Northwest Plains Pest Management News Vol XI Issue 14

Spring seeded crops have progressed to “the short rows”. Corn harvest for both silage and grain has commenced; preliminary yields, while not record breaking, are encouraging. Cotton and sorghum have progressed very well. Cotton , for the most part has shed much of the small immature fruit and looks to have a chance to adequately mature the harvestable bolls. Sorghum seems to have really made the most of available moisture , many fields look surprisingly good considering.  Winter wheat seeding is off to a rapid start, many of the earlier planted fields have emerged and have began to tiller.

Corn and cotton has matured to the point that pest damage is unlikely. Defoliating pests and aphids could still be problematic in cotton but at this point risk appears to be low. Late maturing sorghum may still susceptible to headworms and should me monitored but once sorghum reaches the hard dough stage it should be safe from headworm damage.

Harvest aids can be applied to sorghum to bring grain to a more uniform moisture level and dry down weed escapes. Timing is very important as an application made to early will reduce yield. Once sorghum has reached physiological maturity a harvest aid can be applied without risking yield. Sorghum is considered physiologically mature when the black layer has formed at the base of the kernels (approximately 30% moisture), at this point the grain has reached maximum weight. Once a harvest aid has been applied harvest should be planned accordingly; under normal conditions harvest aids shouldn’t cause a lodging issue for up to 3 weeks but after 30 days lodging could be significant. Ideally sorghum should be harvested 10-14 days after a harvest aid application. Several products are available: sodium chlorate (up to 6 lbs/acre) and glyphosate (up to 2 qt/acre) have been used successfully. Aim is also labeled for use as a harvest aid in sorghum and should be particularly useful in weedy fields.

Large areas of dead wheat as a result of white grubs have been observed in a few fields in the area. White grubs are the larval stage of insects commonly known as May or June beetles. White grubs, sometimes referred to as grubworms, injure wheat by feeding on roots and other underground plant parts.

Emerging wheat damaged by white grubs.

White grubs require 1 to 4 years to complete their life cycle, depending on species. Local observations have documented both Phyllophaga and Cyclocephala species; infestations with near 80% Phyllophaga species have been identified in some fields. Phyllophaga species may have life cycles exceeding one year in which case larger grubs with larger appetites may be present when wheat is most susceptible, in the seedling stage
The adult stage of the various white grub species are heavy-bodied beetles, 1⁄2 to 5⁄8 inch long, brown, with long, spindly legs. In summer adult beetles lay  eggs in the soil, within about two weeks the eggs hatch into small white grubs that feed on plant roots.

White grub feed on wheat roots

White grub larvae are creamy white and C-shaped, with three pairs of legs and tan to brown heads. Larger larvae (1⁄2 to 1 inch-long) are responsible for most damage due to their large size and voracious appetites. Feeding by large numbers of large white grubs can quickly destroy  root systems, killing seedlings.
While there are no registered insecticides for white grub control in wheat, limited field tests suggest that Gaucho® and Cruiser® seed treatments which target aphids and greenbugs may provide some suppression of small larvae but will not likely provide desired results if larvae are large. Lorsban, also labeled for aphid control in wheat, may provide suppression when chemigated.

Small and large white grubs

Fall armyworms, beet armyworms and/or army cutworms have been found in a few area wheat fields, most infestation have not justified treatment at this point but should be monitored closely.  Small larvae are feeding on leaves, creating tiny “window panes” in the leaves Control is suggested when there are four or more larvae, 1 inch or longer, per square foot, and their damage is threatening the stand.  Wheat which is not well established (newly emerged, thin, etc.) may not be able to tolerate as many foliage feeding worms and is at greater risk of damage.  If other species of foliage feeding worms are present, then an aggregate larval population should be considered when making management decisions.    

Beet armyworm feeding on emerging wheat