In the southern part of the state, corn growers are busy either planting or preparing ground to plant. Every day is crucial to move towards hitting the ideal window for good yields in corn. Yet, so many other needs on the farm, need the same attention. If you happen to have any small grain production, the warm weather the last couple of weeks have been ideal for aphid infestations in small grains field. I talked to Dr. David Buntin to get his insight on what we are seeing in many of our fields. He is the current interim Assistant Dean at the University of Georgia-Griffin Campus and stills serves as a UGA Professor of Entomology at the Griffin Campus, His research and extension duties focused on integrated pest management in many agronomic crops . Over the past decades he has research and written extensively on insect pests in corn, sorghum and small grains. The following comes from our conversation and the material he has provided over the years.
You may be unfamiliar with aphids and the damage that occurs from their infestations. Aphids are small, soft-bodied insects that can be found in wheat or other small grains anytime during the growing season. The most common aphids found on wheat are the bird cherry-oat aphid, rice root aphid, greenbug, corn leaf aphid, and English grain aphid. The first four occur mostly in the fall and winter. Only the greenbug causes direct feeding damage that appears speckled brown and discolored with some leaf curling. The other aphids usually do not cause obvious feeding damage. The English grain aphid is mainly present in the spring and can reach large numbers on flag leaves and developing grain heads. Damage from this pest can reduce kernel size and lower grain test weight. Aphids are a serious pest of wheat, barley and oats because they also transmit a viral disease named barley yellow dwarf (BYD) and a related disease called cereal yellow dwarf. Wheat and barley can be severely damaged, but oats are very susceptible to this disease.
BYD is present in most fields in most years throughout Georgia. Yield losses are sporadic but losses of 5-15% are common and can exceed 30% during severe epidemics. Infection can occur from seedling emergence through heading, but yield loss is greatest when plants are infected as seedlings in the fall. Although all aphids can potentially transmit certain strains of the virus, infections in the Southeast are mostly associated with infestations of bird cherry-oat aphid and rice root aphid. Planting date is the single most important management practice, with early plantings having greater aphid numbers and greater BYD incidence than late plantings. For the most part, beneficial insects such as lady beetles are helpful in reducing aphid numbers in the fall before frost and in the spring, but they are not active during the winter when aphids can quickly increase to large numbers during warm periods. Weather conditions lately have been most conducive for rapid aphid production and easily expand to damaging levels.
I strongly encourage all growers with any small grains to take a little time during this week to scout their field for aphids. The information below is a recommendation on how to scout and, the thresholds needed for an positive economical return.
In late winter and early spring, inspect at least 6 inches of row of both stems and leaves. As grain heads emerge, count all aphids on both the flag leaf and head for making control decisions. Sample plants at 5 to 10 locations per field. Treat when populations reach or exceed the following thresholds:
- Stem elongation to just before flag leaf emergence: 2 aphids per stem.
- Flag leaf emergence: 5 aphids per flag leaf.
- Heading emergence to early dough stage: 10 aphids per head. Do not treat for aphids after mid-dough stage.
If you believe that your plants will begin the heading phase within 10 to 14 days and you intend to spray a fungicide AND, you do not meet the threshold above for spraying, but still see a few aphids, I would encourage adding a pyrethroid insecticide to a fungicide to protect the developing grain. If you meet the threshold and your crop is in early stem elongation or Feekes 6, then I would consider an application. There are many good pyrethroids (i.e. Declare, Proaxis, Warrior, Zeon, Lambda, Baythroid, etc) to choose. Please check with your local county Extension agent for help in choosing the right material for your farm and the right rate. The following url is an Extension site that you can down load to review: https://extension.uga.edu/content/dam/extension/programs-and-services/integrated-pest-management/documents/handbooks/2021-pmh-comm-chapters/SmallGrain.pdf