As we enter spring, what insects should we be watching out for in our wheat fields?

In the Mid-South the last few years, we have had aphid pressure in the late fall going into winter.  Aphids have remained a concern into spring time and management is needed in many cases.  While talking with other agronomists who have been surveying fields for aphids this year, the highest concentration has been in fields where no insecticide seed treatment or fall insecticide has been applied. In fields that have been treated, the numbers have been very light to none. 

 

What issues do aphids create in wheat?

Barley yellow dwarf virus (BYDV) is a plant disease transmitted when aphids feed on the wheat plant. It is possible to experience significant yield loss when BYDV is present.  We have seen yield losses of 30% under heavy infections.  BYDV symptoms include yellowing or reddening of leaves, and stunted plants.  The earliest symptoms start occuring Feekes GS 6-8 and may continue showing up later in season.  It’s common to see patchy symptoms throughout a field and these patchy areas can become widespread throughout a field when aphid populations are high and left untreated.  It’s important to note that BYDV is a virus.  Once a plant is infected with the virus, we do not have a cure for it. 

What are thresholds and scouting tips?

There are varying numbers used for a threshold number for aphids. Ten per foot of row is one of the more common numbers used to start treatment. At this time of year, you need to check under the residue and the stem below ground level for aphids. On warm sunny days you can find them on leaves as well.  When temperatures are mild the numbers of aphids can grow quickly.  The time between nitrogen application and spring spray applications can be 4-6 weeks in some cases so that may factor into your decision.

 

What are management practices for aphid control?

In the fall, seed treatments of imidacloprid, clothianidin or thiamethoxam can reduce aphid populations for several weeks after planting.  The AgriMAXX PRIME ST Standard and Advanced seed treatments provide max label rate of insecticide for enhanced aphid control.  Early infections cause the greatest yield loss, thus making seed treatments very important.  

Many areas of the Midwest experienced a very cold January.  Aphids levels may also be reduced when temperatures reach single digits without a snow cover.

In the spring, growers can control aphids with an insecticide application.  Oftentimes, this is tank mixed with a herbicide application.  In the event your field is in excess of threshold populations and needing treatment before your herbicide application timing, growers in the Mid-South have documented lowering aphid numbers by including an insecticide with their liquid nitrogen application.  Bear in mind, this strategy won’t control the total aphid population and there is risk of future insecticide resistance development.