What is eating my soybean pods?

Field crickets
High numbers of field crickets have been reported across the Darling Downs in the last couple of weeks, with some large aggregations of adults attracted to lights at night. Are these crickets doing damage to crops? The answer may well be yes.

Field crickets are generally a pest of pastures but can also attack soybeans, cotton, sugarcane and sunflowers. There are two species commonly found – the brown field cricket and the slightly larger black field cricket. The brown field cricket is the most prevalent at present. Crickets hide during the day in cracking soils or under clods of dirt or crop residue and emerge at night to feed on crops. They usually feed on seedlings but high populations in late summer may feed on more mature plant structures such as sunflower heads and soybean pods.

How do I know that crickets are damaging my soybean pods?
Crickets are not the only pest of soybean pods. Mice can also do considerable damage to pods, with soybeans often the last of the summer crops to mature and as a consequence the only source of food on offer for mice.

Cricket adults and large nymphs chew into pods to reach the seeds but this damage looks similar to damage done by mice. So how do you determine what pest is doing the damage?

The best time to check for crickets is to inspect crops at dusk or later into the night when crickets are most active. Field cricket activity can also be monitored with light traps. Another way to determine whether crickets are present is by using hessian bags placed out overnight at regular intervals across the paddock. In the morning check for the presence of crickets sheltering under the bags.

The best way to determine whether mice are damaging the crop is to go out at night to check for their presence or use mouse bait cards (as described on the DPI&F website).

Mice damage to soybeans can be an ongoing and costly problem as soybeans provide good groundcover for mice and excessive grain losses immediately prior to or during the harvesting operation are likely to increase mouse populations given an ongoing food source. This will also impact on early follow-on cereal crops such as wheat and barley.

For further information on how to manage mice in your crop please visit the DPI&F website through the link provided below:

http://www.dpi.qld.gov.au/cps/rde/dpi/hs.xsl/4790_8283_ENA_HTML.htm

How do I control the crickets if they are damaging my soybeans?
Past experience has shown that foliar insecticide applications do not provide control of crickets. They shelter by day and are found low down under dense canopy at night, making spray contact difficult.

Chlorpyrifos-treated cracked grain baits are registered for cricket control in soybeans, but this is mainly used to protect seedling crops. The bait is prepared by mixing 100 mL chlorpyrifos (500 g/L EC formulation) and 125 mL sunflower oil, and adding this to 2.5 kg of cracked wheat or sorghum/ha. The bait is broadcast evenly by air or ground.

Article by David Murray and Kate Charleston