Big Season for Green Stink Bugs?

Doug Johnson, Extension Entomologist, University of Kentucky.

If you’re not checking for stink bugs in your soybeans you should be. 2015 appears to be producing an extra large population of green stink bugs, at least in western Kentucky.  For example, as of July 10, 2015, a total of 2,184 stink bugs have been captured in a black light trap on the UK-REC in Princeton, Kentucky. That is more stink bugs than were captured in all of last year (2014) in TWO black light traps on the UK-REC (e.g. 121 + 695 = 816). In fact, more stink bugs were captured in the 2015 single trap week ending on June 26^th than in all of 2014). However one looks at it, that is a lot of stink bugs. In addition, you will notice a great deal of difference between the captures at the North Farm in Lexington –vs– The UK-REC in Princeton. This occurs almost every year, but is particularly apparent this year.

We have seen a decrease in capture since that high, but don’t let that fool you as the numbers will likely rise again. Black light traps only capture adult stink bugs. Because the bugs must be able to fly to the trap to be captured, and juveniles do not have wings, only adults are captured. Normally, we would expect to see three generations in each summer season. Sometimes this produces very distinct populations (See Figure 1.) but often the generations tend to show overlap with one another.

Stinkbug populatoins at UK-REC in 2013

Sampling for stink bugs may be done by sweep net or shake cloth. In Kentucky, most of our beans are in narrow rows so the sweep net is the tool most often used. For sweeping, use a 15” sweep net and make 25 sweeps. Then count the number of stink bugs present. Most of the stink bugs will be green but there may also be brown stink bugs. In addition, juvenile stink bugs may be multi-colored. You can tell them from the adults because they do not have wings. Additionally, you will likely see some brown stink bugs whose shoulders come to a very definite sharp point. These are spined-shoulder bugs and are predators. They will not harm the plants. With the exception of spined-shoulder bugs, count all stink bugs as the same.

Armyworm Moth Flight Takes a Down Turn!

Doug Johnson, Extension Entomologist

The most recent capture number for armyworm moths in the UK-REC trap shows a decided decrease, down to 87 moths/trap-week. This is an overall good sign that no large population is in the offing. This does NOT mean that any specific field will not have a problem population, only that there is unlikely to be a widespread large problem. Fields should still be scouted.

Reasons to scout corn for stalk strength

Excellent yields are expected in many corn fields this growing season.  Along with that good news comes concerns over stalk strength.  Plants in many fields have heavy ears, along with shallow roots because of abundant rainfall.  Many of these plants could topple easily as they mature, especially if a late-season storm with high winds blows across the field.  Plus, several extended periods of cloudy weather during grain fill may have increased the risk of stalk weakness in some fields.  This is because, when the corn plant is filling grain, if leaves cannot meet the carbohydrate demand of the grain, the plant may “cannibalize” carbohydrates in stalks in order to fill the grain.

Similarly, infectious diseases may play a role in increasing stalk weakness, by depriving the plant of healthy foliage necessary to maintain stalk strength through crop maturity.  Gray leaf spot (Figures 1-2) is prevalent this year, although levels generally appear to be low to moderate.

Figure 1. Lesions of gray leaf spot, viewed by holding up to the sky. Some hybrids develop an obvious yellow border around these infections, as shown here.

Figure 2. Lesions of gray leaf spot in a highly susceptible variety. They are often described as "match-stick" lesions.

  

I have also observed scattered fields with significant damage from northern leaf blight (Figure 3).  Given the generally mild, wet weather this season, this isn’t surprising.

Figure 3. Lesions of northern leaf blight, with high levels of control by a strobilurin fungicide

Although southern rust has been present in Kentucky for over a month, some cool weather experienced in recent weeks has helped suppress disease activity.  This disease may still contribute to weakened stalks in some late-planted fields, but in general, it appears we have “escaped” widespread damage from this disease this year, especially if cool nights predominate.

Scouting for stalk lodging

Check for stalk weakness by walking the field and pushing plants about 1 ½ feet from vertical.  Those that fail to spring back exhibit lodging potential.  If 10-15% or more of the field show lodging potential, it may be wise to schedule that field for early harvest, before it is laid down by strong winds.