Maize - Insect pests

A field of maize plants.

Quick links to topics on this page:

• Soil insects
• Other insects

Insect management

Soil insects

Paddocks with a history of poor strikes may have high levels of soil insects. Seed dusting helps deter insects. In-furrow spraying helps protect young roots and shoots. Press wheels can reduce damage from false wireworm larvae and earwigs by encouraging plant emergence and firming the soil to reduce insects´ ability to move through it. Soil baiting may reduce damage by black field earwigs and crickets that attack the tips of developing prop-roots (secondary roots). Shallow planting in warm moist soil will encourage rapid crop emergence and growth, thus reducing the effect of insects.

Common soil insects in maize include the following:

Black field earwigs (Nala lividipes) are shiny black insects (up to 15 mm) with a pair of forceps or pincers at the rear end. The immature stages resemble adults but are wingless. They attack seeds, shoots, roots and stems at/or below ground level. Populations are regulated by soil moisture and serious damage is usually confined to soils that retain moisture well. Note: There are beneficial earwigs. These are usually larger and light brown in colour. Control earwigs with insecticidal grain bait.

False wireworm (Gonocephalum spp., Pterohelaeus spp.) are cylindrical, yellow-brown beetle larvae with rounded heads. They attack germinating seeds and seedling roots and shoots and are most active in spring. The beetles feed on dry seed in the ground especially in dry soil conditions. They only tend to become a problem if large numbers are present during dry conditions. Control using chemicals at planting, treated seed and insecticidal grain baits.

Cutworms (Agrotis spp.) are caterpillars up to 50 mm in length. Their colour varies greatly. Often they are grey-brown but may range from green or pale yellow to almost black. Cutworms feed on leaves and stems of young plants, with most damage caused by older caterpillars that may cut down plants to eat the leaves. They may also cause the plant to wilt by partially chewing on stems. Cutworms usually feed at night and hide in the soil during the day. Cutworms may be found in any soil type and often move into the crop from adjoining fence lines, pastures or weedy fallows. Spray when caterpillars are feeding (dusk-night). Spot treatments may be successful. Keep fallows clean and eliminate weeds from paddock perimeters for at least one month before planting.

Wireworms (Family Elateridae) are up to 40 mm long and can vary greatly in shape. They may have soft, flat, creamy-white or pale bodies with dark wedge-shaped heads and forked tooth-edged tails, or have hard smooth round yellow to red-brown bodies with flattened, round or cone-shaped tails. Wireworms can feed on seed but usually attack underground stems of young plants, killing the growing points and causing shoots to wilt. Damage is worse when crop growth is retarded by dry, wet or cool conditions. Wireworms generally favour moist areas. Plant treated seed or use in-furrow application of insecticide.

Other insects

Heliothis or corn earworm (Helicoverpa armigera) caterpillars are up to 50 mm in length. They can vary in colour from yellow to almost black - often with a broad pale stripe along each side. Eggs tend to be laid anywhere on the top 2/3 of the plant. Heliothis are a more serious pest during tasselling and silking. The damage to the silks reduces pollination and grain-set (6-8 larvae per tassel before silk emergence may warrant control). Chemical control should only be aimed at small caterpillars (up to 5 mm), as heliothis has developed resistance to a wide range of chemicals. Before spraying, consider that maize crops often have high levels of beneficial insects (predators and parasitoids) that may be harmed by insecticidal applications.  Some biological insecticides with minimal toxicity to beneficials are available.

Maize leafhopper are small, brownish, translucent insects with dark eyes that spring away (hop) rapidly when disturbed. More than 15 per plant can cause a disease-like condition known as Wallaby ear. Plant resistant varieties.

Thrips may damage crops that are stressed and not growing well.  Infected plants may have a yellow or silvery patches on the leaves of young plants and a desiccated or wilted appearance.  Look in the throat of individual maize plants for the presence of very small, brown/black insects measuring 1-2 mm in size. Control with insecticides. Check with your grain buyer as to which chemicals can be used for the particular target market.