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Extension Entomology

Category: Sorghum

Sorghum Update—headworms, corn earworms, fall armyworms

–by Dr. Jeff Whitworth

Much sorghum has been treated throughout north central Kansas for headworms (corn earworms and/or fall army worms) and most treatments seem to have been very effective. Again, Sorghum is most vulnerable to headworms from flowering to soft dough, so past the soft dough stage headworm treatment will not be necessary.   The headworm shown (see pic1) has approximately 7-10 more days of feeding before pupating. Still no reports of sugarcane aphid problems – but monitoring should continue because in 2016 insecticide applications were still justified into late September.

 

Pic2: These two larvae were collected from a Heligen treated field. The dead (smaller) larva is obviously pathogen-affected. If Heligen is responsible for the death of this larva, then it looks like the application was well timed to kill the larva before it caused much damage.

Photo by Cooper Wyckoff)

 

 

 

 

 

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

 

 

 

Sorghum Update

–by Dr. Jeff Whitworth

The 1st sugarcane aphids have been detected in Kansas (i.e., Mr. Jeff Seiler, et al., reported finding colonies (see pic) on 30 July in Sumner County). Most sorghum is in the whorl to boot stage throughout south central and north central Kansas and thus this situation needs to be closely monitored throughout the rest of the season. Unfortunately, “headworms” will just be hatching, probably at pretty good infestation levels, about the same time as these sugarcane aphids will probably be trying to colonize. Fortunately, however, there are a pretty good number of beneficial insects which seems to have really helped control the aphids the last couple of years.

Predator eating an aphid (picture by Jeff Seiler)

Sorghum “Ragworms”

–by Dr. Jeff Whitworth and Dr. Holly Davis

Much of the sorghum around north central Kansas is at, or just coming into, the whorl stage.  As the leaves unfurl and grow out of the whorls, a pretty high number of plants are showing large holes that have been chewed in leaves.  These holes are from smaller larvae (most that we have sampled are corn earworms) that feed on the leaves while they are still furled. When leaves grow out of the whorl they have showy, ragged looking feeding that may cause concern.

Larvae sampled this week still have about one additional week of feeding within these whorls, then they will exit and crawl down the plant to pupate in the soil.  Larvae in the whorl are rarely worth spraying for four reasons: 1) by the time the leaves unfurl making feeding damage visible, most larvae have already accomplished most of their development and thus feeding, 2) insecticides usually can’t penetrate far enough down into the whorl to actually impact the larvae, 3) a general insecticide will kill most beneficial insects, and 4) ragged looking leaves during this stage have little to no effect on yield, and no, you cannot eliminate the next generation by spraying this generation.

 

Sorghum Update – ‘Headworms’, Beneficials, and Aphids

–By Dr. Jeff Whitworth and Dr. Holly Schwarting

Sorghum continues to get the attention of many pests and beneficials.  Chinch bug populations are not diminishing even though they are not as noticeable because most are feeding around the base of the plants and behind leaf sheaths on the stalks.  Much late planted, or at least slower developing, sorghum is still vulnerable to these chinch bugs.  Bugs may also move up to the heads as they emerge from the whorl to feed on the forming kernels that provide a succulent source of nutrients.

‘Sorghum headworms’, mostly corn earworms but also a few fall armyworms, are infesting all sorghum fields (not yet in the soft dough stage) that we monitored throughout north central Kansas.  Most fields have close to, or are exceeding, 100% infestation levels (1 or more larvae/head).  These larvae are present in all different sizes, or developmental stages, from 1st to 4th instars.  Thus, they will be feeding on these kernels for at least another 7 – 10 days.

Remember, between flowering and soft dough, these larvae will cause 5% yield loss/ worm/ head.  Very few beneficials are available to help control headworm populations.  However, there are huge populations of beneficials currently present to help control any aphid pests that are, or might be present in the near future.

 

 

Corn leaf aphid populations were common on earlier planted sorghum, and still are on later planted sorghum that is just reaching the whorl stage.  These corn leaf aphids have really helped fuel the beneficial populations.  Fields that have headed out are swarming with lady beetle adults and larvae, syrphid or hover flies, green lacewings, and parasitic wasps.

 

 

 

Sugarcane aphid (SCA) populations are becoming scattered around north central KS, slowly so far, and are really attracting the attention of all these beneficials, which will hopefully help control colony growth.

For management considerations and recommendations for these, and other sorghum pests, please refer to the 2018 Sorghum Insect Management Guide:   https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

 

 

Sorghum Update – ‘Ragworms’, ‘Headworms’, and Aphids

–by Dr. Jeff Whitworth and Dr. Holly Davis

Late planted sorghum is still causing considerable concern throughout north central Kansas as the leaves grow out of the whorl and are significantly ‘chewed up’ looking.  These ‘ragworms’, primarily corn earworms and fall armyworms but also a few cattail caterpillars, are still active in younger plants.

 

As these plants reach reproductive stages, i.e. flowering, there will be a high probability of having ‘headworms’ (corn earworms and fall armyworms) infesting the kernels.  Sorghum heads are the most vulnerable between flowering and soft dough.  There are currently significant infestations of these headworms throughout north central Kansas with worms in various stages of development.  Headworms cause approximately 5% loss per worm, per head.

 

There are large numbers of corn leaf aphids, greenbugs, and even a few yellow sugarcane aphids around north central Kansas.  The first report of a sugarcane aphid colony from Saline Co. was made on 16 August. These aphids are attracting, and providing food for, large numbers of beneficials which seem to be keeping aphids relatively well controlled.  Insecticide applications have not been needed for aphids. More information on sugarcane aphids in Kansas can be found at My Fields: https://www.myfields.info/pests/sugarcane-aphid

 

For more information regarding sorghum insect pest management please refer to the KSU 2018 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

Sorghum Update – Chinch bugs, Headworms, and Corn Leaf Aphids

–by Dr. Jeff Whitworth and Dr. Holly Davis

 

Chinch bug populations continue to increase dramatically throughout north central Kansas.  Adults are still active, mating and ovipositing in both the developing heads and around the base of plants.  There are also large numbers of nymphs, mainly feeding in and around the base of plants, but some are on the developing kernels.  The significant populations of chinch bugs, along with continued hot and dry conditions, are causing some plants to lodge as the stalks dry down prematurely.

 

‘Headworms’, both fall armyworms and corn earworms, are also very common in all the fields we sampled that were in the flowering stages.  On 6 August, there were all different sizes of larvae detected in heads.  Many fields throughout north central Kansas are just starting to reach the reproductive stages, so these ‘headworms’ will continue to be problematic in any field that is in the flowering to soft dough stage.  Past research has indicted that ‘headworms’ may cause approximately 5% loss/worm/head.  It is important to sample in a timely manner to detect these pests while they are still small, before most of the feeding damage has been done.

 

Corn leaf aphids (CLA) continue to cause considerable concern throughout north central Kansas as these populations are still very widespread and become more apparent as the heads start to extend out of the whorl.  However, there are many beneficials present as well.  CLA should have little to no negative impact on plant development or yield other than potentially a few individual plants.

 

For more information relative to sorghum insect management, please see the 2018 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

 

 

 

 

Sorghum – Worms and Aphids

–by Dr. Jeff Whitworth and Dr. Holly Davis

 

‘Ragworms’, mostly fall armyworms but a few corn earworms (sorghum headworms) as well, continue to cause considerable concern due to the very ragged looking leaves their feeding produces.  These worms are present every year, to a greater or lesser extent, but this year does seem to be a good year for them.  However, this whorl-stage feeding activity really has little to very little negative impact upon the plants, nor does it reduce yield.  Most of the plants we examined in north central Kansas had feeding damage only – no worms, or a mature larva which had completed most of its feeding.  Therefore, insecticide application will be a waste of time, money, and will kill any beneficials which may be present.

 

 

As sorghum starts to reach reproductive stages, the developing kernels will be vulnerable to attack by the next generation of fall armyworms and corn earworms (sorghum headworms).  Between flowering and soft dough these larvae can cause about 5% loss/worm/head.  Sampling needs to be conducted carefully and in a timely manner during this window.

 

Corn leaf aphids continue to be common in sorghum whorls and are often tended by ants for their honeydew.  Beneficials are still plentiful and corn leaf aphid populations do not seem to be increasing.

For more information relative to sorghum insect management, please see the 2018 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

 

Sorghum Update

–by Jeff Whitworth, Holly Davis and J.R.Ewing

 

Chinch bugs continue to feed and develop all around north central Kansas.  However, growing conditions have improved significantly and thus the plants are much better able to tolerate this feeding.

 

As sorghum reaches the whorl stage corn leaf aphids are becoming more common.  These aphids may cause some concern as their honeydew production will occasionally be so thick and sticky as to retard the heads extending up from the whorl.  This is not typically a field-wide problem, just a few places or plants in a field and these aphids are a good source of nutrition for beneficials.

Photo by JR Ewing

In addition, as sorghum leaves grow out of the whorl stage, they are showing signs of feeding.  Fall armyworms have been feeding as small larvae within the whorl and as plants grow out and the leaves unfurl, these leaves have a very ragged appearance.  Many of these ‘ragworms’ have finished feeding and are now pupating in the soil.  Thus, spraying is not necessary as the damage is done.  Even if the worms are still in the whorl, they will not be contacted by the spray.  This whorl-stage leaf feeding doesn’t negatively impact the plant, or yield.  There will probably be a least one more generation of fall armyworms and these may be more problematic if they start feeding in the head between flowering and soft dough stages.  Feeding on these developing kernels is generally considered to cost 5% loss/worm/head.

 

 

 

 

For more information regarding sorghum insect pest management please refer to the KSU 2018 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf

 

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