–by Eva Zurek
Insect Diagnostic Laboratory Report
http://entomology.k-state.edu/extension/diagnostician/recent-samples.html
Month: August 2016
Sorghum Pest Update
— by Dr. Jeff Whitworth and Dr. Holly Schwarting
The situation seems about the same throughout north central Kansas with regard to insect pests. Still finding mixed populations of aphids (greenbugs, corn leaf, yellow sugarcane, and sugarcane) but beneficial insect populations (mainly green lacewings, lady beetles, parasitic wasps, and occasionally syrphid fly larvae) still remain plentiful. Headworms are also plentiful in just about every field that is not yet at soft dough. Remember, expect 5% loss/worm/head between flowering and soft dough. Chinch bugs, both adults and nymphs, are also plentiful at the base of most plants but can also be found feeding on young developing berries in the heads.
Soybean Pest Update
–by Dr. Jeff Whitworth and Dr. Holly Schwarting
What a difference a few days makes in the world of insects! Two weeks ago, and prior, there were very few insect pests in soybeans throughout north central and south central Kansas. Now, most soybean fields are loaded, with more coming all the time. Some of the insects common to soybean fields throughout north central, south central, and south east Kansas right now are as follows:
Dectes stem borer adults. These have been actively depositing eggs in petioles for a few weeks although populations seem somewhat reduced compared to the past few years. Larval tunneling within the petiole and resultant petiole death has not yet become very apparent.
Bean leaf beetle adults. These feed on the leaves, usually causing mostly round or oblong holes, which are of little consequence. However, these same adults can also feed on the pods which may damage the bean inside and thus cause significant yield reductions.
“Worms”. There are also significant numbers of a variety of “worms” or caterpillars in most soybean fields. These include various stages of yellowstriped armyworms, which may feed on the leaves but not enough to impact plant health or yield.
There are also numerous green cloverworms, which are also leaf feeders. These are the “inchworms” that wiggle like crazy when disturbed.
They are usually highly susceptible to a fungus that turn infected larvae white and decimates the population rapidly over large areas. Green cloverworms may cause a great deal of concern because of the defoliation they cause, but rarely are they any real detriment to the plant. However, make sure to properly identify the worms as there are also corn earworms, aka soybean podworms, which may be mistaken for green cloverworms.
Soybean podworms will feed on leaves but more worrisome is when they start feeding on the developing seeds within the pods. Two or three pods fed on per plant may justify control if there are still larvae in the field. Otherwise, they may have pupated and treatment should be delayed until sampling indicates the next generation of larvae is actively feeding on seeds within pods.
Alfalfa caterpillars are also feeding on leaves and adding to the worm variety but will not cause any detrimental impact on yield.
Sorghum
–by Dr. Jeff Whitworth and Dr. Holly Schwarting
Sorghum is in various stages of development around NC Kansas. The late planted, which seems to be just in the whorl stage- to soft dough, or even farther along. Corn earworms (often called sorghum headworms/soybean podworms etc., depending upon the crop infested) are causing significant infestations and therefore concern because of the highly visible whorl feeding and subsequent “ragged”-looking leaves as they expand from the whorl. This feeding probably will have no effect on yield, and by the time the damage is noticed the worms are mostly finished feeding anyway. Therefore, treatment is rarely justified. Feeding on the kernels however which is the marketable product is a different story. Sampling for head-feeding worms is really relatively easy. Just take a small white bucket, bend the head over into the bucket and vigorously shake it against the sides of the bucket which dislodges the larvae. Then count the worms and divide into the number of heads sampled.
Rule of thumb: kernel-feeding larvae cause 5% loss/worm/head. Sorghum heads are most vulnerable from flowering to soft dough. These larvae are relatively susceptible to insecticides so efficacy is usually pretty good. However, these insecticides will reduce beneficial insect populations which can help later if any aphid populations develop.
Insect Diagnostic Laboratory Report
–by Eva Zurek
Insect Diagnostic Laboratory Report
http://entomology.k-state.edu/extension/diagnostician/recent-samples.html
Sorghum Update
–by Jeff Whitworth and Holly Schwarting
Double cropped sorghum in north central KS seems to have a significant infestation of “ragworms”. The larvae are a combination of fall armyworms and corn earworms and are of various sizes.
Leaf feeding in the whorl by either species is highly visible but should not have a significant effect on the plants or yield.
Also, most fields in north central KS are infested with aphids. Corn leaf aphids can produce a great deal of honeydew but mostly in the whorls. This honeydew may retard head extension but usually does not affect many plants over a large area.
Also found greenbugs and yellow sugarcane aphids. None of the invasive sugarcane aphids were detected in north central Kansas. However, many beneficials are, and will continue to be, present in sorghum fields as evidenced by the numerous green lacewing eggs and lady beetle eggs.
Soybean Update
–by Jeff Whitworth and Holly Schwarting
Ms. Rene Hessel, Assistant Scientist in the KSU Agronomy Dept. found soybean aphids in Dr. Bill Schapaugh’s soybean research plots at Ashland Bottoms in Riley Co. on 1 August. This is the first documented case of these annual migrants we have heard about this year in Kansas. These aphids are most easily detected by finding ants in a soybean canopy. If you do discover ants on the leaves/stems etc. in the canopy, look very closely for these tiny aphids. Since they first migrated into KS in 2002, the easiest and most reliable way of detecting the initial infestation is by finding ants. Hopefully, the heat will help retard the soybean aphid’s population growth over the next few weeks but soybean fields should be periodically monitored.
Sugarcane aphid expanding to other counties in Kansas
Sugarcane aphid has been confirmed in the following counties in Kansas: Marion, Sedgwick, Sumner, Cowley, Labette, Meade, Haskell, and Ford. Populations first reported in Sumner and Cowley counties have reached threshold levels (30% of plants infested with visible signs of honeydew on leaves) and are being treated with insecticides. Scouting fields early will help determine the need for an insecticide application before losses occur. Treating too soon may increase the need for additional insecticide treatments later, as populations can rebound based on immigration events. Scout often, as densities can change quickly. Report any infestations in new counties to your local agent or using http://myFields.info.
Figure 1. Current counties in Kansas confirmed with sugarcane aphid in green.
Recommended treatment options for SCA control are either Transform (Dow AgroSciences) at 1 oz per acre, or Sivanto prime (Bayer CropScience) at 4 oz per acre, applied in 15 – 20 gal of water from a ground rig. Application from the air will be more costly and less effective, as it will not permit application of these materials in sufficient volume to obtain the coverage necessary for good efficacy. The cost per acre is lower for Transform, and this material is also the least toxic alternative for aphid natural enemies. If headworms are present in damaging numbers (1-2 per head or more, the majority still less than 1 inch long), Blackhawk (Dow AgroSciences), Prevathon (Dupont) or Belt (Bayer CropScience) are alternatives that can be considered for controlling them. Note that Belt registration has just been revoked by the EPA, but existing stores may be used. Of the materials labelled for headworm control, these are the ones likely to have the lowest impact on beneficial species assisting with aphid control. We have found Prevathon to be compatible with Transform in a tank mix; all other combinations should be tested first for compatibility by mixing small amounts in a jar to ensure no precipitate forms. Read the label carefully before you spray.