NDSU Entomologist Janet Knodel is recommending that wheat be sprayed this year as soon as cereal aphids are detected in the crop.
Cereal grain aphids beginning to arrive in North Dakota, and some are apparently carrying the Barley Yellow Dwarf Virus, which poses a serious threat to late-planted wheat.
"Barley Yellow Dwarf Virus (BYDV) has already been confirmed by the NDSU Diagnostic Lab in winter wheat samples in North Dakota In other areas, some symptoms that look like BYDV have been reported. Given we've just started to see aphids showing up, we suspect this means that aphids are arriving already carrying virus," she says.
BYBV is easily confused with a nutritional disorder or the effects of adverse weather. Visible symptoms depend on the plant's stage at infection. Leaf discoloration in shades of yellow, red (oats), and purple (sometimes) appear starting from the tip to the base and along the leaf margins to the midrib. If plants are infected with BYDV is the 4- to 5-leaf stage, growth will be slowed, maturity delayed and stunting is possible. Later infested plants do not suffer as much impact and are less likely to benefit from an insecticide application. Infected barley and wheat plants appear quite yellow against the rest of the field and infected oat plants seem to have reddish leaves. This disease is more pronounced during in cool weather (60-70F) with ample sunlight. Infection sites can appear as stunted yellow single plants or as groups or clusters of yellow plants among healthy plants.
"Because we're dealing with late planted small grains, and the long term forecast calls for cool weather, small grains in the area are at a greater normal risk for BYDV if there is an aphid infestation. As a result, producers/crop consultants should be proactive with their cereal aphid control in late planted wheat. The typical economic threshold for aphids in wheat is when 85% stems with more than one aphid present, prior to complete heading. However, knowing that most of our late planted wheat is at 'high' risk for aphid infestation and BYDV transmission, we recommend that producers/crop consultants be more preventative against aphid infestations and treat as soon as aphids are detected or BYDV is observed in the area," she says.
Field scouting should begin earlier than normal (typically before stem elongation) and continue up to the heading stage of wheat. Due to the high risk status, best pest management of aphids may require more than one application of insecticides this year to prevent yield losses from aphids and BYDV.
Even if early aphid populations require treatment because local BYDV symptoms have been reported, uninfected wheat may still require treatment for aphids later in the season if aphid populations rise to yield limiting numbers, she says.
Pyrethroid or organophosphate insecticides registered in small grains should provide adequate control. A listing of insecticides registered for cereal aphid control in small grains is available from the ND Field Crop Insect Management Guide 2011, E-1143, NDSU Extension Service at http://www.ag.ndsu.edu/pubs/plantsci/pests/e1143w1.htm.
Source: NDSU Crop and Pest Report