The phenylpyrrole fungicide fenpiclonil inhibited the metabolism of glucose in mycelium of Fusarium sulphureum Schlecht at a concentration which only slightly inhibited mycelial growth (EC,,). At the same concentration, fenpiclonil also inhibited accumulation and, to a greater extent, phosphorylation of 2-deo~y[U-'~C]glucose in starved mycelium loaded with unlabelled 2deoxyglucose. Fenpiclonil did not affect cell-free phosphorylation of 2deoxyglucose or the ATP content of mycelium. Therefore, the primary mode of action of the fungicide may be based on inhibition of transport-associated phosphorylation of glucose. This may cause a cascade of metabolic events which eventually lead to fungal growth inhibition and death. One major event affected by inhibition of transport-associated phosphorylation is the accumulation of polyols, such as glycerol and mannitol, in mycelium. This was not observed in an osmotically sensitive, fenpiclonil-resistant laboratory isolate of the fungus.

No abstract

Natural products can be used to control pests and diseases in crops. These products include anorganic compounds, but aiso a variety of plant extracts. In the beginning of this century active microbial extracts were discovered as well. Synthetic crop protection chemicals were developed from about 1940 onwards and sustained progress in modero agriculture. The first generation chemicals have aspecific modes of toxic action and are in many instances deleterious to the environment. The second generation chemicals have specific modes of action and meet modero environmental requirements. A disadvantage of these chemicals is the potency of target organisms to acquire resistance. This condition urged agrochemical industry to develop chemicals with new modes of action. Such chemicals can be developed by using natural bioactive products as leads in synthesis programmes.This paper decribes the progress that was made in the development of natural bioactive compounds in pest and disease control.

No abstract

Resistance to phenylamide fungicides in the Phytophthora infestans population in the Netherlands decreased from a level of 77~ of the samples containing resistant strains in 1980 to 0% in 1986 with decreasing use of metalaxyl, the only phenylamide fungicide registered for use against late blight in this country. Use of metalaxyl decreased because the fungicide alone and combinations of metalaxyl with preventive late blight fungicides were not commercially available from 1981 through the first part of the potato growing season of 1984. When metalaxyl was made available again in August 1984 in a mixture with mancozeb and from 1985 in a mixture with almost full rates of maneb and fentinacetate its use remained limited because growers were advised to apply the combination only two times per season in critical situations only to control the severe late blight epidemics of 1984 and 1985. Moreover application on seed potato crops was not allowed. In 1986 the combination was hardly used because the mild epidemic was easily controlled by preventive compounds only.In 1987 and 1988 phenylamide resistance increased to 16 and 42 %, respectively, inherent to a general use of the combination in both years in most potato growing regions of up to two applications to combat a very severe epidemic.In lots of seed potatoes harvested in 1988 the percentage of blighted tubers yielding resistant isolates significantly differed from 13% for regions where seed potatoes are predominantly grown for table and processing crops to 41% for a region where predominantly starch potatoes are grown, both as seed and production crops. The more intensive use of metalaxyl combinations in the latter area through the years as compared to the other areas is assumed to be responsible for the higher incidence of resistance.In most years application of the combination induced a significant shift in the population to resistance as is indicated by the higher frequency at which resistant isolates were present in leaf samples taken from treated fields or tuber samples from the harvested crop.The strategy adopted by Dutch potato growers to combat phenylamide resistance in late blight, involving limited use of metalaxyl mixtures to a maximum of two times in critical situations only, has kept up to now resistance in the population at a level at which metalaxyl still significantly contributes to the efficacy of the combination in controlling the disease. Nevertheless the observed increase in resistance in the population of 1988 after two consecutive late blight years indicates that this may change if severe epidemics occur each year.