Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/17/2006
Publication Date: 7/1/2006
Citation: Porter, L., Cummings, T.F., Johnson, D.A. 2006. Effects of soil-applied late blight foliar fungicides on infection of potato tubers by Phytophthora infestans. Plant Disease. 90:964-968. Interpretive Summary: Reducing the risk of late blight tuber rot due to P infestans is an annual concern for potato growers in the Columbia Basin, WA. Protection of tubers from infection during the growing season and harvest is essential to prevent major yield losses and rot problems in storage facilities. There is limited information on the effects of current foliar fungicides on the survival of spores of the late blight pathogen. Also, there is no information available on their efficacy and duration of activity on the soil surface, and whether they can prevent or reduce tuber infection. Understanding the effects of fungicide activity would assist growers in managing late blight tuber rot. The present study evaluated the efficacy and duration of activity of selected foliar fungicides applied to the soil surface in reducing infection of potato tubers. Mancozeb, metiram, cyazofamid, fluazinam and fenamidone were identified as fungicides capable of limiting late blight tuber infection. It was determined that mancozeb and metiram actively prevented or reduced tuber infection for three to five days when applied to a sandy soil. This information allows growers to choose fungicides with dual foliar and tuber late blight protection and understand the duration that certain fungicides can be expected to protect below ground tubers.
Technical Abstract: Potato tuber infection was assessed under greenhouse and outdoor conditions when late blight foliar fungicides were applied to soil 24 hours prior to soil infestation with a suspension of zoospores and sporangia of Phytophthora infestans. Spore viability of P. infestans in soil was determined using buried healthy whole tubers and by assaying infested soil applied to freshly cut tuber disks. Protection of tubers and tuber disks from infection was most effective when soil was treated with mancozeb, metiram and cyazofamid than with other fungicides. Whole tuber infections were significantly less in soils treated with mancozeb, metiram, fluazinum and fenamidone than when treated with distilled water. Infection of buried tubers and tuber disks was prevented for three to five days following a single soil application of mancozeb or metiram under outdoor conditions. The tuber disk method was more sensitive in determining the efficacy of a fungicide in inhibiting infection and spore viability than using whole buried tubers.