Tuesday, May 19, 2015

Aster Leafhoppers Arrive – but this isn’t Déjà vu all over again

Back in 2012, a very significant migration event involving aster leafhopper occurred in early May. The Aster leafhoppers settled in grasses, particularly wheat fields when they first arrived. Weather events of the past 10 days have also been conducive for bringing in leafhoppers from the southern US into our region, but not even close to the numbers the appeared in 2012. Since they have been reported we want to make you aware of them.

From Southwest MN IPM STUFF 2015-4 (Volume 18 number 4, May 15, 2015):

Weather systems brought a few aster leafhoppers to SWROC spring wheat and oats, probably over the 7th and 8th. The numbers I am finding are very low (1/10 sweeps) but it has been too wet to be in the field most of the week. I am less concerned about aster leafhoppers and the potential transmission of aster yellows virus on wheat, oats and barley than I am on other crops. Aphids and barley yellow dwarf make me more nervous but so far, I have not observed any aphids in grains. Barley yellow dwarf risks of yield loss decline with later infections.

From NDSU Crop and Pest Report (Issue 2, May 14, 2015) they reported:

Aster leafhoppers and other species of leafhoppers were observed in large numbers in a winter wheat field near Aneta in Nelson County (source: Huso Crop Consulting). Aster leafhopper (Macrosteles quadrilineatus) and an unknown leafhopper (possibly a Chlorotettix species) were collected from fields by Leslie Lubenow. Both species of leafhoppers are known to vector aster yellows, (AY) although Chlorotettix species are not documented to feed on wheat. 

The early season aster leafhoppers migrate into the region on southerly wind fronts. Aster leafhoppers are small (1/8 of an inch), wedge-shaped and green to yellow with three pairs of spots on its head. Leafhoppers are very active and can be seen flying ahead of your steps when walking through fields. These leafhoppers feed on plant sap and vector aster yellows, a phytoplasma disease.

There is little research information on pest management of aster leafhoppers to minimize vectoring of AY in small grains. Even though this pest has likely caused some economic yield loss by vectoring AY in wheat, the infections are much more important in crops such as flax, canola, certain vegetables and other higher value crops. The infection levels found in these migrating populations has a huge influence on whether AY outbreaks occur in those crops with greatest susceptibility.

Aster yellows (AY) is caused by a phytoplasma, an organism similar to a bacterium but without cell walls. Symptoms of aster yellows in wheat are similar to Barley Yellow Dwarf Virus (BYDV). Aster yellows can cause yield loss in susceptible wheat varieties when infections are high. Plants are more susceptible to aster yellows during early growth stages. No economic threshold that has been developed for aster leafhopper in wheat, flax or canola. However, you need both high densities of aster leafhoppers and high incidence of aster yellows being vectored by leafhoppers to cause significant yield losses. Spray trials in leafhopper infested wheat back in 2012 reduced leafhopper numbers, BUT did not result in different levels of AY infection between treated and untreated plots (Ian MacRae, personal communication).