Friday, August 22, 2014

Soybean Aphid Populations mixed, Field Infestations can be quite Different

A quick survey of soybeans around the northwest MN region revealed great variability in soybean aphid populations. 

Some fields have not required treatment, many fields have been treated and are in good shape, other fields not treated may have quite variable numbers and often are related to growth stage with R3 fields still vulnerable to losses from threshold populations.

Reports from southwest MN and observations in the Detroit Lakes area have detected aphid movement to buckthorn. We can find winged migrants moving to buckthorn and producing nymphs at those sites. However, not all aphids are heading to buckthorn.  Quick estimates of populations on soybean suggest the aphids are only about 25% with wingpad development. Those without wing pads visible will be staying put;  their babies will likely be winged, though.

Full maturity and later planted soybeans, in general , have the most aphids now and nymphs are still being produced. Each field is different!

Don't quit scouting too early.  If you have questions on when to stop using the 250 aphid/plant threshold - see the video prepared by Bruce Potter, IPM Specialist, SWROC - Lamberton at the https://www.youtube.com/watch?v=VidX3KZEPnI. 

He will mention growth stage information at the end.

If you apply a pesticide to control insects or mites, check the field in 3-5 days to check performance.   Switch insecticide classes if you are re-treating any fields.   

Unless accompanied by high winds, hail or a flood, rainfall events will not eliminate an aphid or spider mite problem. Prolonged cool, wet weather can produce population crashing diseases affecting the aphids and mites.  Heavy dews can be as effective as rain in stimulating the fungal parasites that impact them.