Showing papers on "Leaf spot published in 1989"

Impact of the fungus Balansia henningsiana on Panicum agrostoides: frequency of infection, plant growth and reproduction, and resistance to pests.

Abstract: The impact of the systemic fungus Balansia henningsiana (Clavicipitaceae) on the grass Panicum agrostoides was examined in field and greenhouse studies comparing infected and uninfected plants. Approximately one-half of all plants in three populations located in southern Indiana were infected. In field samples and greenhouse studies infected plants were significantly heavier than uninfected plants and produced significantly more tillers. Infection tended to suppress flowering but occasional asymptomatic tillers on infected plants produced healthy inflorescences. Although infected plants produced fewer inflorescences than uninfected plants as a proportion of total tillers, absolute numbers of inflorescences were similar in the two groups. Because other grasses infected by different species of Balansia and related fungi often are more resistant to insect damage, pest damage was quantified in one population. No differences between infected and uninfected plants were detected in levels of herbivory but infected plants had significantly less damage by the common leaf spot fungus Alternaria triticina. The results suggest that there is no selective disadvantage for plants infected by B. henningsiana.

Survival of Alternaria brassicae and Alternaria brassicicola on crop debris of oilseed rape and cabbage

Abstract: Summary Alternaria brassicae and A. brassicicola lesions present on infected leaves of oilseed rape and cabbage placed outdoors on soil produced viable spores for as long as leaf tissues remained intact. For oilseed rape this was up to 8 wk and for cabbage up to 12 wk. On leaves exposed in November and January spore concentrations decreased with time but on leaves exposed between April and June spore concentrations increased up to 9-fold in the first 4–6 wk and then declined. On stem sections of seed plants of oilseed rape and cabbage similarly placed on the soil, the fungi produced viable spores for up to 23 wk with spore concentrations increasing up to 11-fold in the first 6–8 wk after harvest. These results indicate that infected debris of brassica crops remaining on the ground after harvest may provide a source of dark leaf spot infection which may be implicated in the spread of the disease within and between crops.

Origins of resistances to rust and late leaf spot in peanut (Arachis hypogaea, Fabaceae)

Abstract: The cultivated peanut (Arachis hypogaea, Fabaceae) is believed to have originated along the eastern slopes of the Andes in Bolivia and northern Argentina The crop is now grown throughout tropical and warm temperate regions Among diseases attacking peanuts, rust caused byPuccinia arachidis and late leaf spot caused byPhaeoisariopsis personata are the most important and destructive on a worldwide scale Both pathogens, restricted in host range to Arachis, probably originated and coevolved in South America along with their hosts In recent years there has been much emphasis on screening of peanut germplasm for resistance to these diseases At the International Crops Research Institute for the Semi-Arid Tropics (ICRISA T), India, some 10,000 peanut germplasm accessions were screened for resistance to rust and late leaf spot during 1977–1985 and sources of resistance indentified for either or both pathogens Of the resistant genotypes, about 87% belonged to A hypogaea varfastigiata and 13% to varhypogaea; 84% originated in South America or had South American connections A high percentage (75%) had their origin in Peru (believed to be a secondary gene center for varhirsuta and varfastigiata,), suggesting that resistance to rust and late leaf spot diseases might have evolved in that country

5H-1,3,4-thiadiazolo(3,2-A)pyrimidin-5-one derivatives and functional compositions containing the same

Abstract: A class of novel 5H-1,3,4-thiadiazolo[3,2-a]-pyrimidin-5-one derivatives are disclosed. These compounds exhibit remarkable fungicidal activities for pathogenic fungi of cucumber gray mold, cucumber downy mildew. Alternaria sooty spot of Chinese mustard, apple Alternaria leaf spot, pear black spot, rice blast, tomato late blight, etc.

Susceptibility of flowering dogwood of various provenances to dogwood anthracnose

Abstract: (...) Following exposure for two growing seasons, 73,3% of provenance seedlings were dead, as were 64,8% from intraspecific crosses. Main stems of the remaining seedlings had died back, and the only leaves produced were on epicormic shoots. These results indicate that there may be no host genetic barriers to the continued expansion of the geographic range of the disease. Seedlings of the Chinese dogwood (Cornus kousa) exhibited leaf spot but no dieback

The relationship between Alternaria leaf spot and potassium deficiency causing premature defoliation of cotton

Abstract: Investigations into the relative roles of Alternaria leaf spot and potassium deficiency in causing premature defoliation of cotton showed that severe leaf spotting developed only on plants already showing deficiency symptoms. Defoliation was delayed or reduced by either the application of potassium fertilizer or by fungicide sprays, but significant yield increases required both fertilizer and fungicide. Removal of flowers also prevented the development of deficiency symptoms and prevented the leaf spot disease. Differences between cultivars in susceptibility to the disease were linked to their sensitivity to low levels of available potassium.

Distribution, prevalence, and severity of fungal leaf and spike diseases of winter wheat in New York in 1986 and 1987.

Abstract: Surveys of soft white winter wheat production fields in New York in 1986 and 1987 indicated that leaf spots were moderate to severe in most fields and were the predominant foliar diseases. Septoria nodorum blotch was the most prevalent and severe leaf spot disease, followed in importance by Septoria tritici blotch, tan spot, and Septoria avenae blotch; the latter two occurred sporadically. Several Ascochyta spp. were also recovered from leaf lesions. (…)

The relationship of yield loss to foliar diseases on sorghum grown by subsistence farmers in southern Honduras

Abstract: To develop a multivariate model for predicting yield data were collected in farmers’ sorghum fields where gray leaf spot, smut, rust, and oval leaf spot epidemics occurred in 1985. Several models were tested to explain variation in yield based on a range of variables measured on individual plants. Data were first subjected to principal component analysis, and the major principal components were used as independent variables in a multiple regression model, with yield the dependent variable. The best model included the following variables: per cent severity of the 4 diseases, panicle length, and plant height. Using the model, yield differences of up to 7% were predicted when comparing the minimum‐ and the maximum‐disease severities observed and holding plant height and panicle length at their mean values. Using the observed plant height and panicle length corresponding to actual disease severities, yield differences estimated were 14.6%, 3.6%, and 5.5% for gray leaf spot, rust, and oval leaf spot, ...

Cylindrocladium leaf and fruit spot of custard apple in Queensland

Abstract: A previously unrecorded fruit and leaf spot of custard apple caused by Cylindrocladium colhounii is reported in Queensland. The disease causes considerable damage where leaves and fruit come into contact with contaminated soil. The fungus is pathogenic on fruit, leaves, stems and roots. Control strategies include minimisation of rain splash dispersal by pruning low branches, mulching under trees and grassing inter-tree areas.

Nutritive quality of foliar disease resistant and susceptible strains of intermediate wheatgrass

Abstract: (…) Correlation coefficients between disease ratings and in vitro digestible organic matter, N, and NDF were r=−0.27, −0.71, and 0.76, respectively, in 1983. Correlation coefficients involving these entities were lower in 1985. Plant height did not not affect the plants' resistance or susceptibility to foliar diseases. Results from this study demonstrate over a representative germplasm base that nutritive quality of intermediate wheatgrass is diminished by leaf spot diseases, and that leaf spot resistant plants maintain a higher nutritive quality in the presence of disease

Pollaccia borealis sp.nov. associated with a purple-brown leaf spot of aspen

Abstract: Pollaccia borealis sp.nov. is described from a purple-brown leaf spot disease of aspen (Populus tremuloides Michx.) in northern British Columbia and the Yukon Territory, Canada. Conidia were produced on malt agar at temperatures of 20–23 °C.

Fungicidal control of leaf spot (Septoria apiicola) of celery

Abstract: Ten fungicides were evaluated and compared in glasshouse and field experiments for the control of celery leaf spot caused by Septoria apiicola. In glasshouse experiments propiconazole (25 mg a.i. L-1) inhibited the development of S. apiicola when applied to celery seedlings 2 days after inoculation and in 1 experiment an application 8 days after inoculation reduced by 10-fold the severity of disease as well as the production of pycnidia. Penconazole (25 mg a.i. L-1), myclobutanil (50 mg a.i. L-1), flusilazole (20 mg a.i. L-1), fenarimol (36 mg a.i. L-1), terbuconazole (25 mg a.i. L-1) and triadimenol(25 mg a.i. L-1) also controlled S. apiicola when applied 2, but not 8 days, after inoculation. Anilazine protected celery seedlings for at least 13 days after application and was the most effective of the fungicides applied before infection. In field experiments, the most effective control of leaf spot was achieved with applications, every 7-10 days, of anilazine (1500 mg a.i. L-1), applied either alone or mixed with propiconazole (25 mg a.i. L-1). Similar applications of propiconazole either alone or mixed with chlorothalonil (150 mg a.i. L-1) also controlled leaf spot, whereas penconazole (25 mg a.i. L-1), flusilazole (20 mg a.i. L-1) and myclobutanil (50 mg a.i. L-1) were not effective.