Submitted to: Journal of Plant Protection Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2015
Publication Date: 3/6/2015
Citation: Olanya, O.M., Larkin, R.P., Honeycutt, C.W. 2015. Incidence of Phytophthora infestans (Mont.) de Bary on potato and tomato in Maine, 2006-2010. Journal of Plant Protection Research. 55:58-68.
Interpretive Summary: Late blight of tomato and potato is a devastating disease with enormous economic consequences throughout the world due to crop losses. We assessed the incidences and occurrences of this disease in Maine during 2006-2010 cropping years. As expected, late blight occurrences varied among years and locations. In 2009, a much higher frequency of disease was observed throughout the state. This was attributed to an unprecedented influx of late blight on infected tomato transplants shipped to retail garden centers throughout the Northeast United States, as well as conducive weather conditions, which significantly changed the late blight infection patterns. During 2009, 43% and 57% of diseased samples were recorded from tomato and potato. Overall, disease was randomly distributed throughout the state. Low levels of disease observed in 2010 indicated that high disease and pathogen levels observed in 2009 did not persist to cause widespread disease in 2010. The improved control of late blight can be attained if reduction of disease sources, fungicide protection of susceptible hosts as well as other cultural practices are utilized as consistent late blight management strategies with potentially improved potato yield.
Technical Abstract: Late blight, caused by Phytophthora infestans, is a devastating disease globally. In Maine, we recorded late blight on potato and tomato during the 2006-2010 cropping seasons. From 2006 to 2008, over 90% of diseased samples were collected in potato fields from northern and central Aroostook County in Northern Maine. In 2009, however, an unprecedented influx of inocula on infected tomato transplants shipped to retail garden centers throughout the Northeast U.S. significantly changed late blight infection patterns. In 2009, disease occurred all over the state and 43% and 57% of diseased samples were obtained from tomato and potato, respectively. Moran’s index and spatial autocorrelation analysis of disease occurrence, geographical locations, host factors, and previous years’ infection levels were not statistically significant (P>0.05). Therefore, random distributions of late blight incidences were observed across locations and years. Nearest neighbor analysis revealed mean spatial distances for late blight ranging from 1.51 to 71.4 km for 2006-2008, and 7.4 to 126.5 km in 2009. The frequency and locations of late blight outbreaks in 2009 were much greater than in 2006-2008, due to the influx of inocula and movement of infected tomato seedlings, as well as conducive environmental conditions. In 2010, very few disease samples were collected, indicating that the influx of inocula in 2009 did not persist to cause widespread disease in 2010. The reduction of inocula sources, fungicide protection of susceptible hosts, and the removal and destruction of infected tomato seedlings, potato cull piles, and volunteer plants can greatly reduce late blight occurrences and improve potato production, and should be an integral part of a late blight management program.