Alabama Insect Blog: June 2023

Thursday, June 29, 2023

Alabama Cotton Insect Situation: June 29, 2023: Plant Bugs Continue to Build

The plant bug situation has continued to increase over the past week. Going back at least 51 seasons, this appears to be the most widespread and highest pressure we have seen in Alabama. There are fields with numbers as high as 5x threshold in some places. Many fields have received 2 pre-bloom applications, and some have had three.

The question is “what do we do?”

In a lot of these fields, plant bugs are reinfesting so fast, 7–10-day spray windows are not holding up. Remember that no product provides residual control of migrating adult plant bugs. We may expect 48-72 hours of control, but past that, things get dicey. In other cases, the number of adults in the field is hard to get under control with our “normal” plant bug regime.

In most years, the highest labeled rate of imidacloprid is “good enough” to get populations under threshold, persevere square retention and reduce egg lay. In many fields this year, the ≈60% control we get leaves numbers out there that we can’t live with. In other words, 60% of 8 bugs/100 sweeps is 4.8 bugs in the field (below threshold), while 60% of 12 bugs/100 sweeps leaves 7.2 bugs in the field (right at threshold). Again, in high pressure fields, the highest rate of imidacloprid alone will likely not keep populations in check.

What about pyrethroids? We have a graduate student, TJ Douglas, who has been screen adult plant bug populations for resistance to several classes of insecticides this spring. In his preliminary analysis, he has found HIGH levels of resistance to bifenthrin in the TN Valley (Limestone County, we have known this for years), SW Alabama (Monroe County), and East Central Alabama (Elmore County). A population from the SE Alabama (Henry County) came back with elevated levels of resistance (but ≈62% lower than SW Alabama). Populations in NW (Cherokee County) and West Central (Dallas County) came back much easier to control.

What does this mean for 2023 in regions with resistance?

We have known about pyrethroid resistance in the TN Valley; thus, they have not been recommended for control for years. Over the past 2 seasons, we began receiving scattered field complaints in SW Alabama. Due to these experiences and results from lab tests, we are no longer recommending pyrethroids in SW Alabama for plant bug control. We have not received field complaints from the Wiregrass or East Central Alabama following pyrethroids, so this resistance could be “pocketed” and not widespread across the region. It is hard to say what we will get out of pyrethroids in these regions this year. Choosing a pyrethroid for plant bug controls may come down to a grower-by-grower decision based on their experiences. I would be very cautious using a pyrethroid in the Wiregrass and EC Alabama and scout closely behind to monitor performance.

What does this mean for 2023 in regions with no resistance?

In NW Alabama and the Black Belt, we are still comfortable recommending pyrethroids for control of adult and immature plant bugs.

So, if imidacloprid isn’t good enough and pyrethroids are resistant, what are we going to do with adult plant bugs?

Centric (thiamethoxam) is still an option. Centric is a neonicotinoid (like imidacloprid), just a little more expensive. Centric at 2 oz/A has always been better on adult plant bugs than imidacloprid and resistance monitoring suggests populations are still susceptible across the state. **Note: Centric often does not provide adequate control of immature plant bugs.

Acephate is another good option for control of adult plant bugs. The ½ lb rate of acephate should provide adequate control. In some fields, acephate plus imidacloprid has been used with positive results. Resistant monitoring shows that plant bugs are still susceptible statewide. **Note: Acephate is often associated with spider mite outbreaks in days or weeks following application.

Transform is probably the best plant bug material currently on the market. We typically like to hold the “big gun” until bloom, when immature plant bugs begin to emerge. The 1.5 oz rate of Transform provides good control of all stages of plant bugs, but at a price. This product is important for controlling immature plant bugs.

What about tank-mixing imidacloprid and bifenthrin? We have some data on this from the TN Valley on immature plant bugs. In 2021, it provided pretty good control. In 2022, it did not provide any measurable level of control. This mix may work on migrating adults, but it may be a total miss.

**Bidrin is restricted by label until bloom and cannot be used in the pre-bloom window**

How do I know if my insecticide worked?

While still important, monitoring adult populations in the field following an application is not the best way to determine if the most recent application work. Adults may reinfest fields and it is not uncommon to find as many or more adults in a field 5-7 days after a spray than before. The best way to determine the efficacy of an insecticide application for adult plant bugs is to monitor pinhead square retention 4-5 days later. If retention falls 10% or more 4 days later, then it is likely that either the application did not work or could not perform under the pressure. Use this information to guide follow up applications. If retention is holding (and greater than 85%) but threshold levels of adults are in the field, then a follow-up application is still warranted.

What about cotton with immatures present?

In a lot of the older cotton in Alabama, immature (nymph) plant bugs are beginning to or have been emerging over the past week. In this situation, where adults are still migrating in and nymphs are showing up, Diamond is critical for control. We wrote a lot about using Diamond last week (link), but here are a few reminders: Diamond is not a “knockdown” insecticide and should be tank-mixed with one. Diamond provides residual suppression and does not eliminate plant bugs or the need for follow up applications. Think of Diamond like ThryvOn: populations can still build to damaging levels but are lower than they would be if not used.

After bloom, acephate, Transform and Bidrin are options to consider tank-mixing with Diamond.

Getting off to a good start in this cotton with nymphs emerging will be critical to “set the tone” for the rest of the season.

As always, if we can ever be of any help, or if you would like to provide input on the situation in your area, please don’t hesitate to reach out (Scott Graham: 662-809-3368; Ron Smith: 334-332-9501).

For more information on thresholds and insecticide recommendations, visit the Alabama Cotton IPM Guide (IPM-0415). To stay up-to-date on the Alabama cotton insect situation, subscribe to the Alabama Cotton Shorts Newsletter, Alabama Crops Report Newsletter, and the Syngenta Pest Patrol Hotline.

Friday, June 23, 2023

Alabama Cotton Insect Situation: Friday June 23, 2023: Plant Bug Pressure on the Rise

We have received reports of threshold populations of plant bugs from the Gulf to the Tennessee line and from Mississippi to Georgia. If cotton has squares, it should be scouted for adult plant bugs. In Alabama, our threshold is 8 adults per 100 sweeps -OR- to maintain 80% square retention. Some states recommend only treating adult plant bugs if square retention falls below 80%, regardless of the number of adult plant bugs in the field. We have a couple of reasons for treating 8/100, regardless of square retention.

1. A square will likely not fall off the plant the day it is fed on by a plant bug. In other words, you can find a field with high plant bug numbers and high square retention because plant bugs have moved in recently and fed on squares, but they have not had enough time to fall.

2. Consider the damage potential of plant bugs. A threshold level would result in unacceptable square loss in the following week. The literature says that adult plant bugs feed on 0.6 to 2.1 squares per day. A threshold population of adult plant bugs is ≈1,160 bugs per acre. Assuming a plant population of 36,000 plants per acre and an average of 2 pinhead squares added each week, then a weeklong infestation of a threshold of adult plant bugs will result in up to of 17,052 squares lost, or ≈24% of the pinhead squares in the field. If we know that damage potential is possible, don’t wait for it to happen.

3. In addition to feeding on pinhead squares, adult plant bugs also lay eggs. These eggs will hatch out over the following 7-10 days, resulting in an embedded population of immature (nymphs) causing problems later in the season.

Speaking of egg lay and plant bug nymphs hatching out, this brings up the timing of the insect growth regulator, Diamond. This chemical is only active on nymphs and kills them as they molt (shed skin) and grow from one instar (growth stage) to the next. Immature plant bugs develop through 5 instars over ≈15 days. As mentioned above, the egg stage lasts 7-10 days. This makes the timing of Diamond critical to maximize its effectiveness. We feel that we get ≈2 weeks (TPB nymphal life length) of residual suppression from a 6oz rate of Diamond. Timing this application as close to the initial hatch out as possible helps to get the most “bang for your buck” out of this.

Typically, we say that around 1^st bloom is the best time to apply Diamond. This assumes that a threshold population of adults in June was present in the field and killed with a well-timed spray when found. In a “normal” year, adults move into fields when 3 or 4 pinhead squares are present (≈2 weeks into squaring). Given time for eggs to deposit and nymphs to hatch out, we typically expect to start finding nymphs around 1^st bloom. This year in many fields, adult plant bugs were found in fields with 1 or 2 pinhead squares present (≈1^st week of square). Additionally, there are a lot of fields that had a threshold (or higher) level of plant bugs for 7 or more days before an application could be made due to rain. In these cases, Diamond should be applied earlier than the 1^st week of bloom. The point of this application is not to time up with crop stage, but with plant bug nymph emergence.

Bottom line: In many of the phone conversations we have had with folks this week, we are telling them that if high plant bug populations are in fields and no adulticide has been sprayed, then Diamond should be applied (with a knockdown insecticide) 10-14 days after the initial threshold population was observed. Making a Diamond application does not mean plant bug numbers will not reach threshold in the following 2 weeks, but it will help to keep numbers suppressed, especially if rains or other factors will not allow for timely follow-up applications.

Thursday, June 15, 2023

Alabama Cotton Insect Situation (And Thoughts on Plant Bugs): Thursday June 15, 2023

Plant bugs are on the move. We have heard reports of adult plant bugs moving into fields across Alabama. A lot of fields in SW Alabama and some fields in Central Alabama have been treated over the past couple of days. The rain much of the state is experiencing will likely keep scouts and sprayers out of the field for a few days, but we need to get back in there as soon as we can. Until this week, we had been pretty dry in some parts of the state. The daisy fleabane has begun to play out and plant bugs are looking for better hosts. In most cases, that will be the oldest cotton around. In other areas, we have received timely rainfall and/or soils seem to be holding water better, leaving more fleabane in the environment. In these areas, plant bugs have started moving, but we will likely have another migration as the next generation matures our in a couple of weeks. We have also heard about spider mites and three-cornered alfalfa hoppers in some areas, but plant bugs are the biggest reports we have received.

I also wanted to put in plug from a post by Dr. Camp Hand at UGA discussing hail damage in cotton. I am not sure exactly how much we have in Alabama, but I suspect there are some fields suffering from it. You can read his post here (link).

Managing Plant Bugs Following the Storms

I had a discussion with a consultant this afternoon in central Alabama, and he brought up a good point to consider. He had a couple of fields with plant bug numbers close, but just under threshold earlier this week. Thinking the rain would cause some wash off (which it certainly would have), he and the grower decided to wait until the storm passed to treat. Now, assuming no more rain comes, they will likely be out of the field at least a week, potentially longer if rains continue. Plant bugs will be in the field depositing eggs over a 10–14-day period, meaning immature plant bugs will likely begin hatching around June 20^th and continue through the first of July. His question was basically, is it time for Diamond as soon as we can get the sprayer in the field. In this situation, the answer is probably “yes.” If they can get into the field around June 22^nd, that gives us good timing for the initial hatch out (around the 20^th) and we will expect to get 2-3 weeks of residual immature plant bug suppression from the 6-9 oz rate.

Remember Diamond should be tank-mixed with a knockdown insecticide to kill any adults in the field or immatures that have already hatched. Diamond kills immature plant bugs when they molt from one instar (growth stage) to the next. Plant bugs go through 5 instars with most of the damage being done in the 3^rd-5^th instar stages. This is why the timing of a Diamond application is so important. If the treatment is made too early, then some of the residual is wasted. If the treatment is made too late, plant bugs in the field will continue to feed and cause injury until they molt to the next instar.

We normally do not recommend Diamond being applied until nymphs begin to emerge, typically around first bloom (or the first of July). However, that is considering an application went out for migrating adults in the pre-square stage (mid-June). Others may have this unique situation where they know plant bugs are in the field, but they cannot do anything about it for a week or more. In these situations, I would suggest a Diamond application be made when a treatment goes out. If the ground dries out quicker, or a plane is available, I would suggest going ahead and treating threshold levels of plant bugs (8 bugs/100 sweeps or 80% square retention) now and waiting to make a decision on Diamond around the first of July.

Friday, June 9, 2023

Alabama Cotton Insect Situation: Friday June 9th

We are getting dry in a lot of areas across the state. A few rains have popped up here and there, but much of our cotton needs a drink. The crop also appears to be relatively late. I would say based on a lot of what I have seen and heard from folks we probably have more cotton closer to “first leaf” than “first square.”

The thrips situation picked up heavy in North Alabama, with several applications in NE Alabama and the TN Valley this week but seems to have subsided now. Several applications Reports in central Alabama have been a mixed bag, some are needing to make spray while others have been able to live with seed treatments or other at-plant controls. Most reports from south Alabama have been that cotton is outgrowing thrips at this point.

Spider Mites building in cotton

Something to keep an eye out for now is spider mites. We have seen low levels of mites in cotton approaching pinhead square in central Alabama and have heard about some in north Alabama as well. While populations haven’t reached damaging levels yet, our current weather patterns have us in a spot where mites should be considered when making management decisions. Abamectin is a good option and low to mid-labeled rates can be used in younger cotton.

Adult TPB in terminal

The plant bug situation in Alabama has already begun. We have heard of low levels of plant bugs in older fields in north Alabama and sprays have already gone out in some south Alabama fields. The dry weather is causing fleabane to play out and adult plant bugs will soon be on the move. As cotton reaches the 7^th node or so, we need to start running sweep-nets and checking square retention weekly. Threshold is 8 bugs per 100 sweeps -or- to maintain at least 80% square retention. Remember that in addition to feeding on pinhead squares, adult plant bugs are also depositing eggs that will hatch out into immatures (nymphs) over the next 7-10 days. As far as treatments, imidacloprid is a cost-effective option that provides “good enough” control at the higher rates. Centric and bifenthrin (depending on resistance levels in your location) are other options. Acephate is an option, but with how dry we are in some areas I would be a little hesitant to go that route due to the spider mite situation mentioned above. Remember that the label restricts the use of Bidrin between pinhead square and first bloom.

We have two more opportunities for scout schools on the calendar right now.

Tennessee Valley — Cotton and Soybean
June 13
Tennessee Valley Research and Extension Center
Belle Mina, Alabama

Agenda

Northeast Alabama — Cotton
June 22
McCord’s Fire Station #1
1150 County Road 157
Centre, Alabama

Agenda

Thursday, June 1, 2023

Alabama Cotton Insect Situation: June 1, 2023

The past week has brought slightly cooler temperatures across much of Alabama, resulting in cotton that is not growing off as quick as we would want in some areas. We also have some pockets that are getting dry, further exacerbating the issue.

Overall, thrips pressure has not been too bad this year, but we are starting to see pressure pick up in some areas. For the most part, our at-plant treatments have been holding on pretty well, but some of the seed treatments are starting to break. In “normal” conditions, we don’t see yield loss after about the 4^th or 5^th leaf stage. However, in fields where cotton is not growing, foliar applications may still be warranted. Remember that acephate is effective, but is highly sensitive to wash off after rain and may flare spider mites. Intrepid Edge has better rainfastness and is less likely to flare mites.

TCAH Damage in Cotton

We have also seen and heard reports of three-cornered alfalfa hoppers in some fields. TCAH tend to be worse in dry spells, when weedy hosts are drying down and tender cotton plants are the best thing around. They are usually worse on field borders, however in no-till, high residue fields they may be distributed across the field. Usually, we do not recommend spraying for TCAH because adults are so mobile and reinfest so fast that controls are difficult to evaluate. Typically, cotton plants damaged by TCAH die, and surrounding plants usually compensate for any loss. One consideration for treatment would be in fields with very low plant populations or in fields with spotty stands. Pyrethroids and acephate provide good control, but again adults can continue to move into fields. Generally, cotton is “safe” from TCAH around the 6-8^th node. Cotton plants that have been injured from TCAH appear stunted, leaf veins begin to turn dark red, and leaves take on a red/orange appearance. There will also be a knot or multiple knots on the stem usually below the cotyledons.

One other report we have gotten over the past week is high numbers of stink bugs in corn. Corn is highly susceptible to stink bug injury just prior to tassel (V14-VT). A well timed pyrethroid application will help corn and likely reduce populations moving into cotton later in the season as well.

Plant Bugs: Although we shouldn’t have any cotton squaring (yet), I want to go ahead and mention plant bugs. We have a graduate student (TJ Douglas) traveling the state making collections of adult plant bugs from daisy fleabane for resistance monitoring. The fleabane is loaded with all ages and stages of plant bugs across Alabama. Keep an eye on ditch banks and field edges with fleabane on it. As long as rains persist, and fleabane is healthy, plant bugs will likely stay there. Once the fleabane begins to dry down, plant bugs will start moving to the most mature cotton in the area (first planted cotton). Scout this cotton weekly as soon as squares are in the field. Threshold is 8 bugs per 100 sweeps -OR- maintain 80% square retention. Older fields (later planted) should be monitored for plant bugs as well, but early season populations tend to build most heavily in the earlier planted fields.

Cotton Scout Schools: We have 4 programs planned across the state this year. You can click the link on Agenda for details on each location. We published a story on the longest consecutive running program in Alabama Extension here.

Southeast Alabama — Cotton and Peanut
June 6
Wiregrass Research and Extension Center
Headland, Alabama

Agenda

Central and West Alabama — Cotton and Soybean
June 8
Autauga County Agricultural Center
Autaugaville, Alabama

Agenda

Tennessee Valley — Cotton and Soybean
June 14
Tennessee Valley Research and Extension Center
Belle Mina, Alabama

Agenda

Northeast Alabama — Cotton
June 22
McCord’s Fire Station #1
1150 County Road 157
Centre, Alabama

Agenda