AUBURN, Ala.—Responsible crop management is one of the most important aspects of row crop farming. Producers need to correctly identify and scout for insect, disease, and other problems in order to choose appropriate management strategies.
Alabama Cooperative Extension System Entomologist, Dr. Kathy Flanders, said there are two primary insects to look for in small grains this winter: aphids and Hessian fly. During warmer winters, like the one Alabama is experiencing this year, the populations can multiply quickly.
“While these insects are not closely related and damage plants in different ways, they are similar because they have multiple generations per year,” Flanders said. “The warmer it is, the faster they grow.”
Aphids carry Barley Yellow Dwarf virus — a common wheat disease in Alabama. To learn more about Barley Yellow Dwarf virus, click here.
Flanders said it may be difficult to recognize aphids because some adult aphids have wings, while others do not. Both winged and unwinged adult aphids are fully functioning.
Most researchers believe bird cherry-oat aphids are the primary vector for Barley Yellow Dwarf in the Southeastern region, although there are several other species that can also spread the virus. For example, rice-root aphids are known to bring
Barley Yellow Dwarf virus in the fall. Aphids known as greenbugs are not capable of spreading the virus, but can directly damage small grains as they feed.
“Aphids may be difficult to scout for because they are found on the underside of the leaves, or feed at the base of the stem,” Flanders said. “In cold weather, aphids move to the base of the plant. They may also be found underground.”
Researchers try to predict the yearly risk of Barley Yellow Dwarf virus using research from previous years, because it is not always economical to scout small grains.
When planting during the recommended planting date for grains in North Alabama, a seed treatment or a foliar insecticide spray 30 days after planting is the best course of action. In South Alabama, a late January to early February spray will be most effective. Central Alabama wheat is at risk for an early round of Barley Yellow Dwarf in the fall, and again in the spring. Flanders recommends two rounds of spray in Central Alabama if the producer can afford it—30 days after planting, or at aphid development in late January and early February.
Because many producers planted late due to droughty conditions in late 2016, Flanders is recommending a spray application in late January or early February.
Producers who are able to scout may see numbers of aphids above the threshold, even after a foliar application. Scouting should be done on a day with temperatures above 60 degrees Fahrenheit.
How to Scout for Hessian Flies
Like aphids, earlier planting means a heightened risk of damage from Hessian flies.
“Start looking for plants that just don’t look right,” Flanders said. “When looking for Hessian fly your first assessment will likely be ‘This field just doesn’t look right.’”
Two signs of stunted growth will be discoloration and leaf blades that appear to stick straight out of the ground.
When Hessian flies arrive early and go untreated they can kill the plants outright. During early season scouting, pull the leaf sheath away from the base of the plant and look for larvae. As the wheat plant joints, the infestation will move further up the plant. Hessian fly adults tend to lay eggs on the uppermost newly expanded leaf.
Hessian flies look like many other flies, with beaded antennae and long legs like a mosquito, making it difficult to find them in the field. It is best to look for the pupal, or flaxseed stage of the insect to determine when they will likely change into adults.
Thin, sparse stands and dead tillers are good indicators of Hessian fly damage. If there is already substantial yield loss from heavy infestation in the field, the best decision may be to abandon the field.
“Hessian fly immatures are protected in the plant for most of their life, so it is difficult to control them with foliar insecticides,” Flanders said.
Field rescue may be possible if producers scout several times per week and apply pyrethroids in a timely manner. Spray pyrethroids when adult Hessian flies begin to emerge.
This article is based on information from the monthly Crops webinar, hosted by the Alabama Cooperative Extension System Crops Team. For more information, visit www.aces.edu/crops. To listen to this webinar in its entirety, click here. Contact your local Extension office for assistance in the field.
Featured image by www.shutterstock.com/Grisha Bruev.