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Extension Entomology

Tag: whorl stage

Sorghum Update – (chinch bugs, corn leaf aphids, corn earworms)

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

 

Chinch bugs continue to be very active in both corn and sorghum throughout north central Kansas.  Both nymphs and adults are present.

 

Many adults are still mating, which indicates that there are more eggs, nymphs, and adults yet to come.  One consolation relative to the numerous chinch bugs in sorghum fields is that the four spotted egg eater, Collops quadrimaculatas, seems to be plentiful as well.  They have been collected in samples while sweep sampling alfalfa and are also present in sorghum fields.  These little beetles are predacious on insect eggs, and it has even been reported that they feed on chinch bug eggs.  Not sure they will be able to provide a great deal of control on chinch bug populations but it sure can’t hurt!

 

Corn leaf aphids are also very plentiful throughout north central Kansas.  These aphids usually feed on developing corn tassels and silks, but probably are more commonly associated with, or at least noticed in, whorl stage sorghum.  These aphid colonies sometimes produce enough honeydew, and it is so sticky, that often the sorghum head gets bound up in the whorl and therefore doesn’t extend up properly.  These colonies are not usually dense enough on a field-wide basis to justify and insecticide application.  These plentiful aphids are also serving as a food source for many predators, i.e. lady beetles, green lacewings, etc.

 

 

Corn earworms are still plentiful in corn but as they mature, pupate, and become adults they most likely will migrate to sorghum to feed on developing kernels (between flowering and soft dough), and soybeans where they will feed on developing beans within the pods.

For more information on sorghum and soybean pest management, please consult the KSU Sorghum Insect Management guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

And the KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf

 

 

Corn Earworms/Sorghum Headworms/ Soybean Podworms – Helicoverpa zea (Boddie)

— by Dr. Jeff Whitworth, Dr. Holly Schwarting and J.R. Ewing

There has been much activity this year by this particular insect, starting in whorl stage corn and moving to sorghum (both whorl and heading stages) and now in soybeans.

soybean podworm pod

Likewise, there has been some concern that all this activity and resultant insecticide applications have cause an increase in insecticide resistant Helicoverpa zea populations.  So, thanks to great effort on the part of Ethan Kepley, consultant in south east Kansas, who collected all the Helicoverpa zea larvae in one morning from an untreated soybean field, and Steve Freach, FMC, who was kind enough to transport all the larvae directly from the field to our lab, it was possible to conduct a bioassay.  The results of this insecticide bioassay are shown below.

 

Approximately 300 corn earworm/soybean podworm/sorghum headworm, Helicoverpa zea (Boddie), were collected from an untreated soybean field in south east Kansas.  Larvae (mixed sizes but predominantly relatively large instars, which are known to be more difficult to kill quickly) were equally divided into 6 treatments (Table 1).  Larvae were placed individually in small petri dishes that had been coated with the selected insecticide at the rate listed and set aside to dry for 4 hours prior to adding the larvae.  All treatments were individually evaluated 24 hours after the larvae were placed in the petri dishes.  Larvae were evaluated as live: no apparent effect; moribund: larvae very sluggish, little or no movement unless prodded and then only very slow, unnatural movement, and; dead: no movement even when prodded.  From this bioassay there does not appear to be any insecticide resistance to those insecticides and rates utilized (Table 1).

 

Treatment % of Larvae Live % of Larvae Moribund % of Larvae Dead
Hero @ 6 oz/a 0 3.4 96.6
Lorsban @ 2 pts/a 0 8.6 91.4
Mustang Maxx @ 4 oz/a 0 10.9 89.1
Baythroid @ 2.8 oz/a 0 15.5 84.5
Warrior II @ 1.6 oz/a 0 3.4 96.6
Untreated 87.5 9.4 3.1 (parasitized)

 

 

Sorghum Pests Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Double cropped sorghum may still have some ragworm feeding during the whorl stage (see photo).  In addition, there will probably be at least one more generation of headworms and thus later planted sorghum needs to be monitored for headworms between flowering and soft dough when it is vulnerable.  Also, continue monitoring for aphids as there still seems to be a pretty good mixture of greenbugs, corn leaf, yellow sugarcane, and sugarcane aphids.  Some of the fields treated for headworms have reduced numbers of beneficials so they may not be there in sufficient numbers to help control these aphids.  However, some of the fields sampled this week that were sprayed for headworms at least 2 weeks ago had pretty good populations of beneficials already building back up.

sorghum headwormsfall armyworm_sorghum

 

 

Sorghum

–by Dr.  Jeff Whitworth and Dr. Holly Schwarting

Sorghum is in various stages of development around NC Kansas. The late planted, which seems to be just in the whorl stage- to soft dough, or even farther along. Corn earworms (often called sorghum headworms/soybean podworms etc., depending upon the crop infested) are causing significant infestations and therefore concern because of the highly visible whorl feeding and subsequent “ragged”-looking leaves as they expand from the whorl. This feeding probably will have no effect on yield, and by the time the damage is noticed the worms are mostly finished feeding anyway. Therefore, treatment is rarely justified. Feeding on the kernels however which is the marketable product is a different story. Sampling for head-feeding worms is really relatively easy. Just take a small white bucket, bend the head over into the bucket and vigorously shake it against the sides of the bucket which dislodges the larvae. Then count the worms and divide into the number of heads sampled.

Sorghum headworms_small

Rule of thumb: kernel-feeding larvae cause 5% loss/worm/head. Sorghum heads are most vulnerable from flowering to soft dough. These larvae are relatively susceptible to insecticides so efficacy is usually pretty good. However, these insecticides will reduce beneficial insect populations which can help later if any aphid populations develop.

Sorghum hedworm_single

Sorghum Pests

–by Dr. Jeff Whitworth, Dr. Holly Schwarting and J.R. Ewing

Sorghum fields checked in north central Kansas this week indicated a variety of very active pests.  Fields were anywhere from whorl-stage to flowering.  Regardless of the stage of plant development, 100% of the plants sampled were infested with chinch bugs.  Most are still small reddish to brown or black nymphs, but there are still mating adults as well.  These bugs are feeding mainly around the base of the plants.

Chinch bug nymps many stages

 

 

Some plants in the boot stage have populations of corn leaf aphids feeding right at the top of the about-to-emerge heads.  Occasionally, these aphids are so numerous at the point of head extension that their honeydew interferes with the head’s emergence.  Fortunately, aphid populations were not found frequently enough to potentially impact yield, just an occasional plant here and there.

CLA on sorghum

 

Most of the whorl-stage sorghum (90%) is infested with a “ragworm”.  These are a combination of corn earworms, armyworms, and fall armyworms, Mr. Tom Maxwell, Extension Agent in Saline County, even found a cattail caterpillar.  They are in all larval stages, but mainly smaller, from 1st to 3rd instars.  Thus, they will be feeding in the whorls for another 10-21 days, and then will pupate in the soil.  In approximately 7-10 days, moths will emerge and start ovipositing in sorghum, which is vulnerable from flowering to soft dough, and/or soybeans.  Some early flowering plants already had “headworms” feeding in the just emerging heads.

Ragworm feeding sorghum

 

Sorghum headworm

 

Sorghum Pests

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Whorl stage feeding

Much of the sorghum in north central and south central Kansas will soon be, or is already at, the whorl stage.  That usually causes much concern if there are larvae feeding in the whorls, resulting in many “ragged” looking plants (see pic).  However, please remember that these worms cause highly visible defoliation but that does not translate into later problems with plant growth and development, or yield.  The larvae sampled this week in pre-whorl stage sorghum are mostly corn earworms (80%) with a few fall armyworms (20%) and were about half grown, so this feeding will continue for another 5-10 days.  This is of interest because the adult corn earworm moths, when they begin ovipositing in approximately 2-3 weeks, will probably do so in soybeans where pod feeding by the larvae can have a direct effect on yield.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

sorghum whorl feeding

 

 

corn earworm_sorghum

 

 

Fall armyworm_sorghum

 

Corn Pest Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Checking corn fields between rains indicates some insect activity.  The most visible seems to be corn earworm larvae.  The fields we checked in north central Kansas were in the 8-9 leaf stage and the corn earworm larvae had probably been feeding for about a week.  However, the feeding is only noticed after the leaves unfurl as the larvae are hidden inside the furled leaves.

 

CEW larva

Checking corn fields between rains indicates some insect activity.  The most visible seems to be corn earworm larvae.  The fields we checked in north central Kansas were in the 8-9 leaf stage and the corn earworm larvae had probably been feeding for about a week.  However, the feeding is only noticed after the leaves unfurl as the larvae are hidden inside the furled leaves.

Ragged leaves corn

We also found western corn rootworm (WCRW) larvae feeding on corn roots.  This field was sampled last weekend but no larvae were detected.  However, in this same field, the larvae hatched and have fed on the roots as seen in the picture.  Just in the last 3-4 days, larval feeding has caused some root damage.

CRW larva and damage

CRW larva

Corn and Wheat Pest Update

–Dr. Jeff Whitworth and Dr. Holly Schwarting

Corn

Plants in north central and south central parts of the state are finally starting to grow.  All the cloudy, wet conditions have not been the best for corn development and many fields are a little more chlorotic looking than usual for this time of year.  This stalled development usually allows pests more time to feed and thus cause damage.  Seed treatments only provide protection for 3 to 4 weeks (check label) from planting, so most of that protection has dissipated.  However, we have not seen nor heard about much pest activity yet.  A few thin stands have been noted which can be caused by many different pests, probably most common so far has been wireworms.  Generally, however, most fields are past seedling damage.

wireworm 1

wireworm 2

We have received a few calls about armyworm activity in wheat and sorghum, so when these larvae pupate and then emerge as adults to lay eggs, most corn will be in the whorl stage so there may be some whorl-stage leaf feeding which is always highly visible but causes very little actual impact on yield.

Wheat

We have not seen any “worms” in wheat, but have received several calls about armyworms feeding on leaf tissue.  Armyworms should move to another grass host, i.e. corn, sorghum, brome, etc. as the wheat begins to senesce.  They actually devour leaf tissue and thus are not actually feeding on the grain.

Armyworm

If there are thin, light green or tan worms feeding on the wheat head they are probably wheat head armyworms (see photo).  They can and will actually feed on the grain whereas the armyworm feeds on the foliage around the grain – not the grain itself.

wheat head armyworm

If you decide to treat either pest, please refer to the Wheat Insect Management Guide, 2015: http://www.ksre.ksu.edu/bookstore/pubs/MF745.pdf and make sure to check the label for the preharvest interval (PHI) if spraying wheat this close to harvest.

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