|Author: ||W.R. Stevenson|
|Keywords: ||Phytophthora infestans, Solanum tuberosum, fungicides, integrated control, decision support systems|
Late blight continues to be a sporadic problem in the US, but current outbreaks (typically A2 mating type and US8 genotype) are generally contained and losses are small compared with the widespread outbreaks and extensive losses characterizing the mid 1990s.
Factors related to this improvement in late blight control include extensive grower training, improved rotation, destruction of cull piles and other sources of over wintering inoculum including volunteer potato plants remaining from previous seasonís production, control of late blight in seed production areas, planting of late blight-free seed and the availability of multi-faceted chemical controls.
Rather than depending almost solely on periodic application of protectant fungicides such as fixed coppers, chlorothalonil, maneb, mancozeb, metiram, and triphenyltin hydroxide as was done in the mid 1990s, US growers now have a long list of available fungicides including several QoI materials (e.g., azoxystrobin, famoxadone, fenamidone, pyraclostrobin), cyazofamid, cymoxanil, dimethomorph, famoxadone, fluazinam, mandipropamid (likely for 2008 growing season), propamocarb hydrochloride, and zoxamide, all with useful levels of late blight efficacy.
These chemistries represent many different modes of action and depending on the chemistry, have unique characteristics that help to reduce spore germination, infection, sporulation, inoculum quantity and inoculum quality.
Combined with effective disease forecasting and surveillance systems and improved fungicide application equipment, US growers now have multiple tools with which to avoid early season disease outbreaks and widespread regional distribution of the pathogen.
Although most potato cultivars commonly grown in the US are highly susceptible to late blight, intensive breeding efforts offer the potential in future years for the release of new high quality varieties with greatly improved late blight resistance as well as resistance to other important diseases.
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