Please see event flyer using the following link for more details: 2019 Scouting Clinic Flyer. We hope to see you there!
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:
- 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.
- 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:
- Your risk of aphids and spider mites increases, especially if it does not rain soon.
- Your risk of subsequent plant bug infestations increases.
- 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:
- 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.
- Near corn or double crop wheat/soybeans.
- 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.
Harvest Wheat, Plant Double-Crop Soybean As Soon As Possible
The recent hot and dry weather is really drying the wheat down quickly. We harvested our first wheat today (the moisture was ranging from 16 to 20%) and planted soybean immediately afterwards. Just 2 days ago, the wheat grain moisture was in the mid-20’s!
That experiment is part of our ongoing efforts to harvest higher quality wheat and increase our double-crop soybean yields. Now, I’m not advising you to harvest your wheat at 20% unless you have a buyer that will take it, preferably without a discount, or you have a way to dry down quickly. High moisture wheat will heat up quickly and you will need to do something with it right away.
With that said, we have seen great benefits from harvesting higher moisture wheat and getting the soybean planted immediately. Our Mid-Atlantic regional project conducted from 2015 thru 2017 found greater wheat yields and test weight, and greater soybean yields. Our data is shown below. Note that I’m only showing Virginia wheat data as the date where yield began declining differed among the states (this data was earlier as we moved south), but the general shape of the graph was similar. Different colored symbols represent different years.
Note that our soybean yield usually start declining rapidly in mid-June.
In summary, there is benefit from harvesting wheat and planting soybean as soon as possible. However, read the previous blog, To Plant or Not to Plant into Dry Soil, before making too many decisions. Not only is our topsoil dry, but the wheat may have removed moisture much deeper – giving us little total soil moisture.
To Plant or Not To Plant Into Dry Soils
Rachel Vann, Extension Soybean Specialist – N.C. State University & David Holshouser, Extension Agronomist, Virginia Tech
Now that the weather has turned hot and dry, and with limited rainfall in the forecast over the next ten days, we are starting to get questions about continuing to plant soybeans or halting planting until we catch a rain. There is no consensus on what to do in this situation, but we aim to discuss the pros and cons of the different approaches in this blog post.
Soybean seed must take in 50% of its weight in water to initiate the germination process. Germination is not affected if the seed has imbibed water for 6 hours (seed is swollen, but seed coat in not broken), then it dehydrates to 10% moisture. If the seed has imbibed water for 12-24 hours (seed coat is broken but no radical has emerged) then dehydrates to 10%, germination may be reduced 35-40%. If the radical has emerged and the seed dehydrates to 10% moisture, few if any seedlings will survive (Holshouser, 2012). What we want to avoid with any approach discussed below is exposing the seed to enough moisture to start germination but not enough for the seed to get out of the ground.
The general optimum planting date range for planting soybeans across North Carolina was identified by Dr. Dunphy as May 1 to June 10. This optimum planting range varies from year-to-year based on rainfall, soil water holding capacity and soybean maturity, but the goal is to get the soybean plants to lap the middles before reproductive growth begins. We still have 10 more days before we get to the end of that optimum range this year and parts of the state have a chance for rain before June 10. Continuing to wait to plant is more of a concern for our growers who still have seed from early maturing varieties to plant (<MG5), as these varieties will have less time for vegetative growth prior to the beginning of reproductive development. The three major options growers in the region are facing are discussed below.
- Plant shallowly in the dry and hope for enough rain to get the seed out of the ground. If you decide to take this approach, you want to ensure you achieve uniform seed depth and that you are not allowing the seed access to moisture below the seed that could lead to variable emergence. This approach would be less risky in clean-tilled situation where you are more confident that you have dried the soil out at shallow depths. Dr. Dunphy said he has seen soybeans planted shallowly into dry conditions before that have sat in the ground >5 weeks and still had excellent emergence when rainfall occurred. The biggest risk with this approach is that you catch a small rain that allows the soybean seed to imbibe water but does not provide enough moisture to get the soybeans out of the ground. We would also suggest you exercise caution using this approach in a no-till situation where you would be more likely to see problems with lacking uniformity of moisture across the field leading to variable seed access to moisture and ultimately emergence variability. In many cases, part of the field will have adequate moisture to get the soybeans out of the ground, other parts will be completely dry as in tilled conditions, and much of the field will be in between. Those in-between areas are likely to have enough moisture to swell the seed and/or initiate germination but not have enough moisture to allow the seedling to emerge. We have had several inquires on the impact of planting into dry conditions on soybean seed treatments. What we can say is that fungicidal seed treatments are less likely needed in this situation where we already have high soil temperatures and lacking soil moisture than they are in earlier planting situations where the soils are cool and wet.
- Plant deep to the moisture. Under most conditions, soybeans should be planted 0.75 to 1.5 inches deep. Soil temperatures are high enough right now to germinate and emerge quickly, even at deeper depths than recommended. But soybeans should not be planted deeper than 2 inches. We’ve talked to several growers and County Agents across the region who are not finding soil moisture until 3 to 4 inches deep; we definitely do not recommend planting this deep. Growers should exercise caution using this approach if your soils are prone to crusting, because a heavy rainfall could seal the soil before the soybeans emerge. In addition, if the planter pushes the soil down a little in tilled conditions, creating a ridge of fluffy soil on each side, a heavy rain will cause this fluffy soil to move into that furrow and possibly add another ½ to 1 inches of soil to your depth. If you are going to go this route, check the emergence score on the variety.
- Keep the seed in the bag until the next time we catch rain. This is the safest approach
at this point. Based on historical data, we have another 10 days or so before we start seeing yield declines from delayed planting. Parts of the state have a chance of rain in the next 10 days. Data from recent research throughout the Mid-Atlantic shows that each day delay in planting past mid-June can result in a ½ bu/A or more yield loss and in general these yield declines begin in the second or third week of June; we still have some time before we get to that point.
Whatever decision a grower makes, uniform seed placement in critical to achieve uniform emergence and ensure each seed has as equal of access to water as possible. We have discussed the importance of uniform emergence in soybeans here: https://soybeans.ces.ncsu.edu/2019/04/how-important-is-uniform-emergence-in-soybeans/
In conclusion, there are advantages and disadvantages to each planting option discussed, but we still have time to plant soybeans in our region before we see drastic yield declines. All options discussed will likely result in delayed emergence due to environmental conditions.
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!
Wheat Disease Update – May 9, 2019
Fusarium head blight (FHB) risk is continuing to increase in parts of Virginia. Upcoming rain events will increase risk over the next three days (see figure below). Much of the wheat in the southern part of the state is past the vulnerable flowering stage, but wheat that is at or about to enter flowering may be at risk. Consider applying a fungicide if risk is moderate to high, especially on susceptible or moderately susceptible varieties. Fungicides should be applied at early flowering or up to one week later. Do not apply a strobilurin-containing fungicide since this can increase DON contamination. Recommended fungicides include Prosaro, Caramba, Proline, and Miravis Ace. Increased incidence and severity of leaf blotch and powdery mildew have been observed in some fields, and these fungicides will also provide control of foliar diseases.
