There are several different species of aphids that can be found infesting wheat. The two that most commonly occur in Arkansas are the bird cherry-oat aphid and the corn leaf aphid. Even though these two species can reach high numbers in wheat, they seldom cause significant economic damage. Treatment is not recommended unless numbers are extremely high and the crop is otherwise under some kind of additional stress. We are seeing high numbers in some fields in south Arkansas at this time. A few fields have reached such high numbers that the leaves are beginning to yellow and wilt. In these situations we are recommending an insecticide treatment.
Greenbugs are the third species and can cause significant economic damage when they reach treatment threshold. Greenbugs differ from the other species in that they inject a toxin when they feed. The areas where a greenbug has fed will show yellow discoloration. Heavy feeding can cause leaves and sometimes entire plants to die. Treatment level for greenbug varies with the time of year and the size of plants as shown in the table below.
Treatment levels for greenbugs in wheat.
|Number per row foot||Plant height||Time of season|
|50||4 – 6 inches||fall and early spring|
|200||6 – 10 inches||Mid-March|
|300||10 – 20 inches||Mid-April|
(For broadcast wheat, use a square foot measurement and double the numbers in the 1st column above)
As plants grow larger they can withstand much higher populations. Much of our wheat is at the 6 – 10 inch size and would require treatment if greenbug numbers are around 200 per row foot.
Aphids have many natural enemies that attack them. Lady beetles and parasitic wasps do an effective job in keeping aphid populations in check. Aphids that are parasitized will become brown and bloated in appearance. If predator numbers are high and/or the number of parasitized aphids in a field are approximately 20 percent of the population, growers should consider waiting before making an insecticide application. Often when the level of parasitized aphids reaches 20 percent, aphid populations will crash. If treatment is needed, avoid using pyrethroid insecticides. Pyrethroids will give some suppression of greenbugs, but they will often rebound to higher numbers later. Dimethoate, malathion, methyl parathion or Lannate are recommended for control of greenbugs in wheat.
One other topic that needs to be addressed is Barley Yellow Dwarf (BYD). BYD is a viral disease that can be vectored by aphids. However, controlling aphids to avoid BYD in the spring is not recommended. Spring BYD infections seldom cause significant yield loss.