Cereal Aphids Present in both ND and MN this Past Week (06/27/13)
Cereal Aphids Present in Both ND and MN this Past Week
Cereal aphids (mostly English grain aphids) have been reported from small grains in SW, SC and WC MN, and from SE, EC and NC ND (Sources: IPM Scouts for ND and MN, and Dr. Chapara at NCREC, Minot, ND). Currently, populations in southern MN have grown to high levels and symptoms of Barley Yellow Dwarf Virus (BYDV) have been reported. South Dakota also has reported rapidly increasing populations of cereal aphids. Aphid populations in small grains in central and northern MN and in ND are significantly lower and disease symptoms have yet to be reported. However, populations from southern MN are reported to contain high numbers of winged aphids, indicating a dispersal phase. Southerly wind events may facilitate the movement of aphids carrying BYDV to more northerly areas, including ND.
Most of our small grain aphids don’t overwinter here in ND and MN. They re-populate every year via migrants coming in from states to the south. Aphids do not directly feed on leaf material; they damage plants by sucking sap, thereby robbing the plant of nutrients. Generally, the greatest potential for yield loss is when the plant is between the boot and heading stage. After heading, there is a rapidly decreasing period during which aphid feeding can rob small grains of yield. Scout for aphids by examining the whole plant and underside of leaves. Thresholds for aphids on small grains are generally when 85% of plants are infested (have 1 or more aphids on them); by the time 85% of plants in a field harbor aphids, there’s generally an average of 14-18 aphids per plant. Field scouting should be conducted from stem elongation until heading. In areas with high risk of BYDV, more aggressive management may be required.
Aphids vector Barley Yellow Dwarf Virus in small grains, and the late planting in most areas makes grain fields especially susceptible to the disease this year. The English grain aphid, which is bright green with long black cornicles (tailpipes), is an effective vector of BYDV. English grain aphids are most frequently found on the leaves themselves. When aphid populations are high, BYDV can spread quickly through small grain fields. At greatest risk are fields containing younger plants (the earlier the stage of the plant when the disease is contracted, the greater the potential for yield loss). Insecticide applications targeted against aphids cannot cure infected plants but may prevent further spread of the disease. Please consult NDSU Extension Service publication E-1143, North Dakota Field Crop Insect Management Guide, for insecticide information.
The visible symptoms of BYDV depend on the plant's stage at infection. See NDSU’s Barley Disease Handbook on BYDV symptoms. Leaf discoloration in shades of yellow, red (more common in oats), and purple (sometimes) appear starting from the tip to the base and progressing 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 cool weather (60-70 F) 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, small grains in the area are at a greater normal risk for BYDV and producers/crop consultants should actively scout for aphids.
UMN Extension Entomologist NDSU Extension Entomologist