Mirids

• Low numbers (≤1 per m²) are often present in vegetative crops, but do not damage vegetative terminals or reduce yield.
• Mirids are very mobile and in-crop populations can increase rapidly as the crop reaches the budding stage.

Damage includes flower and bud abortion. Mirids release a chemical while feeding that destroys cells in the feeding zone causing black spots.

Soybeans/peanuts are not at risk.

• Population increases – cloudy days with temperature around 30°C.
• Population decreases – temperatures above 35° C for 3 or more days.

Numbers may be lower after heavy rains or storms, though storm fronts may also bring influxes of adults. Mirid migrations from inland areas are associated with weather fronts. Mirids can also move in from surrounding crops and weed hosts early in the summer.

Monitor twice weekly using a beat sheet from budding to early podding. Sample 5 one-metre lengths of row (non consecutive) within a 20 m radius, from at least six sites throughout a crop. Avoid sampling in very windy weather as mirids are easily blown off the sheet. Record the numbers of mirid nymphs and adults, and number and types of beneficial insects.

• Control weeds, as mirids will move into crops as alternative hosts dry off. Examples include wild turnips, wild beans, wild sunflower, marshmallow, noogoora burr, verbena and thistles.
• Mirids can migrate between crops. Cultivated mirid hosts include cotton, safflower, sunflower, and lucerne.
• Shorten the crop flowering period by planting on full moisture profile and water crops just before budding.
• Mirids have a preference for lucerne – strip cropping with lucerne may prevent movement of mirids into pulse crops. Lucerne may also help promote natural enemies.

Peanuts and Soybeans: Only spray if populations exceed 5/m². Populations up to this level have not reduced yield in field trials.

• Trials have shown that the addition of salt (0.5% NaCl) as an adjuvant can improve chemical control of mirids at lower chemical rates.
• Salt mixtures allow a reduction in chemical rate of 50-60%, which significantly reduces impact on beneficials and the risk of flaring helicoverpa.
• Refer to the impact of pesticides on beneficials table when choosing between chemical options
• Insecticide resistance has not been detected in mirids.  The continual influx of mirids into cropping areas from inland regions reduces selection pressure for resistance.

• To reduce the risk of flaring helicoverpa, delay spraying by up to 1 week (unless populations are at least 1.5x threshold).
• Consider mirid sprays with dimethoate at lower than the full registered rate of 500 mL/ha to reduce the risk of flaring helicoverpa. If using a lower rate, always include a 0.5% salt adjuvant.

Industry publications can provide up to date information about regional pest issues.