Figure 1. Bird cherry oat aphids.
Figure 1. Bird cherry oat aphids.
South Dakota winter wheat planting is fast approaching, and with that comes an opportunity to employ a few preventative management solutions. Although we cannot predict aphid pressure in winter wheat for 2015, there are some steps that may be taken in an attempt to reduce the risk associated with these insects. There are four species of aphids that will infest winter wheat in South Dakota: the bird cherry oat aphid (Figure 1), English grain aphid, greenbug, and Russian wheat aphid. While direct feeding injury is always a concern for yield, bird cherry oat aphid, English grain aphid, and greenbug are also vectors of Barley yellow dwarf virus (BYDV).
 
Bird Cherry Oat Aphid
 
This aphid is generally dark green to olive in color, and has a characteristic red-orange patch at the base of its abdomen near the cornicles (tailpipes). Bird cherry oat aphids overwinter as eggs on Prunus species, and migrate to cereal crops in the late spring to early summer. This aphid is also known to infest corn and populations can be very abundant in the fall on winter wheat.
 
English Grain Aphid

English grain aphid. Although found in South Dakota, this aphid is rarely of economic concern for small grain farmers. It is typically light green to brown in color. The distinguishing characteristics for the English grain aphid are its black antennae, cornicles, and leg joints. This aphid causes direct feeding injury to the heads of small grains, and will aggregate and feeding on the kernels once heading initiates. The English grain aphid overwinters in southern states, and migrates to South Dakota in the spring.

Greenbug

This aphid is light green in color with a dark green stripe on its back. The antennae are generally black. Greenbugs feed on the underside of lower leaves of wheat. Feeding by the greenbug causes yellow discoloration and red spotting on leaves due to a toxin present in their saliva. This aphid does not overwinter in South Dakota, and migrates from southern states in the spring.

Russian Wheat Aphid

This aphid is a dusty blue-green color. The distinguishing characteristics for the Russian wheat aphid are its short antennae, and reduced cornicles. This species of aphid is generally found on younger leaves, and its feeding prevents the leaves from uncurling. In addition to curled leaves, Russian wheat aphids inject a toxin into plants that cause long white or yellowish streaks. During cold weather infested plants will exhibit a purple color. Movement to winter wheat occurs in October and early November. The Russian wheat aphid is found in neighboring states, including Nebraska, North Dakota, and Wyoming. Although it is not a major pest in South Dakota there is the possibility for it to be found in the western portion of the state.

Cultural Preventative Practices

Field sanitation can be important to reduce aphid infestations in winter wheat. Volunteer cereals should be removed to prevent the buildup of aphid populations in the field prior to planting. However, even if in-field populations are reduced, aphids are capable of flying from neighboring fields so infestation is still possible. Resistant wheat varieties exist for Russian wheat aphid, but not for the other three aphid species present in South Dakota. An additional method to prevent or reduce the likelihood of aphid infestation is to delay planting. Optimal winter wheat planting in South Dakota is from September 10 to October 10. Delaying winter wheat planting to the 20 September or later reduces the chances for aphid infestation, which in turn reduces the incidence of BYDV.

Insecticide Seed Treatment

Another preventative management tactic is to use systemic insecticides as seed treatments. Although these insecticides will not be effective for the entire fall season, they do have the potential to reduce early aphid infestations. Because the insecticides are present in plant tissue, they are reported to reduce the incidence of BYDV by managing aphid populations before the virus is vectored to the wheat. Common insecticide seed treatments that are labeled for wheat can be found in Table 1.

Table 1. Insecticide seed treatments labeled for aphids in wheat.

Insecticide
(active ingredient)
Rate
(for aphids)
Cruiser 5FS
(thiamethoxam)
0.75 to 1.33 fluid oz. per 100 lbs. seed
CruiserMaxx Cereals
(thiamethoxam + fungicides)
5.0 fluid oz. per 100 lbs. seed + 0.48 to 1.0 fluid oz. Cruiser 5FS
Gaucho 600
(imidacloprid)
0.8 to 2.4 fluid oz. per 100 lbs. seed
Gaucho XT
(imidacloprid + fungicides)
3.4 to 4.5 fluid oz. per 100 lbs. seed