Maize is a C4, so it is designed to grow in warmer climates. Unfortunately, as the weather and soil temperatures rise, so do the number of bugs with vociferous appetites.

This is bad news for crops like maize. If pests are not under control, the crop production has the potential to be severely reduced or lost altogether. Here are two to keep an eye on. 

Argentine stem weevil (Listronotus bonariensis) 

Argentine Stem Weevil (ASW) is a major insect pest of grasses and cereals, including maize. It is responsible for a substantial decrease in plant populations in some maize crops. 

ASW completes two generations per year in most parts of New Zealand. The first generation develops during the spring/early summer and the second in summer/autumn. The weevil over-winters as an adult and starts laying eggs from July. The first generation larval numbers peak in October to November, coinciding with the main planting period for maize. Maize can become infested with ASW larvae if it is sown too soon (less than four weeks) after cultivation from pasture or other grass crops. This applies to previously cropped ground where grass weeds are abundant as well. 

Partly developed larvae transfer from the decaying grass tillers and tunnel into the young maize plants. The centre leaves turn a blue-grey colour and if they are gripped, they pull out of the plant easily. Removal of the plant from the soil reveals a small round hole (about the size of a pin head) at the base of the plant where the larva has entered or exited the plant. Almost all ASW damage occurs during the first four weeks of maize plant growth. 

Greasy cutworm (Agrotis ipsilon)

Greasy cutworm numbers vary greatly from year to year, either reaching epidemic proportions or being rarely seen. 

Adult cutworms are small brown moths with a wingspan of 5 cm. Once soil temperatures reach above 10 degrees Celsius in the early spring, the adults emerge from the soil, mate and lay eggs on vegetation or cracks in the ground. They usually lay in clusters of 600 to 800 eggs and hatch into caterpillars a week after being laid. 

The caterpillars live underground but appear above the surface at night to feed. The small caterpillars eat the leaves, but the bigger ones feed on the maize seedlings just above the ground. The severity of the damage depends on the number of cutworms and their size. Once the maize has passed the four to five leaf stage, it is usually too big to sustain damage by the cutworm.

The best method of ASW and greasy cutworm control in maize crops is to plant insecticide treated seed. Poncho® is the preferred choice, because it controls black beetle as well as greasy cutworm and ASW.

For advice on pests affecting your maize crop, contact your local PGG Wrightson Technical Field Representative.