Role of wind and rain in dispersal of Botrytis fabae conidia

Numbers of Botrytis fabae conidia dispersed in plots of winter-sown field beans in which chocolate spot developed were monitored with vertical cylinder and horizontal slide samplers exposed within crops for 3- or 4-day periods. Cylinders collected more conidia than slides before stem extension of the crop; later slides collected more conidia than cylinders. The greatest numbers of conidia were collected by slides during periods in June or July when there was heavy rain. On dry days between mid-May and mid-July a Burkard sampler collected most conidia in the morning when wind speed was increasing and relative humidity was decreasing. On wet days during this period, there were smaller maxima in numbers of conidia collected during heavy rain.Peer reviewe

Role of wind and rain in dispersal of Botrytis fabae conidia

Numbers of Botrytis fabae conidia dispersed in plots of winter-sown field beans in which chocolate spot developed were monitored with vertical cylinder and horizontal slide samplers exposed within crops for 3- or 4-day periods. Cylinders collected more conidia than slides before stem extension of the crop; later slides collected more conidia than cylinders. The greatest numbers of conidia were collected by slides during periods in June or July when there was heavy rain. On dry days between mid-May and mid-July a Burkard sampler collected most conidia in the morning when wind speed was increasing and relative humidity was decreasing. On wet days during this period, there were smaller maxima in numbers of conidia collected during heavy rain.Peer reviewe

Epidemiology and control of chocolate spot (Botrytis fabae) on winter field beans (Vicia faba)

Dispersal of Botrytis fabae spores and the development of chocolate spot lesions were monitored in crops of winter-sown field beans during the 1980/81, 1981/82 and 1982/83 seasons. The greatest numbers of B. fabae spores collected on horizontal sticky slides exposed in crops were associated with periods of heavy rain and numbers declined if weather was dry. Amounts of chocolate spot developing on leaves of young potted plants exposed in crops near the slides followed the same trends as spore numbers. When numerous spores were collected, abundant chocolate spot developed on the leaves of tagged plants in the crops. Benomyl sprays were applied (at 0·5 kg a.i./ha) either after peaks in numbers of spores collected or according to crop growth stages. Sprays applied in January–April generally gave no increase in yield whether or not timed according to spore peaks. The greatest yields were obtained from plots sprayed in late May, at the midflowering stage of crop growth.Peer reviewe

Pathogenicity to wheat seedlings of wheat-type and rye-type isolates of Pseudocercosporella herpotrichoides

Four groups of isolates of Pseudocerosporella herpotrichoides (wheat-type carbendazimsensitive, wheat-type carbendazim-resistant, rye-type carbendazim-sensitive and rye-type carbendazim-resistant) were tested for pathogenicity to wheat seedlings (cv. Armada), using mycelial or conidial inoculum. With either form of inoculum, wheat-type isolates usually produced more severe lesions than rye-type isolates, although the most pathogenic rye-type isolates were as pathogenic as the least pathogenic wheat-type isolates. Regressions of pathogenicity score on spore concentration (log10-transformed) were calculated for each of the four groups of isolates and showed that the data were best fitted by two lines with different slopes and different intercepts, one for the wheat-type isolates and one for the rye-type isolates. Conidia of wheat-type isolates generally included a greater proportion of curved spores than those of rye-type isolates. There was little difference between conidia of the wheat-type and rye-type isolates in length, number of cells or ability to germinate, nor between carbendazimsensitive and carbendazim-resistant isolates of either wheat- or rye-type in pathogenicity or spore characteristics.Peer reviewe

Effects of rainfall intensity and duration on dispersal of Rhynchosporium secalis conidia from infected barley leaves

Simulated rain of two intensities was allowed to fall for 30 min on to barley leaves infected by Rhynchosporium secalis. The resulting splash droplets were collected on horizontal pieces of fixed photographic film. Most spore-carrying droplets were in the 400–800 μm diam range. They were dispersed as far as 1 m from the barley leaves and the number of conidia collected on horizontal microscope slides declined exponentially with distance from the leaves. It was estimated that, of the conidia dispersed in 30 min of simulated rainfall with an intensity of 12 mm h−1, 40% were dispersed in the first 10 min and 27% in the last 10 min, and with an intensity of 65 mm h−1 39% were dispersed in the first 10 min and 25% in the last 10 min. Horizontal pieces of film and microscope slides were placed, under rain-shields, at 15 cm above ground level in an infected crop of winter barley during June and July 1985. Of the spore-carrying droplets collected during periods of rain, most were less than 400 μm diam, but most spores were in 400–800 μm diam droplets. No conidia were collected during dry weather or during rainfall with intensity less than 0.2 mm h−1. During showers most conidia were collected when rainfall intensity was greatest; a regression of number of conidia collected cm−2 min−1 on rainfall intensity (both square-root transformed) accounted for 76% of the variance.Peer reviewe

Changes in populations of Pseudocercosporella herpotrichoides in successive crops of winter wheat in relation to initial populations and fungicide treatments

The effects of two applications annually of carbendazim, prochloraz or a mixture of carbendazim and prochloraz on five populations of the eyespot fungus, Pseudocercosporella herpotrichoides, were studied in successive crops of winter wheat. Initially, populations were established by inoculation of plots with mixtures of isolate types which were mainly MBC-sensitive W-type, MBC-resistant W-type, MBC-sensitive R-type or MBC-resistant R-type. Further plots which were not inoculated had, initially, a mainly MBC-sensitive W-type population. Plants were sampled each April and July for 3 years. Carbendazim treatments resulted in an almost entirely MBC-resistant population by July of the first year, regardless of the proportion of MBC-resistant isolates in the initial inoculum. Although treatment with prochloraz greatly decreased populations of the eyespot fungus, its effect on the number of MBC-sensitive isolates was usually not significant. Prochloraz effectively controlled the MBC-resistant fungus and was usually more effective against the W-type than the R-type of the fungus. Treatment with the mixture of carbendazim and prochloraz also greatly decreased populations, but the selective effect of each component fungicide was less marked. Regardless of fungicide treatment, a smaller proportion of R-type isolates was recovered from severe than from slight stem lesions in July, indicating that the times of lesion establishment or rates of development of the R-type and W-type were not the same. Migration of fungal types between plots appeared to have little influence on the outcome of selection.Peer reviewe

Pathogenicity to wheat and rye of Pseudocercosporella herpotrichoides isolates from France and the UK

Isolates of Pseudocercosporella herpotrichoides from France and the U.K. were tested for pathogenicity to wheat and rye seedlings in parallel controlled-environment experiments in both countries. There was no difference in pathogenicity to wheat or rye seedlings between isolates from France and isolates from the U.K., but both groups of isolates generally penetrated more seedling leaf sheaths in French than in U.K. experiments. Both W-type and R-type groups of isolates were more pathogenic to wheat than to rye, but W-type isolates were generally more pathogenic to wheat than were R-type isolates, and R-type isolates were generally more pathogenic to rye than were W-type isolates. There were large differences in pathogenicity to wheat or rye among isolates in each group, but pathogenicity to wheat did not appear to be related to pathogenicity to rye for either W-type or R-type isolates. There were no differences in pathogenicity between carbendazim-resistant and carbendazim-sensitive isolates.Peer reviewe