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Seed treatments containing fluquinconazole, silthiofam or a standard fungicide mixture with no activity against take-all were compared in all combinations of sequences in successive second and third winter wheat crops in five field experiments and second to fourth crops in a sixth experiment. Compared with the standard treatment, silthiofam decreased take-all more effectively than fluquinconazole when crops were sampled at tillering. In samples taken in summer, during grain filling, silthiofam often decreased the incidence of take-all (percentage of plants with root symptoms) more than fluquinconazole, but fluquinconazole more effectively decreased the incidence of severe take-all (percentage of plants with more than 75% of their root systems blackened). It is suggested that these differences are a consequence of more effective control of primary infection of roots by silthiofam and of secondary, root-to-root, infection by fluquinconazole. Silthiofam usually increased yield more than did fluquinconazole, perhaps as a consequence of better early protection during tiller and/or spikelet formation. Treatment with either of the fungicides affected epidemic development in the treated crop and in crops grown subsequently. In particular, decreased take-all had the effect of delaying the year-to-year epidemic, so that nontreatment of a subsequent crop resulted in an upsurge in disease. Treatment with either take-all fungicide of a crop grown after a treated crop was relatively effective if the epidemic in the comparable nontreated crop sequence was continuing to increase. It was, however, detrimental if the disease was approaching its peak in the first treated crop, particularly if a treated (fourth wheat) crop was being compared with a similar crop in a nontreated sequence in which take-all decline had developed. These results provide a basis for recommendations for the use of seed treatment fungicides in sequences of wheat crops. [ABSTRACT FROM AUTHOR]

Take-all disease ( Gaeumannomyces graminis var. tritici) in wheat crops is known to be suppressed by naturally occurring antagonistic fungi, closely related to the pathogen, that infect grasses and cereals. This form of suppression was re-investigated because of the changing importance and role of grass weeds and grass covers in arable farming. Natural populations of the competitive fungus Gaeumannomyces cylindrosporus, allowed to develop under rye-grass, were more effective than artificially introduced populations in suppressing the development of take-all in following wheat crops. To be effective, the antagonist needs to be present before the start of wheat cropping. Introducing G. cylindrosporus, but not G. graminis var. graminis (a potential antagonist that is faster growing), into a previous crop, or just after the previous crop, sometimes suppressed take-all, but the effect was small. It is concluded that, for any future attempts at biocontrol by these fungi, they should be introduced into a preceding crop not susceptible to take-all. Take-all inoculum in the soil should be at a minimum and effective hosts of the take-all pathogen must not be present as weeds or volunteers. [ABSTRACT FROM AUTHOR]

Field isolates ( n = 144) of the wheat take-all fungus Gaeumannomyces graminis var. tritici ( Ggt) were tested for sensitivity to silthiofam, a take-all-specific fungicide used as a seed treatment, and identified as A- or B-type by PCR–RFLP analysis of nuclear rDNA. A possible association was identified between polymorphisms in ITS2 of the nuclear rDNA and sensitivity to silthiofam. A Ggt-specific PCR assay was developed which simultaneously identified isolates of Ggt as A- or B-type, based on the polymorphisms in the nuclear rDNA. A highly significant correlation between Ggt type using the PCR assay and sensitivity to silthiofam was demonstrated in a collection of 358 isolates from three field experiments designed to test the effects of seed-treatment fungicides on take-all and Ggt populations in winter wheat. In one experiment the percentages of silthiofam-sensitive and B-type isolates were significantly less in populations from plots sown with silthiofam-treated seed in two consecutive years than in populations from plots sown with nontreated seed. However, silthiofam still provided a significant amount of control of take-all. The natural occurrence of fungicide-insensitive isolates, up to about 30% in soils in which the fungicide had never been used, is unusual. The new PCR assay provides a useful tool for studying the population structure of Ggt, and may provide a novel method for assessing the incidence of insensitivity to silthiofam (the target site for which has not yet been identified) in field populations of Ggt. [ABSTRACT FROM AUTHOR]

A seed treatment containing fluquinconazole as the only active ingredient was tested in sequences of up to six consecutive crops of winter wheat. It was applied or not applied in each year, and was tested in all possible combinations with treatments applied in previous years. Take-all was controlled effectively, and grain yield usually increased, when the disease intensity was moderate or severe in non-treated crops, but control of the most severe take-all did not result in acceptable yields or grain quality. Treatment of a first wheat or second wheat with little take-all did not usually benefit the subsequent crop. Non-treatment of a crop grown after a treated, diseased crop usually resulted in a marked increase in disease, indicating that treatment had delayed progress of the epidemic. Take-all was controlled by treatment of a crop grown after a treated, diseased crop but the amount of control and of increased yield was often less than that in a treated crop grown after a non-treated crop in the same crop sequence. Similar effects of seed treatment were apparent in crops grown on a site with take-all decline. The alternative fungicide, silthiofam, applied as a seed treatment in the later years of some experiments, was usually as effective as fluquinconazole. From these experiments, it is recommended that: a) fluquinconazole seed treatment should be applied to a second or third wheat crop, grown after a first wheat crop that was managed to avoid rapid take-all development (e.g. by avoiding very early sowing); b) a break crop should follow the treated crop; c) the seed treatment should not normally be used in longer sequences of wheat or on take-all decline soil unless it is planned to follow the treated crop with a non-cereal break. [ABSTRACT FROM AUTHOR]

Communities of fungi on roots increased in diversity between second and third cereals, and were more diverse on winter wheat than on winter barley in a field experiment conducted over 3 years. Seed treatment with formulations containing fluquinconazole or fluquinconazole plus prochloraz had little effect on these communities, which include potentially beneficial, antagonistic fungi. Seed treatment decreased take-all and increased yield of wheat, especially in the second wheat in which take-all was building up, and in the third wheat when take-all was at its peak. It was less effective in the fourth wheat when take-all appeared to be in decline in plots that had no seed treatment throughout the experiment, and in barley, in which take-all was usually less severe. Take-all increased in untreated fourth wheat crops grown after third wheat crops that had been treated, suggesting that treatment had delayed take-all build-up and eventual progress into take-all decline. [ABSTRACT FROM AUTHOR]