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Extension Entomology

Category: Sorghum

Correction to Sorghum Pests Article in Aug. 26, 2022 Newsletter

–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

Sorghum Pests

–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

Fall Armyworms

–by Jeff Whitworth – Field Crop Entomologist

Adult fall armyworms are moths (fig. 1) and have been reported from southern Kansas for about the last 2 weeks and probably will be in the rest of the state soon-if not already. A quick refresher relative to this pest: they normally do not overwinter in Kansas, but in the lower portions of southern states, and down into Mexico and Central America. The moths usually arrive in Kansas anywhere from mid-June to mid-July as they fly/are blown here on southern winds. Fall armyworms have a wide host range but in Kansas are most often a cause for concern in corn and/or sorghum and later sometimes in wheat depending on planting date and weather. Also, in Kansas, especially the last 2 years, brome has been seriously defoliated (in combination with armyworms) in many areas around the state. Armyworm larvae may be part of the “ragworm” complex of larvae feeding in the whorl of corn and/or sorghum and then later the next generation become part of the complex of “headworms” or larvae feeding in the sorghum head directly on the developing grain. So the moths are here, ovipositing and thus the larvae are, or soon will, be feeding on whatever host the eggs were deposited on. Fall armyworms were quite common (in combination with other species) in 2020 and 2021 and thus monitoring should be initiated in any potentially susceptible crops. For management considerations please refer to the 2022 KSU Insect Management Guide for the crop of interest.

(Photo of fall armyworm moths taken of a Riker mount provided by revered KSU Extension entomologist, now retired, Dr. Bob Bauernfeind).

 

Figure 1: Fall armyworm moths

 

 

Scout for headworms in sorghum from flowering into milk stage

–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/

 

 

Chinch Bugs

–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

 

Control of Headworms in Kansas Sorghum –Research Spotlight

–by J.P. Michaud, Professor in Entomology–Agriculture Research Center, Hays, KS

Collaborative research in China was featured in this summer’s edition of American Entomologist, and is relevant to control of headworms in Kansas sorghum.

https://academic.oup.com/ae/article-abstract/68/2/4/6605209?redirectedFrom=fulltext

 

This work was done on ‘Old World bollworm’, H. armigera, but its biology is very similar to that of corn earworm, H. zea.

The mechanisms by which the virus manipulates host behavior described therein are likely the same as those used by the HzeNPV that is the organism in the Heligen product we are using to control corn earworm in sorghum.

Instead of trying to pupate in the soil, infected larvae climb to the tops of plants where they die, assisting in the dispersal of the virus.

Here is the full abstract:

 

Abstract

Baculoviruses can induce climbing behavior in their caterpillar hosts to ensure they die at elevated positions to enhance virus transmission, providing an excellent model to study parasitic manipulation of host behavior. Here, we demonstrate that climbing behavior occurs mostly during daylight hours, and that the height at death of Helicoverpa armigera single nucleopolyhedrovirus (HearNPV)-infected larvae increases with the height of the light source. Phototaxic and electroretinogram (ERG) responses were enhanced after HearNPV-infection in host larvae, and ablation of stemmata in infected larvae prevented both phototaxis and climbing behavior. Through transcriptome and quantitative PCR, we confirmed that two opsin genes (a blue light-sensitive gene, HaBL, and a long wave-sensitive gene, HaLW) as well as the TRPL (transient receptor potential-like channel protein) gene, all integral to the host’s visual perception pathway, were significantly up-regulated after HearNPV infection. Knockout of HaBL, HaLW, or TRPL genes using the CRISPR/Cas9 system resulted in significantly reduced ERG responses, phototaxis, and climbing behavior in HearNPV-infected larvae. These results reveal that HearNPV alters the expression of specific genes to hijack host visual perception at fundamental levels – photoreception and phototransduction – in order to induce climbing behavior in host larvae.

 

 

Sorghum Midge Update at the Southwest Research and Extension Center

–by Anthony Zukoff — Southwest Research and Extension Center

 

The recent freeze and a lack of flowering sorghum has ended adult sorghum midge activity in the area. Adult midges were observed on station grounds in Garden City starting the first week of July and were still present on late flowering panicles into the first week of September.   As sorghum reaches maturity, it is easy to find evidence of midge activity even if you did not see adults when the fields were blooming.  Simply look for flattened, blank zones on the heads.  These seeds never developed because the maggots consumed them from the inside.  A general recommendation for avoiding losses due to midge is to make sure the field blooms uniformly and before mid to late August.  For comparison, in the Texas panhandle, growers are encouraged to have fields blooming no later than the first of August to avoid issues with sorghum midge.  Beginning the last week of July, sorghum on the station this year bloomed over a long period of time, which allowed some general observations to be made regarding blooming time and midge damage once heads reached maturity.  Plants that began blooming on July 25 were free of noticeable midge damage.  Those that began blooming around August 5 experienced damage to the upper 1/5th of the panicles.  A final location that bloomed very unevenly starting August 11 experienced significant losses with most panicles being almost completely blank (Figure 1).  While midge damage is very easy to spot on varieties with red panicles, it might be more challenging to see on varieties with white panicles; however, damage will show up the same regardless of color (Figure 2).  In addition to midge damage, headworm and bird damage were prevalent in the later blooming field but are easy to differentiate (Figure 3).  If you have observed midge damage this season anywhere in the state, consider sending me a report including an estimate of acreage impacted and panicle damage.  For additional information and control options, please refer to the Sorghum Insect Management Guide.  https://bookstore.ksre.ksu.edu/pubs/MF742.PDF

 

Figure 1.  From left to right: example of undamaged panicle from plants that began blooming July 25, slightly damaged panicles from plants that began blooming August 5 and severely damaged panicle from plants that began blooming August 11.

 

Figure 2. White panicle variety: undamaged head on the left severely damaged head on the right from a plant blooming the first week of September.

 

 

Figure 3. Various types of damage to sorghum heads.  Left to right: undamaged head, severe sorghum midge damaged head, a head with heavy bird damage and on the right, a head exhibiting headworm damage.

Sugarcane aphids

–by Jeff Whitworth — Field Crops

Sugarcane aphids are still quite active throughout the eastern 2/3rd’s of Kansas in fields that still have some green leaves. These aphids are continuing to migrate in and almost as soon as they land on green leaf tissue, they start producing the tiny nymphs (see fig 1-just produced nymphs with winged female that produced them). These aphids are still infesting sorghum but, so far, have not caused any problems throughout northcentral Kansas. It is getting late enough in the growing season that they should not have enough time to increase to the point where they will be a problem.

 

Figure 1: SCA nymphs and mother (photo by Cody Wyckoff)

 

Figure 2 shows an area outlined by a marker, on the underside of a sorghum leaf that was infested by a substantial (200+) colony of sugarcane aphids in early September but was subsequently eliminated by natural causes-no insecticides. This has been typical for the last 3 years, i.e. sugarcane aphids migrate into Kansas, starting in about mid-July and continue until late October, and establish small isolated colonies but with very few areas actually developing significant populations that require treatment.

 

Figure 2: Underside of leaf previously infested by SCA colony (photo by Cody Wyckoff)

 

 

 

WORMS, WORMS, and MORE WORMS (army cutworms, fall armyworms)

–by Jeff Whitworth — Field Crops

 

2021 might be called the “year of the worm”. Starting in late winter/early spring, 2021, there was considerable activity by army cutworms. Most of the problem was caused by the larvae decimating thin strands of wheat and/or alfalfa. Then, since late spring/early summer, a combination of armyworms and fall armyworms have been causing serious concern and damage in lawns, pastures, and alfalfa fields throughout about the eastern 2/3rd’s of the state. Army cutworms spend the summer in the Rocky Mountains but start to migrate back into Kansas in early fall every year. The larvae may feed on just about any plants but mostly affect wheat and alfalfa, as these are usually the only plants actively growing this time of year. Armyworms, probably more so than fall armyworms, may continue to cycle through another generation or even two as they overwinter in Kansas, and thus it will probably take a “hard” frost or freeze to stop them. Fall armyworms, since they don’t usually overwinter in Kansas, may migrate south after this generation become adults-but there could be another, or at least partial generation. Armyworms infest primarily grasses, i.e. sorghum, corn, brome pastures, lawns, and often this time of year, wheat, but occasionally alfalfa, etc. Thus, if armyworms are the problem they could be around through another generation or maybe even two depending upon the weather. So, if armyworms are relatively small (see pic 1) they will probably feed for another 10-14 days then pupate (stop feeding). If they are relatively large (see pic 2) however, they will probably pupate in the next 3-7 days. There will probably be at least one more generation of armyworms. Fall armyworms (see pic 3) have a little wider host range, which includes alfalfa, soybeans, corn, sorghum, wheat, etc., but don’t usually overwinter in Kansas, thus, hopefully, will be heading south after these larvae finish feeding and become moths. Also, in the next 30-60 days army cutworm moths should have returned from their summer Rocky Mountain retreats to deposit eggs throughout at least the western 2/3rd’s of the state and thus, these tiny worms will start feeding on wheat and/or alfalfa all winter.

Picture 1: Small Armyworm (pic by Cayden Wyckoff)

Picture 2: Larger Armyworm (pic by Cayden Wyckoff)

Picture 3: Fall Armyworms (pic by Jay Wisbey)

 

 

Grasshoppers

–by Jeff Whitworth — Field Crops

As noted before, grasshoppers seem to be really numerous this year throughout northcentral Kansas. We have seen, or heard about, more grasshopper-riddled fields (see pic 1) then we have maybe in the last 15-20 years. The species responsible for most of the crop damage is the common, relatively large, yellow, differential grasshopper (see pic 2). These grasshoppers are still feeding a little, but are also moving to grassy/weedy/undisturbed areas where they are depositing eggs in the soil. These eggs will then hatch next spring and the young nymphs can start feeding on any nearby crops.

Picture 1: Grasshopper riddled field (pic by Cayden Wyckoff)

Picture 2: Differential grasshopper (pic by Cayden Wyckoff)