–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
Wheat and alfalfa fields throughout south central and north central Kansas should be monitored for signs of defoliation. Many pests can defoliate either crop this time of year, i.e. grasshoppers and flea beetles (usually around borders), and “worms”. These larvae are most commonly armyworms, fall armyworms, and/or army cutworms. Identification is important for these “worms” because armyworms and fall armyworms will feed until the temperatures cool into the mid-20’s or they pupate, whichever comes first.
Army cutworms, however, are and have been hatching from eggs deposited by moths as they return from over-summering, probably in Colorado.
These army cutworm larvae will feed a little this fall, overwinter, then start feeding again in early spring. So, if the “worms” causing the defoliation now are relatively large, ½ inch or more, they are probably armyworms and/or fall armyworms.
We have been hearing about and seeing a mixture of both armyworms and fall armyworms (see pics below). These small worms start by causing small “windowpanes” in wheat or alfalfa. No army cutworm infestations have been verified yet.
Flocks of birds in wheat or alfalfa fields in fall or early spring are often indicative of a “worm” infestation as the birds are feeding on the larvae. Fields with 25-30% of the plants showing “windowpane” feeding need to be monitored frequently as these larvae consume more as they get larger. Treatment should be applied before stands become threatened. For more information on treatment thresholds and management options please see the Wheat Insect Management Guide: http://www.bookstore.ksre.ksu.edu/pubs/mf745.pdf
–by Dr. Jeff Whitworth and Dr. Holly Schwarting
Most corn pests have come and gone throughout north central and south central Kansas, with a few exceptions. Japanese beetle adults have been causing concern in north eastern KS, from about Topeka to the Nebraska border and east to the Missouri border.
These beetles are attracted to green silks and can feed so voraciously that they eat into the husks and damage some of the kernels on the tip. These populations usually do not occur in such numbers to affect pollination over a large area of many fields. However, in small areas they can cause concern but are relatively well controlled if a foliar insecticide is justified. Some adult green June beetles are also feeding on corn silks and/or ‘naked ears’ and have been mistaken for Japanese beetles. Japanese beetles usually migrate to soybean fields to feed on pollen when fields start pollinating but probably not to the extent that they affect yield.
— by Dr. Jeff Whitworth and Dr. Holly Schwarting
Soybeans seem to be growing well throughout north central Kansas. Not too many pests have been noted. However, there seem to be some spider mite populations building throughout the south central and north central parts of the state. These need to be monitored, especially if adequate moisture is not forthcoming. Mite populations can expand very quickly and really add stress to plants that are already moisture stressed.
Also, blister beetles are starting to swarm, especially in alfalfa and soybean fields. This swarming behavior is primarily for mating purposes and may involve anywhere from a few hundred to thousands of individuals. They may feed a little while swarming and actually cause plant loss, but only in small areas where the swarming occurs. Thus, treatment is rarely warranted.
By — Dr. Jeff Whitworth, Dr. Holly Schwarting
Most corn has been planted in SC and NC Kansas, although some has been struggling somewhat with the cooler temperatures, wet soils, etc. Whatever the case, please remember insecticide seed treatments do a good job of protecting the seed and germinating plants, but not forever. About 3-4 weeks of protection from the time of planting can be expected but after that, wireworms, white grubs, etc. may affect the seedlings, especially under less than ideal growing conditions.
–by Dr. Jeff Whitworth and Dr. Holly Schwarting
Still finding aphids in wheat throughout NC and SC KS. But in all fields sampled last week there were many lady beetles and mummies, indicating the beneficials are also very active. Spraying aphids will kill most of the aphids at the top of the plants– but won’t kill all the aphids down in the canopy just because the leaves in the canopy intercept the spray. But it will, typically anyway, kill all the beneficials as they move around searching for aphids to consume. Therefore, it is rarely a good idea to add an insecticide to a fungicide application to save application costs UNLESS the insecticide is warranted-not “just in case”