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 yield reduction o f about one third in 1986 com pared to norm al years.
42.4 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.