Field crop pest and beneficial organisms.
–by Jeff Whitworth — Field Crops
“Worms” are not the only pests feeding on crops right now! Grasshoppers (see fig 5) are especially numerous this year and will also continue to feed into the fall and continue to deposit eggs in the soil mainly in undisturbed areas adjacent to crop fields. (All pictures by Cody Wyckoff)
Figure 5: Grasshopper feeding in corn
–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.
–by Anthony Zukoff — Southwest Research and Extension Center
Weather patterns can have a significant impact on grasshopper populations year to year. Hot, dry summers increase survival of nymphs and adult grasshoppers, leading to increased egg production during the growing season. Cool, wet weather promotes fungal pathogens that can reduce egg and nymph survival, but if the following spring is warm and wet, egg hatching will increase and more nymphs survive. So, several years of hot, dry summers followed by warm, wet springs can eventually lead to large populations of grasshoppers in some regions.
As the weather in western Kansas continues to be hot and dry this summer and areas of drought increase, larger populations of grasshoppers going into the fall season could be possible. This year’s USDA Rangeland Grasshopper Hazard map (Figure 1) may explain the recently observed buildup of grasshoppers along field edges and in grassy areas. As non-crop sources of food are exhausted, grasshoppers will shift their grazing over to anything still growing in the landscape. In areas with greater grasshopper pressure seedling alfalfa and wheat could be at risk.
Before planting alfalfa, treatment should be considered if there are 15 or more grasshoppers per square yard around the planting area. Once planted and growing, consider treatment if 3-5 grasshoppers per square yard are found in the seedling alfalfa stand.
Vegetated borders around areas where wheat will be planted should be scouted 10 days before planting. Consider treating those borders if there are 7 to 12 grasshoppers per square yard. Once growing, 3 or more grasshoppers per square yard within the field can destroy seedling wheat stands. If grasshopper populations are low to moderate, seed treatments can protect emerging wheat plants for several weeks if products are applied at the highest registered rate. Seed treatments will be less effective under severe grasshopper pressure. Avoid planting too early as this will help reduce the time that wheat will need to be protected.
In either crop, depending on the products used and severity of the season’s grasshopper buildup, multiple applications might be necessary. Please refer to the most recent Alfalfa and Wheat Insect Management Guides for specific control information.
Alfalfa Insect Management Guide: http://www.bookstore.ksre.ksu.edu/pubs/MF809.PDF
Wheat Insect Management Guide: http://www.bookstore.ksre.ksu.edu/pubs/mf745.pdf
Figure 1. Areas shaded in orange and red could experience increased grasshopper pressure through this fall.
–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.)
— 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
–by Dr. Jeff Whitworth — Field Crops
Usually in Kansas, as spring passes into summer and summer becomes hotter and drier, the threat of tick bites is reduced. However, this year we are still seeing and getting reports about tick activity throughout the state. There are four different species of ticks found in Kansas, but probably the most common tick encountered by agriculturalists and other persons enjoying the outdoors is the American dog tick or sometimes called the wood tick (see fig.1)
Figure 1. American Dog or wood tick (pic by Cody Wyckoff)
These are the ticks that most commonly get on us when walking in grassy or weedy areas beside crop fields or walking through those types of areas for recreation or anything else. These ticks need three hosts (blood donors) during their lifecycle but finding these three suitable hosts may take a year or more. These ticks cannot fly, jump or even crawl very fast for very far and thus primarily they just crawl up onto low vegetation and wait there to “ambush” a host. When a suitable host comes within contact of the hungry tick, the tick grabs onto the prospective host and immediately searches for a suitable feeding site on that host. They then insert their mouthparts and start engorging with blood until satiated, which may take more than 1 day. Once satisfied, they drop to the ground to molt, if they are in the larval or nymphal stage, or to start depositing eggs if an adult female. This searching/feeding activity can occur from March to October depending upon weather. Once a tick becomes attached, removal needs to happen ASAP. The safest way to remove an attached tick from its host is to gently-but firmly-grasp the tick with fine forceps and apply steady pressure until the tick releases its hold. Then always inspect it to make sure the mouthparts are still attached to the tick (see fig 2)
Picture 2. Firm grip to remove tick (pic by Cody Wyckoff)
then preserve it in alcohol or freeze for later identification if necessary. Ticks may feed for a few days before becoming satisfied and disengaging, however, tick feeding sites may stay red and inflamed for several days afterward (see fig 3-tick removed intact 5 days prior). If a rash or flu-like symptoms develop after about 10 days consult your physician and take the preserved tick with you for specific identification.
Picture 3. Tick irritation 5 days after removal.
–by Dr. Jeff Whitworth — Field Crops
The pest situation, so far anyway, looks really encouraging throughout most of northcentral Kansas. Very few pests in sorghum, including chinch bugs, have been noted or reported at least as of 22 July. Sorghum seems to be all over the place, however, as far as developmental stages are concerned. There is some double-cropped sorghum that has just recently germinated (also some that was just planted late due to the weather) all the way to some that is just reaching the boot stage. So there is a long ways to go yet–but so far, the pest situation looks good.
Soybeans also seem to have relatively few pests so far this year. There are a few stink bugs (which will be depositing eggs soon) and Dectes stem borers (see fig 1 -adult green stinkbug and Dectes stem borer) neither of which are causing any problems yet–but may in the future before harvest. There are a few bean leaf beetle adults just emerging (see fig 2-bean leaf beetle adult eating hole in leaf) so these populations need to be monitored throughout pod set. There also seem to be relatively more spined soldier bugs (see fig 3) than usual this year. These are often confused with phytophagous stinkbugs but these” look alikes” are predators on other insects.
Figure 1. Adult green stinkbug and Dectes stem borer (pic by Cody Wyckoff)
Figure 2. Bean leaf beetle adult eating hole in leaf (pic by Cody Wyckoff)
Figure 3. Spined soldier bug (pic by Cody Wyckoff)
–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)
–by Dr. Jeff Whitworth — Field Crops
Whiteflies (see fig. 3) are very common in soybeans throughout most of the eastern half of Kansas. This is not uncommon, but they seem to be more plentiful this year. However, there is no treatment threshold or even any problems that have been determined from these tiny whiteflies in Kansas soybeans. Potato leafhoppers are also still very common in soybeans where they also never seem to have much impact.
Figure 3. Whitefly
Also, at least for the last week, most soybean fields seemed to have very few defoliators.
–by Dr. Jeff Whitworth — Field Crops
Western corn rootworm adults have been emerging throughout north central Kansas since at least 6 July. One relatively easy and quick method of detecting corn rootworm adults if they emerge prior to tasseling/silking is to look for characteristic signs that the adults have/are emerging and feeding on leaves (see fig. 1) This type of leaf feeding, where the beetles just feed on the top side of the leaf, is very characteristic of adult western corn rootworms– this type of leaf injury can be from other causes, but is very symptomatic of adult western corn rootworms. They will move up to feed on the silks, however, when they start emerging (see fig. 2, from 14 July). Please remember, if there is a 50%+ adult infestation (5 adults/10 plants, etc.) this year in any continuous corn fields, those fields should be considered for a corn rootworm control method (adult spray this year-crop rotation, etc.) if destined for corn next year.
Figure 1. CRW leaf feeding
Figure 2. Corn rootworms (note the gravid female at the top)
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