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Extension Entomology

Month: August 2019

Bug Joke of the Week

–by Dr. Jeff Whitworth

Q: What was the spider doing on the computer?

A: Just searching the web!

 

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A man hears a knock at the door. When he opens the door there is a snail looking at him. He picks up the snail and walks to his back door and throws it into his back yard.

 

Five years later the man hears a knock at his door. When he opens the door the snail is back and says “what the heck was that all about?”

Sorghum Update—cattail caterpillars, sugarcane aphids, headworms

–by Dr. Jeff Whitworth

Cattail caterpillars are still abundant throughout North Central Kansas causing considerable leaf feeding (see pic). Sugarcane aphids are still migrating into Kansas. However, up to now only small colonies and sporadic infestations have been reported. Every report, so far, also has reported good numbers of beneficials associated with and seemingly reducing the colonies that do get established. These aphids will probably continue to migrate into the state for some time yet but, hopefully, the beneficials will keep them under control. However, sorghum “headworm” populations are really becoming active and thus, if fields are treated with a conventional insecticide it will probably kill the headworms, any sugarcane aphids that may come into contact with a treated surface, and most, if not all of the beneficials. Yes, the conventional insecticides used for “headworms” will kill the sugarcane aphids. However, there are some problems with this. 1st, many of the aphid colonies will be on the undersides of the leaves and many of these leaves will be in the middle region of the plant, somewhat sheltered by higher leaves. 2nd, these insecticides are contact insecticides, thus, they need to contact the insect to kill it. However, all the beneficials will be very active searching for aphids, thus they have a high probability of coming into contact with, and being killed by, the insecticide. Then, number 3, the aphids reproduce parthenogenically thus these populations will increase quite rapidly if there are no beneficials hindering them. So, they will recolonize much quicker than the beneficials and thus start stressing the plants. However, “headworms” cause 5% loss/worm/head and they feed on the marketable product, thus if they get to the treatment threshold something needs to be done.

Now, there is a product available that uses a virus that is relative specific for corn earworms (Heligen) or fall army worms (Fawligen). If you are not sure which species is present in your field, you can mix these two products together. These two products then, could be an alternative to the conventional synthetic organic insecticides and thus, spare the beneficials to help control sugarcane aphids if they do start to migrate into Kansas in large numbers.

These products do need to be treated a little differently than the more common insecticides. 1st – timing is very important in any management program but even more so with these products then the regular insecticides. These virus compounds take a few days to actually work on the pest vs. the common insecticides which kill on contact. Thus, the Heligen or Fawligen compounds need to be applied as soon as the 1st (see pic. 3 day old larvae – smaller ones vs 6 day old larva – larger one) hopefully, very small worms are detected to give it a chance to work before the worms cause too much damage. This then highlights one of the problems with these products i.e., detecting the very small larvae in your bucket (see pic) because they blend in very well with all the pollen, florets/ etc. that shakes loose.

Also, these products are more sensitive to sunlight which can deactivate the virus within 24 hours after application. Virus containers that are sealed should not be exposed to direct sunlight for more than 2 hours, or in temperatures over 95℉. Product should be mixed in water with a pH of ≤ 8.0, and enough carrier used to adequately spread the product over the entire target. If you decide to try these products, it is best to leave an untreated check strip – which you should do with any products.

 

 

Sorghum Pest Update

–by Dr. Jeff Whitworth

Much disparity in sorghum development exists throughout north central and south central Kansas, mostly due to weather-caused delays in planting. So, there are many different levels of “worms” infesting this sorghum from whorl stage to some that is already soft dough stage. Therefore, there are also different stages of “headworms” (see pic) from small 2nd instar larvae to almost mature 5th instar larvae. Sampling needs to be initiated as soon as plants start flowering to determine infestation levels.

Different headworm instars

Additionally don’t forget about chinch bugs (see pic). These don’t usually affect plants as much under good growing conditions, which we have had for the most part, but there are still significant populations present which may affect plants if growing conditions become more stressful.

Chinch Bug Nymph

Also, some fields throughout north central Kansas have significant infestations of cattail caterpillars (see pic). These are often confused with corn earworms or fall armyworms, but they are leaf feeders, not part of any “headworm” complex.

Cattail Caterpillar

 

 

 

Soybean Pest Update

–by Dr. Jeff Whitworth

Defoliators are still present in most soybean fields throughout north central and south central Kansas, especially in double cropped fields. However, infestation levels are still relatively low and growing conditions still seem to be really good.

Podworms (corn earworms/sorghum headworms) are just starting to move into soybeans from sorghum as the sorghum gets past the soft dough stage. Thus, as the soybeans are in the reproductive stages, with new succulent pods being added to the plants, these larvae, plus adult bean leaf beetles and possibly stink bugs, may start feeding on them, which can impact yield pretty quickly. Therefore, using a drop cloth and vigorously shaking the plants over it to count the bugs that fall on it is highly recommended to quantify the pests present, which is necessary to determine management options.

 

Also, the results of Dectes stem borer tunneling is becoming visible as scattered petioles start to die. Most of the larvae sampled were still relatively small (see pic), i.e., probably only 1/4 – 1/3 grown.

Dectes stem borer

 

Twospotted Spider Mites

–by Dr. Raymond Cloyd

The recent hot weather we are experiencing throughout Kansas is conducive to the development of the twospotted spider mite, Tetranychus urticae (Figure 1), resulting in extensive feeding damage to the leaves of horticultural plants in gardens and landscapes (Figures 2 and 3). Twospotted spider mite is a warm-weather mite with populations commonly active from late spring through early fall. Summer temperatures allow twospotted spider mite females to reproduce rapidly, which helps to overwhelm natural enemy (e.g. predators) populations by producing multiple generations throughout the season.

Fig 1. Close-up of twospotted spider mite adults.

Fig 2. Twospotted spider mite feeding damage on euonymus bush leaves (Auth–Raymond Cloyd, KSU)

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

The management of twospotted spider mite populations involves maintaining plant health by avoiding ‘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, which will be helpful in minimizing potential problems with twospotted spider mite populations. For instance, inadequate moisture or over fertilizing plants, especially with water-soluble nitrogen-based fertilizers, can enhance development and reproduction of twospotted spider mites.

It is important to monitor for twospotted spider mite populations regularly by shaking plant parts (e.g. leaves, branches, or twigs) onto a clipboard with a white sheet of paper, and then look 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 example, plant-feeding spider mites typically leave a green streak when crushed whereas predatory mites leave a red streak.

A quick and effective method of managing 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 fact, the only “true miticide” still available is hexakis or fenbutatin-oxide, however, this active ingredient cannot be purchased alone as the active ingredient is typically formulated with another pesticide (insecticide) such as acephate (Orthene). However, homeowners can apply commercially available insecticidal soaps (potassium salts of fatty acids) or horticultural oils. Always read the label and apply miticides before twospotted spider mite populations are extensive and causing damage. Moreover, be sure to rotate miticides with different modes of action to avoid twospotted spider mite populations developing resistance. If possible, 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.

 

 

 

Crop Update – Soybean & Alfalfa

–by Dr. Jeff Whitworth

There doesn’t seem to be a lot of pest activity, at least at the present time, in any of the crops throughout north central Kansas. However, there does seem to be a relatively large number of green cloverworms of different stages (see picture)

 

in both conventionally planted double cropped soybeans. There is enough foliage, however, in all fields that these larvae should not cause any problems, although in some fields they are chewing multiple ragged holes in leaves. There are also a few thistle caterpillars and webworms but again, all defoliators together should not cause enough damage to impact yield. There are also large numbers of potato leafhoppers in both soybeans and alfalfa. They should not cause problems in soybeans. However, they will cause problems in alfalfa if they continue to feed and inject a toxin into the leaves as they do this feeding. Swathing should help mitigate this problem, but monitoring the stubble for leafhoppers should continue to ensure adequate regrowth.

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