Maize Downy Mildew Control

Symptoms

Affected plants show pale yellow or whitish streaks along the leaves and a white downy fungal growth on the lower surface of leaves in the early morning when there is dew. Plants are often stunted with narrow erect leaves, and in severe cases the tassel becomes leafy and malformed and the plant produces little or no cob. Symptoms usually start when plants are young.

Damage

Downy mildew can cause heavy losses in maize, especially in warm humid and high rainfall areas, because severely affected plants are stunted, may not form cobs and can be a total loss individually. When many plants are infected early the field yield drops sharply. The disease spreads through infected seed and through spores in humid weather.

Organic & cultural control

Grow resistant hybrids recommended for your area and use healthy certified seed from a disease free source. Rogue out and destroy infected stunted plants early before spores spread. Ensure good drainage and avoid waterlogging, follow crop rotation away from maize, and control alternate grassy hosts and weeds in and around the field that can carry the pathogen.

Chemical control

Treat seed before sowing with a registered fungicide such as metalaxyl based seed treatment which protects young plants from early infection, and where needed a foliar spray of a recommended metalaxyl plus mancozeb combination can be used on the standing crop. Always follow the product label dose, observe the pre harvest interval and consult your KVK or agronomist for the correct seed treatment and spray.

Always follow the product label, the recommended pre-harvest interval, and your local KVK or agronomist. Pesticide approvals change, so verify before use.

Prevention

Use resistant hybrids and metalaxyl treated certified seed as the foundation of control. Sow on time, ensure good drainage, follow crop rotation and keep fields free of grassy weeds. Remove infected plants promptly and avoid carrying seed from infected fields, since seed borne infection is an important source of the disease.