Farmers around the State should be on the lookout for heliothis (Helicoverpa punctigera) as westerly winds carry large numbers of moths into crop growing regions.

During winter, budworms breed in central Australia and are carried east in September winds.

The moths are attracted to the flowers of crops like field peas, faba beans, chickpeas, canola and horticultural crops where they lay small white spherical eggs.

Eggs turn brown with time, and eventually hatch within five to 10 days depending on temperature.

Small larvae (grubs) then emerge and love feeding on the reproductive parts of plants causing damage to pods and seeds.

These larvae are one of the worst pest species in pulses and horticultural crops in eastern Australia.

If you are growing pulse or horticultural crops now is the time to start looking for heliothis eggs and larvae.

Eggs will usually be laid on the flowering parts of the plant, however they can be found on young tender leaves, growing points and stems.

The eggs will be white and spherical, about the size of a pin head.

As they mature they turn brown and eventually a small larva will emerge.

When the larva emerges, it will be about three millimetres long.

It will immediately start feeding on leaves and pods causing damage which is easily spotted by the trained eye.

After about 10 days the larvae usually triple in size and can easily make a meal out of developing seeds and fruit.

The best way to monitor for heliothis in most crops is by using a sweep net, which traps larvae in the net as it is swept through the crop.

By sweeping a certain number of times (usually 10) over several areas of the paddock you can quickly gain an idea of the numbers of larvae in the crop.

In thicker crops such as canola and faba beans, placing a white or yellow sheet (a beat sheet) on the ground and vigorously shaking foliage to drop grubs onto the sheet is a preferred method.

Each crop has a threshold of larvae that is usually determined by the value of the crop and its intended use.

Most markets will specify maximum heliothis damage limits, giving a guide to the attention you must pay to the pest.

Common thresholds vary quite widely and can be found in the Insect and mite control in field crops publication available from NSW DPI.

Once the threshold has been reached the main way to control grubs is to use insecticides.

Most insecticides work best before the grubs reach 10mm in length.

In some cases more than one insecticide application is warranted to minimise crop damage.

Contact your NSW DPI agronomist

This story appears Agriculture Today.