B. Pesticide R esearch Institute, Lyngby
III. A griculture
Fungal diseases (Bent J. Nielsen and Lise Nistrup Jørgensen)
Control of net blotch (Drechslern teres), scald (Rhynkhosporium secalis) and powdery mildew (Erysiphe gram inis) in barley
T he trials are carried out in w inter barley and spring barley to obtain a sufficient basis for approval of fungicides.
Powdery mildew (Erysiphe gram inis)
T he propagation and spread o f overw intered mildew from w inter barlev norm ally starts during A pril, and if untreated, it may develop rapidly during M ay an d June.
However, very little mildew survived the very cold w inter o f 1985/86 with long periods of black frost. A s it was followed by a spring which did not favour th e propagation and spread o f mildew, only 0.8% attacks w ere seen by the end of Ju n e in 19 field experim ents. This is considerably below w hat was seen in th e previous years (1984: 21.7%, 1985: 27.5% ).
In spring barlev the attacks started in June, but they w ere m oderate, and in 23 field trials the average percentage o f attacks by the beginning o f July was 8.9% . This was half as m uch as in 1984 and 1985. In susceptible varieties (V ega, C erise) the attacks w ere very severe in the second half of June.
In recent years, th e risk of resistance developm ent has increased the interest in products against mildew consisting of agents with different m odes of action. T h e result of com bining two com pounds with an effect against mildew may b e a product with a good effect against mildew for as m uch as 30-45 days. This is th e case with mixed products containing tridem orph (D orin, D PX , N 7873, Tilt tu rb o ) or mixed products with fenpropim orph (Rival, Tilt T op). A new com pound, ethyltrinol (Folicur) has effect in two stages o f the ergosterol synthesis, i.e.
bo th as a D M I and m orpholin type. D ifferent form ulations have been tested an d shown good effect.
M ost of the o th er fungicides which have been tested for use against barley m ildew have had good effect. However, a poor effect o f A fugan, flusilasol (D P X H 6573) and Bayfidan was seen in this year’s experim ents. Similar results w ere seen by the tests in 1985.
Pesticide dosages according to requirem ents has also been studied with great interest. Pow dery m ildew in spring barlev is a disease which may be controlled by use o f reduced dosages under certain conditions. In 1986 tests have been made in spring barley with different dosages of Tilt turbo, Tilt Top, Folicur Combi and Rival. R educing the dosages of Tilt turbo, Tilt T op or Folicur Com bi from 1.0 to 0.75 1 did not influence the effect against powdery mildew in barley.
Nor did it result in any significant yield decrease. The experim ents have only been carried out in 1986 under m oderate disease pressure, and further experim ents should be carried out.
Rival has b een tried at 1.5 and 1.0 1, and 1.0 1 must be considered sufficient against pow dery mildew in barley.
Net blotch (D reschlera teres)
In recent years net blotch has mainly occurred in winter barley, w here it may cause som e dam age in June. In 1986 the attacks were m oderate with 8.5%
attacked plants in an average o f 19 trials. This was m ore than what was seen in last year’s trials. In certain cases the attack am ounted to 20-30%. In spring barley attacks w ere only seen in a few experim ents, and they w ere fairly weak.
Scald (R hynchosporium secalis)
The scald attacks in w inter barley started at the beginning of Ju n e and peaked later in th e m onth with up to 30% attacked plants in certain areas. O n an average the attacks am ounted to 8% in 19 trials, which corresponded to the level of attack in 1985. Sim ultaneous occurrence of both net blotch and scald led to severe dam age in exposed fields, stressing the necessity for efficient products for use if the problem arises.
In spring barley the attacks averaged 0.1% (23 trials), and w idespread attacks were seen only in a few fields.
Net blotch and scald may cause serious dam age, especially in w inter barley, and it is im portant that the fungicides used have good effect. T he supply of compounds is being restricted considerably, and only D PX N 7873, the Folicur products, Rival, Tilt Top, Tilt turbo and Sportak 45 E C have had a satisfactory effect, i.e . p ro d u c ts containing flusilasol, ethyltrianol, p ro c h lo ra z and propiconazol. A tridem orph and particularly fenpropim orph content may increase the effect. D airin in com bination with Bayfidan has given good control, especially o f scald. T hese results are in accordance with findings in previous experiments.
R educed dosage for control o f net blotch and scald m ay w eaken the effect.
Especially when the o ther com ponent is tridem orph, the effect becom es too weak.
If net blotch or scald is a problem in w inter barley, a reduction of the dosage is not recom m ended for the tim e being.
M ore experim ents will b e carried out in the future in o rd er to throw light on the problem s in connection with reduced dosages.
Yield
In view o f the m oderate attacks o f leaf diseases in spring barley in 1986, m any o f the treatm ents which took place w ere not profitable.
O ut o f 23 experim ents in spring barley in 1986 treatm ent was unprofitable in 65%
if the costs of pesticides and application w ere estim ated as corresponding to 2.9 hkg. In th e experim ents carried out by the C rop H usbandry D epartm ent the treatm en ts in 66% o f 48 spring barley experim ents tu rn ed out to b e unprofitable.
In 1984 treatm en t was unprofitable in 25% of the 20 spring barley trials, and in 1985 in 43% of 23 spring barley trials.
Pow dery mildew is a serious disease in spring barley, and th e ra re occurrence of pow dery mildew in 1986 is the reason for the high n u m b er o f trials with unprofitable treatm ents.
A ccording to the present regulations, w inter barley has to b e tre a te d twice. This is done in o rd er to protect spring barley against overwintering powdery mildew.
F o r w inter barley as such the treatm ents have not been very econom ic as 58% o f the treatm ents w ere unprofitable.
Eyespot on w heat (P seudocercosporella herpotrichoides) (Lise N istru p Jørgensen a n d Bent J . Nielsen)
19 experim ents with control of eyespot were carried out in 1986.
T he need for treatm en t against eyespot was estim ated on th e basis of plant sam ples received in A pril. T rea tm e n t was considered necessary in 44% of all w heat fields (Schulz, personal com m unication). However, the early sum m er offered very poor conditions for the developm ent of the fungus, and therefore only weak attacks w ere found in several o f the trials when they w ere inspected in July.
A new system o f assessing the eyespot attacks was started in July: The straws w ere divided into 4 categories o f attack, and a new m ethod of index calculation was introduced. T he index corresponds to the previously used sum figure for the categories 3 and 4 for m edium and severe attacks, w hereas the index gives higher figures by weak attacks.
t v . j ( O X a-) + f l X b t + (2X c) + (3 x d l 100 Disease index = *--- ' — *■--- ' — ' --- — *■---* x —
(a + b + c + d) 3
A, b, c and d a re th e num ber of shoots. T he four categories in the form ula have the values 0 ,1 , 2 and 3.
Based on th e results o f the experim ents o f the year Prochloraz (Sportak 45 ec) must still be considered the only efficient product for control of eyespot. The alternative products which have been tested (Folicur, P C 1003, D P X N 7872) have shown t<^ w eak effect.
The effect o f P rochloraz was the sam e w hether it was applied in the autum n or in the spring. A m ore differentiated tim e schedule showed best control at Feekes stage 5.
Eyespot control only gave small and insignificant yield increases in 1986.
Control of leaf diseases in winter wheat
Mildew ( Erysiphe gram inis), Septoria spp. a n d Puccinia spp. on w heat
The attacks o f leaf fungi - especially mildew - occurred late in the season and were weak. H ow ever, it was possible to get a fairly good im pression of the effect on m ildew o f th e various products as the very susceptible K anzler variety was grown in several of th e fields.
The attacks o f glum e blotch and leaf spot w ere weak in 1986, and although the diseases o ccurred in m any trials, th ere was little possibility of estim ating the effect of th e products on these diseases. Only weak attacks of yellow and brow n rust were seen in a few trials.
In 1986 a n u m b er o f new products w ere tested for control of fungal diseases on leaves. A relatively new phenom enon was the high num ber of mixed products registered. Since a considerable num ber o f the com ponents are unknown, a test plan covering all the ergesterol inhibitors was set up in o rd er to get a basis for estimating th e potential of the mixtures. It turned out that it is possible to m ake a rough division into tw o groups: (1) T hose which give good mildew control, and (2) com pounds w ith w eak effect on mildew.
The following products belong to group 1: Tilt 250 ec, Folicur, SN 108 266, PC 1002, Im pact an d C orbel.
T he following belong to group 2: Bayfidan, Sportak 45 ec, D P X H 6573, Vigil and Calbdn.
T he m orpholins C orbel and Calixin plus Bayfidan and Vigil were the only products with a w eak effect on the relatively m oderate attacks of Septoria. T h e o th er products tested gave a uniform good control. M ost treatm ents gave significant yield increases, but not sufficient to be financially profitable.
A num ber o f new mixed products (Tilt turbo, Folicur Com bi, Rival, Tilt top and D P X N7873) w ere tested. In several cases, experim ents w ere made with two different dosages. It appears from the results th at the m ixtures examined gave the sam e good effect against mildew and Septoria spp. w ith corresponding yield increases. This also applies in m ost of the cases w here low er doses have b een applied. In fields w ith severe attacks of mildew, however, the high doses gave b e tte r control and higher yield increases than reduced doses.
In 27 experim ents with 2 sprayings against leaf fungi the average yield increase o btained was not financially profitable.
Control of fungal diseases on potatoes, root crops, industrial crops and vegetables grown outdoors (Lise Nistrun Jørgensen and H. Schulz)
Seed tre a tm e n t of peas
11 products for seed treatm en t w ere examined in 8 experim ents on peas. T he treatm en ts did not have any effect as to germ ination, tu b er form ation, colouring of roots o r yield.
T re atm en t of potatoes a g ain st black sc u rf (R hizoctonia solan i)
6 products for treatm en t of potatoes have been tested in 3 experiments. Several of the new seed dressings are liquid, and special spraying equipm ent is required.
M any products had a good effect assessed on the basis o f th e percentages of sprouts, stem s and tubers attacked. No significant difference in yield could b e seen. T he m ethod of applying liquid products should be improved. N o new products w ere approved in 1986.
C ontrol of diseases in ra p e
3 products w ere tested in w inter and spring rape. W eak attacks of S clerotinia sclerotiorum w ere seen. T he yield increases by treatm en t w ere not significant.
R ovral flo was approved for control of stem rot.
Control of diseases in peas
4 new products w ere tested in 6 experim ents. Experim ents w ere m ade with 2 different tim es o f treatm ent. T he attacks of grey m ould (Botrytis cinerea), leaf and pod spot (A scoch yta p isi) and stem rot (Sclerotinia sclerotiorum ) w ere very limited and did not give any possibility of assessing the efficiency o f the products. N o significant yield increases w ere obtained during the experim ents.
Control of p o ta to blight (Phytophthora infestans)
5 products w ere tested in 5 experim ents. Satisfactory attacks w ere seen in all the experim ents. PLK Trim angol fl. was approved on the basis of 2 years’
testing, w hereas D airin SC 480, which has been tested for several years, still did not dem onstrate sufficient effect. The treatm ents resulted in satisfactory yield increases.
Control of downy mildew on onions (Peronospora destructor)
4 products w ere tested in 2 experim ents. Ridom il M Z and Sandofan M8 gave the best effect. R idom il M Z was the first product approved for control o f downy mildew on onions.
Fungicide re sista n c e of plant-pathogenic fungi (U ntil 31st M arch: K irsten Ju n k e r, from 1st June: C onnie N ina C hristensen)
This project includes a surveyance of resistance developm ent in cereal mildew (Erysiphe gram inis) against ergosterol-inhibiting fungicides. M ildew was collected regularly in selected fields, partly regionally and partly countrywide. T he sensitivity o f m ildew is tested on plants grown in glass tubes with addition of different dosages o f fungicide (propiconazol).
So far, the investigations seem to indicate that there is a considerable variation in the sensitivity of sam ples taken out at the sam e tim e in the sam e field. A ny connection betw een attacks in the field, fungicide treatm ents and the sensitivity of mildew could n o t be ascertained.
The sensitivity o f barley mildew fell from 1984 to 1985, and it is m arkedly lower than the sensitivity of isolates from the late sixties. T he final results from 1986 are not available at the m om ent.
Examinations o f w heat mildew received from different parts of the country show a somewhat reduced sensitivity in populations from N orthern Jutland. No significant difference was seen in the sensitivity of populations from various parts of the country.
In o rd er to be able to register the developm ent in the sensitivity of the m ildew population to propiconazol, the population was exposed to different selective pressure under laboratory conditions. At the sam e tim e th e latent period was registered. The m ethod has not yet been fully developed.
Investigation o f pathotypes a n d tests fo r fungicide resistance en eyespot (.Pseudocercosporella herpotrichoides) (Lise N istru p Jørgensen)
W ith a view to the potential risk of eyespot resistance to prochloraz, our only approved eyespot product, a m onitoring program m e was set up in 1986.
346 isolates of eyespot (Pseudocercosporella herpotricholdes), collected from w heat trials on the islands of Zealand and Lolland-Falster in 1985 and 1986, w ere tested for sensitivity to benomyl (2 ppm ) and prochloraz (0.01-2.00 p p m ).
T he sam ples w ere taken in July with a maximum o f 20 isolates from each treatm en t in a field. Sam ples w ere taken from plots tre a te d with prochloraz and with benzim idazol, as well as from untreated plots.
Small pieces from eyespot lesions were placed on PD A . From the resulting cultures, tests w ere m ade with mycelial inoculum on P D A (control) and P D A + chemical.
T he average E D ^ value of prochloraz was found to b e about 0.1 ppm varying from 0.005 to > 2 ppm prochloraz.
A pproxim ately 10% of isolates from 1986 had an ED<-n betw een 0 and 0.01 ppm , approx. 40% betw een 0.01 and 0.1 ppm, approx. 25% betw een 0.1 and 1.0 ppm , while 20% had an E D ^^ value g reater than 1.0 ppm.
61% of the isolates w ere determ ined as R-type and 33% as W-type. It was n o t possible to assess 5% as either R - or W-type. Prochloraz has not, in contrast to other ergosterol inhibitors which were tested, shown a significant difference in inhibiting effect betw een R and W pathotypes.
Isolates from 3 localities with prochloraz-treated and u n treate d spots show ed no significant difference in sensitivity to prochloraz for isolates from treated plots when com pared to isolates from untreated plots.
Pests in ag ric u ltu re a n d field vegetables (Bent B rom and)
Bird-cherry a p h id s (R hopalosiphum p a d i), rose-grain a p h id s (M etopoloph ium dirhodum ) a n d g ra in ap h id s (Sitobion avenae) in w inter w heat a n d sp rin g barley
In winter w heat 6 experim ents were carried out with a num ber of pyrethroids and dim ethoat com pounds. The aphid attacks started in the beginning o f July, and 100% plan ts attacked was reached by the end o f the m onth. A t the beginning, th e grain aphid was the dom inant species, but later the rose-grain aphid was dom inating, which was a quite unusual situation. G ood results w ith 5- 10 hkg/ha in yield increase w ere obtained. In spring barley, 3 field trials w ere carried out w ith m ainly the sam e chemicals as in w inter wheat. Fairly weak attacks by th e bird-cherry aphid occurred, and yield increases from 1.9-5.0 h k g /h a were obtained.
T hrips (H aplothrips aculeatus a n d L im othrips den ticom is) in rye
3 field trials w ere carried out with fenitrothion and 3 pyrethroids. D ue to rainy w eather, spraying took place at stage 10.2 Feekes, which was later than originally intended. G ood effect of spraying with pyrethroids was achieved, but with insignificant increases in yield.
F rit flies (O scinella frit) in cereals, m aize a n d undersow n g rass
In a single trial w ith seed treatm ent on w inter w heat with lindan, phoxim and furathiocarb only the latter im proved em ergence. T h ere w ere no differences in the percentage o f attacked shoots or in the num ber of larvae in the shoots.
In maize, spraying at the 2-3-leaf stage with R ipcord, Decis, Cybolt 100 E and Sumithion 50 gave good effect with 5-6% increase in yield.
3 trials were c arrie d out in undersown grass. Spraying took place 7-10 days after the cover crop h a d b e en harvested. T he effect of 6 tested pyrethroids was very fine, and yield increases of up to 14% were registered with 1 spraying.
Spraying ag ain st v a rio u s p ests in g rass for seed
7 trials w ere carried out with various pyrethroids and fenitrothion due to previous trials w ith good results after spraying with A m bush. A ttacks o f the following pests could b e expected: Aphids, various species of thrips, frit flies, Siteroptes gram inum and the larvae o f Ochsenheimeria vacculella.
From mid-M ay to mid-July, grass sam ples were trea ted in a Berlese apparatus every week. C o n trary to 1985, few thrips were found w hereas the num ber of m ites increased to several hundreds in 100 g grass at the end of the test period.
O ther pests w ere p resent in small num bers only, and no increase in yield was found.
The p o tato a p h id (A ulacorthum solan i) a n d the peach-potato ap h id (M yzu s persica e) in potatoes
T rials w ere carried out with fenitrothion, pyrethroids an d a mixture of K arate and Pirim or. Two trials resulted in poor effect o f the spraying in general b o th on the aphids and in a virus test m ade on the tubers in a glasshouse test. In another trial, poor effect was registered on the aphids, b u t yield increases o f up to 10% was obtained.
Soil-borne pests in su g a r beet
In cooperation with the D anish Sugar Factories and the Zoology D ep artm en t, experim ents w ere m ade with seed dressing and spraying against soil:b orne pests, such as collem bola, millipedes, symphilids, pygmy beetles, wireworms and thrips.
M oderate attacks o f thrips occurred in the beginning o f M ay, and good co n tro l was obtained with seed treatm ent with furathiocarb. T h e sam e com pound had effect on the m angold fly until the end of June.
The black bean ap h id (A p h is fa b a e ) an d the peach-potato ap h id (Myzus p ersica e ) in beets in relation to v iru s control
3 field trials w ere carried out with K arate EC, P irim or G and a m ixture of K arate and Pirim or. G enerally, low effect was found on th e black bean aphid.
Very few peach-potato aphids w ere found, and in O cto b er 16.7% of the plants w ere attacked by virus in the untreated plots and 12-13% in the various treatm ents.
M angold flies (P egom ya h yoscyam i) in beet
In beet 3 trials w ere carried out with Sum ithion 50, Sum icom bi 30 FW, T rig ard and KVK Perm ethrin. T he phosphorus com pounds reach ed about 100% effect in a few days, w hereas it took 8 days to reach the sam e level of effect w ith the o ther com pounds.
Black bean a p h id s (A ph is fa b a e ) in beet
D ue to the poor effect o f treatm ents against the black b e a n aphid in 1985, 3 trials w ere carried out with 8 approved com pounds: pirimicarb, dim ethoate, p a ra th io n , fen itro th io n , form othion, oxydem eton-m ethyl and phospham idon.
Pirim icarb reduced the percentage of attacked plants from 45.6 in the co n tro l to 14.4. T he o ther com pounds reduced the attack to 17.2-19.4%.
Blossom beetles (M eligethes aeneus), cabbage seed weevils (Ceutorrhynchus assimilis), cabbage stem weevil (Ceutorrhynchus p allidactylu s) a n d b ra ssic a pod midges (D asineura brassica) in oilseed rap e
The experim ental w ork with pyrethroids against pests in oilseed rap e continued
The experim ental w ork with pyrethroids against pests in oilseed rap e continued