Effect of fungicide use strategies on the control of early blight ( Alternaria solani ) and potato yield

A series of experiments were undertaken to evaluate fungicide use strategies for the control of early blight ( Alternaria solani ), the most significant foliar disease of potatoes in Australia. The protective and curative activity of fungicides was evaluated in glasshouse and field studies. Boscalid, azoxystrobin and difenoconazole were highly effective in the control of early blight when applied up to three days before or three days after inoculation. Boscalid completely inhibited disease development when applied one day before inoculation. Applied five days after inoculation boscalid did not control early blight while difenoconazole was the most effective fungicide. Spray programs of 4–6 applications of fungicides from several different mode-of-action groups were evaluated in 4 field trials on commercial properties in South Australia, Western Australia and Queensland. All spray programs inhibited the development of disease and improved marketable tuber yields compared with unsprayed plots. The most effective spray programs included those with boscalid + metiram in the first two applications, and resulted in significant increases in early blight control and tuber yields of over 20%. These findings show that products with strong protective activity such as boscalid were more effective when applied earlier in the spray program. Products with strong curative activity such as difenoconazole were more effective than protective fungicides when early blight infections were well established in the crop. This information can be used to assist potato growers to improve early blight control and increase marketable tuber yields.