With the wheat planting time approaching, it should be time for you to think about insect management. You’ve likely already ordered your seed, so choosing whether or not you will buy a seed treatment or whether or not you’ve purchased a Hessian-fly resistant variety is not an option at this point. If you did purchase an insecticide seed treatment, expect less than three weeks control against Hessian fly and aphids. You may have less control than this under heavy insect pressure and/or if you planted a Hessian-fly susceptible variety. If you’ve purchased a number of different varieties, it is likely that they will have variable resistance to Hessian fly. This link will take you to an up-to-date guide for resistance to Hessian fly in North Carolina for 2012. The remainder of this article contains suggestions for other practices to help manage insects in wheat during the fall.
Plant on time: Early-planted fields are susceptible to armyworm, Hessian fly and aphid infestation. There is no such things as a “fly-free date” in North Carolina, but later planted fields escape more insect pressure.
Rotate fields: Hessian fly can be problematic when planted into wheat stubble (double cropped with beans) or next to wheat stubble. This is because Hessian fly uses volunteer wheat as a bridge to harbor oversummering populations. We’ve had good moisture this summer that likely encouraged a good bit of volunteer wheat. Watch out for fields that may be planted for cover crops or dove hunting nearby. They were likely planted early and can serve as a source of infestation.
Till: Ok, so this is not an option in the Piedmont and your tillage system should reflect what brings your farm the most profit in conjunction with soil conservation. However, you should be aware that no-till fields with corn stubble are more attractive to aphids. Additional residue from no-till can be a place for things like cutworms to hide. Finally, the slower growing conditions associated with no-till wheat seedlings can predispose these fields to more tiller death from Hessian flies.
Foliar insecticides: These should only be applied if insects are present, with the rare exception of some fields where Hessian fly is a perennial and historical problem. Fall thresholds are:
1) armyworm, six 1/2 inch or longer caterpillars per square foot
2) Hessian fly, IF a source of fly is nearby (i.e., wheat has been planted in the same field, adjacent to, or within 1/4 of the previous year’s crop), a susceptible variety has been planted, seeds have not been treated with an insecticide, and Hessian fly has caused yield losses on this farm or nearby farms in previous years or Hessian fly eggs are present
3) aphids, 20 per row foot. The bird cherry oat aphid is the species that generally causes the most barley yellow dwarf virus in North Carolina wheat.
A spray at the 2-3 leaf stage is probably the best time to spray to prevent Hessian fly and barley yellow dwarf virus transmitted from aphids. Spray only when the threshold is reached.