in Small Grains Fact Sheet No. 5.568 Series|Crops by F.B. Peairs* Russian Quick Facts The (RWA) was • Several kinds of aphids infest first reported in Colorado in March 1986. small grains. Good RWA management practices have emphasized resistant varieties, cost-effective • The Russian wheat aphid use of insecticides and certain cultural (RWA) and the greenbug are practices. Resistant varieties and biological the most destructive species control agents have been effective enough in the state. to replace the need for insecticides in many cases, however, recent occurrence of new • Chemical control of other biotypes have made resistant varieties much Figure 1: The Russian wheat aphid. aphid species rarely is less useful. necessary. The RWA damages small grains by injecting saliva into and sucking sap from • Use the key (Figure 5) to plants. Yield losses of 50 percent or more determine what aphids are to this can be expected if economic present in the crop. infestations are left untreated. U.S. research has shown that RWA is not an important vector of yellow dwarf virus or other cereal diseases. Figure 2: Discoloration caused by the Russian wheat aphid.

Life Cycle These grasses serve as alternate hosts Two forms of RWA are found in Colorado for RWA during the period between grain during the year: a wingless female and a harvest and the appearance of new wheat winged female. It is difficult to determine in the fall. Volunteer wheat and barley also if an individual aphid will be winged or may become infested. Volunteer wheat and wingless until it is near maturity. barley are important sources of RWA for the In Colorado, most severe spring new fall crop as soon as it emerges. Weather infestations of winter grains are caused by conditions that favor cool season grasses and wingless aphids that overwintered in the volunteers will increase the number of aphids crop. Winged aphids begin to appear in April infesting the new wheat crop in the fall. and May and flights peak during July in most Movement to the new crop occurs wheat-producing areas of the state. At this in October and early November. RWA time, winged aphids include both local aphids can survive the winter in most Colorado and immigrants from the south. grain growing areas, except the San Luis Winged aphids infest late-maturing Valley. Winter weather conditions that are winter wheat and spring grains but not detrimental to RWA in Colorado include corn, millet or sorghum. They also infest a several cycles of wet snow followed by a rapid number of cool-season grasses, particularly melt and a quick freeze, prolonged exposure wheatgrasses. Damage to newly seeded to temperatures below 15 degrees F, and ©Colorado State University grasses can be significant. extended periods of snow cover. Extension. 6/98. Revised 4/16. extension.colostate.edu

*Colorado State University Extension entomologist and professor, bioagricultural sciences and pest management, emeritus. 4/2016 Cultural Controls Planting-Time Soil and Seed Treatments Although insecticides provide the most effective RWA control, several other Treatments with soil systemic practices can help minimize the need for insecticides and certain seed treatments chemical applications. can control RWA for a substantial period of 1. Control volunteer wheat and barley. time if adequate soil moisture is available. Although many grass species help RWA Since the fall RWA flight is expected six to survive the summer, volunteers are the eight weeks after planting, such treatments most important source of infestation for may not last long enough. Figure 3: Wheat plants damaged by the Russian the new crop in the fall. Try to have a The risk of significant fall infestations wheat aphid. three week volunteer-free period prior is generally considered to be low in to emergence of fall seedings. Colorado. Consider using planting-time Signs of Infestation 2. Adjust planting dates. Plant winter treatments only when the risk of fall RWA can be found in winter wheat, wheat as late as possible in northeastern, infestation is high, for example: when usually on the younger leaves, from southwestern and western Colorado. planting near uncontrolled volunteers, emergence in the fall to grain ripening. Recommended planting dates have when planting early, when planting near Aphid feeding prevents young leaves from not been determined for southeast other common alternate hosts such as unrolling. RWA colonies are found within Colorado. Plant spring grains as early one of the wheatgrasses, when planting the tubes formed by these tightly curled as possible. near rangeland or CRP, or if the area has a leaves. This not only makes it difficult to 3. Produce a healthy, stress-free crop. history of fall RWA infestations. achieve good insecticide coverage but also RWAs often get their start in stressed interferes with the ability of predaceous fields or stressed portions of fields Fall Aerial or Ground Applications of and parasitic to reach and attack and cause relatively more damage to Foliar Insecticides aphids. New beneficial insect species better stressed plants. Test the soil and fertilize These should be considered if more able to attack RWA were identified in areas accordingly. Plant certified, treated seed. than 10 to 20 percent of the plants in a field where the aphid is native. Promising species Select a variety that is well adapted to show RWA damage and weather conditions are being imported and released by the local growing conditions. are expected to remain favorable for an Colorado Department of Agriculture. extended period. To determine the level Leaves infested by RWA have long Resistant Varieties of infestation, walk a diagonal or zigzag white, purple or yellowish streaks. Under pattern across the field and stop at least 10 some conditions, infested wheat tillers have These resistant varieties are still the times to examine 20 consecutive plants. a purplish color. Heavily infested plants most economical and effective management It also is best to examine some damaged are stunted and some may appear prostrate option for Biotype 1. Also, they are well plants for RWA, but they may be difficult to or flattened. adapted to Colorado production conditions find on cooler days or during bad weather. After flowering, some heads are and should be good variety choices Scout fields every two weeks in the fall. twisted or distorted and have a bleached regardless of their resistance to Russian Visit a field more often if a RWA infestation appearance. Heads often have a “fish hook” wheat aphid. Biotypes other that Biotype is detected. shape caused by awns trapped by tightly 1 must be managed with the methods Fall control generally has been more curled flag leaves. At this time, most RWA developed before resistant varieties were effective than spring control. The risk of are found feeding on the stem within the available. These include biological control, increased winter injury and some loss of flag leaf sheath or on developing kernels. cultural controls and judicious insecticide yield potential if treatment is delayed until There may be poorly formed or blank treatments based on appropriate scouting spring needs to be balanced against the grains. The entire head sometimes is killed. and economic threshold information. possibility that RWA overwintering success There are also important differences will be low. among the small grain crop species. are resistant to RWA. Although heavy Spring Insecticide Treatments infestations have been observed, little These are recommended according to economic damage has been detected. the guidelines below. Plants with even a Resistant barleys have been developed single infested or damaged tiller should be including Stoneham and Sidney. considered infested. Regrowth to early boot stage: Insecticides 5 to 10 percent damaged and infested Insecticides recommended for RWA plants. control are in the High Plains Integrated Early boot to flowering: Pest Management Guide, which is available 10 to 20 percent damaged and infested Figure 4: “Fish hook” distortion caused by plants. trapped awns. Each damaged head is compared at www.highplainsipm.org. Be sure to read to an undamaged head. and follow all label directions. Insecticides After flowering: may be applied at one of several times More than 20 percent damaged and during the growing season. infested tillers. A more accurate method to determine Control of Greenbug and the need for treatment is to walk a diagonal Other Aphids Some greenbugs are resistant to or zigzag pattern across the field, stop 10 some insecticides. Resistant greenbugs times and collect 10 tillers at random at Like the RWA, greenbugs damage small are not widespread. If a control failure is each stop. (Avoid bias in selecting tillers at grains by injecting toxic saliva into and experienced, it is unlikely that control will each stop. For example, take the 10 tillers sucking sap from the plant. It also is an be achieved by retreatment with the same closest to your foot or every fifth tiller important vector of product or a different insecticide with the starting with the one closest to your foot). virus. Other aphid species are important same mode of action. Most insecticides More efficient sampling procedures are transmitters of barley yellow dwarf and currently registered on small grains have described in Sampling Russian Wheat Aphid other viruses and may reduce yields as well. one of three modes of action. The best way in the Western Great Plains, Great Plains For economical control of the greenbug to avoid such problems is to treat greenbug Agricultural Council Publication 138. and other aphids, combine biological infestations only when they exceed action Examine the tillers and count the control, cultural practices and, if necessary, thresholds. Ask your local Colorado State number that contain RWA. This number insecticide treatments. Lady beetles and University Extension county office or other is the percent infested tillers and can be parasitic wasps often keep these aphids reliable source whether greenbug failures compared to the economic threshold below economically important levels. have occurred in your area. calculated with the following formula: Use the field key below to determine ET = (CC * 200) / (EY * MV) which aphids are infesting your crop. *This key requires observations of aphid where: Descriptions of the major species as well cornicles, which are tubular structures ET = Economic threshold or the percent as a list of insecticides for their control found at the rear of the aphid, and infested tillers above which an are found in the High Plains Integrated antennae. In some aphids the cornicles are insecticide application will be cost Pest Management Guide (www. easily observed, while in others they are effective. highplainsipm.org). Minor species can greatly reduced in size. You will need to CC = Control cost per acre (insecticide be managed in the same manner as the observe the cornicles through a 10X hand plus application) important species. lens before you go through the key. EY = Expected yield per acre MV = Market value per bushel Field Key to Important Small Grain Aphids*. After flowering, substitute 500 for 200 in the numerator of the formula. If the 1. A. Cornicles long and tubular in 6. A. Cornicles all black. English calculated ET is lower than the percent shape. Go to 2. grain aphid. infested tillers observed, a treatment B. Cornicles very short and B. Cornicles black just at the tips. should be cost effective. There probably is rounded. Go to 8. Rose grass aphid. no benefit from insecticide applications made after the crop has reached the soft 2. A. Body greenish, yellowish or 7. A. Cornicles dusky. Corn leaf dough stage. pinkish. Go to 3. aphid. Scout fields at least weekly in the B. Body dark, chocolate brown. B. Cornicles black just at the tips. spring. Spring foliar treatments have been Rusty plum aphid. Usually with a darker green stripe on back. the most common type of treatment in Greenbug. Colorado. Chlorpyrifos is available in 3. A. Red coloration on abdomen. several restricted use products and has been Go to 4. 8. A. Shiny brown to black aphid, the most consistent product commercially. B. No red coloration on spiny appearance under magnification. Both cool temperatures and drought abdomen. Go to 5. Hedgehog grain aphid. stress can interfere with the plant’s ability B. Spindle-shaped gray to green aphids, to absorb systemic insecticides. If the 4. A. Antennae with five segments usually associated with tightly rolled and crop is stressed, consider using a contact and long fine hairs. root aphid. discolored leaves. Go to 9. insecticide alone or a contact/systemic tank B. Antennae with six segments mix. Avoid herbicide/insecticide tank and short antennal hairs. Bird cherry- 9. A. When viewed from side, mixes if the crop is stressed. aphid. a single projection from the tip of the Make ground applications in at least abdomen. Waxy, gray appearance. Western 10 gallons of spray volume per acre. Aerial 5. A. Cornicles relatively long, wheat aphid. applications can be made in one gallon almost reaching the tip of the abdomen. B. When viewed from side, a double of spray volume per acre prior to jointing Go to 6. projection from the tip of the abdomen. and after flowering. Otherwise, use 2 B. Cornicles relatively short, Greenish appearance. Russian wheat gallons per acre. shorter than the distance to the tip of the aphid. If greenbugs are present in the field, see abdomen. Go to 7. the recommendations below. Insecticide applications generally are Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. CSU Extension programs cost effective in Colorado, but do not are available to all without discrimination. No endorsement completely prevent yield losses. of products mentioned is intended nor is criticism implied of products not mentioned.