–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
–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
— by Dr. Jeff Whitworth, Dr. Holly Schwarting and J.R. Ewing
Much sorghum throughout north central Kansas is at least in the soft dough stage and thus has passed through the most susceptible stages for sorghum headworm infestations. However, any sorghum yet to head out will still be susceptible to these headworms as there will still be at least one more generation.
All four aphids species, corn leaf, greenbugs, sugarcane, and yellow sugarcane, are still in every sorghum field we sampled throughout north central Kansas. All populations seem to be increasing but there are relatively healthy populations of beneficials present as well.
–by Jeff Whitworth and Holly Schwarting
Double cropped sorghum in north central KS seems to have a significant infestation of “ragworms”. The larvae are a combination of fall armyworms and corn earworms and are of various sizes.
Leaf feeding in the whorl by either species is highly visible but should not have a significant effect on the plants or yield.
Also, most fields in north central KS are infested with aphids. Corn leaf aphids can produce a great deal of honeydew but mostly in the whorls. This honeydew may retard head extension but usually does not affect many plants over a large area.
Also found greenbugs and yellow sugarcane aphids. None of the invasive sugarcane aphids were detected in north central Kansas. However, many beneficials are, and will continue to be, present in sorghum fields as evidenced by the numerous green lacewing eggs and lady beetle eggs.
–by Dr. Jeff Whitworth and Dr. Holly Schwarting
Aphids are becoming easier to find in sorghum fields throughout south central and north central Kansas. However, they are a mixture of greenbugs, corn leaf aphids, yellow sugarcane aphids and the new-to-Kansas sugarcane aphid.
Probably the easiest way to find aphids is to look for the shiny/wet looking leaves and then examine the undersides of the leaves immediately above the ‘wet’ leaves. This is the honeydew produced by a colony of aphids.
Headworms are still very common throughout north central and south central Kansas. There are all stages present, but remember the sorghum is vulnerable from flowering to soft dough. These headworms may cause up to 5% loss/worm/head throughout the approximately two weeks that they are feeding directly on the grain.