Blackdot of potato in Manitoba and foliar fungicide options for control
Blackdot of potato in Manitoba and foliar fungicide options for control. Vikram Bisht, Crop Industry Branch, Manitoba Agriculture & Resource Development, 65-3rd Ave NE, Box 1149, Carman, MB, R0G 0J0, Canada. Blackdot disease, Colletotrichum coccodes (Cc) has been increasing in prevalence and severity in the last few years, leading to higher levels of Potato early dying in Manitoba. Along with verticillium wilt, the blackdot disease is an important component of the Potato Early Dying Complex in Manitoba. Inspite of in-furrow fungicide treatments at planting, the disease appears to be getting more pronounced in Manitoba; probably due to early in-season spread and infection of aerial plant parts. Isolates of Cc from across MB were pure-cultured from disease samples. Selected fungicides, some based on their potential use as a late blight fungicide, were tested in-vitro for their efficacy against four Cc isolates. As expected, there was dose response to fungicide concentration of many fungicides. Fluoxastrobin (Evito), azoxystrobin (Quadris), pyraclostrobin (Headline) and cyprodinil+fludioxonil (Switch) were highly effective against mycelial growth, but chlorothalonil (Bravo), mancozeb (Manzate Pro-Stick), boscalid (Cantus) and phosphorus acid (Phostrol) had little activity to no effect. Also, there was variability between isolates to the fungicides tested on mycelial growth. In 2019, foliar application of five fungicides, was tested in field. These fungicides did not affect the yield as compared to the control (no fungicide); however, Evito and Headline were most effective in reducing blackdot on daughter tubers. Stem assessment for BD found Evito, Headline and Manzate Pro-Stick as highly effective. The study suggests that foliar application of fungicides with late blight activity could be an effective strategy in managing aerial spread of blackdot disease, while reducing risk of late blight.