Weeds, pests and diseases

The incidence of insect pest populations varies from season to season and growers normally monitor fields and adjust rotations to reduce risks.

Soil or seed treatments are useful where wireworms have been a problem in the past or if conditions are conducive for rootworm or seed corn maggots. 

Biologically engineered maize hybrids that produce an insecticidal toxin using a gene from the bacterium Bacillus thuringiensis (Bt) provide a modern method for managing European corn borer, some other caterpillar species, and corn rootworm. Aphids, corn leafhopper, corn leafminer, beetles, grasshoppers and thrips are also common pests in maize, particularly in warmer climates.

(a) Eyespot, (b) Helminthosporium, (c) Leaf chlorosis from herbicide damage

Maize diseases are strongly influenced by weather conditions and are difficult to predict. Not every disease will cause economic losses and in grain maize the most important leaves to protect are from the ear leaf further up the stalk – any loss of photosynthetic area in these leaves will reduce grain yield.

In severe cases of attack by diseases such as gray leaf spot or leaf blight, Cercospora zeae-maydis, lodging will increase because the plant pulls all of the nutrients out of the stalk to devote to grain fill, bringing harvest forward. In more temperate regions, diseases such as eyespot Kabatiella zeae, which appear late in the crop, can lead to significant defoliation, reducing yields in forage maize.

(a) P deficiency induced by cold temperatures, (b) Leaf color can be due to variety not nutrient deficiency, (c) Leaf discoloration caused by waterlogging.