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Extension Entomology

Category: Alfalfa

Alfalfa Update – aphids, potato leafhoppers

–by Dr. Jeff Whitworth

Pea aphids (see pic) are and have been returning, or at least increasing in numbers, to many alfalfa fields throughout north central Kansas. These are primarily cool weather aphids and are usually the last ones still feeding in the fall on alfalfa and the 1st ones in the spring. However, with the advent of cool/cold weather this late fall feeding should be negligible. Potato leafhoppers (see pic), for the most part, have emigrated, or at least are not present in easily detectable numbers, so “hopper burn” (see pic) and its consequences, should not be problematic this fall/winter.

 

Pea aphids

 

Potato leafhopper

 

Hopper burn

 

Alfalfa and Soybeans

–by Dr. Jeff Whitworth

Green cloverworm adults (see pic) have been very common in soybean and alfalfa fields the last couple of weeks, and this has caused concern about potential green cloverworm infestations next year. However, green cloverworm adults are, or have been, migrating to the southern US for overwintering. Thus, since they do not overwinter in Kansas, infestations next year will depend on wherever the adults come back to, so predicting future infestations after overwintering adults return from the southern US are not possible.

Adult green cloverworm

 

 

 

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.

Alfalfa Update

–by Dr. Jeff Whitworth and Dr. Holly Davis

Potato leafhoppers are rapidly increasing throughout alfalfa fields in north central Kansas for two reasons:  1) potato leafhopper adults are still migrating in and 2) the eggs are hatching and nymphs seem to be everywhere.  These nymphs are very small and very shy – which means they are easily under counted as they hop to the underside of leaves, or even off the leaves, at the least disturbance.

Alfalfa weevils mating—(photo by T. Sexton)

Parasitized Alfalfa Caterpillar

Alfalfa weevil adults have mostly migrated out of alfalfa fields in north central Kansas, however there are a few that pupated late and that are just emerging out of their pupal cells.  Interesting, at least to us, was that some of these adults were mating (see picture).  Most of the literature reports alfalfa weevils mating in the late summer, fall/winter  —  not soon after becoming adults.

Alfalfa or garden webworms are also relatively common in alfalfa, where they may cause a problem in new alfalfa, and soybeans.  The next generation will probably be more problematic in small soybeans because there will probably be more webworms as this generation is more of a “spring board” generation.

Alfalfa caterpillars (see picture of larva with attached parasitoid eggs) are also quite common in alfalfa fields as are the white and/or yellow butterflies that they develop into.  However, they have not ever been found in densities great enough to cause any negative impact on yield.

 

Alfalfa Update – Potato Leafhoppers and Pea Aphids

–by Dr. Jeff Whitworth and Dr. Holly Davis

Alfalfa seems to be growing very well and many fields around north central Kansas have finally dried out enough to swath and remove the hay from the field.  However, potato leafhoppers continue to migrate into the state and will continue to for about another month.  Most are still adults and have been/are now depositing eggs in stems and the tiny nymphs are just starting to emerge.  Thus, potato leafhopper feeding will become more evident as “hopper burn”, the yellowing of leaves which can reduce the health of the plants and the nutritive value of the foliage.  Therefore, if fields were just recently cut, or will be in the near future, while potato leafhoppers are still migrating into the state, they will be very vulnerable to potato leafhopper feeding damage.

Pea aphids are still plentiful throughout alfalfa fields in north central Kansas.  Populations should not reach treatable levels this late in the year, and they are a good host for many beneficial insects.

For more information regarding these and other alfalfa pests, please see the KSU Alfalfa Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf

Bean Leaf Beetles

— by Dr. Jeff Whitworth and Dr. Holly Davis

Bean leaf beetle adults that are out and about now have successfully overwintered, probably fed a little in an alfalfa field, and are now eagerly awaiting soybean germination.  These adults are amazing at finding the first, small soybean plants where they begin feeding, causing the characteristic round and/or oblong holes in the small leaves.  These beetles will feed for just a little while and then begin depositing eggs in the soil around the stems of these plants.  These young plants are usually very resilient at overcoming this early season leaf feeding, until it reaches 50% defoliation or more. For more information on bean leaf beetle biology and management, please see Bean Leaf Beetle:  https://www.bookstore.ksre.ksu.edu/pubs/MF2824.pdf

For more information relative to all soybean pests, please see the KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

Pea Aphids and Potato Leafhoppers

— by Dr. Jeff Whitworth and Dr. Holly Davis

Recently mowed alfalfa around north central Kansas still seems to have relatively robust populations of pea aphids.  These aphids tend to be more problematic during the cooler weather of spring and fall, but with the cloudy, cooler temperatures so far this spring, they are still doing quite well. Also, most fields treated for alfalfa weevils have few beneficials yet, although they do appear to be coming back. Warmer temperatures and resurgent densities of beneficials should help control these pea aphid populations without the need of an insecticide application.  However, if summer temperatures are lower than usual, pea aphid populations may persist and thus monitoring should continue.

Potato leafhoppers are increasing in north central Kansas.  Populations sampled were all adults, which means they have recently migrated into the area.  These adults will be depositing eggs in alfalfa stems and the nymphs will emerge to begin sucking plant fluids from the alfalfa.  If potato leafhopper populations are at, or exceed, treatment thresholds and the alfalfa has recently been swathed, so that it is a few weeks prior to the next cutting, an insecticide application may be justified.

Keep in mind that potato leafhopper and pea aphid populations can be greatly impacted by weather so they should continue to be monitored.  For more information regarding these and other alfalfa pests, please see the KSU Alfalfa Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf

 

Alfalfa Weevils

— by Dr. Jeff Whitworth and Dr. Holly Davis

Alfalfa has mostly passed the alfalfa weevil vulnerable time of year.  However, there are still highly visible signs that there was a significant weevil infestation, i.e. some fields with characteristic striping, which is usually partly attributed to weevil feeding under windows and the “barking” of stems by adults.

Grasshoppers

— by Dr. Jeff Whitworth and Dr. Holly Davis

Grasshopper nymphs, both longhorned (typically not a pest), and shorthorned are common and they will probably just keep increasing in density for another month or more. Another reminder that the best time to manage them is while they are still small and thus, less mobile.  An application of an insecticide labeled for grasshopper control is most effective, cheaper, and less environmentally disruptive if applied in a timely manner relative to grasshopper development.

Potato Leafhoppers

— by Dr. Jeff Whitworth and Dr. Holly Davis

These small, lime-green, wedge-shaped, herky-jerky moving insects have already migrated into the state.  Some fields are at or exceeding treatment thresholds.  However, swathing should cure this problem, at least temporarily.  Historically, potato leafhoppers migrate into Kansas a little later in the season, i.e. between the 2nd and 3rd cutting. Some “hopperburn” is already becoming evident.

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