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Extension Entomology

Category: Sorghum

Sorghum Pests

–by Jeff Whitworth — Field Crops

Much of the sorghum around northcentral Kansas is just starting to reach the flowering stage. This is the most susceptible stage for the attack of “headworms”. To visualize the potential of a “headworm” infestation in sorghum, or even a “podworm” infestation in soybeans, just remember all the armyworms/fall armyworms/corn earworms that have been chewing on alfalfa/brome/and lawns the past few weeks. These larvae are, or have been, pupating and the adult moths will be, if they are not already, flying around depositing eggs on susceptible plants. Remember, sorghum is vulnerable to “headworms” from flowering until soft dough. “Headworms” cause 5% loss/worm/head but the infestation needs to be detected as early as possible while the larvae are still small (see fig 1. Relatively young corn earworm larvae from sorghum head on 24 Aug). The larger the larvae the more grain they have damaged and will continue to damage until they pupate.

Figure 1. Young corn earworm larvae from sorghum (pic by Cody Wyckoff)

At the same time, sugarcane aphids are continuing to migrate into Kansas. Individual winged aphids are relatively common now, plus a few colonies. There are even a few colonies that are starting to cause concern (see fig 2. of a field in Geary County). Monitoring for “headworms” thus needs to continue in each field until the soft dough stage and for sugarcane aphids through the hard dough stage. For more information, regarding treatment thresholds/sampling/and products registered for the control of “headworms” or sugarcane aphids please refer to the 2021 KSU Sorghum Insect Guide.

 

Figure 2. Sugarcane aphid colonies – photos provided by Mr. Chuck Otte, Geary County Extension.

 

Worms, Worms, Worms (Fall armyworms, armyworms, Alfalfa caterpillar)

–by Jeff Whitworth — Field Crops

 

 

“Worms” have been voraciously feeding throughout at least the eastern 2/3’s of Kansas for about the last 3 weeks. However, they have only recently gotten large enough to cause considerable damage and thus concern. The main problem in alfalfa, so far, seems to be a combination of fall armyworms (see fig 1), armyworms (see fig 2), and somewhat surprising, alfalfa caterpillars (see fig 3).

Figure 1: Fall armyworm

 

Figure 2: Armyworm

 

Figure 3: Alfalfa caterpillar

Alfalfa caterpillars are usually quite common in alfalfa and soybeans, however, not at the densities detected this year. Alfalfa caterpillars pupate then emerge as the common yellow (see fig 4) or white butterflies usually seen flying around alfalfa and soybean fields.

Figure 4: Adult alfalfa caterpillar

Regardless of which larval species, it is apparent that the majority of the larvae are relatively mature and thus will be/or are pupating soon. Pupation will probably take 4-5 days. Then the adults will emerge, mate and start depositing eggs. These eggs will hatch, and then in 4-7 days the new, but very small, larvae will start the feeding process all over again. Armyworms (fig 2) will attack mainly grasses, i.e. brome, late-planted sorghum, wheat, etc. Alfalfa caterpillars (fig 3) will mostly stay in alfalfa or soybeans, before they get too mature, and fall armyworms (see fig 1) may feed on just about any crop. However, sorghum should only be susceptible to “headworms” from flowering until soft dough. All three species may have at least one more generation, if not more, until a hard freeze puts a stop to them.

 

 

Sorghum Pests

–by Dr. Jeff Whitworth — Field Crops

 

Sorghum throughout north central and southcentral Kansas is still in many different stages of development. So far, sorghum pest problems have not been as readily apparent as in most past years–but there is probably still 2 months remaining to stay vigilant. Chinch bugs have not been as problematic as in past years, because either populations are down or we are learning how to better manage early season chinch bug problems.

Many corn earworms (see pic 1) are still feeding in corn and thus have yet to pupate, emerge as adults, and then start flying around after mating looking for oviposition sites in soybeans or sorghum. Sorghum is attractive to these “headworms” only between flowering and soft dough. Therefore, some sorghum fields may be past the susceptible stage. The moths will then usually head to soybeans to deposit eggs.

Picture 1: Corn earworm (pic provided by Cody Wyckoff)

 

The other problem we may have in sorghum in southcentral and north central Kansas are aphids. Corn leaf aphids have been in corn and sorghum in easily detected numbers since the whorl stage corn (mid-June) and are still relatively abundant in whorl stage sorghum (see pic 2) on 11 August. Corn leaf aphids rarely occur in densities to cause a negative impact on many plants. However, they do provide a good source of food for beneficials, i.e. please note the “mummies”(parasitized aphids) in the photo provided by Mr. Mills.

Picture 2: Corn leaf aphids (pic provided by Mr. Sean Mills, BASF)

 

 

This beneficial buildup may aid greatly toward controlling other aphid infestations like the one shown here (see pic 3) of sugarcane aphids which seem to be just starting to colonize sorghum in southcentral KS. from migratory adults just arriving from infested fields south of Kansas. Sugarcane aphids have been detected in several counties south of Hwy 50, so far, but not yet in densities approaching treatment thresholds. Hopefully, with healthy populations of beneficials these sugarcane aphids will be kept under treatment thresholds. As south winds continue, however, expect sugarcane aphids to continue to migrate into southern counties and then north throughout the state. Thus, monitoring and early detection are important.

 

Picture 3: Sugarcane aphids (pic provided by Mr. Jeff Seiler, Sg. Co.)

Sorghum Midge Activity in the Southwest

— by Anthony Zukoff — Southwest Research and Extension Center

Grain sorghum is in various stages of flowering in the southwest right now.  Once flowering begins, growers might want to keep an eye out for sorghum midge.  Historically, sorghum midge has not been a significant pest in Kansas and has been primarily observed in the southeast portion of the state.  However, in the last several years, there have been localized outbreaks in the south central and southwestern portions of the state.  Growers that had issues in previous seasons should pay close attention to their fields, as it is unclear if this pest is going to start playing a bigger role in our annual sorghum pest line up.  Sorghum growers in these regions are encouraged to scout for sorghum midge this year.  If midges are observed, sharing that information with your local extension specialists would provide useful information as to the distribution of the midge during the 2021 growing season.  To scout for sorghum midge, carefully observe a flowering head while the anthers are still bright yellow and look for tiny red flies (Figure 1)

Figure 1: Adult sorghum midge;  KSU Entomology

on and around the flowers.  The best time of day to do this is in the morning before the afternoon sun and wind pick up.  Midges are delicate fliers and do not live more than 48 hours.  Alternatively, you can use a clear plastic bag to scout.  To use the bag, place it over the flowering head and shake the bag.  Keeping the bag on the flowering head, look to see if any midges fly up and collect inside at the top of the bag.  Later in the season as heads mature, growers can scout for evidence of midge damage as well.  The damage will appear as blank zones on the flowering heads (Figure 2).

In these blank zones, the grains never formed because the midge larvae consumed the seeds while they were developing; the area where a mature seed should be will be relatively flattened.   Be careful not to mistake bird damage for midge damage.  Bird damage will have more of a “blasted” look (Figure 3).

Sharing reports of damage would be useful as well while we track this pest.  At the time of this writing, midge has not been observed on any sorghum flowers so far in the Garden City area.  However, sorghum midges were collected in the area from flowering Johnsongrass (another host) on July 1st.

Figure 2 and 3 by Anthony Zukoff — Southwest Research and Extension Center

Beneficial’s

–by Dr. Jeff Whitworth — Field Crops

Beneficial’s continue to be very active throughout all crop fields in the eastern half of Kansas (please see fig 4–pink spotted lady beetle depositing eggs, 15 July). Thus, the practice of just adding an insecticide into any tank mix with fungicides and /or herbicides “just in case” is NOT recommended. Please ensure any targeted pest meets, or is close to, a treatment threshold before utilizing an insecticide application.

Figure 4. Pink Spotted Lady Beetle depositing eggs (pic by Kaysie Morris)

Click Beetles

–by Dr. Jeff Whitworth — Field Crops

Click beetles (fig 1) are becoming very active and this activity will continue for at least the next month. There are several species of click beetle in Kansas that can be a pest of crops. The larvae of these species are generally called wireworms and may feed on roots, root hairs, germinating seedlings, etc. In other words, just about any plant parts found underground including seeds can be damaged by click beetle larvae. The adults, of all species, are often attracted to lights at night or may be found under plant residue in fields. Insecticide seed treatments do really well at protecting seeds and seedlings, from planting up to about 28 days post-planting, from wireworm attack.

Figure 1.  Click beetle   (picture by Cody Wyckoff)

 

Sorghum

–by Dr. Jeff Whitworth

 

Most sorghum throughout south and north central Kansas has developed past the stage that might be susceptible to infestations by sorghum headworms (susceptible stage is generally considered to be between flowering and soft dough). However, some late-planted fields may still be vulnerable to headworm infestations (see Fig 1) but fortunately, infestations remain very low.

 

Figure 1 Headworm (found 8 Oct 2020) (Cayden Wyckoff)

Sugarcane aphids are still migrating into the state, and probably will until we get much cooler temperatures and fewer south winds. Fortunately, beneficials (see fig 2 of pink spotted lady beetle) are still plentiful in most sorghum fields. All sugarcane aphids detected in the last 10 days on later planted sorghum had only small, scattered colonies of sugarcane aphids (see fig 3).

Figure 2 Pink spotted lady beetle (Cayden Wyckoff)

Figure 3 Sugarcane aphid colonies (Cayden Wyckoff)

 

Sugarcane Aphids

–by Dr. Jeff Whitworth

Sugarcane aphids (fig. 4) are still migrating into sorghum fields throughout Kansas. However, most fields still have large populations of beneficials, thus, so far, sugarcane aphids are present but not in sufficient numbers to cause problems. However, monitoring should continue.

Figure 4 Sugar Cane Aphids (Jay Wisbey)

Soldier Beetles

–by Dr. Jeff Whitworth

Have had several inquiries regarding soldier beetles (please see fig 3 provided by Kaysie Morris). These beetles are quite common throughout Kansas and most commonly noticed in late summer as the adults are highly mobile, relatively large, and are very active searching for and feeding on pollen. Thus, they can be very common on any crop, or weed, that is pollinating, especially sunflowers, sorghum, and cucurbits such as cantaloupes and watermelons. Soldier beetles are often mistaken for blister beetles because of their size and shape but are not in the same taxonomic family and thus, produce no cantharidin, the chemical that causes external blisters in humans and other problems in livestock when ingested. However, soldier beetles are harmless.

Figure 3 soldier beetle

 

SORGHUM HEADWORMS

–by Dr. Jeff Whitworth

Sorghum headworm populations have not been as substantial, yet this year, compared to the last few years throughout southcentral and northcentral Kansas. There are still a few larvae  (fig. 3), and many fields have not yet developed past the susceptible stage, however, and thus there could still be problems with “headworms”. Please remember the “susceptible” timeframe or stage of sorghum is flowering to soft dough. Headworms can cause 5% loss/worm/head.

Figure 3 Sorghum headworm larvae  (Picture by Amy Meysenberg