Aster Leafhoppers in Winter & Spring Wheat (5/3/12)
This week we have received some reports of large numbers of aster leafhopper on winter wheat in central ND near Steele in Kidder County and in Wilkin County, MN. More calls are coming in for aster leafhoppers on young spring wheat. We suspect that some aster leafhoppers overwintered successfully as eggs in wheat in North Dakota, given the mild winter. However, most aster leafhoppers migrate into North Dakota from the south. It’s a good idea to scout fields regularly for influxes of large populations of aster leafhoppers.
Aster leafhoppers are small (1/8 of an inch), wedge-shaped and green to yellow with three pairs of spots on its face. Leafhoppers are active and mobile insects. These leafhoppers feed on plant sap and vector aster yellows, a phytoplasma disease. Disease symptoms are similar to barley yellow dwarf virus (BYDV), appearing as yellowing (or chlorotic appearance) at first, and then leaves turn more reddish-purple with brown edges. Aster leafhoppers do not transmit BYDV, which is transmitted by cereal aphids. Local populations of leafhoppers typically have low infection rates (only 1%), and need to feed on diseased plants to obtain the aster yellows phytoplasma. Migratory aster leafhoppers have a higher infectivity rate about 5%. Then, leafhoppers must incubate the disease for 9 to 21 days to become infective. Infected leafhoppers inject the aster yellows phytoplasma with its saliva during feeding and the plant becomes infected. Disease symptoms will appear in 2-3 weeks. Plants infected earlier in crop development are more susceptible to yield loss than mature crops. For example, wheat infected with aster yellows at the seedling stage will not produce kernels due to stunting. A heavy infestation of aster leafhoppers in the field also will increase the incidence of aster yellows.
Aster leafhopper feeds on over 300 species of plants including crops, vegetables, flowers and weeds. Some field crops attacked in North Dakota include: sunflower, canola, flax, potato, wheat, barley and oats. Vegetable crops such as carrots, celery, or lettuce are more sensitive to aster yellows. Examples of weeds infested by aster leafhopper include quackgrass, plantain, lambsquarters, common milkweed, wild asters, sowthistle, ragweed, stinkweed and wild carrot.
Aster leafhoppers are not a common pest problem of wheat in North Dakota. But, this is not a typically year! Unfortunately, there is little research and no recommended treatment threshold for leafhoppers in wheat. A general suggestion from a 1932 paper states that an “insecticide treatment show be considered when disease symptoms are noticeable and leafhopper numbers are high (clouds when you walk in field).” Any insecticide labeled in wheat should work for control; but consider using a pyrethroid for a longer residual to minimize any re-infestation.
Janet J. Knodel