Assessment of barriers to prevent the development of potato tuber blight caused by Phytophthora infestans

Experiments were conducted in an irrigated, sandy loam soil to evaluate mul ches and hill sizes as barriers to prevent the development of potato tuber blight caused by Phytophthora infestans. In mulching experiments, five trea tments were applied to field plots of cv. Red LaSoda: 1, no mulch; 2, polyu rethane spray foam in an 8-cm-diameter area immediately surrounding the pla nt stem; 3, black polyethylene film over the entire hill except near the st em; 4, a combination of treatments 2 and 3; and 5, a water-permeable, agric ultural textile treated with copper hydroxide applied over the same hill ar ea as in treatment 3. In 1998, the incidence of tuber blight in plots mulch ed with black film (treatments 3 and 4) averaged 32% compared with 56% in p lots without this mulch (treatments I and 2). In 1999, incidence of tuber b light in plots with and without black film averaged 9 and 20%, respectively . Mulching the stem area with spray foam (treatments 2 and 3) did not reduc e the incidence of blighted tubers when compared with the appropriate contr ol. The copper-treated textile mulch (treatment 5) provided reductions in t he incidence of tuber blight similar to those observed with the use of blac k polyethylene film. In a hill size experiment conducted once in 1998 and t wice in 1999, three hill size treatments were established on cvs. Red LaSod a, Shepody, and Russet Burbank. Red LaSoda was the most susceptible and Rus set Burbank the least susceptible to tuber blight. Comparison of blight inc idence in tubers classified by depth in the hill revealed few differences a mong the hill size treatments, although over all treatments, tubers covered with more than 15 cm of soil had a lower incidence of blight (1 to 14%) th an tubers with less soil cover (13 to 59%). Most tuber infections were appa rently initiated in eyes and were not concentrated on a portion of the tube r such as the stolen (proximal) or distal end. The fact that black film and textile mulches reduced tuber infection indicates that inoculum of P. infe stans can move from foliage to tubers through soil and that inoculum moveme nt is not limited to large channels in the hill such as those created by th e potato stems. The mulch treatments, however, provided only partial protec tion of tubers, limiting the practicality of such treatments to commercial producers. Hill size treatments had little effect on tuber blight incidence , indicating that adequate suppression of tuber infection in an environment conducive to late blight may be inseparably linked to adequate suppression of the foliar phase.