Systemic fungicides in the control of strawberry wilt (Verticillium dahliae)

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Abstract
SUMMARY: In a series of experiments between 1970 and 1973 the application of benomyl or thiophanate methyl to field‐grown strawberries, planted on Verticillium‐mtested land, gave control of wilt for up to 5 months, the duration of control being related to the amount of fungicide applied in the spring. Treatment of inoculated plants grown on in chloropicrin‐fumigated soil was effective for at least two seasons.An autumn‐planted multi‐factorial experiment in heavily‐infested soil showed that, to achieve maximum wilt control, it was advantageous to grow cv. Gorella rather than cv. Cambridge Vigour; to drench the runners at planting rather than to dip them in the fungicide suspension; and to use a high concentration (0–075 % a‐i‐) and large volume (600 ml per plant) for a supplementary treatment in May rather than a lower concentration (0.025 %) or smaller volume (400 ml). There were small but significant advantages in applying benomyl rather than thiophanate methyl, and in using 0–2% a.i. suspension at planting rather than 0–05%. No advantage was gained by dividing the spring application into two equal doses applied 2 wk apart. Extrapolation from the logarithmic relation between wilt index and total dose of fungicide applied in the spring suggested that I.I g/plant would have given almost complete control until October; such control had been achieved in an earlier experiment in which 1–2 g/plant was applied. Crop yield in the second year was determined by the treatment applied in the first year, but although these treatments had given significantly better control of wilt in Gorella than in Cambridge Vigour, the greater growth and yield potentials of the latter cultivar had an over‐riding effect on crop production; Cambridge Vigour yielded more than Gorella under all chemical treatments, but in the absence of treatment Gorella gave a larger crop than Cambridge Vigour.A proposed regime, entailing spring and autumn applications, is aimed at minimizing the colonization of the plant throughout the year, thus reducing the production of new inoculum and, by limiting the quantity of the pathogen in contact with the systemic chemicals, minimizing the probability of selecting fungicide‐resistant variants of V. dahliae.