Kansas State University

–by Dr. Jeff Whitworth

Still getting many calls about corn leaf aphids and many folks seem to still be getting them confused with sugarcane aphids (see fig. 2-cornleaf aphids and fig. 3-sugarcane aphids; photo provided by Jay Wisby) just because of the amount of honeydew produced by both species. Sugarcane aphids have now been verified as far north in Kansas, at least as far as I have heard, as Saline and Dickinson Counties. None of the colonies, yet, however have reached field-wide treatable levels and beneficials seem to be plentiful around every colony so far.

Figure 2  cornleaf aphids on leaf

Figure 3  sugarcane aphids on leaf

–by Dr. Jeff Whitworth

Cattail caterpillars are a perennial cause of concern throughout south central and north central Kansas. They are usually found on cattails, thus the name. However, every year some sorghum fields are infested. These infestations are usually most intense around field borders, and most especially in sorghum fields near water, i.e., a creek or pond, etc. The adult is a tan or dusky white, heavy bodied moth, which looks somewhat like a southwestern corn borer moth. The females usually start depositing eggs just about at the whorl stage of sorghum. However, the cattail caterpillar is rarely found within the whorl like “ragworms”, i.e., corn earworms/fall armyworms/etc. are. The cattail caterpillar is mostly found on the leaves themselves but may add to the “ragging” up of the leaves after they unfurl from the whorl (fig. 1) due to their voracious leaf feeding. The cattail caterpillar is a relatively hairy but very distinctive larva with bright orange/white/and black body markings (figures 2 and 3). A relatively high percentage of the older, larger, more mature larvae have been found to be parasitized, thus stop feeding, become very sluggish, and eventually just die from these natural enemies of these caterpillars. There is no established treatment threshold.

Figure 1 “Ragging” up of the leaves (Tom Maxwell)

Figure 2 Cattail Caterpillar (Tom Maxwell)

Figure 3 Cattail Caterpillar feeding on the edge of the leaf (Tom Maxwell)

–by Dr. Jeff Whitworth

Most sorghum throughout north central Kansas is past the soft dough stage, thus not susceptible to “headworms.” However, a few late-planted fields, just coming into the “boot” stage, have sporadic small colonies of sugarcane aphids (SCA) (see pic of SCA’s from Saline and Dickenson counties (pic3)). However, there seems to be significant numbers of beneficials, but these late developing fields should still be monitored as these populations can “explode” quite quickly.

(Pic 3) SCA Colony

–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)

–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. 1^st, 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. 2^nd, 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. 1^st – 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 1^st (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.

–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 2^nd instar larvae to almost mature 5^th 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

–by Dr. Jeff Whitworth

The 1^st 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)

–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 1^st to 4^th 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