Category Archives: Cotton

The value of scouting for plant bugs

The entomology program recognizes the logistic difficulty in scouting. We know that you have to cover a large acreage in a limited amount of time, you manage multiple crops, and some weeks, frankly, you would rather spend the time with your family. We get it.

So, let’s chat about how to scout cotton for plant bugs, and the amount of money that it will make you, in the fewest possible bullet points:

  1. Decisions can be quick and easy – if scouting multiple locations in a field (either by quadrant or on the diagonal) results in numbers over threshold (8 per 100 sweep or 2-4 per beat sheet sample), spray the field. Likewise, if you are seeing consistently below threshold numbers, don’t spray. The only scenario where more time is warranted is when you capture near-threshold numbers in multiple spots. In this scenario, you must decide: 1) how much yield you want out of this field, 2) whether you have time to revisit this field in 3 to 5 days to scout again, and 3) how spraying right now fits into your schedule. Remember two things: 1) it always pays to spray on threshold, and 2) spraying in this hot, dry year increases your risk of secondary pests with any insecticide application. I favor treating the problem that I have and dealing with the problem that may occur, but this is entirely up to you and your operation. An additional 15 minutes of scouting may be more profitable than spraying an entire field. It’s ultimately your choice.
  2. Any sampling method works. Our data (below) from 2018 show that when you scout with a sweep net, a beat sheet, or both combined, you are profiting over not scouting at all. This is why we are distributing beat sheets free of charge at the Tidewater AREC. The companies that have paid for your beat sheets (Corteva, BASF, and FMC) agree. No one wants you to spend money unnecessarily – especially in this difficult time.

Figure 1. Comparison, in terms of lint yield, of different sampling methods for tarnished plant bug (sweep net, drop cloth, and sweep net until 2nd week of bloom combined with drop cloth after) and different thresholds (low, medium or recommended, high, and very high). Favoring the low threshold (1 per drop cloth sample) was profitable when using a drop cloth alone, but this did not make money over using a medium threshold in the combined method. Regardless, you make money if you sample and spray by any method. Not every Virginia field will experience this high pressure.

 

 

 

Table 1.  Net economic returns (per hectare) for threshold trial in 2018 above the untreated control. Cotton was priced at $0.77 per acre for 2018; nitrogen (32-0-0) was priced at $49.18/acre (120.0 lb/acre); bifenthrin (6.4 oz) was priced at $2.90/acre; acephate (8 oz) was priced at $3.12/acre; sulfoxaflor (2.25 oz) was priced at $13.80/acre; thiamethoxam (2 oz) was priced at $15.61/acre; chlorantraniliprole (27 oz) was priced at $26.35/acre

 

 

 

 

 

 

As always, best wishes for a profitable 2019. Please reach out to Sally or myself if you have questions or concerns. I hope that you have the opportunity to spend this weekend with the people and activities that you value most. Happy 4th y’all!

Plant bugs in cotton update

Plant bug populations have been spotty, and lower overall than this time last year (click to see map). 10% or fewer of Virginia fields need insecticide applications this week, but, unfortunately, a much higher percentage will end up treated. Before making a decision to spray without scouting consider several things:

  1. Your risk of aphids and spider mites increases, especially if it does not rain soon.
  2. Your risk of subsequent plant bug infestations increases.
  3. You spend money that you did not have to spend.

Spraying for plant bugs at or exceeding threshold will pay off. Keep in mind that sprays during flowering typically yield higher returns. These two Focus on Cotton presentations by NCSU (click here) and VT (click here) will tell you what you need to know about plant bugs in our region (follow links).

If you need help scouting, ANR agents Josh Holland (Southampton) and Elizabeth Pittman (Suffolk) will be hosting scouting clinics in July. More information coming soon. Beat sheets are available to you free of charge at these events and at the Taylor lab at the Tidewater AREC. Stop by anytime Monday through Friday 8 am – 4 pm. We are closed next Thursday and Friday.

A big thank you to FMC, BASF, and Corteva for sponsoring this round of beat sheets!!

A big thank you to Josh Holland for his help scouting this week!

Click this link for interactive map with insect density and square retention data (click points for summary data).

Plant bug spray thresholds in cotton

Early season scouting (pre-bloom cotton)

We recommend scouting for plant bugs as soon as cotton begins squaring. We encourage everyone to scout for plant bugs, especially those that saw high numbers last year. Early in the growing season (pre-bloom) we are scouting for adult plant bugs immigrating into cotton from flowering weedy hosts and other cultivated hosts nearby (corn, wheat, soybean). Plant bug adults (pictured below) are approximately 5-6mm in length (quarter inch) and can be identified by their yellowish brown body color, conspicuous “Y” shape on their scutellum or upper back, and two yellow dots on their cuneus or lower back. For pre-bloom cotton, we recommend sweep net sampling with an action spray threshold of eight plant bugs (adults and nymphs) per 100 sweeps. This can be done by conducting four to eight random 25-sweep samples throughout each field. We also recommend measuring square retention before bloom by sampling 25 random plants in each field and calculating the percentage of missing or black squares from all first positions on whole plants or the top five nodes. Consider a spray application for plant bugs if the insect threshold is reached (8 plant bugs per 100 sweeps) and square retention is below 80 percent.

Click on this video link to see sweep net sampling technique in cotton.

Plant bug pre-bloom action threshold in cotton.

Mid- to late-season scouting (flowering cotton)

For mid- to late-season scouting, when cotton is flowering, we are mainly sampling for plant bug nymphs using a black drop cloth. The action threshold for triggering sprays in flowering cotton is 2-3 plant bug nymphs and adults per drop cloth sample. For drop cloth sampling, we recommend placing the drop cloth in between two rows and vigorously beating plants onto the drop cloth. We also recommend taking at least four samples per field. 

Click on this video link to see drop cloth sampling technique in cotton.  

Plant bug action threshold in flowering cotton.

Insects often mistaken for plant bugs 

Common insects in cotton fields that are often confused with plant bugs include big-eyed bugs, aphids, and stink bug nymphs (pictured below). Big-eyed bugs head and eyes are wider than their body. Aphids are a secondary pest and are generally smaller and slower than plant bug nymphs with two tailpipes or cornicles on their lower back. Stink bug nymphs have a more shield-like body shape with three black stripes on their antennae.

Insects that are often confused with plant bugs include big-eyed bugs, aphids, and stink bug nymphs.

Economic benefits of managing plant bugs in cotton

The single most important management strategy for plant bugs in cotton is applying insecticides at the recommended action thresholds described above. The bar graph below highlights lint yield gained when applying insecticides at various thresholds (low, medium/recommended, high, very high) using sweep net only, drop cloth only, or both (as described above). We see that the highlighted recommended threshold using sweep net sampling pre-bloom and drop-cloth sampling during flowering was one of the highest yielding treatments with the highest economic returns among treatments with five or fewer spray applications. The major take-home from these data is that any scouting technique (sweep net and or drop cloth sampling) at any threshold, is going to significantly increase lint yield and economic returns when plant bug infestations are present!

Bar chart highlighting lint yield gained above the untreated control using various sampling techniques and spray thresholds for plant bugs.

Economic returns above the untreated control when properly managing cotton for plant bugs.

Scouting and spraying plant bugs in pre-bloom cotton

Virginia cotton fields are a mixed bag when it comes to plant bug infestations this week – some fields will require sprays and most will not. The only way to know what is in your field is to look in your field. It is time to scout when cotton starts squaring.

Spray cotton for plant bugs when square retention drops below 80% and you capture 8 or more plant bugs per 100 sweeps. Inevitably, there will be fields where bug numbers exceed threshold and square retention is >80%. In this case, I favor spraying to prevent bugs from reproducing in the field, but only if numbers exceed threshold.

As far as I’m concerned, all Virginia cotton fields are at risk for plant bugs. This animal has over 200 known hosts and you will find one in any field if you look hard enough. There are fields that are predisposed to higher populations. These field, in general, are:

  1. In Eastern cotton growing counties. Plant bugs populations benefit from warmer low temperatures. Abundant water in the landscape contributes to warmer lows and cooler highs.
  2. Near corn or double crop wheat/soybeans.
  3. In areas with high deforestation and new growth forests.

Results from our 2018 survey are below. Note that infestations cluster in the eastern region. However, fields in all regions are at risk.

I recommend a neonicotinoid insecticide pre-bloom. This class includes Belay, Centric, and Admire Pro. There is a lot of debate on using Admire Pro. In field tests, sometimes it is as good as Centric/Belay and sometimes it is not. This is why I recommend Centric or Belay. However, spraying Admire Pro will be better than not treating if you are over threshold. If you are not over threshold, do not spray any product. You will put yourself at high risk for infestations. This cannot be overstated.

As always, call me with your questions and concerns. If you do not know how to sample for plant bugs, I will show you. My program has beat sheets for you – free of charge. We will be distributing them at scouting clinics and field days this summer. If you need one before then, please stop by the Tidewater AREC. Please thank your sales reps from Corteva, BASF, FMC, Amana, and Bayer for funding this program. Cotton Inc. and the Virginia Cotton Board also generously provided support. Please thank Seth Dorman and his awesome plant bug scouting crew for generating data specific to our region.

 

Section 18 Emergency Exemption approved for Virginia cotton

Virginia cotton growers can now use Transform to control tarnished plant bug in cotton in 2019 (June 1 – Oct 1). This product will allow us to rotate modes of action and reduce our dependence on acephate and pyrethroids to manage this potentially destructive pest. Transform is softer on beneficials too, but you must notify beekeepers within 1 mile of cotton fields and, if there are known hives, apply before 7am or after 7pm when cotton is flowering. Transform is applied at 1.5-2.25 oz/A. Follow all label directions and keep a copy of the label with you when applying.

19VA02_Transform_WG_Label_Cotton

Based on early sampling numbers, we will have another high pressure year. Spray test results from the Tidewater AREC (shown below) can help you chose insecticides. Neonicotinoids (Admire, Belay, Centric, Endigo) should not be used after first bloom and are less effective during this time. Diamond is a growth regulator and is more effective against nymphs. There is evidence that it suppresses adult reproduction.

The single most important thing you can do to protect cotton from plant bugs is to spray at extension recommended thresholds (8 per 100 sweeps or 2-3 per drop cloth sample). As always, the only way to know what is in your field is to scout.

Call/text/email me if you have questions.

Thrips dispersal and foliar sprays

Virginia cotton requires a thrips control product at planting to preserve yield and avoid maturity delays. This is especially true since the arrival of tarnished plant bugs. Any maturity delay early-season will likely magnify plant bug injury. Cotton planted at the end of April and first week of May has put on 1-2 true leaves. It is time to scout for thrips injury and make foliar applications when necessary.

Levels of injury to cotton seedlings rated from ‘0’ (no damage) to ‘5’ (dead terminal
or plant) from thrips. Injury at ‘2-3’ or above approximates a threshold for intervention with an
insecticide application. (Photo and caption from Kerns et al., 2018)

Using a seed treatment alone will likely require a foliar spray based on research from the Tidewater AREC. In-furrow aldicarb and in-furrow imidacloprid with a seed treatment should not need a foliar spray. Scout cotton planted with in-furrow imidacloprid alone and determine if a foliar application is necessary (often it is not – saving you time and money).

All cotton planted in Virginia is under high risk for thrips injury. NCSU prediction model shows risk increasing in later-planted cotton. This model was highly accurate in 2018.

Tips for foliar applications: Consider plant-date and growing conditions. Cotton planted late-May into warm soil may not need a foliar spray. Do not apply foliar acephate if plants are growing fast with no to minimal thrips injury. Thrips injury is likely for all cotton planted in Virginia and risk will be high until plants are no longer susceptible. The three diagrams below from the NCSU model show when seedling susceptibility declines based on planting date (May 1, May 8, May 15). The blue line on these diagrams shows you when risk for thrips injury is highest.

Spraying is most effective when the first leaf is the size of a pencil tip to a mouse ear. I recommend a 6-8 oz. rate of acephate. Several scenarios may be responsible for reduced efficacy of sprays:

1. Rain. Acephate is not a rain fast product. Consider reapplying if necessary.

2. Resistance. Acephate at 3 oz. per acre has become less effective in spray tests. Rotate to Radiant if another spray is required or use a higher rate.

3. Species composition. Tobacco thrips are most common in VA, but western flower thrips can co-infest. Acephate is less effective on this species. Rotate to Radiant if another spray is required.

As always, call/text/email me with any questions. Good luck and happy planting!

Dicamba Training Opportunities

If you intend to apply Engenia, Xtendimax, or FeXapan this year, you need to complete the annual dicamba specific training requirement in addition to being a certified pesticide applicator. In Virginia, this training is conducted by the registrants (manufacturers), but can also be completed in another state including registrant training, state mandated training, and state approved training. Both in person and online training is acceptable. Training is not product specific; you do not have to take the training from the registrant of the product you apply.

Make sure to document your training.

Here are links to find a training event near you or complete online:
BASF

Bayer

Corteva

University of Nebraska

Please note that some some events require pre-registration.

The following links are under revision for 2019 but will be useful shortly:
Mississippi State Extension

Plant Bug Update – 02 Aug 18

Tarnished plant bugs have continued to be a problem in flowering cotton in some Virginia cotton fields. This week, scouts found 10 out of 30 fields above the bloom threshold of 2-3 plant bugs per drop cloth sample across Virginia’s cotton-growing region. Six of these fields averaged above the bloom threshold for the past two weeks (see map below). Dirty blooms may indicate plant bugs are present but should not be used as a threshold for spray decisions. Cracking bolls and observing internal boll injury in small dime and quarter-sized bolls is also a great indicator bugs may be present and causing significant damage. Internal boll injury includes raised warts or outgrowth on the carpel wall, small black punctures that usually match an external lesion, and stained lint. We recommend observing at least 25 bolls per field for internal injury in addition to drop cloth sampling to make informed spray decisions. Plant bug populations have peaked in mid-August over the past few years in Virginia so we recommend continued scouting during the coming weeks. Check out this video if you would like to see a short tutorial on drop cloth sampling.

Plant bug density averaged over two weeks from 24 July to 02 August 2018.

Plant bug internal boll injury symptoms.

Plant bug nymph feeding on a dirty bloom.

 

2018 survey of field corn for corn earworm larvae

Statewide, approximately 18% of ears were infested with corn earworm larvae. Corn is considered a nursery crop for corn earworm, allowing the pest to complete a lifecycle and then move on to other crops such as soybean, cotton, and peanut in August. There is a linear correlation between the infestation level in corn and the amount of soybean acreage that gets treated with insecticide for this pest. Please see the attached pdf for more details: CEW_survey_results_2018

Plant bug control in blooming cotton

Tarnished plant bugs continue to be a problem in some Virginia cotton fields. This week, scouts found 14 of 32 fields over the pre-bloom threshold (8 per 100 sweeps) and increasing numbers of nymphs. Drop cloth sampling is recommended for blooming cotton and counting squares is no longer a good indication of feeding. Threshold is 2-3 bugs per sample. Check out this short video (https://www.youtube.com/watch?v=XRnZhLczZJ0) if you have questions on how to use this method or are unsure of what nymphs look like. Dirty blooms indicate feeding, but active populations should be confirmed before a spray is made.

As cotton begins to bloom, neonicotinoids (e.g., Admire Pro, Centric, Belay) lose efficacy and I recommend rotating to a pyrethroid, a pyrethroid/acephate mix, or Bidrin. These products will  also control stink bugs if present. Transform is not labeled in Virginia, but our representative in Richmond is working hard to get us a Section 18 and I hope to have one in place by next year at the latest. All of these products will kill beneficial predators in your field. This is a concern as we near bollworm egg lay in cotton.

I encourage you to treat for insect pests only when thresholds are reached. Plant bug control will likely be needed through mid-August when populations peak, even in fields that have been previously sprayed. Spider mites, aphids, and bollworm (in two-gene cotton) risk increases with each broad-spectrum insecticide use, as does the risk for sprayer fatigue.

Special thanks to graduate student Seth Dorman and crew for their continued scouting efforts.