Raul Villanueva, Extension Entomologist, University of Kentucky
|Figure 1. Pictures of the bird cherry oat aphid and|
a winged English grain aphid found in wheat fields
in February 2017. (Photo credits Yaziri Gonzales).
grain (Fig.1), the greenbug, and the corn aphids are the most important species. Their role as vectors of plant viruses, particularly Barley Yellow Dwarf Virus (BYDV), branded them as the key pest on
Also, uncharacteristically warm temperatures (above 50⁰ F) were present during most days of November (Fig. 2). Based on historical records and comparing mean temperatures for the bimonthly periods November–December 1976, 1996, and 2016; and January-February 1977, 1997 and 2017 (periods were separate to facilitate the analysis). We can notice that mean temperatures (linear regression analysis) for 2016 and 2017 were higher than the previous year for the same periods,
respectively (Fig. 2). It may be possible that the continuous alterations on the climatological events are influencing these warmer temperatures (more frequent rains, storms out of the normal patterns, sudden ice storms, etc.) as shown on these 20-year intervals.
Table 1. Accumulated degree days for wheat and aphid species for Caldwell,
Monroe and Fayette Counties in Kentucky from January 1 to February 20,
2011 to 2017. (Data source: http://weather.uky.edu/dd.php)
Other pests such as Hessian fly maggots that are in root system of volunteer wheat or other plants also can be a problem. They can continue feeding as long as temperatures are above 40⁰ F. For this pest a chemical control would not work. However, for Hessian flies or BYDV there are resistant varieties that growers should have been using to reduce pest damages.
We have been sampling for aphids here at the UK’s Research and Education Center and other counties (Lyon, Trigg, Christian) and no aphids were found so far. However, we found aphids in early or late when? December. No aphids were found from mid-December to mid-February. However, aphids were found in low numbers after February 15 (when temperatures were >65⁰ F). Most of these aphids were nymphs although we had some adults and winged aphids.
A question still remains about to spray or not to spray. There are many factors to consider but the most important is the economic value of the crop. The best alternative here is to continue monitoring for the presence of aphids and if the tallies are above the threshold levels indicated in Table 2, an insecticide spray need to be considered.
Table 2. The number of aphids per foot of wheat row required to support
an insecticide application for management of BYD