Alabama Insect Blog

Thursday, July 25, 2024

Tales of Cotton Insects: Thursday July 25, 2024

The cotton insect situation is as it has been all year, all over the board. Reports from South Alabama are that plant bugs are finally beginning to build in many fields but continue to be the heaviest near corn. Overall, bug pressure has been light in Central Alabama, but the bug complex (stink bugs and plant bugs) are beginning to be more common in some fields. Pressure is also picking up in some areas of North Alabama.

Bug Complex

In some fields, plant bugs are easily found above threshold (3 per 5 row feet) and dirty blooms are apparent. This makes for an easy treatment decision. In other fields, numbers have been just below threshold for a couple weeks and the call is more difficult. In many cases, we have recommended “cleaning up” these fields. Conducting research on subthreshold populations is difficult, but I believe multiple weeks of numbers just under threshold will result in similar losses to one week of populations at threshold. Depending on planting date (or really age of cotton) insecticide options vary. In fields in early bloom, Transform is still a good option, however, fields at the 3^rd week of bloom or later need a material that also cleans up stink bugs. That means a pyrethroid or organophosphate. A few things to consider for decisions are rain patters, variety and efficacy. We observed ≈10% damage from bollworms in our Non-Bt cotton at the Prattville research station this week. While overall pressure was low in our Bollgard 2 (DP 1646) cotton, consider a pyrethroid for bug control to get the additional bump on bollworms.

Overall, stink bug damage has been light across the state, but our observations on research farms and in grower fields in central Alabama is that stink bugs are just now beginning to infest older fields. Threshold during peak bloom is 10% internal damage of 10-12 day old bolls (1 inch diameter, about the size of a quarter). Sample 20-25 bolls across a field and look for signs of feeding.

Aphids

The aphid fungus has caused populations to crash in many areas of the state. Before treating for aphids, look for the grey, fuzzy looking cadavers. The fungus is highly effective and will crash populations across a field in a matter of a few days.

Rainfastness Considerations

While some fields are still pretty dry, many are receiving rainfall pretty consistent. Rainfastness of insecticides has been a common question over the past couple days. Several factors impact the effectiveness of an insecticide application after a rain event.

In general, most insecticides are “safe” after about 6 hours. If a rain event happens 3-4 hours after an application, I would consider a reapplication. If rainfall happens 4-8 hours after, I would scout the field 3-4 days later to determine efficacy and treat accordingly. Two insecticides that are “exceptions” to the rules are Diamond and Acephate. Diamond has better rainfastness (≈2 hours) than most insecticides (Miss State Blog). Many of the insect growth regulators (like Diamond) have good rainfastness. On the other side, Acephate is among the least rainfast materials we have. At least 8 hours of no rain is needed, and up to 12 hours is better.

Amount and Intensity of Rainfall: More rain will intuitively have more impact than less rain. A hard, driving rain will probably be more detrimental than a slower, steady rain. In other words, a half inch in 30 minutes will probably be worse than a half inch in 3 hours.

Activity of Insecticide: Systemic insecticides (move inside the plant) are less likely to be severely impacted than contact insecticides. Most systemic insecticides require 2-4 hours to move into the plant. While some contact insecticides aren’t very rainfast, insects may come into contact quickly and have enough exposure immediately following the application to die.

The question remains, should you go ahead and “beat the rain” or hold off until it passes. That can be a difficult one to answer. Action will depend on how bad the infestation is, how likely the rain is, and how quickly you can get back into the field. If plant bug populations are well above threshold (3-4x threshold), I would consider taking the risk of wash-off and partial control vs allowing them another week to feed if I could not get into the field.

Soybeans

Things have been relatively quiet on the soybean front, outside of kudzu bug. This has been the worst year of my career with kudzu bugs. Many fields reached threshold for adults and needed treatment. In general, we do not recommend treating adult kudzu bugs, however populations were so high they could not be left unchecked. Kudzu bug feeding causes similar impacts as drought stress in soybeans. Many dryland fields across the state could not take the additional stress of kudzu bugs during a droughty period. We have observed reproduction in south and central Alabama and have even seen some naturally occurring fungus taking out kudzu bugs in central Alabama. We typically wait to trigger on nymphs and use a threshold of 1 nymph per sweep (=15 in 15 sweeps). Most pyrethroids provide good control of kudzu bug.

Defoliating caterpillar and stink bug populations have been low thus far in soybeans across the state. We will continue to monitor the situation and provide updates as pressure builds.

If we can be of any help, please don’t hesitate to reach out and let us know (Scott Graham: 662-809-3368; Ron Smith: 334-332-9501). To stay up-to-date on the Alabama insect situation, subscribe to the Alabama Cotton Shorts Newsletter, Alabama Crops Report Newsletter, and the Syngenta Pest Patrol Hotline.

Monday, July 8, 2024

Tales of Cotton Insects: Monday July 8, 2024

Insect Pressure All Over the Board

Over the past week, we have received feedback from all cotton producing areas of Alabama. Adult plant bugs are still infesting some fields with nymphs showing up, while other fields do not have much, if any, plant bug pressure. Aphids are finally beginning to build, and spider mites are showing up in hot spots. Overall, insect management is a much of a field-to-field basis as I have seen in my career. Recommendations have been nuanced and rarely are the same from one call to the next.

Plant Bugs

North Alabama has experienced extreme plant bug pressure so far this year (both TN Valley and NE AL). Many fields received 2 adult plant bug sprays and some have received 3 applications. Overall, square retention remained above threshold (=80%) but continued infestations required multiple applications. Overall, the immature populations building in these fields has not materialized to heavy pressure yet. This is possibly due to a couple of reasons.

1. Timely applications on migrating adults reduced egg lay. This is one reason why we recommend treatment if adult counts reach 8/100 sweeps, even if square retention is above 80%.

2. I believe environmental conditions also play a role in the survival of plant bugs in the egg and early instar (hatchling) stages. The hot, dry weather we have faced over the past couple of weeks has likely killed many of the immature plant bugs that ordinarily would have hatched and developed over this time.

With all of this in mind, what does it mean for plant bug controls this week? For most of the older cotton, we are in the window where Transform (1.5 oz/A) has the best fit. Transform does a good job on adult and immature plant bugs, as well as aphids, without flaring spider mites. Traditionally, this is the window where we also recommend Diamond (6 oz/A) as a tank-mix partner to give residual suppression of immature plant bugs. However, this year, based on reports we are receiving, some fields may not need Diamond right now. Fields that received an initial adult plant bug spray in the first week or 2 of June still do not have either high numbers of immatures or many dirty blooms (a common symptom of immature plant bug damage). In these cases, we are recommending to “treat what’s in the field” and not make an automatic Diamond spray right now. Immature plant bug populations are too sporadic to make blanket sprays. That is not to say that Diamond is not or should not be going out in many fields, but our recommendations are on a case-by-case basis.

Aphids

As mentioned above, aphids are beginning to build across the state, and we have not received any reports of the fungus showing up. Aphids feed on plant juices and secrete a sugary substance called honeydew. This feeding slows down plant growth and development. This is exacerbated in situations where cotton is already not growing well, such as the hot, dry weather we have been experiencing. We do not consistently get yield responses when conducting efficacy trails for aphids, but we can see increased yields when cotton is drought stressed. In trials done across the southeast in 2019-20, Transform and Assail provided the most consistent control, while imidacloprid, Centric and Bidrin provided less consistent control, but enough to alleviate plant stress from heavy plant bug pressure.

In most cases, we do not recommend aphid treatments, and typically plant bug sprays “clean-up” any aphid populations. Populations will continue to increase until the naturally occurring fungus, Neozygites fresenii, takes over. Generally, populations crash about a week after these grey, fuzzy aphids appear.

Soybeans

A quick note on soybeans. Kudzu bugs have begun infesting fields in big numbers over the past 10 days or so. In central and south Alabama, reproduction is beginning to occur. In north Alabama, egg lay has not been observed. The presences of immatures is important, because this generally signals the end of adult movement into fields. Our threshold from R1 through R6 is 10 adults per sweep (250/25 sweeps) or 1 nymph per sweep (25/25 sweeps). If immature kudzu bugs are easily and repeatedly found on petioles and main stems during visual inspection of the canopy, treatment is likely warranted.

Thursday, June 13, 2024

Tales of Cotton Insects: Thursday June 13, 2024

Critical Window for Early Planted Cotton in Central and North Alabama

The plant bug situation has exploded over the week in Central and North Alabama. Based on reports and observations from about Montgomery north through the TN Valley and NE Alabama, all cotton planted on or before ≈May 10^th likely needs a plant bug spray. Overall, square retention is still high, but with some of the numbers reported, it will start dropping quickly if action is not taken (goal is to maintain 80%). Overall, pressure appears to be lighter in cotton planted on or after ≈May 15^th (much of that is just starting or not squaring yet). Note: Reports are that adult plant bug numbers are similar in ThryvOn and Non-ThryvOn cotton in most areas. This is not unexpected as most of ThryvOn’s impact is against immature plant bugs.

Multiple reports from Cherokee county are that the earliest planted fields are running anywhere from 20-35 adult plant bugs per 100 sweeps (threshold = 8). In these situations, imidacloprid alone may not be enough to preserve square retention. Adding mid-rates of acephate or a pyrethroid (depending on location) may improve control. Centric is another option for control.

In most situations populations are above threshold but in more manageable numbers. Our May 1^st planted cotton at Prattville averaged ≈12 adults per 100 sweeps this week and ≈9 per 100 sweeps at TN Valley. We have received some reports from the field of similar populations and that some fields are receiving a 2^nd adult application this week (following applications last week). High rates of imidacloprid alone, Centric (2 oz), acephate (0.5-0.67 oz) or pyrethroids (highest labeled rate, dependent on location) should suppress populations and preserve square retention. Keep in mind that no insecticide will provide more than 2-3 days of residual control for adults and square retention is the best way to determine efficacy, adult numbers can rebound from week to week as more move into fields.

Thus far, reports from south Alabama are that plant bugs are scattered here and there, but few fields are above threshold. These fields should be closely monitored as the migration will likely begin soon.

The next 10-14 days will be critical for plant bug management in central and north Alabama cotton. Timely applications of recommended insecticides will preserve square retention and reduce egg lay and nymphs hatching out in the coming weeks. Consider being prepared to make an application of Diamond with a knockdown insecticide ≈10-12 days following the adulticide applications going out now. One consideration for the “automatic” follow up may be weather. If fields do not receive rain in the next couple weeks, that may impact immature plant bug populations in our favor. Plant bug nymphs do not seem to handle hot, dry conditions very well. Particularly in the hatchling stage.

Reminder: The 65^th Alabama Cotton Scout Schools kicked off this week in Headland. We have a few more opportunities to go.

June 25^th: EV Smith Research Center (4725 County Road 40, Shorter, Alabama 36075)

June 26^th: McCord’s Fire Station #1 (1150 County Road 157, Centre, Alabama 35960)

Wednesday, June 5, 2024

Tales of Cotton Insects: June 4, 2024

Plant Bugs Invading Alabama Cotton

Over the couple days, we have received multiple reports or observed adult tarnished plant bugs in April or early May planted cotton across central and north Alabama. In most cases, populations were below threshold, and a few squares were missing. However, some fields are at threshold and treatments are going out. Thus far, reports from southwest and southeast Alabama are that few or no plant bugs are being observed.

As our earliest fields begin to square, monitor pinhead square retention on the upper 2 or 3 nodes of plants. Our goal is to maintain 80% of these first position squares (closest to the mainstem). The reason to monitor the upper 2 or 3 nodes each week is that these are the “new squares” that were put on in the current week (added since last week’s scouting trip). In addition to monitoring square retention, a sweep-net is a good monitoring tool to determine the level of adult plant bugs in the field (threshold is 2 adults per 25 sweeps). Even if square retention is above 80%, we recommend treating adults because they will start feeding on pinhead squares and depositing eggs that will hatch in the following 7 to 10 days.

Our general recommendation for adult plant bug control is the high rate of imidacloprid or 1.75-2oz of Centric. In some areas, bifenthrin is also an option. In cases of high pressure, acephate may also be considered or tank-mixed with imidacloprid. We generally try to stay away from acephate and bifenthrin to preserve better beneficial insects and for resistance management, however under heavy pressure we need to worry about plant bugs and deal with other issues if/when they arrive.

Based on our observations in daisy fleabane this spring, we suscept this could be a multiple spray year for adults in June, particularly for early planted cotton. Remember that as long as square retention is at or above 80% a previous application “did its job” and more adults have moved into the field. Also keep in mind that June applications for adult plant bugs can set the tone for the rest of the season. By knocking back adults, we are reducing egg lay and nymphs that hatch out later as blooms begin to appear.

Reminder: The 65^th Alabama Cotton Scout Schools kicked off this week in Headland. We have a few more opportunities to go.

June 11^th: Associated Growers Gin (15031 Brownsferry Road, Athens, Alabama 35611)

June 25^th: EV Smith Research Center (4725 County Road 40, Shorter, Alabama 36075)

June 26^th: McCord’s Fire Station #1 (1150 County Road 157, Centre, Alabama 35960)

Monday, May 20, 2024

Tales of Cotton Insects: May 20, 2024

We have received several calls about thrips over the past 5-7 days. Right now, cotton planted in May is at the highest risk of thrips injury and cotton planted through about the 20^th is at very high risk across most of the state. This has changed over the past week with all the rains we have received. One thing to consider is that a heavy rainstorm can alleviate some thrips pressure. However, they may not always do enough. On Saturday (May 18), we received a report from Cherokee county of multiple fields with anywhere from 2 – 6 thrips per plant on 1-2 leaf cotton (threshold is 1-2 with immatures present). Other reports are that cotton treated with AgLogic looks good and cotton with a seed treatment or imidacloprid in-furrow needs a spray.

Note: All reports are that ThryvOn cotton looks as expected and is not taking on injury justifying a foliar spray.

The question is, what to spray. There are a couple of options for foliar treatments for thrips:

Acephate is an effective and relatively inexpensive option, however it has the potential to flare secondary pests such as spider mites and is the least rainfast of the available recommended options. (With the recent weather we have had, I am not concerned about flaring spider mites)

Bidrin is another option that is effective and less likely to flare spider mites and is more rainfast than acephate, however it is more likely to cause crop injury when tank-mixed with herbicides.

Intrepid Edge is another effective option. Intrepid Edge is less likely to flare secondary pests but may need the addition of a surfactant to help with efficacy.

Below is a chart with thrips counts and injury ratings from an on-farm trial we did in 2020 in Madison County (AL).

On-farm thrips trial in 2020. Cotton was treated with Gaucho (insecticide seed treatment). Foliar application was made at the 1 true leaf stage. Ratings were made 7 days after application. An injury rating (yellow line) of "3" indicates unacceptable injury.

We are still receiving reports of grasshoppers threatening stands in central Alabama and the Wiregrass region. In some areas, we have a good stand but rain is keeping us out of the field for a few days. In others, the question has just been should we pull the trigger or not. In fields with historic issues of stand loss from grasshoppers and high numbers in the field, treatment should be considered. We don’t want to get into replant situations, especially in areas where we lost a few days in the field and are trying to get caught up. Acephate (2/3 lb) is needed to kill adults and in some fields nymphs are still hatching and Dimilin can provide residual suppression. Cotton is most susceptible in the "crook" stage, but grasshoppers can still threaten stands once it has fully emerged.

Friday, May 3, 2024

Tales of Cotton Insects: May 3, 2024

The Alabama cotton insect situation has started to pick up over the last few days. We have received several reports of grasshoppers in fields across central Alabama. Our observations and reports are that grasshoppers have reached the adult stage in some of the fields, which is a little earlier than normal, but the winter was also somewhat mild. This is important to note, because adult grasshoppers are harder to kill and are not affected by the growth regulator Dimilin. The presence of wings is the only way to identify adult grasshoppers as the immature stages do not have them. We do not have a threshold for grasshoppers. With that in mind, treatment decisions are made based on the level of risk a grower is willing to take in a given field (how many grasshoppers are out there?). In some fields, grasshoppers do not eat cotton while in others they may destroy dozens of acres. Field history can provide some indication of what may happen this year. If grasshoppers have eaten cotton in a field previously, they seem to be more likely to do so again.

Treatment Decisions

At this point, I would probably assume adults are present in fields. That means acephate (0.67 lbs ai/A) is the go-to product. I would also tank-mix Dimilin (2-3 oz/A) to provide residual control of nymphs still emerging. Pyrethroids have provided poor to sporadic control of adult grasshoppers in previous years.

Adult differential grasshoppers

Cotton seedlings damaged by grasshoppers

Thursday, April 18, 2024

Alabama Thrips Risk: April 18, 2024

The Thrips Infestation Predictor Model for Cotton (link) is a useful tool to use to help understand which planting dates or planting windows are at the highest risk of thrips injury. This model predicts how thrips movement and cotton growth will line up based on recent and predicted weather patterns. The model also provides some context with the last 5 years for thrips pressure at your given planting date. We started running the model to get an idea of what thrips pressure is predicted as we move into the early planting window.

South Alabama

We ran the model in Henry and Escambia counties and cotton planted until about the first week of May is at the highest risk of thrips injury.

Central Alabama

The model showed in Autauga, Lee, Talladega and Fayette counties that cotton planted after about May 10^th is at the highest risk of thrips injury.

North Alabama

North Alabama (Cherokee and Limestone counties) were similar to central Alabama with cotton planted after about May 10^th being at the highest risk of thrips injury.

To look at the models we ran, you can click here.

Keep in mind that the model is fluid and things can change based on an unexpected rain event (or a missed expected rain). You should update the model every couple days before and after planting to make sure you are seeing the most accurate version. Remember that the model is used to understand risk of thrips injury and which fields may need a supplemental foliar application.