Kansas State University

–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

–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

–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

–by Dr. Jeff Whitworth and Dr. Holly Davis

Chinch bugs continue to develop and increase in numbers throughout north central Kansas.  However, recent rains have significantly improved growing conditions.  Thus, sorghum seems to be tolerating these chinch bug populations well.  However, some fields and field borders have been treated for chinch bugs.

Fall armyworm larvae have been feeding in sorghum whorls and this leaf feeding is starting to unfurl from the whorl and thus become highly visible.  That is where the name “ragworms” comes from as they do cause ragged looking leaves, although this foliar feeding does not impact yield.

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

–by Dr. Jeff Whitworth and Dr. Holly Davis

Chinch bug adults continue to mate and deposit eggs, especially around the base of young sorghum plants.  As these eggs hatch, nymphs are increasing in both numbers and size and thus are removing more and more of the moisture from the plant.

This trend will probably continue from now until September and thus cause serious stress to plants, especially if environmental moisture is limited.   If treatment is warranted, it is important to use directed sprays and adequate carrier to reach the base of plants where chinch bugs are actively feeding.  This will also avoid non-target organisms as much as possible. For more information on chinch bugs, management decisions, and/or insecticide recommendations, please see:

Chinch Bugs MF3107:  https://www.bookstore.ksre.ksu.edu/pubs/mf3107.pdf

2018 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf742.pdf