Balancing Pest Management and Agronomic Benefits: Wireworms and Cover Crops in the Texas High Plains

Over the past decade or so, wireworms have emerged as prominent pests in the Texas High Plains and parts of the Rolling Plains. Wireworms are not a new pest. True wireworms and false wireworms are larvae of click beetles and darkling beetles, respectively. Multiple species of these groups of insects have been present in these regions for a long time. Two primary factors likely contribute to the rise in their numbers and pest status: the reduced use of at-planting broad-spectrum insecticides like aldicarb and other products, and the increased adoption of conservation practices such as cover crops, particularly those with preferred hosts such as wheat and rye.

Field research indicates that wireworm populations are significantly higher in fields with cover crop residue compared to conventional fields. Cover crops provide continuous food sources for wireworm larvae and shelter for adult beetles to lay eggs. Such observations and experiences often lead to skepticism about the practice of using cover crops. I come across many entomologists who frequently express reservations, noting that cover crops can exacerbate pest issues, including cutworms, pill bugs, wireworms, and slugs, particularly in regions with higher moisture, humidity and insect abundance.

While cover crops may harbor pests, they offer numerous ecological and agronomic benefits. For example, in the Texas High Plains, where high wind speeds and sandy soils are prevalent, cover crops play a crucial role in mitigating sand damage to young seedlings. Sandblasting—caused by blowing sand—is a serious issue in the region. Farmers often resort to a practice known as “sand fighting,” which involves opening the soil crust to slow sand particles and protect seedlings. On bare ground, sand burn can cause more damage to cotton seedlings than wireworms. Cover crops can help reduce sand injury and soil erosion, offering significant advantages. Rather than rejecting cover crops outright due to increased wireworm presence, it is essential to adopt a balanced view. The benefits of cover crops, such as protecting young plants from sand damage, often outweigh the drawbacks in regions like the Texas High Plains.

Sand damage to young cotton

To harness the benefits of cover crops while minimizing pest buildup, proactive management strategies are necessary. Applying preventative insecticide seed treatments to cover crop seeds can help minimize wireworm numbers if they are present. Terminating cover crops at the appropriate time (60 days prior to planting the main crop) can help prevent them from serving as a bridge for pests to the main crop. Although this may not help with wireworm larvae in the soil, it can be beneficial if damaging beetles (e.g., Blaptinus) are present.

To manage wireworms in cotton, we need to minimize exposure time by facilitating quicker seed germination and emergence. Planting when conditions are good, such as optimal soil temperature and moisture, is important. Similarly, the seeding depth and rates are critical. In fields with a known history of wireworms, increasing the seeding rate may help compensate for stand loss to some extent.

Other measures to combat wireworm issues in cotton include preventative insecticide seed treatments and at-planting in-furrow applications. When purchasing seeds, making sure the seed treatment package selected has a commercial rate of insecticide (e.g., imidacloprid, thiamethoxam) is critical. Although these products are not a silver bullet against wireworms in cotton, they can help reduce injury to young seedlings.

While research into biological controls such as fungi and predatory nematodes has been conducted, these methods have shown limited success against wireworms. They are particularly challenging pests to study and manage because of their long-life cycle (>5 years in some species), subterranean habitat, ability to move in soil, wide host range, and patchy distribution within and among fields.

Finally, though cover crops can favor the survival of pests such as wireworms, we also need to weigh the agronomic and ecological benefits they provide before excluding the idea completely. We need to understand the complexities of agricultural landscapes and perform the balancing act of harnessing the benefits of cover crops while minimizing the harm with proper management.

 

Texas High Plains Cotton: Insects to Watch Out For

Insect pest pressure continues to be relatively light across the South Plains. The major pests to monitor closely at the current stage of crop development include cotton bollworms, plant bugs, and stink bugs. Cotton bollworm population remains extremely low in cotton. I have noticed some lygus activity, but the populations are well below threshold. At this stage, stink bugs are the primary insects on my radar.

We deal with several species of stink bugs in cotton, with the most common being the green stink bug and the Conchuela stink bug. Stink bugs are challenging to scout, especially in tall, vigorous cotton. I have observed stink bugs in several fields, but their numbers are very low, and there has been no internal boll injury detected yet. Based on my experience over the last few seasons, stink bugs often go unnoticed during August and early September, and their damage becomes apparent in the later stages of crop development when it is too late to prevent losses.

Conchuela stink bug adult

Stink bugs have piercing-sucking mouthparts and damage cotton by piercing the bolls and feeding on the developing seeds. Infestations cause economic losses through reduced yield and loss of fiber quality. Stink bug feeding can also transmit plant pathogens that cause boll rot.

External signs of stink bug feeding

Generally, stink bugs prefer medium-sized bolls but can feed on bolls of any size. Feeding on young bolls (less than 10 days old) usually causes the bolls to shed. In larger bolls, stink bug feeding often results in dark spots about 1/16 inch in diameter on the outside. These dark spots do not always correlate with internal damage, such as callus growths, warts, or stained lint. There may be several spots on the outside of a boll without internal feeding damage.

Decisions to treat stink bug infestations are best made based on the percentage of bolls with evidence of internal damage (warts or stained lint associated with feeding punctures). To use this technique:

1. Remove about 10 to 20 bolls, 1 inch in diameter (about the size of a quarter), from each of the four parts of the field, avoiding field edges.

   

   Boll wall warts (Photo: Pat Porter)

2. Break open the bolls by hand or cut them with a knife. Look for internal warts on the boll walls and stained lint on the cotton locks.
3. Check bolls with visible external lesions first to determine if the internal damage threshold has been met, as bolls with external lesions are more likely to be damaged internally.

   

   Lint staining caused by stink bug feeding
   
   

 

Alternatively, detection of one or more stink bugs per 6 row feet can also be used as an action threshold.

South Plains Field Scout School

The South Plains Field Scout School is scheduled for the Friday, May 31, at the Hale County Texas A&M AgriLife Extension Office (225 Broadway, Plainview). There is no fee, and preregistration is not required. Registration begins at 8:30 AM with the program starting at 9 AM. Content will include classroom and hands-on training. Topics covered will include cotton agronomy, plant mapping, identification and symptoms of insect pests, plant d

iseases, and weeds.

Texas High Plains cotton: watch out for thrips

We are going to see most of our cotton emerging from the ground over the next week or so. I am seeing swarms of thrips coming out of drying wheat and other vegetation, which will be moving into cotton. It is important growers start thinking about thrips management if they haven’t already. Insecticide seed treatments such as imidacloprid still work in our region where thrips species composition in seedling cotton is mainly comprised of onion thrips and western flower thrips. 
There has been a decent amount of soil moisture to start with this season, which should help the activation and absorption of seed treatments little better. Seed treatments usually run their course by the second true leaf stage, requiring a foliar application under high-pressure scenarios such as in the northern regions of the South Plains and the Northern High Plains. The presence of immatures (wingless) is a good indicator of seed treatment not being sufficient. Rarely do we need two over-the top-applications for thrips, but there have been situations in the past where a second application was needed, especially in the northern counties. Our action threshold for thrips is one thrips per true leaf on an average in non-ThryvOn cotton. 

Thrips injury to seedling cotton

ThryvOn cotton does not need additional control measures for thrips. Field trials conducted throughout Texas have demonstrated that ThryvOn has excellent activity on all commonly encountered early-season thrips species, including western flower thrips and onion thrips. Adult thrips may still be found in ThryvOn cotton, but they do not feed as much or reproduce. The fact that fewer eggs are laid results in a great reduction in immature thrips in ThryvOn cotton. Our research indicates that ThryvOn cotton does not economically benefit from additional thrips control delivered from foliar insecticides.

As far as foliar insecticide choices are concerned for non-ThryvOn cotton, acephate at 3 to 4 oz/a still works well in our region, and so does Bidrin. Bidrin does provide a bit longer residual activity and is more rainfast than acephate. We had included Intrepid Edge in last year’s trials. This product offers a different mode of action, but its performance at the 3 fl oz/a rate was not necessarily any better than acephate.

Many of you must have heard of EPA’s interim decision to ban acephate uses in agriculture. It is one of the most widely used insecticides in cotton for the management of various insect pests, including thrips, cotton fleahopper, plant bugs, and stink bugs. The 60-day comment period is open until July 1. I would encourage folks to submit their thoughts on the EPA’s website.

Click here to access our cotton insects guide

ThryvOn Cotton 101

WHAT IS THRYVON™ COTTON?

ThryvOn^TM is a cotton biotechnology trait that expresses the Mpp51Aa2 protein (also known as Cry51Aa2). Unlike other Bt proteins used in cotton, this particular Bt protein does not affect caterpillar pests like bollworms. However, it has activity on thrips and plant bugs.

HOW DOES THRYVON TECHNOLOGY AFFECT GROWERS’ THRIPS MANAGEMENT DECISIONS?

ThryvOn cotton provides excellent control of thrips and eliminates the need for additional insecticide inputs. Against thrips, ThryvOn provides protection by deterring feeding and oviposition (egg-laying). Thus, adults may still be readily found in ThryvOn cotton, but they will not be feeding as much, or laying eggs, and will be repelled. The fact that fewer eggs are laid results in a great reduction in immature thrips. Comprehensive field trials conducted throughout Texas have demonstrated that ThryvOn has excellent activity on all commonly encountered early-season thrips species, including tobacco thrips, western flower thrips, eastern flower thrips, and onion thrips.

Data collected by Texas A&M AgriLife Extension has demonstrated that ThryvOn cotton does not economically benefit from additional thrips control delivered from insecticide seed treatments, in-furrow insecticides, or foliar insecticides. ThryvOn cotton not treated with these insecticide treatments may exhibit slightly more damage from thrips feeding, but the damage is very superficial and is not economically significant. In essence, ThryvOn cotton should not need additional control measures for thrips. However, seed treatments or in-furrow insecticides may still be desired for aiding in the management of wireworms, nematodes, or other early-season pests.

ARE INSECTICIDE SEED TREATMENTS OPTIONAL IN THRYVON COTTON?

Yes and no. While current research has documented limited benefits of adding insecticide seed treatment to ThryvOn, the seed will be marketed only with an imidacloprid seed treatment in the eastern half of Texas, where tobacco thrips are the predominant early-season thrips pest. Insecticide seed treatment is optional in the western half of Texas (Fig. 1). The reason for requiring insecticide seed treatment in the region of the state where tobacco thrips are common is for resistance management. The risk of tobacco thrips developing resistance to ThryvOn is considered higher than for other thrips species.

Fig. 1. ThryvOn cotton seed planted in the counties highlighted in blue will only be sold with the addition of an insecticide seed treatment, whereas an insecticide seed treatment will be optional for the red counties.

HOW EFFECTIVE IS THRYVON ON TARNISHED PLANT BUGS?

Although the Bt protein expressed in ThryvOn cotton has activity on tarnished plant bugs, it primarily offers suppression. ThryvOn has little known activity on adult plant bugs, but it can kill small nymphs. Thus, plant bug populations should not develop as quickly in ThryvOn as in non-ThryvOn cotton. However, insecticide applications targeting plant bugs may still be required. Currently, Texas A&M AgriLife Extension recommends utilizing the same action thresholds for plant bugs in ThryvOn cotton as for non-ThryvOn cotton but anticipates fewer insecticide applications being necessary.

DOES THRYVON HAVE ANY ACTIVITY ON COTTON FLEAHOPPERS?

ThryvOn cotton is not labeled for managing cotton fleahoppers. However, data collected by Texas A&M AgriLife Extension has demonstrated that ThryvOn has activity on cotton fleahoppers, similar to that observed for tarnished plant bugs. ThryvOn cotton will be readily colonized by adult cotton fleahoppers, but fewer large nymphs will survive. Furthermore, the authors have observed that ThryvOn does affect cotton fleahopper feeding behavior, which results in less cotton fleahopper-induced square loss. Thus, when cotton fleahoppers are present, ThryvOn cotton tends to have better square retention relative to non-ThryvOn cotton. Currently, Texas A&M AgriLife Extension recommends utilizing the same action thresholds for cotton fleahoppers in ThryvOn cotton as for non-ThryvOn cotton. However, data suggests that cotton fleahopper management with insecticides in ThryvOn cotton will be superior to non-ThryvOn cotton.

WHAT ABOUT THRYVON’S ACTIVITY ON OTHER COTTON PESTS?

The Mpp51Aa2 protein in ThryvOn has no known activity on caterpillars, stink bugs, aphids, or whiteflies. However, it is unknown whether this technology will impact mid- to late-season thrips species, such as chili thrips, bean thrips, or Kurtoma thrips. Additionally, it is unknown if ThryvOn has activity on cotton pests similar to plant bugs, such as the verde plant bug or the rapid plant bug. Efficacy data on these pests has yet to be collected.

DOES THE THRYVON TECHNOLOGY HAVE ANY IMPACT ON BENEFICIAL ARTHROPODS?

ThryvOn has little impact on the most beneficial arthropod species. The Mpp51Aa2 protein has been shown to have some activity on minute pirate bugs in that it delays their development. Also, it does affect thrips, which are often important predators of spider mites.

ARE THERE ANY UNEXPECTED RISKS FROM PLANTING THRYVON COTTON?

Because ThryvOn has very good activity on thrips and thrips are effective predators of spider mites, it has been observed, but not quantified, that spider mite outbreaks may be more likely in ThryvOn cotton than in non-ThryvOn cotton. However, more research is necessary to better understand the magnitude of this risk.

HOW WOULD THRYVON HELP WITH OVERALL CROP MANAGEMENT?

ThryvOn does offer some management flexibility to growers. Managing insecticide applications across a large span of farmland with limited equipment can pose timing challenges. Weather conditions can exacerbate this issue. ThryvOn offers growers a level of flexibility, enabling them to undertake certain activities that were previously unattainable under such circumstances. For instance, during a cool and damp period in the initial stages of the growing season, maneuvering a sprayer across the cotton field might be unfeasible despite the presence of thrips actively feeding. However, with the inherent thrips protection integrated into ThryvOn cotton, growers would not have to worry about this issue. Another advantage of the built-in protection is the elimination of concerns related to chemical wash-off problems and potential insecticide loss due to heavy rainfall events.

DOES THRYVON COTTON NEED A DIFFERENT PLANT GROWTH REGULATOR (PGR) REGIMEN THAN NON-THRYVON COTTON?

Overall, ThryvOn cotton exhibits better fruit retention than non-ThryvOn varieties, which can affect plant growth and maturity. Thus, although the ThryvOn trait in itself does not warrant a different PGR regimen, better square sets may reduce the need for some PGR applications.

DOES THRYVON OFFER GREATER ECONOMIC RETURNS THAN THE NON-THRYVON COTTON?

The economic benefit from planting ThryvOn cotton is dependent upon the pest pressures of thrips, tarnished plant bugs, and cotton fleahoppers. If these pests are not common issues on a particular farm, there is probably little benefit from planting the technology. However, eliminating the need for an insecticide seed treatment or foliar insecticides can provide tangible benefits. In general, if the cost of one insecticide application can be realized on ThryvOn, the cost of the technology will easily pay for itself.

THRYVON TAKE-HOME POINTS

ThryvOn Bt technology has excellent activity on thrips and eliminates the need for supplemental thrips control measures. This technology will aid in managing plant bugs and cotton fleahoppers. Though it will not eliminate the need for insecticides to manage these pests, it may reduce the number of insecticide applications necessary. Timely field scouting, use of action thresholds, and insecticide selection are still important for plant bug and cotton fleahopper management in ThryvOn cotton. Finally, ThryvOn cotton has no efficacy on insect pests, such as aphids, spider mites, grasshoppers, stink bugs, etc., and therefore, regular field scouting and monitoring is still critical in ThryvOn cotton.

Authors: Suhas Vyavhare and David Kerns; Extension Entomologists, Texas A&M AgriLife Extension Service

Consider using preventative insecticide seed and at-plant treatments to manage wireworms in cotton

Wireworms are a common pests of seedling cotton across the High Plains and Rolling Plains regions of Texas. Increased wireworm abundance over the last decade or so is partly due to reduced use of broad-spectrum insecticides such as aldicarb (currently available under the trade name AgLogic) and to some extent due to the increased adoption of cover crops and conservation tillage practices in the agricultural landscape. All wireworm species, including true (larvae of click beetle) and false (larvae of darkling beetle) wireworms, inflict damage as worms or immature stages that live exclusively underground. One genus of darkling beetles i.e. Blapstinus, however, can also cause damage as an adult. Often, during drier years, these beetles (~1/4 inch long) migrate from nearby grasslands, and fallow fields to cotton and cause damage by chewing on stems of young and tender seedlings at or slightly below the soil surface.

The incidence of wireworm is more severe in fields with known history of its infestation, those followed by grain crops such as sorghum and wheat, and the fields planted with no insecticide seed treatments. In my observation, wireworm infestation and injury level tend to be much higher in fields that are planted with untreated seed consecutively for more than two years. Although there are no insecticide seed treatments that are specifically labeled for wireworms in cotton, those used for other early-season insect pests such as thrips (e.g. neonicotinoids) do offer some level of wireworm suppression.

There are no rescue treatments for wireworms. Therefore, it is critical to make sure that you are getting a seed treatment package that has the full rate of insecticide (e.g. imidacloprid). Although almost all commercially available cotton seeds come treated with fungicide, they would not necessarily be treated with an insecticide. In addition, some companies have insecticides applied to seeds at a very low rate to protect seeds from storage pests. Such treatment at storage rate will not provide any control against pests in field condition. Different companies provide different combinations of fungicide, insecticide and nematicide active ingredients in their seed treatment product portfolio and it is important that you pay close attention to what you are getting when you opt for a certain package. For instance, under Acceleron brand (Bayer CropScience), the basic treatment (Acceleron Basic) comes with no insecticide, while the Acceleron Standard and Acceleron Elite both have imidacloprid (0.375 mg ai/seed) as an insecticide component. Similarly, BASF offers their Core Seed Treatment Package with imidacloprid at only storage rate (4.7 oz/ 100 lbs seed) and to get the full rate of imidacloprid (0.375 mg ai/seed or ~11 to13 oz/100 lbs seed), you need to get their Prime Seed Treatment Package. Whatever brand of seed you choose, if you are considering seed treatments for managing early-season insects, make sure the seed treatment package you select has a full rate of insecticide active ingredient.

In addition to seed treatment, I would also suggest using at-plant treatments such as in-furrow application of Admire Pro, AgLogic, or pyrethroids (e.g. bifenthrin) in fields where wireworms have been an issue in the previous year/s. These products are labeled for use in cotton for early-season insect pests such as thrips and aphids and have wireworm activity. Considering the long life cycle of these worms (3-4 years), it is very likely that they will be there for next season if were present in the past.   

Table. 1. Insecticide ingredients of selected seed treatment packages in cotton.

Company	Cotton Seed Brand	Seed Treatment Product Trade Names	Insecticide Active Ingredient (at standard rate)
Bayer CropScience	DeltaPine	Acceleron Basic	none
		Acceleron Standard	imidacloprid
		Acceleron Elite	imidacloprid
BASF	FiberMax, Stoneville	Core Seed Treatment Package	none*
		Prime Seed Treatment Package	imidacloprid
Corteva AgriScience	PhytoGen	PhytoGen TRiO	imidacloprid
Americot	NexGen	CottolyST Base	none
		CottolyST IMI+	imidacloprid, acephate
		CottolyST Enhanced	imidacloprid, acephate
		CottolyST Premier	imidacloprid
Syngenta		Avicta Elite Cotton	imidacloprid + thiamethoxam
*imidacloprid at storage rate

 

Darkling beetle, Blapstinus sp. (photo: Pat Porter)

Wireworms (photo: Pat Porter)