–by Dr. Jeff Whitworth, Dr. Holly Schwarting & JR Ewing
Alfalfa weevil larvae have been hatching throughout north central and south central Kansas for the last couple of weeks. However, as of 9 March, there doesn’t seem to be much feeding or development yet (Photo1). There are also a few of these tiny larvae that are dead (Photo2). Because these larvae are so small and vulnerable it is difficult to determine the cause of death. At least some of the mortality could be related to weather fluctuations that have reached mid 70’s for several days but also dropping into the mid to low 20’s some nights.
Most of these larvae are so small that they are well enclosed within the plant terminals to the point that they cannot be dislodged by shaking the stems into a bucket, as the most accurate sampling method specifies. This can definitely cause you to underestimate larval populations. Probably the easiest solution is to hold off sampling until the middle of next week, if the weather turns cooler as predicted. There are a few more mature larvae present, along with adult weevils (Photos 3, 4). Adults will probably continue depositing eggs for a few more weeks, thus extending the period of larval hatching.
There are also a few pea aphids present. Populations do not seem to be increasing now, and there are lady beetles and parasitoid wasps actively attacking these aphids. Also, reports of cowpea aphids in south central Kansas bear watching. These aphids are usually more numerous in warmer summer months. They can add stress to plants by feeding, but they also produce copious quantities of honeydew which can become covered with sooty mold. This may further stress alfalfa by interfering with photosynthesis, especially with small plants coming out of winter dormancy and experiencing dry conditions and fluctuating temperatures.
— by Dr. Jeff Whitworth and Dr. Holly Schwarting
Green Cloverworms in Soybeans
Remember a few weeks ago when there was considerable concern relative to all the green cloverworms causing irregular holes in leaves? Even skeletonizing some areas of some fields until treated with an insecticide and/or and entomopathogenic fungus started decimating the larval populations? Well, the surviving larvae pupated and now are annoying little aerodynamically shaped dark brown moths flying around lights at night or trying to get in through doors and windows.
These moths will mate and then begin ovipositing in soybean and/or alfalfa fields. Eggs hatch in approximately 10-14 days and the larvae will again start feeding on leaves of either crop. By this time of year, the larval feeding is usually of little consequence relative to yield. However, really late planted soybeans, and all alfalfa fields, should be closely monitored to ensure leaf feeding in either crop does not affect pod fill in soybeans or leaf area in alfalfa.
These insect pests seem to be on about the same developmental schedule as green cloverworms. So, late planted soybeans may be at risk for bean feeding within the pods.
Adult bean leaf beetles, while probably not as numerous as in past years, may still be feeding on the pods themselves. This can cause yield reductions. For more information on bean leaf beetle biology and control, please visit: https://www.bookstore.ksre.ksu.edu/pubs/MF2824.pdf
Another leaf feeder that can cause concern this time of year is woollybear caterpillars. There are several different species but all are foliage feeders although they rarely cause any economic problems.
Hopefully, most soybeans are past the stages that are succulent enough for stink bugs to be feeding on. However, there are still some late planted beans setting pods with seeds that may be vulnerable to stink bug feeding. So, until pods are turning yellow or brown, fields probably should continue to be monitored for soybean podworms, adult bean leaf beetles, and stink bugs.
–Dr. Jeff Whitworth and Dr. Holly Schwarting
The first western corn rootworm adults were collected on 17 June from a corn field in north central Kansas. Development is being completed very quickly, which should be expected based upon the temperatures we have been experiencing. However, there are still some larvae feeding on roots.
None of the plants sampled have started tasseling and therefore adults are feeding on leaves. This typical leaf feeding by adults will not impact yield.
Adults will probably start feeding on emerging tassels and then shift to silk feeding when silks start emerging. Remember, corn plants are very efficient pollinators, so as long as a little silk is showing above the husk, the pollen will be successful. There are still many adult tarnished plant bugs in the corn fields and these are quite commonly confused with adult western corn rootworms. However, they will NOT clip silks.
Some leaf feeding is also evident by corn earworms and fall armyworms. Again, these leaves can look ragged, thus the name ragworm, but will not impact yield.
–Dr. Jeff Whitworth and Dr. Holly Schwarting
Ticks are very active throughout the state, and have been for the past month. The most commonly reported species has been the American dog tick, Dermacentor variabilis.
The cool, humid weather over the past month has provided great conditions for tick development. These annoying, and potentially dangerous parasites have even been encountered in corn fields, which is unusual as they typically develop in more undisturbed areas of grasses, weeds, and other overgrown vegetation. But, they are very good at finding hosts and getting the blood meal they require for development and reproduction. For more information on ticks in Kansas, please visit: https://www.vet.k-state.edu/vhc/docs/ticks-in-kansas.pdf
—Dr. Robert Bauernfeind
Not to beat a dead horse given that Dr. Cloyd’s KIN #2 article addressed the facets of ALB development/damage/control, and last week’s update in KIN#3 substantiating the actual initiation of the 2015 flight activity, but I noted that the table was incorrect in the “Date” column. So to correct that, I have entered the proper dates, and also added in this week’s flight numbers. Again, as can be seen, these moths just don’t fly at temperatures below 70. So this week when temperatures were into the 70’s, moths were active. And, no more wrens.
—by Dr. Jeff Whitworth and Dr. Holly Schwarting
Alfalfa weevils continue to be very active in north central Kansas. The recent cooler weather has slowed down development a little but they are still feeding. We determined development from larvae collected on 20 and 22 April. Here is what the population breakdown looks like:
|20 AprilNo. larvae
||23 April No. larvae
So what does this mean? Alfalfa weevil larval feeding will continue for another 7-10 days, depending on the weather. Egg hatch and consequent larval feeding has been going on since 13 March in north central KS. Insecticides applied since that time have provided adequate protection, for the most part.
This photo shows KSU chemical efficacy trials with many different products being tested, and the obvious untreated plots plus the border around the plots. The rest of the field was treated with Stallion® by MKC in Abilene, KS and, as illustrated here seemed to work relatively well with 1 application. Remember, feeding will continue for at least another week and therefore treatment (or re-treatment) may still be appropriate.
Alfalfa aphids, mainly pea aphids, are becoming more numerous throughout north central Kansas. Treating for alfalfa weevils probably pretty much decimated the natural enemies/beneficials and they will not repopulate as quickly as the aphids migrate in to infest fields.