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Extension Entomology

Tag: cooler weather

Aphids

Posted on by Sharon Schroll

–by Dr. Jeff Whitwoth

Every field sampled throughout North Central Kansas last week had pea aphids (fig. 3) and many had scattered infestations of cowpea aphids. Pea aphids are usually considered more of a cool weather insect while cowpea aphids more of a warmer (i.e. later in the season) insect, so that just illustrates the weather roller coaster we have been experiencing this spring. Treatment recommendations for pea aphids will probably work for cowpea aphids and/or mixed populations, which calls for 50+ aphids/stem, to justify an insecticide application.

Alfalfa Weevils

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth

Alfalfa weevil activity has increased significantly in the last week throughout North Central Kansas. The recent warm weather has really stimulated egg hatch thus there are large numbers of very small 1st instar larvae just starting to feed, plus older, larger larvae (fig. 1) that have been feeding for a week or so. However, some fields have very low infestation levels, while others have already reached the 100% infested level. Recent freezing temperatures appeared to have killed some top growth in some fields, which can be mistaken for insect damage.

Thus, sampling each field is always prudent, but even more so this year. We have gotten many questions recently about the predicted cold weather and its effect on the weevils, but remember, alfalfa weevils are cool weather insects. Temperatures into the mid 20’s for a couple hours may kill small larvae, as we saw in 2018, but probably won’t affect the eggs or adults. Then, anytime the temperatures are over about 45°F, the larvae feed and do so 24/7 as long as temperatures are above 45°F. Many fields were treated this week and probably should be whenever the treatment threshold is reached as the predicted temperatures for the next 10 days looks like it will slow the feeding activity down but probably not be cold enough to kill very many larvae. Have also gotten the question about spraying for army cutworms and that effect on alfalfa weevils. If both occur at threshold or one or the other does and you make an application of an insecticide you should get pretty good control of both. However, remember, cooler weather will slow down the effect of the insecticide.

 

Also, check this super neat picture of biological control at work (fig. 2). A turkey harvested by a Kansas youth hunter on 6 April had a crop completely filled with large army cutworm larvae.

 

Alfalfa Update

Posted on by Sharon Schroll

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevils are cool weather insects, thriving when temperatures are between 50-75°F and thus mostly affect alfalfa prior to the 1st cutting. That has been the case for about the last two weeks in north central KS. Temperatures have been on the cool side and the alfalfa has not been growing as well as most producers would like.  However, alfalfa weevils have been very active to the point where there are many pupae and even pupal webbing with holes indicating the adult weevils have already emerged and dispersed.  Infestations as of 6 April were composed of very small 1st instar larvae to larger, more mature 3rd instar larvae, as well as pupae, and newly developed adults.  Also, lady beetle larvae were quite common in most alfalfa fields, but no aphids were detected.

Alfalfa weevil feeding damage

 

Alfalfa weevil feeding damage – close

 

Alfalfa Update

Posted on by Sharon Schroll

–Dr. Jeff Whitworth and Dr. Holly Schwarting

Much of the alfalfa in northcentral Kansas that could be swathed has been in the last week.  The cool damp weather has kept the adult alfalfa weevils in the fields.  They are congregated under windrows in the cut fields where they do a little feeding on the stems, resulting in characteristic spots of epidermis removal, called ‘barking’.  As these windrows are picked up there will be the characteristic striping across the fields where the windrows held back the regrowth underneath, plus provided the weevils with a protected site to continue feeding.  Fields not yet swathed also have significant populations of adults but this should not impact the foliage prior to cutting.

AW adult and barking

Windrows

Pea aphids are also present in both cut and uncut fields, but lady beetles and green lacewings are also, so would not expect pea aphid populations to have a negative impact on alfalfa.

Pea aphids adult and nymph

greenlacewing

pinkspotted lady beetle

Sevenspotted lady beetle

Potato leafhopper adults are already present in all alfalfa fields we checked over the past week.  This is earlier than usual for these pests as they typically don’t migrate into the state for another month, between the 2nd and 3rd cutting.  Some of these populations already exceed the treatment threshold with just adults, so hatching nymphs will just increase the populations further.  These potato leafhopper populations need to be monitored throughout the rest of the growing season.

PLH adult and nymph

Winter Grain Mites

Posted on by Sharon Schroll

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

This time of year there is usually considerable interest in winter grain mites and this year is no exception.  A little refresher relative to winter grain mites:

  • Adults can be seen by the naked eye, but they are tiny.

winter grain mites_size

  • They have dark colored bodies with distinctive red legs and a red spot at the rear of their back, which is an anal pore.

Winter grain mite_close

  • There are 2 generations per year.
  • Adults will be actively feeding in the fall and spring and overwinter and oversummer as eggs.
  •  This feeding will continue as long as temperatures are cool (not cold), i.e. they are most active from 40°F to 70°F.

Feeding activities usually peak about this time of year and will cease during winter, when temperatures usually are just too cold.  This 1st generation deposits eggs in November and December and these eggs will hatch in late February to March.  This is about the time wheat is breaking dormancy, thus another time for grower concern.  Under dry conditions winter grain mite feeding may cause plants to take on a silvery appearance because mites penetrate individual plant cells and remove the plant juice, resulting in this silvery look.  Serious feeding, again in dry conditions, may result in yellowing of plants but, more commonly, just the tips. Under good growing conditions this feeding will not even be noticed.  Hot weather causes adult populations to quickly decrease.

Winter grain mite feeding

In summary, mite feeding activity will be terminated by cold weather in winter and hot weather in the spring, both of which cause eggs to be deposited into the soil to withstand the unfavorable conditions.  Winter grain mite feeding is only noticeable when wheat is under moisture stress, is reversed by adequate moisture, and rarely, if ever, results in any impact on yield.