|Carrington Research Extension Center
North Dakota State University
NDSU Extension Service
North Dakota Agricultural Experiment Station
July 15, 1999
WHEAT MIDGE FLIGHT NEAR COMPLETION
The presence of adult orange wheat blossom midge is expected to end at about 1800 degree day (DD) units. The following is a listing of accumulated DD units, as of July 15 and based on the ND Ag Weather Network, for selected south-central ND locations: Oakes = 2065, Edgeley =1870, Dazey = 1855, Linton = 1845, Robinson = 1815, Jamestown = 1785, Carrington = 1765, McHenry = 1735, and Harvey = 1715. Thus, the period for midge scouting has ended in the southern part of south-central ND and can be terminated within the next few days in northern counties of this region. Additional details on obtaining DD units for your area, and wheat midge scouting and management may be obtained from NDSU Extension Service offices.
BARLEY YELLOW DWARF VIRUS IN WHEAT
Barley yellow dwarf virus (BYDV) is commonly found in wheat this year although at generally low levels. The disease is transmitted by several grain aphid species. Disease symptoms appear 7 to 20 days after infection. Green tissues of older leaves become unevenly discolored in blotches along their margins, at their tips, or within the leaf blade. The discolored areas are often bright yellow, but the tissue may also turn red or purple. Discolored areas subsequently enlarge and coalesce toward the base of the plant. The tissues next to the midrib tend to remain green longer than the rest of the leaf. The youngest leaves usually have no unusual color, except in very late infections, in which the flag leaf alone may discolor. Yield losses may reach 15 percent with early crop infection.
The majority of wheat in south-central ND is at the heading stage or beyond. Once the crop has headed, it is too late to control aphids for the direct plant damage they cause or for the purpose of controlling BYDV. If BYDV symptoms are showing up late, damage may be minimal or possibly 5 to 10 percent, depending on how uniform infection is in the field.
ASTER YELLOWS IN FLAX
Dry bean growers should continue to monitor their crop for leafhoppers. Assistance with insect identification, bean injury symptoms, and control recommendations are available from NDSU. Leafhoppers also transmit aster yellows, a disease recently found in flax grown in the Carrington area. The disease symptoms are most conspicuous during and after flowering. Leaves in the upper half of affected shoots are a bright yellow and do not turn brown. Flower parts become leaf-like and are greenish yellow. Healthy and diseased shoots may occur on the same plant. Severely diseased plants are stunted. Currently, an economic threshold for leafhoppers in flax is not available and control using insecticides is questionable.
Greg Endres, Area Extension Specialist/Cropping Systems, Email: firstname.lastname@example.org
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