Kansas State University

–by Jeff Whitworth – Field Crop Entomologist

Figure 1 should have been:

Figure 1: Sorghum (Sugarcane) aphids

Aphids are rapidly increasing around South Central and North Central KS., both corn leaf aphids (as seen in the Fig 2 in last week’s newsletter) which was miss labeled as sorghum (formerly sugarcane) aphids! These sorghum (sugarcane) aphids are rapidly increasing as seen in Fig 1 here (which was only a 2-week-old infestation) as are corn leaf aphids (again-seen in Fig 2 from last week’s Newsletter).

Figure 2:  Corn leaf aphids

Thus, monitoring should continue for these aphid populations, especially since, as yet, there do not seem to be many beneficials, see Fig 3 (ladybeetle larva decimating aphid nymphs) in most fields monitored.

Figure 3: Ladybeetle larva feeding on aphid nymphs

–by Jeff Whitworth — Field Crop Entomology

Sorghum is really struggling across north and south-central Kansas, due to the hot dry conditions. Much is, or just has, started to head out and because of these hot /dry conditions we are seeing quite a lot of incomplete or nonuniform development, even within fields. This makes management decisions for “headworms” even more difficult– but fortunately, at least so far, “headworm” populations have not been much of a problem. Remember, sorghum is vulnerable to “headworm” feeding mainly between flowering and soft dough. We are continuing to see sorghum aphids (sugarcane aphids) migrate into Kansas, as EVERY field monitored in the last 7 days had various levels of infestation, from winged females just starting to produce nymphs (see fig. 1), to fields which have been infested for a week or two (see fig. 2), to a few fields that have substantial populations (see fig. 3 by Marvin Pipes). So far, beneficials seem to be helping to keep most of these aphid populations below treatment thresholds. However, monitoring should continue as these aphids will continue migrating into the state until the advent of much cooler weather.

Figure 1: Winged female sugarcane aphid + nymphs

Figure 2: Sugarcane aphid non-winged adults and nymphs

Figure 3: Substantial sugarcane aphid infestation

–by J.P. Michaud, Professor of Entomology, Agricultural Research Center, Hays, KS

Relatively new, cost effective, and environmentally friendly products are available for controlling headworms in sorghum. These are pest-specific viruses, formulated as biological pesticides that can be sprayed on the same as any foliar insecticide, or delivered via overhead irrigation sprinklers. But application must be made early in the infestation, while the majority of larvae are still small. These products should not be used as rescue treatments, but an early application will ensure infections propagate naturally throughout the field and that reapplication will not be required.  Sold under the brand names Heligen® (for corn earworm) or Fawligen® (for fall armyworm), these products are highly specific, killing only the target pest, sparing beneficial insects, and using other insects as vectors to create a local ‘epizootic’ of disease in the field. Thus, there is no environmental impact of treating below threshold (conventionally one or more worms per head), and it is valid to use these products as a relatively low-cost insurance policy, especially in a year when earlier sorghum to the south is already experiencing fall armyworm damage.

Farmers should be aware that many of the generic pesticides that might appear attractive on the basis of low cost are now much less effective against these pests, due to their repeated exposure to the same modes of action on many different crops over the years. In contrast, there are no known cases of pests evolving resistance to a virus, and unlike fungal pathogens, virus infections do not require humidity or leaf wetness. However, the product must be consumed by the pest, and larvae take up to a week to die, depending on temperature, but will stop feeding 48-72 hours post-injection. These virus formulations are also compatible with tank mixes of other materials, provided pH is held below 8.0, and combinations of both products are available if both species of headworms are present. More information is available from the supplier:

https://www.agbitech.us/

–by Jeff Whitworth — Field Crop Entomologist

Chinch bug populations seem to be increasing throughout south central and north central Kansas. Adults are currently very actively feeding, but more importantly, depositing eggs. This has been going on for the last couple of weeks in both corn and sorghum, which are still vulnerable to this chinch bug feeding, especially in later planted sorghum under hot dry conditions. Much sorghum is in the whorl stage or just starting to head out. Chinch bugs are usually difficult to control, but are especially difficult during these growth stages because, for the most part, the chinch bugs are feeding in and around the base of the plants and behind leaf sheaves. Either way they are relatively well protected from insecticides. The younger, tiny chinch bug nymphs are reddish with a white stripe while the older instar nymphs turn gray with a white stripe (see fig). For treatment recommendations please refer to the 2022 KSU Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF742.pdf