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Extension Entomology

Month: June 2018

Alfalfa Update

— by Dr. Jeff Whitworth and Dr. Holly Davis

Several alfalfa fields were sampled in north central Kansas this past week.  The alfalfa canopy remains an excellent habitat for many insects, especially those fields not treated for alfalfa weevils this year.  Many of these insects are beneficial.

Very few pests, or potential pests, were detected although there were a few potato leafhoppers present.  These small, lime green, herky-jerky, moving pests are apparently just beginning to migrate into KS, as we didn’t find any earlier in the week, and now are only finding a couple of adults.  For more information relative to potato leafhopper management, please refer to the KSU 2018 Alfalfa Insect Management Guide:  https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf

 

 

 

Corn and Sorghum Update

— by Dr. Jeff Whitworth and Dr. Holly Davis

Chinch bug populations continue to increase at a very disconcerting rate.  Most corn throughout north central Kansas is far enough along in its development to tolerate large numbers of chinch bugs.  Smaller sorghum can still be seriously stressed by growing populations of chinch bugs, especially as the hot and dry conditions return.  For more information of chinch bug management in sorghum, please see the KSU 2018 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

 

One relatively mature fall armyworm larva was also detected.  Thus, in approximately 2-3 weeks there will be a new generation of fall armyworm larva ready to start feeding, most likely, on sorghum.

 

Soybean Update

— by Dr. Jeff Whitworth and Dr. Holly Davis

The first adult Dectes stem borer was detected on 23 June, from north central Kansas (specifically, DK Co.).  These beetles traditionally spend approximately 7-14 days congregating or aggregating around the borders of stubble fields near where they overwintered.  Then, they disperse throughout soybean and sunflower fields and begin depositing eggs in plants of either crop.  Several more have been collected since the 23rd.

Bean leaf beetle adults have been and will continue chewing characteristic round or oblong holes in soybean leaves.  However, at least around north central Kansas, populations seem reduced from recent years.

 

So far, other than a few small grasshopper nymphs, there seem to be less defoliators than usual in either alfalfa or soybeans.  However, there is still time left for significant populations to develop.  A few garden webworms and yellowstriped armyworms were collected from a couple of fields and many of the soybeans are still very small, in the 3-5 trifoliate stage.

 

Grasshoppers

— by Dr. Jeff Whitworth and Dr. Holly Davis

 

Grasshoppers

Grasshoppers continue to feed and thus get larger.  As they feed and develop, they often move out of the grassy areas where they hatched and start feeding on a nearby crop.  Thus, the best time to control grasshoppers is before these nymphs move into crops, or at least while they are still just feeding on the crop borders.  Grasshopper baits work, but often do not compete well with green, succulent, growing crops.

Green June Beetles vs. Japanese Beetles

— by Dr. Jeff Whitworth and Dr. Holly Davis

Adults of both green June beetles and Japanese beetles seem to be ramping up their activity throughout eastern Kansas.  These two relatively large, conspicuous beetles are being confused.  Green June beetles, at 1 inch long, are considerably larger than Japanese beetles.  Also, green June beetles are green to copperish green in color and more pointed toward the anterior (head) end.  Japanese beetles are probably only 1/3 to ½ as big as the green June beetle.  They also have small, but highly visible, little white tufts of hair on both sides of the abdomen sticking out from under the elytra.

 

 

Japanese beetles may be found feeding on silks in corn fields and/or pollen or leaves in soybeans while green June beetles are more confined to feeding on nectar from flowering bushes or trees close to where the larval stage, i.e. grubs, were developing in the soil.  Green June beetles are not an agricultural concern while Japanese beetles occasionally can be.

 

Chinch Bugs

— by Dr. Jeff Whitworth and Dr. Holly Davis

 

All life stages of chinch bugs seem to be extremely active at the present time in both corn and sorghum.  Nymphs and adults started migrating out of wheat fields at least two weeks ago, moving into any adjacent corn or sorghum fields.  Those smaller reddish nymphs have grown considerably since then, and are now either late instar nymphs or adults.

 

Many of these recently matured adults are now mating and have even started egg deposition.  These eggs are, and will continue to be, hatching which means more bugs and thus more feeding on these plants.  Fortunately, most corn is large enough to withstand considerable feeding by chinch bugs. Plus, the recent rains greatly enhanced growing conditions, which increases the plant’s tolerance for chinch bug feeding.  However, most sorghum is much less developed and won’t be able to tolerate as many chinch bugs as the larger corn plants.  Treating plants much after the V-6/V-7 growth stages is not as effective as treating smaller plants.  Like corn, good growing conditions significantly help plants withstand chinch bug feeding.  However, if dry, droughty conditions return, chinch bug feeding can significantly weaken stalks and cause lodging later in the season.  For more information on chinch bugs, management decisions, and/ or insecticide recommendations, please see:

Chinch Bugs MF3107:  https://www.bookstore.ksre.ksu.edu/pubs/mf3107.pdf

2018 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

 

Corn Rootworms

— by Dr. Jeff Whitworth and Dr. Holly Davis

The first western corn rootworm (WCR) adults were observed on 12 June from north central Kansas.  There are still larvae feeding on roots but most are/have pupated and adults are emerging from soil.

 

None of the corn sampled in north central Kanas has tasseled or started silking yet.  Thus, these adult WCRs are feeding on leaf tissue in the early morning or early evening and resting in shady places during the hottest part of the day.

A great example of WCR larval root pruning is seen in this picture compared to a non-infested root system.

Twospotted Spider Mites

— by Dr. Raymond Cloyd

The extreme heat and lack of moisture we are experiencing throughout most of Kansas is conducive to the development of the twospotted spider mite, Tetranychus urticae (Figure 1),

Figure 1. Close-up of twospotted spider mite adult (Author–Raymond Cloyd, KSU)

horticultural plants in gardens and landscapes (Figures 2 and 3).

Figure 2. Twospotted spider mite feeding damage on clematis leaf (Author–Raymond Cloyd, KSU)

Figure 3. Twospotted spider mite feeding damage on tomato leaves (Author–Raymond Cloyd, KSU)

Twospotted spider mite is a warm-weather mite with populations typically active from late spring through early fall. Summer temperatures allow by producing multiple generations throughout the season.

The management of twospotted spider mite populations involves maintaining plant health in order to avoid ‘stress,’ implementing sanitation practices, and/or using pesticides with miticidal activity (miticides/acaricides). First, prevent plants from experiencing moisture ‘stress’ by maintaining proper watering and mulching practices to reduce potential problems with twospotted spider mite populations. For example, inadequate moisture or overfertilizing plants, particularly with nitrogen-based fertilizers, can enhance development and reproduction of twospotted spider mites. Furthermore, be sure to monitor for twospotted spider mite populations regularly by shaking branches or twigs onto a clipboard with a white sheet of paper, and looking for the mites crawling around (you can actually see the mites). You can crush the mites on the white sheet of paper to determine if they are a pest or not. For instance, plant-feeding spider mites typically leave a green streak when crushed whereas predatory mites leave a red streak. A quick and effective method of dealing with twospotted spider mite populations is applying a forceful water spray throughout the plant canopy at least twice per week during the season. Forceful water sprays will dislodge eggs and the motile life stages (larvae, nymphs, and adults). Be sure to direct forceful water sprays toward the leaf undersides where all life stages (eggs, nymphs, larvae, and adults) of the twospotted spider mite are located. The removal of plant debris and weeds eliminates alternative hosts and overwintering sites.

There are a number of pesticides with miticidal activity available to professionals for suppression of twospotted spider mite populations outdoors, including: abamectin (Avid), acequinocyl (Shuttle), bifenazate (Floramite), etoxazole (TetraSan), hexythiazox (Hexygon), potassium salts of fatty acids (M-Pede), and horticultural oils (petroleum, mineral, or neem-based). Homeowners do not have as many options in regards to miticides. The only “true miticide” still available is hexakis or fenbutatin-oxide, however, this active ingredient cannot be purchased by itself as the active ingredient is usually formulated with acephate (Orthene). However, homeowners can apply commercially available insecticidal soaps (potassium salts of fatty acids) and horticultural oils. Always read the label and apply miticides before twospotted spider mite populations are extensive and causing damage. Furthermore, be sure to rotate miticides with different modes of action to avoid twospotted spider mite populations developing resistance. If possible, try to target ‘hot spots’ or localized infestations of twospotted spider mites, which will reduce the potential for resistance developing. Be sure to thoroughly cover all plant parts with spray applications; especially when using pesticides with contact activity. Some miticides such as abamectin (Avid) and etoxazole (TetraSan) have translaminar activity, which means the material penetrates into leaf tissues and forms a reservoir of active ingredient within the leaf. This provides residual activity even after spray residues have dried. Mites that feed on leaves will ingest a lethal concentration of the active ingredient and be killed.

It is important to note that many pesticides used to suppress other insect pests encountered on plants in landscapes and gardens may be harmful to the natural enemies of twospotted spider mite; consequently, resulting in an inadvertent increase in twospotted spider mite populations or secondary pest outbreaks.

 

Fall Webworm

–by Dr Raymond Cloyd

The fall webworm (Hyphantria cunea) is prevalent throughout most of Kansas with webs noticeable on certain trees and shrubs. Fall webworm nests are typically quite evident, with silk webbing enclosing the ends of branches and foliage or leaves (Figures 1 and 2).

Figure 1. Fall webworm nest on birch tree (Author–Raymond Cloyd, KSU)

 

Figure 2. Fall webworm nest on walnut tree (Author–Raymond Cloyd, KSU)

Fall webworm larvae or caterpillars are pale-green to yellow to nearly whitish with black spots (two per each abdominal segment). Caterpillars are covered with long, white hairs (Figure 3).

Figure 3. Close-up of fall webworm larvae (Author–Raymond Cloyd, KSU)

They feed on a wide range of trees, including: birch, crabapple, maples, hickory, pecan, mulberry, and walnut. Fall webworm caterpillars, unlike eastern tent caterpillars, remain within the enclosed webbing and do not venture out to feed. Caterpillars consume leaves, resulting in naked branches with webbing attached that contains fecal deposits or ‘caterpillar poop.’

Although feeding by fall webworm caterpillars may ruin the aesthetic appeal of infested trees; the subsequent damage is usually not directly harmful to tree, especially larger trees because larger trees are primarily allocating resources for storage with less being allocated to producing new vegetative growth. However, smaller trees infested with fall webworm may look awful (Figure 4).

Figure 4. Young tree heavily-infested with fall webworm (Author–Raymond Cloyd, KSU)

The most effective means of dealing with fall webworm infestations is to simply prune-out the webs that enclose the caterpillars. Insecticide sprays may not be effective because the caterpillars remain in the webbing while feeding; thus reducing exposure to spray residues. If insecticides are used be sure to use high-volume spray applications that penetrate the protective webbing or use a rake to disrupt or open-up the webbing so that the insecticide spray contacts the caterpillars.

 

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