Control of silver scurf (Helminthosporium solani) disease of potato with benomyl and thiabendazole

Abstract

SUMMARY Benomyl and thiabendazole, applied as dusts to seed potatoes before chitting (sprouting), reduced the incidence of silver scurf disease on the progeny at lifting and during subsequent storage. Treatment of seed tubers 4 months prior to planting almost completely suppressed sporulation during storage, even under conditions very favourable for the growth of the fungus. The fungicides appeared not to act systemically because developing tubers grown from treated seed were just as susceptible to infection after inoculation as those from untreated. Control was due to effective inhibition of sporulation on the surface of diseased seed tubers after planting. There was no reduction in the amount of disease in subsequent generations of potato crops without further fungicidal treatment. Seed virtually free from silver scurf, produced from seed treated with fungicide in the previous year, yielded progeny with as much disease as progeny from untreated seed stocks.

Factors aflfecting the development of silver scurf (Helminthosporium solani) on potato tubers

“…The results confirm that seed tubers with very little inoculum can be produced by the stem-cutting system or if treated with benomyl, which reduces sporulation (Hirst et al, 1970). However, contamination of untreated stocks with H. solani occurs very rapidly (Jellis and Taylor, 1977), so that repeated chemical treatment would be necessary to prevent a build-up of the disease in initally healthy stocks.…”

Resistance to thiabendazole in isolates of Helminthosporium solani, the cause of silver scurf disease of potatoes

“…can be controlled by applying this fungicide to tubers immediately after harvest and such treatment prevents spread of lesions during storage. The disease is also controlled in ware crops by treating seed tubers; this inhibits production and release of conidia after planting and so prevents the infection of progeny tubers (Jellis & Taylor, 1977), However, the efficacy of both control methods is dependent on the amount and uniformity of thiabendazole deposits on the tubers (Cayley et ai, 1979(Cayley et ai, , 1987 and lack of disease control can often be attributed to poor application.…”

Treatment of seed potatoes with prochloraz for simultaneous control of silver scurf and black dot on progeny tubers

“…Hughes respectively, are surface-blemishing diseases spoiling the appearance of potato tubers (Mooi, 1968: Read & Hide, 1984: Langerfeld, 1985. Infection not only results in the downgrading of consignments destined for the consumer market (Hunger & McIntyre, 1979), but also incurs losses in seed production where only limited infection is allowed on certified seed, Silver scurf on tubers can be reduced by treating seed with fungicides like benomyl, thiabendazole (TBZ), imazalil, propiconazole and prochloraz (Jellis & Taylor, 1977b: Cayley et al, 1983: Hide et al, 1987, 1994, although development of tolerance to benzimidazoles by the pathogen limits the usefulness of the first two compounds. By contrast, black dot responds less readily to chemical treatment (Jellis & Taylor, 1977b: Hide et al, 1987, and has been observed to increase following treatment of tubers with benomyl, TBZ or imazalil applied to control silver scurf (Jellis, 1972: Jellis & Taylor, 1977b: Hide et al, 1994.…”

“…Infection not only results in the downgrading of consignments destined for the consumer market (Hunger & McIntyre, 1979), but also incurs losses in seed production where only limited infection is allowed on certified seed, Silver scurf on tubers can be reduced by treating seed with fungicides like benomyl, thiabendazole (TBZ), imazalil, propiconazole and prochloraz (Jellis & Taylor, 1977b: Cayley et al, 1983: Hide et al, 1987, 1994, although development of tolerance to benzimidazoles by the pathogen limits the usefulness of the first two compounds. By contrast, black dot responds less readily to chemical treatment (Jellis & Taylor, 1977b: Hide et al, 1987, and has been observed to increase following treatment of tubers with benomyl, TBZ or imazalil applied to control silver scurf (Jellis, 1972: Jellis & Taylor, 1977b: Hide et al, 1994. Of the fungicides previously reported effective against silver scurf, prochloraz appears to have the most pronounced inhibitory activity on growth (but not spore germination) of C. coccodes (Marais, 1990: Read & Hide, 1995, although the latter authors found it less effective for field control of black dot and silver scurf than fenpiclonil.…”