Many wheat fields in southwest Missouri have infestations of greenbug and bird cherry-oat aphids. These aphids can cause direct feeding damage by sucking plant juices, but may also transmit barley yellow dwarf virus (BYD) in wheat. Greenbugs are light or pale green in color with a predominant dark green line running down the back. They may damage wheat plants in both fall and spring, however numbers of this pest have remained low until about 3 weeks ago, when numbers began to build following early spring storms and strong winds blowing into Missouri from more southern regions of the U.S. Thresholds for this aphid are based on the average number of aphids present per foot of row depending on plant height and stage of growth. In general, traditional economic thresholds would be as follows: treatment is justified if 50 or more aphids are present per linear foot of row in the seedling stage; 100 or more present during the 3- to 6-inch stage of growth, and 300 or more aphids when the plants reach 6- to 10-onches in height. Recent research in Missouri and other states suggest that these thresholds may be too high and allow for more damage and subsequent yield loss than necessary. Much of this variability is due to plant size and stand density when infested, the number of aphids and amount of BYD virus present, and spring growing conditions. Another factor to consider is whether biological control agents such as ladybugs and parasitic wasps are active in the field.

Insecticide Recommendations for Greenbug
Chemical Name	Product Name	Rates: Amount of Product (Unless otherwise noted)	Preharvest Interval (PHI)
Dimethoate	Dimethoate; Dimate	See specific label	See specific label
Chlorpyrifos	Lorsban 4E*	0.5 to 1 pt / acre	28 days
Chlorpyrifos	Nufos 4E*	0.5 to 1 pt / acre	28 days
Chlorpyrifos	Several formulations*	See specific labels	See specific label
Gammacyhalothrin	Proaxis*	3.84 fl oz / acre	30 days
Lambdacyhalothrin	Warrior*	3.84 fl oz / acre	30 days
Lambdacyhalothrin	Several formulations*	See specific labels	See specific labels
* Indicates Restricted Use

Based on the preceding information, the recommendation for management of the greenbug is as follows: If the average number of greenbug per linear foot of row equal or exceed 50 to 100 on wheat less than 6-inches in height, then treatment may be needed. Producers should consider the number of beneficial insects present (examples: adults and larvae of pink ladybugs and other species of ladybird beetles, parasitic wasps) and whether the wheat is under other stressors such as drought. The presence of high numbers of beneficial insects will increase the threshold and reduce the need for insecticides, whereas, the greater the stress on the plants, the lower the thresholds as stressed plants are less able to withstand aphid infestations.

The bird cherry-oat aphid is typically dark olive in color with a rosy patch of color found on the back of the abdomen. This is a relatively large aphid which can look black in color at times. This insect is present in wheat in most years, but is often control by beneficial insects. The bird cherry-oat aphid can transmit BYD, but because this aphid often attacks the wheat at boot to heading stages of growth, thresholds are based on numbers of aphids present per tiller. In general, if an average of 50 or more bird cherry-oat aphids are present per tiller when the wheat is in the boot to heading stages of growth, then treatment is justified. Feeding by this aphid may result in damage to the flag leaf with the head taking on a hooked appearance as it emerges. We will continue to monitor this pest over the next couple of weeks. Remember to follow all label precautions, instructions and restrictions.

Wayne Bailey
573-882-2838
573-864-9905