild oats, po tato w art, potato ring rot, the C olorado p otato beetle, po tato cyst nem atodes, the carnation leaf roller, fireblight, the San José scale and the m uskrat.
T he first com prehensive plant disease law dates from 1927. In 1957 another law was passed about the control of dangerous plant diseases and pests.
T he present legislation is based on "Law about agents harm ful to plants" from 1984.
D uring 1986 the Plant H ealth Council treated questions regarding Dutch elm disease, fireblight, red core of strawberry, potato ring rot, barley yellow mosaic, rhizom ania, potato cyst nem atodes, the A m erican flower thrips and several other m atters.
D utch elm disease spread to m ore areas in 1986, especially in the eastern p art o f Jutland.
E radication o f this disease is considered impossible, b u t th e spread can be considerably delayed by im m ediate rem oval of diseased trees.
Fireblight was not very severe in 1986, and th ere was only one re co rd o f the Colorado beetle.
N either red core o f straw berry nor barley yellow mosaic o r rhizom ania have so far been found in D enm ark. Legislation preventing the introduction o f these pathogens is u n d er preparation.
In 1986, the A m erican flower thrips dam aged cultures of Gerbera, Chrysanthem um, Saintpaulia and roses.
In the autum n of 1986 Plum pox (Sharka) was found in a fruit tre e variety trial where 9 varieties w ere infected. All diseased trees w ere destroyed, and comprehensive m easures w ere taken to ensure com plete eradication of the disease.
T he potato m eristem program m e, which was initiated in 1977, has been successfully concluded, and in accordance with an order from the M inistry of A griculture, a total replacem ent o f all seed potatoes in the D anish com m ercial potato production took place during 1985 and 1986. Consequently, all the seed potatoes which are planted out, originates from the m eristem program m e.
The Nursery C o n tro l Com m ission carried on as usual in 1986.
T he compulsory plant health control com prised 2243 enterprises in 1986 w here the total n u m b e r of inspections carried out by the Plant P rotection Service am ounted to 6100.
T here has b ee n a considerable decrease in the num ber o f attacks of pests and diseases registered during the last few years.
T he production o f healthy nuclear plants which is a result o f a cooperation between the N ursery C ontrol Commission, T he Institute for Plant Pathology and other relevant horticultural research institutes reached quite considerable dimensions.
A t present, healthy plant m aterial is available for 262 varieties of plant genera for use outdoors as well as in greenhouses.
III. ADVISORY WORK. Ghita Cordsen Nielsen and Lars A. Hobolth.
A s in previous years, the advisory work was carried out b o th at Lyngby a n d at the P lant P rotection Advisory D ep artm en t at G odthåb, Skanderborg, which prim arily deals with the enquiries from Jutland.
A s for articles and reports, see the list o f publications.
T he d epartm ent again sent out handbooks in plant protection for use by grow ers and agricultural advisors.
45 Plant P rotection Bulletins w ere issued in 1986.
W eather conditions fJflrpen E. O lesen, the A grom eteorological Serviced
A s a whole, January was som ew hat colder and had m ore precipitation than usual.
T he cold w eather was particularly pronounced during the first third of the m onth, w here th ere was a heavy snowfall. D uring the rest o f the m onth the w eather was mostly m ild and w ithout m uch snow. By the end o f the m onth, the w eather was dry and windy, so that soil drift occurred in several places.
In F ebruary the w eather was very cold, dry and sunny. T h e average tem p eratu re for the whole of the country was 4.8°C below norm al. T h e 3 mm precipitation m ade F ebruary 1986 the driest F ebruary ever registered. T h e cold weather w ithout m uch snow cover had the effect that the fields w ere m ore or less u n protected against the cold during m ost o f the m onth.
T he very cold w eather in F ebruary continued for the first few days of M a rc h . T hen mild air from the A tlantic invaded the country. A s a whole, the w eath er was grey and dry for the first 3 weeks of M arch and th en unstable with heavy rainfall. T hus the te m p eratu re for the whole of the m onth was a little below and the precipitation m uch above norm al.
A pril was m ostly cold for th e first three weeks. Sunny w eather did not occur until the last week, w here day tem peratures of up to 15° were registered in areas away from the coast. From the 10th to the 15th the w eather was cold with frost during the day in m any places and night tem p eratu re down to 10 C below zero.
In M av the tem p eratu re fluctuated around the norm al average tem perature for the m onth. D uring the first 4-5 days the w eather was dry, sunny and w arm , w hereas it was changeable during the rest of the m onth. T hus the May rainfall was considerably above norm al.
During the first half of June the w eather was cold and unsettled. F o r the last two weeks it w as dry, sunny and warm . T h e tem p eratu re for the whole o f the month was close to norm al, w hereas the rainfall was considerably below norm al.
The hot and sunny w eather of June continued for a few days in July. T he w eather during rest o f the m onth was dry and cold. T he average tem p era tu re for the whole of the country was 0.7°C below norm al, and the rainfall was 23 m m below normal. H ow ever, the rainfall was very unsteady and mostly in connection with thunderstorm s. T hus a fierce thunderstorm on the 24th was accom panied by m ore than 100 m m rainfall at several places in Storstrøm s A m t (S outhern Z eeland, Lolland, F alster, etc.)
During the first half of A ugust the w eather was mostly dry and sunny. T hen there was a cool and grey spell with som e rain. O n the 25th tem p eratu res near zero was registered in several places in C entral Jutland.
In Septem ber b o th tem p eratu re and rainfall w ere considerably below norm al. T he average day-and-night tem perature only rose above norm al during the last few days of the m onth. T he highest maximum tem p eratu re registered in any p a rt of the country w as 18.2°C, which is the lowest ever registered for th e m onth of September.
For the first two weeks of O ctober the w eather was mostly dry and w arm , w hereas it was unsettled and rainy for the last two weeks.
The te m p eratu re and precipitation in N ovem ber was som ewhat above norm al, and the w eather w as influenced by mild and som etim es moist air from the A tlantic.
However, frost occurred in m ost places at the beginningof the m onth.
D ecem ber w as m ild until the 19th. T he rest o f . the m onth was colder, and a there was a light snowfall in m ost places by the end of the m onth.
T em p eratu re °C No. of sunny hours
1986 N orm al 1986 N orm al
Jan u ary -1.5 -0.1 53 41
F ebruary -5.2 -0.4 115 65
M arch 1.4 1.6 80 127
A pril 4.5 6.1 140 181
M ay 11.5 11.1 225 256
Ju n e 14.3 14.4 268 257
July 15.8 16.5 214 247
A ugust 14.7 16.2 192 221
S eptem ber 10.8 13.0 151 166
O ctober 9.3 8.6 103 98
N ovem ber 6.8 •4.9 42 42
D ecem ber 2.5 2.1 34 28
A nnual average H o u rs in all
7.1 7.8
1621 1729
P recipitation in mm Deviations from norm al 1986 norm al Jutland Islands B ornholm
January 85 55 32 25 49
F ebruary 3 39 -39 -31 -21
M arch 57 34 29 9 22
A pril 30 39 -9 -8 24
M ay 48 38 12 4 -1
Ju n e 28 48 -20 -21 1
July 51 74 -36 6 20
A ugust 73 81 1 -29 -21
S eptem ber 42 72 -37 -16 -10
O ctober 94 70 25 23 -7
N ovem ber 76 60 17 11 12
D ecem ber 79 55 29 14 20
T otal
precipitation 666 665 4 -13 88
1. Diseases in a g ric u ltu ra l crops 1986 Ghita C ordsen N ielsen
Cereals a n d g ra sse s
Overwintering. A s in 1984/85, a great part o f the w inter cereals suffered from severe frost w hen th ere was no snow cover. No connection betw een the tim e of sowing and frost dam age could b e seen. A bout 70% of the w inter barley and 19%
of the w inter w heat had to be resown w hereas only 3% o f the w inter rye was severely dam aged. A pproxim ately 50% o f the seed crops and 30% of grass fields with Italian ryegrass had to be resown.
Barley yellow m o saic virus. See page 35.
Barley yellow d w a rf virus. Only one severe attack was registered.
Snow ro t (Typhula in cam ata). Severe attacks were only m entioned in two reports.
Snow m ould (G erlachia nivalis). T he attacks w ere neither severe nor widespread.
Eyespot (P seu docercosporella herpotrichoides) was considerably less prom inent than in 1985. In the autum n, the climatic conditions w ere favourable for the fungus from th e beginning o f O ctober to the end of D ecem ber, but in the spring, the weather w as to o dry for infection and developm ent. In w inter rye 10% o f the fields investigated had m ore than 20% attacked plants. In w inter w heat 16% of the fields h ad m ore than 20% attacks, and only a few fields w ere severely damaged.
Sharp eyespot (.R h izocton ia cerealis). See page 33.
Take all (G aeu m an n om yces gram inis). T he attacks w ere rath er insignificant compared w ith th e preceding years. In w inter w heat 5% o f the fields had attacks of some im portance. In w inter rye and w inter barley the attacks w ere insignificant. See page 32.
Mildew (Erysiphe gram inis). In w inter barley, w here m any fields suffered from frost damage, th e m ildew attacks were weak. The reason m ay also b e the two obligatory fungicide treatm en ts in the early spring.
In general, the mildew attacks in spring barley w ere extremely weak, an d chemical control was only profitable in fields with the m ost susceptible varities.
A s to investigations o f the virulence gene frequencies, see page 34.
Yellow r u s t (Puccinia striiform is) was only observed in w heat, and the attacks w ere lim ited and weak on all localities except one.
Brown r u s t of w heat (Puccinia recondita). In general, only weak attacks w ere seen. In a few fields, severe attacks w ere found, but they cam e late.
Brown ru s t of barley (P. hordei) was seen in a few fields.
Net blotch (Drechslera teres) was found to be less w idespread and less severe than usual, both in w inter and spring barley. It was m ostly seen in winter barley grown after w inter barley.
Scald (Rhyncosporiunt secalis). T he tren d was the sam e as for net blotch.
Speckled leaf sp o t (Septoria tritici) was often found in w inter wheat, but only on the lower leaves.
G lum e blotch o f w heat (Septoria n odoru m ) was o f very little significance due to the dry w eather in Ju n e/Ju ly .
B unt of w heat (Tilletia caries). Two reports of attacks w ere received.
Legumes
A bnorm al germ ination in peas occurred in several fields. T h e plants affected w ere small, had thickened roots and leaves with light veins. In som e fields, resow ing was necessary. T h e cause is not clear.
Grey m ould (Botrytis cinerea) was m uch less of a problem in peas than in 1985, due to dry spells in Ju n e and July. T he disease m ostly occurred in irrigated fields.
O th e r fungal diseases on peas (Ascochyta pisi, M ycosphaerella pin o d es and P h o m a m edicaginis) w ere not im portant either, according to reports from th e agricultural advisers.
Sclerotinia sclerotiorum is rep o rted to have occurred in a few cases and was often found in seed samples.
Downy mildew (Peronospora p is i) is mostly seen in areas with long tradition for pea growing. In general, the disease was not widespread, but a few severe attacks were re co rd ed in June.
Fusarium wilt (Fusarium oxysporium f. sp. p is i) was not w idespread, and only two reports in July m entioned m ore severe cases connected with insufficient crop rotation.
Chocolate sp o ts (Botrytis fa b a e ) a n d leaf sp o t of b ro a d beans (A scochyta fa b a e ) was only of m in o r im portance in 1986. L eaf spots w ere often seen, b u t it turned out that they w ere caused by herbicides.
Clover ro t (Sclerotinia trifoliorum) was recorded in 4 fields with re d clover. In all cases the attacks w ere weak.
Oil seed rap e a n d o th e r cruciferous crops
Overwintering o f w inter rape was not too good. A bout 20% had to be ploughed in and resown.
Club root (P lasm odioph ora brassicae) was found in spring rape with m edium to severe attacks in som e regions, b u t m ost of the reports only m ention weak o r no attacks. T he infected plants w ere m ore easily observed in 1986 due to drought at midsummer.
Downy mildew (Peronospora parasitica) is mostly seen in w inter rape in the autumn. In Ju n e 1986 the attacks in spring rap e w ere m ore w idespread and severe than usual, and spraying with M aneb was tried in several cases.
Stem ro t (Sclerotinia sclerotiorum ) was lim ited by the w eather conditions in June, and severe attacks w ere only observed in two areas. See also p. 36.
Leaf spot (Alternaria brassicae) a n d A . brassicicola) was o f very little importance. In A ugust, a few cases of severe attacks were observed in spring rape adjacent to w inter rape.
C anker (P h om a Ungarn) in w inter rape was rare and insignificant.
Verticillium wilt (V. dah liae) was observed in spring rape with a severe attack in one locality. T he disease is w idespread in Southern Sweden, b u t not yet in Denmark
Beet
O verw intering of plants for seed was poor. In storage, b eet kept quite well in spite of the cold winter.
M anganese deficiency was fairly w idespread, and about one third of the re p o rts described the symptoms as rath er prom inent.
V irus yellows (Beta v iru s 4) was less w idespread than usual, and the attacks w ere very w eak in general. M ore severe attacks than usual w ere found in coastal areas o f Lolland w here m ost o f the sugar beet is grown.
R hizom ania. See page 36.
Damping-ofF a n d ro o t ro t (Pythium spp., P h om a betae a. o.) were seen, b u t mostly with weak attacks.
Powdery mildew (Erysiphe betae) started in July, but rainy w eather in A ugust- Septem ber m ade fungicide control unnecessary.
Potatoes
O verw intering in clam ps was satisfactory.
L eaf roll (Solanum v iru s 14) a n d stre a k (Solanum v iru s 2). These diseases w ere not w idespread, and the attacks w ere extrem ely mild.
R attle virus. V ery severe attacks w ere seen in a few fields.
Black leg (Erwinia carotovora var. atroseptica) was rep o rted to be rather serious in a few areas, but on the whole, the disease was not w idespread or severe.
P otato w art (Synchytrium en dobioticu m) was not rep o rted to have been found in any new localities. T he disease is only registered as occurring in 5 gardens.
L ate blight (Phytophthora infestans). T he first w arning was sent out on the 27th June. T he first fairly w idespread attacks were found in mid-July in irrigated fields with the varieties Bintje, H ansa, K aptah and Sirtem a. These attacks did not cause serious dam age because of the dry w eather. In A ugust-Septem ber stronger attacks w ere recorded.
Stem can k e r a n d black sc u rf (R hizoctonia solan i) was quite widespread in th e spring.
2. Pests on agricultural crops Cereals and grasses
Cereal nematodes (H eterodera avenae)
Very few severe attacks w ere reported in spring barley and oats.
Crane flies (Tipula p a lu d o sd )
The num ber o f leatherjackets found in the soil in the autum n of 1985 indicated that the level of attack would be fairly m oderate in 1986. However, the dam age threshold had b een passed in several cases w here beet was grown after grass.
In April and May, respectively 92% and 76% of the agricultural advisers rep o rted attacks below m edium . Severe attacks w ere only seen in H øjer and Sindal in grass on low ground.
Wireworms (Agriotes spp.)
The attacks w ere m ostly scattered and weak, but a few severe attacks were seen, mostly in fields w here grass had been the preceding crop.
Bibionid flies (B ib io hortulanus) was not any problem in 1986 either.
Saddle gall midges on barley (H aplodiplosis equestris) and wheat blossom midges ( Contarinia tritici, S itodiplosis m osellana)
No reports w ere received o f any serious attacks.
Bird-cherry aphids (R h opalosiphu m p a d i), grain aphids (S itobion avenae) and rose- grain aphids (M etopoloph iu m dirhodum )
As usual, th e attacks started in the southern part of the country. In general, the attacks w ere less severe than usual, b u t big variations occurred. In recent years, reports have m ostly been received of S itobion on w heat and R h opalosiphu m on barley. In 1986, M etapoloph ium could be found on the w heat straws, but not on the ears.
The com puter-based advisory service to farm ers was continued, and the m ain results are show n on page 51.
Rosy rustic moths (H ydraecia m icacea)
O n several locations m ore serious attacks than usual w ere registered in maize.
C ereal leaf beetles (O ulem a m elan opa) were w idespread in barley and w heat.
A b o u t 30% of the agricultural advisers give reports o f m edium -strong attacks.
G rain th rip s (L im oth rips cerealium a.o.) were found in a num ber of fields, especially in rye, w here the light sheaths w ere easily seen. Only 23% o f th e reports speak o f m edium -severe attacks in rye.
F rit flies (O scinella frit)
M igration of the first generation started 17th-19th M ay and culminated ab o u t the 20th June, which was a little later than usual. B ecause of the unstable w eather, the second generation did not start m igrating until about 21st July w ith a culm ination about the 18th August. Control of the third generation by the end o f A ugust in seed grass was not necessary because of rainy w eather.
It appears from the rep o rts o f the agricultural advisers th a t frit flies were n o t very w idespread and only weak attacks occurred in w inter crops, grass, m aize and oats. R eports o f severe attacks in winter crops in A pril w ere only received from one adviser, w hereas two others registered serious attacks in Ju n e on grass.
Yellow cereal flies (O pom yza flo ru m ) and w heat bulb flies (D elia coarctata) w ere observed in several w inter crop fields with severe attacks in May.
Pests on legumes
Pea a n d bean weevils (S itona lineatus)
58% and 27% of the agricultural advisers give reports o f m edium to severe attacks in peas and b road beans, respectively. This is an increase compared w ith the previous year.
T he pea and bean weevils w ere fairly w idespread in clover already in M ay.
H ow ever, the attacks w ere not severe. In August, on the o th e r hand, m ore th a n 60% o f the rep o rts m ention very widespread and m edium -severe attacks o f p e a and bean weevils in clover.
1986 m ust b e described as the year with the m ost serious attacks of pea and bean weevils. In late sum m er many complaints w ere received about m assive invasions of pea and b ean weevils in gardens.
C abbage th rip s (Thrips angusticeps) and pea th rip s (K akothrips pisivom s) on peas w ere found in a num ber o f fields in May and July, b u t m ostly with no or w eak attacks.
Pea m oths (C ydia tiigricana) w ere not seen very m uch in 1986. In pherom one traps placed in about 200 p ea fields the dam age threshold was only exceeded in a few cases. A few cases of severe attacks w ere seen at Kolind and Ikast.
Pea aphids (A cyrthosiphon p isu m ) occurred in m any fields, but only 14% o f the advisers report m edium -severe attacks in July.
Black bean a p h id s (A phis fa b a e ) were very w idespread in broad beans, mostly with medium attacks.
Pests on rape
Thrips (Thrips angusticeps) w ere fairly w idespread in spring rape, and a few severe attacks w ere rep o rted in May.
Blossom beetles (M eligethes aeneus) w ere very w idespread in w inter and spring rape. The b eetle attacks w ere weak-m edium in w inter rape, w hereas th ere w ere a number of severe attacks in spring rape.
Cabbage seed weevils (Ceutorhynchus assim ilis)
It appears from th e reports that the attacks o f cabbage seed weevil attacks were weak in winter and spring rape.
Brassica pod m idges (Dasyneura brassicae)
In about 86% o f the reports, the attacks are described as below the average in winter rape in spite of good overwintering conditions. A w arning about th e 1st generation was issued on 21st May, which is a little earlier than usual. The migration of th e 2nd generation started 25th-28th June.
Cabbage stem weevils (Ceutorhynchus quadridens)
According to th e reports, the occurrence of cabbage stem weevils was limited, and the attacks w ere weak, but several fairly severe attacks w ere seen.
Cabbage ro o t flies (D elia radicum ) w ere noticed m ore than usual. T he reason was probably not g re a te r populations, but rath er the drought from the m iddle of June. If the ro o ts are dam aged, the plants will m ore quickly be suffering from water deficiency.
The following pests in w inter and spring rap e w ere only seen in sm all num bers and were w ithout im portance in 1986: D iam ond-back m oth (Plutella xylostella), swede midges (Contarinia nasturtii), cabbage ap h id s (Brevicoryne brassicae),
large w hite butterflies (Piens brassicae, P. rapae) and cabbage stem flea beetles (Psylliodes chrysocephalus).
Pests on ro o t crops
Beet cyst nem atodes (H eterodera schachtii) T he attacks in 1986 w ere few and insignificant.
C abbage th rip s (Thrips angusticeps)
A bout half the sugar beet grow ers and several fodder b e e t growers saw for the first tim e in 1986 the effect in practice o f the new seed dressings P ro m et (furathiocarb) and carbofuran.
Thrips w ere fairly w idespread in beetroot, and 44% o f th e agricultural advisers rep o rt m edium -severe attacks. In several places control m easures had to be taken in spite o f treatm en ts with the new seed dressings.
M angold flies (Pegom yia h yoscyam i)
In May, reports w ere received from several advisers th a t mangolds were laying m ore eggs than had been seen in many years. A lthough not all eggs w ere hatched, the attack by the 1st generation was m uch m ore severe than usual. T h e 2nd generation in the m iddle o f A ugust was also considerable, and control was necessary in several cases w here the tops were to b e utilized.
The new seed treatm ents had a clear effect on the n u m b er of lst-generation larvae.
Pygmy beetles (A tom aria linearis) w ere observed in a n u m b er of fields, and 18%
rep o rt m edium -severe attacks.
Clivina fo sso r is a fairly new pest - a carabid w ithout a D anish name. It was observed in a few b eetro o t fields. They were m istaken for pigmy mangold beetles.
However, this beetle is m uch sm aller.
Beet c a rrio n beetles (Blitophaga o paca) were less w idespread and only occurred in weak attacks, especially at the field edges, just like the potato cap sid s (C alocoris norvegicus a.o.).
Peach-potato a p h id s (M yziis persicae)
The first reports of peach-potato aphids w ere received from Lolland-Falster
during the w eek starting June 16th. O ne w eek later reports w ere also received from W estern Z ealan d and Funen.
In June, all agricultural advisers rep o rted no o r weak attacks, w hereas 77%
report attacks below average in July and August. Consequently, the attacks of beet yellows w ere weak.
Investigations of sam ples with peach-potato ahids showed high insecticide resistance in several areas.
Black bean a p h id s (A ph is fa b a e) w ere w idespread in beet fields. In June, the attacks w ere fairly weak, and in July-August they w ere o f m edium strength, b u t with a num ber o f severe attacks. A ccording to the reports, control was difficult.
Cabbage m o th s (M am estra brassicae a.o.) occurred in several areas, but with few serious attacks.
Potato cyst nem ato d es (H eterodera rostochiensis)
5 agricultural advisers reported weak attacks in A ugust. O ne adviser speaks of medium attacks, and one of severe attacks. They mostly occur in gardens.
Colorado beetles (Leptinotarsa decem lineata)
The G overnm ent P lant Protection Service reports that only in one garden at Nakskov w ere 2 surviving Colorado beetles found on bait plants in 1986. T he bait plants w ere put th ere by the P rotection Service, as som e thousand beetles had been found in th at place in 1985.
Cutworms (Agrotis segetu m )
The situation in 1986 was m ost unusual. Catches in the pherom one traps started 10-12 days la ter than norm al, and they w ere very small. This was the case in almost all 60 localities with traps. T hus control was only to be considered on very light soils with redbeet, carrots and leek, w here the only rainfall was during the first two weeks o f July. T he agricultural advisers reported no o r weak attacks, except for one severe attack in potatoes and carrots.
C arrot flies (Psila rosae)
M igration w as very lim ited at the trap localities - except on the island o f Samsø.
O th er pests
Field slugs (Agriolim ax agrestis)
A s severe attacks occurred in the autum n of 1985, attacks w ere expected in 1986. However, by m id-Septem ber no reports had been received o f severe attacks although the rainfall in A ugust-Septem ber was considerable. T h e drought in Ju n e- July m ust have kept down the reproduction.
In the spring th e re was only one rep o rt about a severe attack in spring ra p e sown after w hite clover. T he spring rape had to be resown.
3. Diseases in h o rtic u ltu ra l p la n ts 1986 Lars A. H obolth
The percentual distribution of registered enquiries appears from T able 1. It appears th at th e increase in enquiries about special subjects which was seen in 1985 continued in 1986. F o r instance, th ere is a m arked increase in the num ber of mycological enquiries com pared with the average for the 5 preceding years.
Table 1. P ercen tu al distribution of registered enquiries
Phy- Myco Bacte- Viro- Zoolo- Di- U nex
sio- logi rio- logi- gical verse plai
logi- cal logi- cal ned
cal cal
Average of 5 years
1981-1986 13.1
1986 9.3
(Total: 1870) Climatic dam age
The low te m p era tu res during the w inter appear not to have dam aged the woody plants w hen no o th er factors contributed to w eakening the plants. D ead branches occurred in blackcurrant, but the dam age was mostly seen in fairly old orchards where the b e rries h ad been m achine-harvested. M any straw berry plants w ere either killed or m uch w eakened by the black frost during the later part of the winter. It was obvious th at where the snow had not m elted during the w arm er period, the plants thrived when spring came. T he cold spring resulted in very insufficient pollination o f the strawberries, and for m any grow ers the bad weather conditions in the early sum m er as well as the overwintering resulted in yield reduction o f about one third in 1986 com pared to norm al years.
42.4 48.0
8.5 5.8
5.2 6.0
25.6 27.9
4.7 2.6
0.5 0.16
Many o ther o u td o o r crops suffered under the cold spring, especially heat- requiring cultures like sugar m aize and large cucum bers.
In the cases w here flower bulbs w ere kept in clamps before being forced, damage som etim es occurred because frost had pen etrated into the clamps.
Fungal diseases
Club ro t (P la sm o d io p h o ra brassicae) occurred relatively late in the different cabbage varieties. T he late appearance of the disease is probably due to the cold spring w here th e soil tem perature did not rise so high that the fungus becam e
active. L ater in the year, attacks were seen in norm al stren g th in the infected areas.
Pythium spp. A ccording to the registrations m ost dam age occurred in greenhouses. Very different cultures are attacked by the fungus. Among th e potted plants the following may be mentioned: A zalea, chrysanthem um , cyclamen, gerbera, pelargonium and m onstera. In a num ber o f cases, it is possible to ascribe the attack to faults in the cultural technique. In o th e r cases, however, the seed o r seedling seem to have been infected from the beginning.
Blight (Phytophthora infestans). A ttacks on solanum pot plants were registered, especially on the fruits, w here the fungus produces brow n ro t, so that it can be seen on tom atoes.
Phytophthora porri caused quite considerable dam age in leek cultures. T h e attacks w ere seen both in early and late varieties, b u t w ith th e strongest attacks in late crops.
Phytophthora spp. is fairly com m on in many nurseries with p o tted plants. A m ong the cultures w here the disease is found particularly often a re cyclamen, g erbera, hibiscus, poinsettia and prim ula.
Downy black mildew (Peronospora sparsa) was found very early in the year b o th in greenhouses and outdoors. Apparently, the cold start of th e sum m er was ideal for the fungus.
Downy mildew of peas (Peronospora p isi) was fairly w idespread by the end of th e sum m er, w here attacks w ere seen both in peas for canning and for the g reen m arket trade.
Downy mildew of cabbage (P eronospora parasitica) was registered as w idespread in m any cruciferous crops. A num ber of attacks in broccoli showed that th e sym ptom s in this crop are very sim ilar to those seen in cauliflower.
Downy mildew of cucum ber (Pseudoperonospora cubensis) sta rte d with scattered attacks late in July and increased during August. T he severe attacks meant th a t the yield o f large cucum bers was considerably reduced. D uring August an d Septem ber, the disease was furtherm ore observed on cucum ber in greenhouses. T o GASA, O dense, the attacks m eant that the quantities they received were far below expectations based on the area with cucumber.
Grey m ould (Botrytis cinerea) is quite com m on b o th outdoors and in greenhouses. In the fields the fungus reduced the yield o f strawberries. A p a rt
from the usual attacks on the fruits, the lower parts o f the plants w ere also attacked during th e spring, so that leaf and flower stem s b roke ju st above the root collar. In greenhouses, attacks w ere seen on the following plants: azalea, begonia, chrysanthem um , cyclamen and pelargonium . M any o f the attacks on greenhouse cultures m ay be explained by the fact that the greenhouses have become m ore tightly sealed in order to reduce heating expenses.
Smoulder (B otrytis narcissicola) ruined m any pot plant cultures of narcissi. The attacks were first noticed in connection with the forcing w here one or several bulbs may fail com pletely, or the developm ent may be m uch retarded. Some attacks may b e ascribed to the m aterial used while others have developed later.
Thielaviopsis basico la
Attacks were found on cyclamen and poinsettia. As regards cyclamen, it was noted that one of th e reasons for the attack may have been deep potting.
Penicillium sp. was registered in a num ber of Egyptian onions. It is typical that the most severe attacks w ere seen in onion sets, where the attack is seen as a brown discolouring of the utterm ost couple of turgid scales.
Cylindrocladium scoparium is a fungus which is quite often seen in azalea cultures. T he first sign of an attack is usually the w ithering o f one or m ore branches.
Shoot blight o f p o p la r (F usicladium radiosum)
The weather in th e spring and early sum m er was favourable to this disease. Thus many rows o f poplars had periods with dead black leaves and shoot tips.
Fusarium spp. is a serious disease both in the field and in greenhouses. The attacks are m ost often found where the plants are weakened in som e way. Thus it has been n o ted that in Egyptian onions attacks mainly occur w here the soil has at som e point been waterlogged, so that the roots have not been able to breathe. In leeks, m ost of the attacks were seen in connection with insufficient crop rotation. M any greenhouse cultures are attacked. A m ong them are aster, begonia, cam panula, coffea, crassula, cyclamen, hibiscus and m onstera.
Myrothecium roridum was found both in kalanchoé and in gardenia. In kalanchoé, m ost o f the attacks were found in the variety ’Pollux’. T he attack usually occurs around the stem, which becom es black. A t the beginning, the attack is very superficial, but after som e tim e, it p enetrates so deeply into the plant, that it collapses.
Phyllosticta dracaenae is found on im ported seedlings from Africa b o th on dracaena and on codiaeum . The attacks may spread very wide at the high relative hum idity during rooting.
Cryptocline cyclam inis (syn.: G loeosporiu m cyclam inis)
A few scattered attacks w ere seen in different cyclamen cultures. The attac k seem s to start at an early point of the cultivation and stop alm ost entirely w hen the plants are later grown under drier conditions.
P estalotia funerea is a fairly com m on fungus which m ay cause withering o f sm all plants and shoots o f larger plants. D am age by this fungus was registered in azalea, camelia, rhododendron and thuja.
L eaf disease of plane (G n om on ia veneta) was very w idespread during the early sum m er. T he rainy w eather seem s to have been ideal for spreading the fungus.
Black sc u rf (R h izocton ia so la n i) causes much dam age in sm all plants. T he m o st severe dam age, for instance on begonia, usually occurs w hen the cuttings are taken, as the fungus is favoured by the high humidity.
P e a r scab (Venturia p in n a) was very com m on, especially in private gardens.
Usually, the attack started around the m ain nerves of the leaves and resulted in w ithering of the leaf.
S traw berry mildew (Sphaerotheca m acularis)
Severe attacks w ere seen in Z ephyr where both leaves and fruits were dam aged.
In o ther varieties, the attacks w ere lim ited to the leaves.
A m erican gooseberry mildew (Sphaerotheca m ors-uvae) w as very widespread in blackcurrant w here bushes with white shoot tips w ere quite com m on.
B lack c u rran t r u s t (Cronartium ribicola) was mostly seen in private gardens, b u t a num ber of attacks w ere seen in com m ercial orchards.
4. Pests in h o rtic u ltu ra l p lan ts 1986
L eaf a n d b u d nem atodes (A phelenchoides fragariae) w ere found in m any straw berry-grow ing areas. T h e m any registrations may b e connected with the fact that m any plants w ere dam aged during the winter, so th at m ore attention w as paid to the grow th of the plants.
M illepedes (B laniulus guttulatus) caused dam age to straw berries and potatoes as well as windfalls. In m any cases, it appeared th at insufficiently decom posed m anure had b een used for the cultures, so that large quantities o f millepedes were introduced in this way.
T hrips (Thysanoptera) caused dam age to m any different plants. A ttacks by the common thrips species w ere seen in cyclamens, carnations and roses. Besides the wellknown thrips species, another flower thrips (Frankliniella occidentalis) appeared. T his thrips stays inside the flowers w here it is well protected against control. Investigations show that it is extrem ely resistant to m any kinds of control agents. This thrips species has been found on dendranthem a, gerbera, schlum bergera, ro se and saintpaulia.
C hafer beetles (Phyllopertha horticola) are still quite com m on on the light soils in the m iddle o f Jutland w here the gnawing of the larvae are seen in lawns and sports areas.
Blossom beetles (M eligethes aeneus) are particularly noticeable w hen the second generation a p p ears as it attacks m any different crops. D am age was seen on cauliflower an d fuchsia.
Pea and bean weevils (S itona lineata). T hese weevils seem to increase in num ber all the time. It is not unusual to see dam age to the foliage of the small plants.
Later the dam age is seen for instance on fuchsia and straw berries.
Cabbage stem weevils (Ceutorhynchus quadridens) have a preference for Chinese cabbage w here th e larvae are found deep inside the head.
(Arge pu llata) a re still causing dam age at the known localities. It has not been registered in any new areas in 1986.
(Spodoptera littoralis) has again been im ported together with cuttings from E astern M ed iterran ean regions. The pest is noticed as the larvae a re voracious, and control is difficult.
St.-M ark’s flies (Sciaridae) may cause dam age in m any cultures, especially when cuttings are used for reproduction in greenhouses. Frequently, dam age done by the larvae is th e reason why secondary parasites attack the plants. Poinsettia and chrysanthem um are favourite feeds for the flies.
Gall mites (E rioph yes) w ere registered on m any different plants. O utdoors, attacks were seen on acer, alnus, fraxinus, plum and pear. In greenhouses, laurel and yucca w ere attacked.
IV. BOTANY D EPARTM ENT, Ib G. Dinesen, Acting H ead of D ept.
Experim ental w ork
B acterial diseases (Ib G. Dinesen an d K aren Jørgensen) B acterial rin g ro t of p o ta to (Corynebacterium sepedon icu m )
A s in 1985, the num ber of sam ples for testing was ra th e r low. The m aterial tested was plantlets produced at the Virology D ep artm en t, which am ounted to about 300 samples. 350 sam ples were tested for the Plant Protection Service.
H ealthy n u clear stock p lan ts
In connection with the renew al of the nuclear stock plants at the Institute of G lasshouse Crops, the bases of cuttings were exam ined for plant-pathogenic bacteria. D ieffenbachia m aculata w ere examined for E rw inia chrysanthemi and Pelargonium hortorum for X an th om on as pelargonii. H edera helix, Ficus benjam ina, N ephrolepis exaltata and Schefflera arboricola w ere also tested. All the sam ples w ere free from plant-pathogenic bacteria.
T he Institute o f G lasshouse C rops was visited regularly to m ake sure that the nuclear stock plants w ere still free from symptoms.
22 varieties of Begonia elatior are now being cleaned by m eristem -tip culture.
T he tube plants are exam ined twice for X an th om on as begon iae before delivery to the Institute o f G lasshouse Crops.
A m ongst the future nuclear stock plants are Pelargonium cultivars, clones of E piprem num aureum and a D ieffenbachia variety. T hese w ere examined for plant-
pathogenic bacteria.
Fungal diseases
T ake-all a n d eyespot in cereals (H. Schulz)
Take-all (G aeu m an nom yces gram inis). In 1986, the total num ber of stubble sam ples exam ined for take-all was 1010. T he attacks in spring barley w ere at a lower level than in 1985. In w inter barley, no fields w ere found with infection of m ore than 20% o f the root mass. In winter w heat and w inter rye, infection of m ore than 20% of the root mass was found in as little as 3% of the fields examined.
Eyespot (Pseudocercosporella herpotrichoides). In the spring, about 350 sam ples of w inter crops w ere exam ined for eyespot with a view to prognoses, w arning
and guidance ab o u t treatm ent. Climatic observations and spore counts showed that the prim ary infection possibilities w ere at the beginning of O ctober. The infection level in th e spring was generally the sam e as in the year 1984/85.
It was estim ated th at treatm en t was necessary in about 50% of the w heat fields and about 40% o f th e rye fields.
The sum m er estim ates of 1010 samples showed w eaker and less w idespread attacks of eyespot th an in 1985.
Sharp eyespot (R h izocton ia cerealis) occurred in 60% of the fields with spring barley and in 35% of the fields with winter barley.
In 80% of th e fields with w inter wheat and in 47% of the fields with w inter rye, sharp eyespot w as found, b u t always with a rather low level o f attack.
Economic th re sh o ld values fo r leaf diseases in cereals (Sten S tetter)
Epidan is a com puter-based program which enables the farm er to treat spring barley fields w ith about half the norm al quantity of fungicides, and consequently with a higher financial yield. T he program is p art of a larger com puter program called "Optim al Plantebeskyttelse" (optim al plant protection), which was tested by agricultural advisers in 1986. In 1987 this program will be in general use by m ost advisers.
Now and in th e n e a r future, only a few com puters are used in D anish agriculture, an d the program can b e used on less than 1000 barley fields.
Therefore, a sim plified system - M ini-Epidan - will be published in 1987. Mini- Epidan has so m e lim itations, but can still be used on m ost barley fields by farmers who do n o t own a com puter.
A similar p ro g ram for w inter w heat is being developed, and the first experimental p ro g ram will be tested in plot experim ents in 1987.
Variety m ixtures in w inter barley (Boldt W elling, M ogens S. H oum øller a n d C arl C hr. Olsen)
For 3 years, experim ents with variety mixtures in w inter barley have been carried out at th e localities Rønhave, Roskilde and T åstrup. In 1986 the varieties Igri, Marinka, G erb el and H asso were examined. T he attack level o f net blotch and barley scald was lower in mixtures of these varieties than in the individual varieties. The level o f m ildew attacks was low in all varieties.
The highest yield increase was 2.0 h k g /h a w ithout use o f fungicides, but th e re w ere big variations betw een localities, which is in ag reem en t with experiences from 1984 and 1985.
T reatm en t with th e fungicides Bayleton 25 W P o r T ilt 250 EC was n o t profitable.
M ildew disease p re ssu re in w inter barley afte r different num bers of fungicide ap p licatio n s (Boldt W elling, Jø rg en Sim onsen an d Fynbo H ansen)
A fter 0, 1 and 2 fungicide treatm ents with Bayleton 25 W P o r Tilt 250 E C , the disease pressure o f mildew was assessed at the localities R ønhave and F oulum . T he mildew level was m onitored in neighbouring spring barley fields w ithout resistance (cv. G unhild) and in m obile nurseries w ith th e non-resistant variety Pallas. In the past two years, the mildew level was very low giving insignificant results.
S torage fungi (B oldt W elling a n d A nita Idoff)
Studies of the content o f storage fungi in sam ples w ere carried o u t in cooperation with the N ational Institute of N atural Sciences. The results w ere published in leaflets 603 and 622,1986, from the Institute.
D iseases in g rass fo r seed production (Boldt W elling a n d A nton N ordestgård)
F or 3 years, the occurrence of leaf pathogens and saprofytes have b e e n m onitored in u n treated plots and plots sprayed with Tilt 250 EC .
It was very difficult to find any correlation betw een disease occurrence and yield. Som etim es th ere was a positive correlation, and sometimes it w as negative.
It was concluded th at it was very difficult to advise farm ers as to w hen fungicide treatm en t of grass for seed production was profitable.
V irulence analysis of barley a n d w heat powdery mildew (Erysiphe graminis f.sp.
hordei a n d Erysiphe gram inis f.sp. tritici) (M ogens S. H oum øller)
A D anish national virulence survey was initiated in 1985. Until now, th e investigations have concentrated on powdery mildew in barley and wheat, b u t very soon the activities will b e extended to include net blotch and spot blo tch of barley.
Two different m ethods are used:
a. Estim ate o f virulence frequencies based on colony countings on seedlings in m obile nurseries exposed at 8-10 localities several tim es a year.
b. D eterm ination of virulence gene frequencies by genotype testing o f single
colony isolates.
In b o th cases, the differentials w ere near-isogenic lines on a Pallas background o f barley, and near-isogenic lines of w heat on a C hancellor background.
Mildew of barley
T he results show ed th at the efficiency of specific pow dery mildew resistance varied very m uch am ong the varieties. Totally resistant varieties w ere found as well as some which w ere just as susceptible as Pallas, which is the susceptible control.
Frequencies o f M l-a l3 (R upee) and M l-a3 (R icardo) virulence were below 5 % in general. Thus varieties containing R upee or R icardo resistance and A pex w ith ml- 0 resistance h ad the m ost effective powdery mildew resistance am ong the D anish spring barley varieties. O n the other hand, varieties containing M l-a6 (Spontaneum ) o r M l-g (W eihenstephan) w ere extremely susceptible to the D anish powdery m ildew population, which was dem onstrated by virulence frequencies n ear 100.
Mildew of w heat
Widely grown varieties such as Kraka, A nja, V uka and D isponent w ere all very susceptible to th e D anish population o f w heat pow dery mildew. A m ong the varieties on th e D anish list of recom m ended varieties, Kosack and Sleipner had the most effective pow dery mildew resistance in 1986.
Barley yellow m osaic v iru s a n d its fungal vector Polym yxa gram inis (Lilian K loster)
T he occurrence o f ’barley yellow mosaic virus’ BaY M V was investigated in 27 winter barley fields on Zealand, Lolland, Falster and in the southern p art of Jutland close to th e D anish-G erm an border. Sam ples of field-grown w inter barley w ere tested fo r th e presence of virus and the fungal vector Polym yxa graminis.
T h e virus was n o t detected in any sample. P. gram inis was found in 4 out o f 15 samples.
70 soil sam ples w ere taken by the end of 1985 and in M ay 1986 from fields w here winter barley had been grown at least one tim e during the past 4 years.
T h e samples w ere exam ined using w inter barley (Igri) as susceptible control. The
