Sensitivity to prochloraz in populations of the eyespot fungus, Pseudocercosporella herpotrichoides, in relation to fungicide treatments and their efficacy in continuous winter wheat

Eyespot was assessed and grain yields determined in the eighth and ninth years (1992 and 1993) of a field experiment in which the fungicides carbendazim and prochloraz were applied, separately or in mixtures, to plots of successive crops of winter wheat. Populations of the eyespot fungus, Pseudocercosporella herpotrichoides, were characterised by the proportions of cultures grown on agar from infected stems that were W-type or R-type, or were carbendazim-resistant or carbendazim-sensitive. Sensitivity to prochloraz in agar was determined for isolates from populations sampled in 1992 using restricted maximum likelihood analysis of EC50s (concentrations needed to decrease colony growth by 50%), to deal with the unbalanced data, and comparisons were made by Wald statistics. Control by prochloraz was maintained but in 1992, as in some previous years, its application with carbendazim was more effective than its application alone. Selection by prochloraz for strains sensitive to carbendazim continued to occur and may have contributed to its sometimes relatively poorer performance in the absence of carbendazim. R-type isolates taken from prochloraz-treated plots, with or without carbendazim, in 1992 were less sensitive to prochloraz than were isolates from plots untreated with prochloraz. There was evidence of a greater range of sensitivities to prochloraz in R-type than in W-type isolates (although some uncertainty results from the small numbers of W-type isolates obtained from some treatments), which would explain the selection of the R-type by prochloraz. The significance of these findings to modern wheat growing practices is considered.     

The effect of treating seed potato tubers with benzimidazole, imidazole and phenylpyrrole fungicides on the control of rot and skin blemish diseases

Over 6 yr the effectiveness of imazalil, prochloraz and fenpiclonil, applied either alone or in a mixture, in controlling gangrene, dry rot, skin spot and silver scurf on potato tubers in store was compared with that of 2-aminobutane and thiabendazole. An assessment was also made of their efficiency in controlling the development of these diseases on the daughter tubers of seed tubers treated at harvest or before planting. Overall, 2-aminobutane was more effective in controlling gangrene (Phoma foveata) in store than the spray-applied fungicides. Deposits of imazalil, thiabendazole and fenpiclonil were greater when sprays were applied with an electrostatic sprayer than with a hydraulic sprayer. The opposite was found with the mixture of prochloraz Mn and tolclofos-methyl. More effective gangrene control was associated with the highest deposits. Fenpiclonil and the mixture of thiabendazole and imazalil were more effective in controlling dry rot (Fusarium solani var. coeruleum) than imazalil alone. The development of dry rot was, however, increased by 2-aminobutane treatment on eight out of 14 stocks. 2-aminobutane gave the greatest reduction (83%) in the severity of skin spot during storage whereas thiabendazole alone, and the mixture of thiabendazole and imazalil, gave mean reductions of 70% and 65% respectively. This mixture and fenpiclonil gave the greatest reduction in the severity of silver scurf although, in general, reductions in silver scurf with fungicide treatment were less than with skin spot. The type of sprayer used to apply a fungicide did not affect the effectiveness of the fungicides in controlling either skin spot or silver scurf on tubers in store, or on the daughter tubers. The incidence of gangrene and dry rot on daughter tubers was not reduced consistently by fungicide treatment of seed tubers of the six stocks tested. However, the severity of skin spot and silver scurf was reduced by fungicide treatments of all eight stocks but the reduction in disease was greater for skin spot than for silver scurf. All fungicides gave reductions in the severity of skin spot, and fenpiclonil and the mixture of thiabendazole and imazalil were the most effective for silver scurf. The effectiveness of the fungicides in controlling these diseases was similar for seed treated at harvest and that treated before planting.     

珍珠李炭疽菌对三种杀菌剂的敏感性测定

由胶孢炭疽菌复合种(Colletotrichum gloeosporioides species complex)引起的炭疽病是珍珠李(Prunus salicina Lind1)产业生产上的主要病害，为明确珍珠李炭疽菌对吡唑醚菌酯、苯醚甲环唑和咪鲜胺的敏感性，比较不同地理来源及不同种炭疽菌对三种药剂敏感性差异。采用菌丝生长速率法分别测定三种杀菌剂对采自不同地区26株珍珠李炭疽菌的药剂敏感性。结果表明，供试的26株珍珠李炭疽菌对咪鲜胺的敏感性最高，EC₅₀值介于0.010 8～0.645 2μg/mL之间，平均值为(0.191 2±0.03)μg/mL;苯醚甲环唑次之，EC₅₀值介于0.165 8～2.168 0μg/mL之间，平均值为(0.725 8±0.088 0)μg/mL;吡唑醚菌酯最低，EC₅₀值介于0.058 3～84.566 0μg/mL之间，平均值为(6.276 3±3.525 5)μg/mL。供试的26株珍珠李炭疽菌整体对以上三种杀菌剂敏感，且对咪鲜胺的敏感性最高，苯醚甲环唑次之，对吡唑醚菌酯的敏感性最...     

Effect of five fungicides with different modes of action on cobweb disease (Cladobotryum mycophilum) and mushroom yield

The fungicides chlorothalonil, metrafenone, prochloraz‐Mn, thiabendazole and thiophanate‐methyl were tested in vitro and in vivo for their effect on Cladobotryum mycophilum, the mycoparasite that causes cobweb disease in white button mushroom. In vitro experiments showed that metrafenone (EC₅₀= 0.025 mg L^?1) and prochloraz‐Mn (EC₅₀= 0.045 mg L^?1) were the most effective fungicides for inhibiting the mycelial growth of C. mycophilum. Selectivity indexes of the tested fungicides on both C. mycophilum and Agaricus bisporus indicated that metrafenone was also the most selective fungicide, while chlorothalonil was the most toxic fungicide against A. bisporus mycelium. The in vivo efficacy of fungicides for controlling cobweb was evaluated in three mushroom cropping trials, which were artificially inoculated with C. mycophilum (10⁶ conidia m^?2). Prochloraz‐Mn provided good control, although the surface colonised by cobweb reached 12% by the end of the crop cycles. None of the inoculated cropping trials treated with metrafenone showed any cobweb disease symptoms, and neither were any significant phytotoxic effects on mushroom yield recorded. These results indicated that metrafenone can be used as an alternative to prochloraz‐Mn in the control of cobweb disease.