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Extension Entomology

Category: Field Crops

Field crop pest and beneficial organisms.

Alfalfa Caterpillars

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth — Field Crops

Alfalfa caterpillars are currently very common in both alfalfa and soybean fields. They are shy and extremely well camouflaged (see fig 2) and therefore rarely noticed. They are voracious leaf feeders, however, populations rarely reach densities in either crop to warrant an insecticide application. These larvae are the feeding stage of the common yellow or white butterflies often seen flying around either soybean or alfalfa fields where they can be seen often dipping down into the canopies to deposit eggs or gathering around water to drink. This activity, coupled with often large numbers of these butterflies, sometimes causes concern to growers. Howe

Figure 2. Alfalfa caterpillar  (picture by Cody Wyckoff)

 

 

Click Beetles

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth — Field Crops

Click beetles (fig 1) are becoming very active and this activity will continue for at least the next month. There are several species of click beetle in Kansas that can be a pest of crops. The larvae of these species are generally called wireworms and may feed on roots, root hairs, germinating seedlings, etc. In other words, just about any plant parts found underground including seeds can be damaged by click beetle larvae. The adults, of all species, are often attracted to lights at night or may be found under plant residue in fields. Insecticide seed treatments do really well at protecting seeds and seedlings, from planting up to about 28 days post-planting, from wireworm attack.

Figure 1.  Click beetle   (picture by Cody Wyckoff)

 

Green Cloverworms

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth — Field Crops

 

 

Green cloverworms are quite common right now in most alfalfa and soybean fields throughout north central Kansas. They are in various stages of development (see fig. 1), i.e. sizes are variable, but most will be pupating within a week or two. The adult moths will then emerge, mate, and start depositing eggs, probably mostly in soybean fields. This next generation of green cloverworm larvae then maybe more significant as they are voracious leaf feeders and can quickly cause noticeable defoliation in soybeans. Populations of green cloverworms have occurred in significant densities periodically in past years as to cause considerable concern. Defoliation of 50-60% during the vegetative stage may justify an insecticide application. However, there is often an entomopathogenic fungus that attacks green cloverworm larvae when the larvae reach significant densities. This fungus can really decimate these larvae and thus help control their populations.

Figure 1.  Green Cloverworm   (pic by Cody Wyckoff)

Dectes Stem Borers

Posted on by Sharon Schroll

–by Jeff Whitworth — Field Crops

The 1st adult Dectes stem borers (see pic 4) were observed in soybean fields on 21 June. These adults are usually 1st observed a week or two prior to the 4th of July and so this year is no exception. As the adults emerge, they usually aggregate on weeds around soybean field borders for a few days then disburse throughout the soybean fields where they deposit their eggs in petioles and stems over the next 6-8 weeks.

Picture  4: Adult Dectes stem borer

Pictures by Cody Wyckoff

Potato Leafhoppers

Posted on by Sharon Schroll

–by Jeff Whitworth — Field Crops

Potato leafhoppers (PLH) started their annual migration back into Kansas about 7-10 days ago, at least in numbers that could be noticed. Potato leafhoppers are small lime green, wedge-shaped plant sucking insects (see pic 1-nymph) that have a characteristic white spot between their eyes on both adults (see pic 2) and nymphs. Adults have wings and readily fly when disturbed. Nymphs do not have wings but will quickly move to the underside of leaves or jump into the leaf litter below the canopy when disturbed. Females deposit eggs in stems and the tiny nymphs emerge ready to feed. Both nymphs and adults suck plant juices and in so doing inject a toxin into the plant. Signs of potato leafhopper feeding on alfalfa leaves then is often called “hopper burn”. This starts out as a yellowing at the leaf tip (see pic 3) but if feeding continues, it may cause the whole leaf/stem/plant to turn yellow and wilt which may significantly reduce nutrient quantity and quality. PLH is usually affect the 2nd-4th cuttings. Swathing is probably the best way to control PLH populations but if populations exceed the treatment threshold and the alfalfa won’t be ready to swath for 3 weeks or so, then an insecticide application may be justified.

Picture 1: PLH nymph

Picture 2: PLH Adult

Picture 3: “Hopper burn” on alfalfa leaves

 

Corn Rootworms

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth — Field Crops

 

Fields planted to corn rootworm susceptible varieties for 3+ years should probably be monitored for corn rootworm larval feeding. Several fields were sampled this week (13-16 June) that have been planted for at least 3 consecutive years without regard for corn rootworms, i.e. not varieties that had a Bt event to help control rootworms. All varieties, however, had commercially applied fungicide+insecticide seed treatments. All fields were planted this year from 15 Apr-3 May, but regardless, were all in the 8-10 leaf stage of development. Insecticide seed treatments seem to always work well but the toxins are only active for up to 21-28 days from the day of planting. Even though rootworm larvae were found in each field, no obvious signs of lodging or goosenecking were evident in any of the fields, which could be indicators of root pruning by rootworm larvae. However, northcentral Kansas has not had a great deal of wind over the last couple of weeks and the majority of the root feeding will probably occur over the next 10-14 days as the rootworm larvae get larger (see fig. 1). If there is not much wind or wind events over the next couple of weeks, the plants may compensate for the root damage and the lodging may be inconsequential. Most larval development in northcentral Kansas, thus seems to be on track to be completed prior to 4 July,–as it has been every year for at least the last 25 years.

Figure 1. Corn rootworm larvae (14 Jun 2021)  (pic by Cody Wyckoff)

Bean Leaf Beetles

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth — Field Crops

 

Many soybeans have been planted recently and seem to be doing really well under good growing conditions. Most (if not all) fields with germinated beans have a few bean leaf beetle adults feeding on them (see pic 6). However, seedling soybeans can withstand considerable defoliation, especially under these good growing conditions, without any adverse effect. These adults usually cause round or oval holes in leaves (see pic 7) but it takes approximately 6-8 beetles/row foot to justify a rescue insecticide application. These adults will feed a little on leaf tissue then start depositing eggs around the base of soybean plants where the larvae feed for 2-3 weeks.

 

Picture 6  Bean leaf beetle adult

 

Picture 7  Soybean leaves with round or oval holes from Bean leaf beetle feeding

(All Photos by Cody Wyckoff)

 

Alfalfa Pests

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth — Field Crops

Most alfalfa around north central Kansas, has been swathed at least once and some fields even twice. Adult alfalfa weevils were very common in many fields up until about 10 days ago, which caused considerable concern. When temperatures finally approached and/or exceeded 80-85 °F, however, most adults migrated out of the fields and should not cause any more concern, or return in large numbers, to alfalfa fields, until September. Adult alfalfa weevils do feed just a little-but not anywhere as voraciously or as long as the larvae (see pic 1-alfalfa weevil larva noted still in the field on 8 June, 2021)

Picture 1 Alfalfa weevil larva

 

Picture 2 Grasshopper Nymph

Very few actual pests have been noted in alfalfa fields over the last couple of weeks. However, grasshoppers are hatching and these small nymphs (see pic 2) should be closely monitored. Adult leafhoppers have started migrating back into the state so as fields start to grow back after cutting these should be monitored also. Fortunately, there seem to be good numbers of lady beetles (see pic 3-lady beetle larva; pic 4-lady beetle pupa; and pic 5-adult- -this adult has the neatest name in entomology in my opinion–twicestabbed lady beetle) which should help control any aphid problems going forward.

Picture 3 Lady beetle larva

Picture 4 Lady beetle pupa

Picture 5  Lady beetle adult (Twicestabbed lady beetle) – two distinct red spots on their back

(All Photos by Cody Wyckoff)

 

Wheat Aphids

Posted on by Sharon Schroll

–by Jeff Whitworth — Field Crops

 

Wheat aphids, primarily bird cherry oat but with a few greenbugs mixed in, have been migrating into Kansas, especially the southern parts, over the last couple of weeks. Sampling a couple dozen fields throughout the central part of the state, however, over the last week (from I-35 to Hwy 77 west to east and from Hwy 24 north to Hwy 56 on the south) yielded very few aphids but also very few beneficials-which makes sense. However, in one field we did find one aphid — just as the only lady beetle we found in that field also found it and promptly gobbled it up (see fig 3). Most wheat was at least at the jointing stage. If aphid migrations increase significantly in the next couple of weeks, coupled with the lack of beneficials, these aphid populations could explode and thus cause some stress to the developing wheat. Thus, monitoring should continue — but please remember it takes approximately 20+ aphids/tiller throughout the field, with very few beneficials, to actually cause a negative effect on yield. Also, please remember adding an insecticide to an application of a fungicide to kill any insect pests, “just in case” is never a good idea.