{"id":996,"date":"2015-02-24T15:39:13","date_gmt":"2015-02-24T20:39:13","guid":{"rendered":"http:\/\/site.extension.uga.edu\/applingcrop\/?p=996"},"modified":"2015-02-24T15:40:33","modified_gmt":"2015-02-24T20:40:33","slug":"problems-in-small-grains","status":"publish","type":"post","link":"https:\/\/site.extension.uga.edu\/applingcrop\/2015\/02\/problems-in-small-grains\/","title":{"rendered":"Problems in Small Grains"},"content":{"rendered":"

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I’ve looked at numerous small grains exhibiting\u00a0leaves and tillers that have yellowed and are showing red\/purple damage. These symptoms can be caused by many things, including nutrient deficiency, cold injury, and disease.\u00a0But some (not all)\u00a0of these cases have been barley yellow dwarf virus (BYD). BYD\u00a0is vectored by aphids. Below is a little info on aphids from Dr. David Buntin, Entomologist at UGA Griffin Campus:<\/p>\n

\u201cAphids are small, soft-bodied insects that can be found in wheat anytime during the growing\u00a0season. The most common aphids found on wheat are the\u00a0bird cherry-oat aphid, rice root aphid,\u00a0greenbug, corn leaf aphid, and English grain aphid. The first four occur mostly in the fall and\u00a0winter. Only the\u00a0greenbug causes direct feeding damage that appears speckled brown and\u00a0discolored with some leaf curling. The other aphids usually do not cause\u00a0obvious feeding damage.\u00a0The English grain aphid is mainly present in the spring and can reach large numbers on flag leaves\u00a0and developing grain\u00a0heads. Damage from this pest can reduce kernel size and lower grain test\u00a0weight. For the most part, beneficial insects such as lady beetles are not\u00a0active during the winter\u00a0and only exert some control over aphids during the spring in wheat. \u201cAphids also vector a viral disease named barley yellow dwarf (BYD) and a related disease called\u00a0cereal yellow dwarf. Wheat and barley can be\u00a0severely damaged, but oats are most susceptible to\u00a0this disease. BYD is present in most fields in most years throughout Georgia. Yield losses of 5-15%\u00a0are common but losses can exceed 30% during severe epidemics. Infection can occur from seedling\u00a0emergence through heading, but yield loss is\u00a0greatest when plants are infected as seedlings in the\u00a0fall. Although all aphids can potentially transmit certain strains of the virus, infections in the\u00a0Southeast are mostly associated with infestations of bird cherry-oat aphid and rice root aphid.\u00a0Planting date is the single most important management\u00a0practice, with early plantings generally have\u00a0greater aphid numbers and greater BYD incidence than late plantings. \u201cSystemic seed treatments, imidacloprid (Gaucho, Attendant, Axcess), thiamethoxam (Cruiser), and\u00a0clothianidin (NipsIt Inside), are available for\u00a0controlling aphids in the fall and winter and may\u00a0reduce infection rates of BYD. These seed treatments are more effective in the northern half of the\u00a0seed treatments have been inconsistent in control and are not recommended for\u00a0routine use.A single, well-timed insecticide application of the\u00a0insecticide lambda cyhalothrin (Karate Zeon,\u00a0Silencer, and similar products) or gamma cyhalothrin (Declare) also can control aphids, reduce the\u00a0incidence of BYD and increase yields. The best time for treatment in northern Georgia usually is\u00a0about 25 \u2013 35 days after planting although an\u00a0application at full tiller also may be beneficial. In\u00a0southern Georgia, the best treatment time usually is at full-tiller stage in early to mid-February. But,\u00a0scout fields for aphids at 25 \u2013 35 days after planting\u00a0and during warm periods in January to\u00a0determine if an insecticide application is needed. A lambda\u00a0cyhalothrin or gamma cyhalothrin\u00a0treatment at full tiller can be applied with top-dress nitrogen. OP insecticides, such as dimethoate\u00a0and methyl\u00a0parathion, also will control aphids but are not effective in preventing barley yellow\u00a0dwarf infection. \u201cTo sample aphids, inspect plants in 12 inches of row in fall and 6 inches of row in winter. In spring,\u00a0inspect 10 grain heads (+ flag leaf) per sample.\u00a0Count all aphids on both the flag leaf and head for\u00a0making control decisions. Sample plants at 8 to 16 locations per field. Treat when populations reach or exceed the following thresholds at various stages of development:<\/p>\n