Chemical protection using drip irrigation and seed coating against maize late wilt disease in the field

Late wilt, a disease severely affecting maize fields throughout Israel, is characterized by relatively rapid wilting of maize plants before tasseling and until shortly before maturity. The disease’s causal agent is the soil-born and seed-born fungus Harpophora maydis. The pathogen is currently controlled using maize cultivars having reduced sensitivity. In an earlier study, we showed that Azoxystrobin (AS), injected into a drip irrigation line assigned for each row, prevent the disease symptoms in the field. Here, we examine an economically practical treatment using the AS fungicide in a mixture with difenoconazole (DC), or other new fungicide mixtures, in a combined treatment of seed coating and drip irrigation protection, for two coupling rows (row spacing was 50 cm instead of 96 cm). A recently developed Real-Time PCR method enables us accurate and sensitive tracking of the fungal DNA inside the host tissues during pathogenesis. AS-DC seed coating alone, managed to delay the pathogen spread in the maize tissues up to the age of 50 days (near the appearance of the first symptoms and the fertilization at day 55-57), but was not sufficient to protect the crops later (at the age of 70 days). Drip protection with AS-DC was the most successful treatment and in the double-line cultivation reduced the fungal DNA in the root and shoot host tissues to near zero levels. This treatment inhibited the development of wilt symptoms by 41% and recovered cob yield by 36%. Moreover, the yield classified as A class (cob weight of more than 250 gr) increased from 27% to 63% in this treatment. No residuals of this fungicide were identified in the maize cobs. This successful economical treatment to prevent maize late wilt disease in infested fields can now be applied in vast areas to protect sensitive maize cultivars against the pathogen.