It has been an interesting week in agriculture in Colquitt County. The illustration from NOAA shows the observed rainfall total for the past week. Growers have been starting to irrigate cotton and peanuts again. Corn harvest is starting and whitefly populations are building in area cotton fields.
Cotton: Whitefly has been the topic of discussion in Colquitt County. White fly populations have increased quickly across the county with numerous cotton fields are being treated.
Following is the method to check for whiteflies: 1) Count down from the terminal of the plant to the 5th vegetative leaf (starting with any leaf that is the size of a quarter or bigger), 2) Slowly turn the 5th leaf over to view the underside of the leaf, 3) See if there are any immature whiteflies present. If 50% or more of the 5th leaves checked have multiple immatures on them, then treatments should be started.
Dr. Phillip Roberts, UGA Cotton Entomologist, wrote this article below in the last UGA Cotton Newsletter. If you would like to see it please go here.
Silverleaf Whitefly Management (Phillip Roberts): Silverleaf whitefly (SLWF) populations have
increased significantly in areas we most commonly observe whiteflies. Insecticide applications targeting SLWF began in some fields about 10 days ago and the frequency of fields exceeding threshold has been increasing. Only time will tell how populations will expand from these core areas. Hot and dry conditions favor whitefly population buildup. It is extremely important that we scout all fields for SLWF and do everything we can not to exacerbate populations. Most importantly we need to conserve beneficial insects, do not treat other pests unless thresholds are exceeded and avoid using insecticides which are prone to flare SLWF populations. The presence of SLWF in a field should influence every decision we make. It is also extremely important SLWF insecticides are applied in a very timely manner if SLWF infestations exceed threshold. Being late with the initial insecticide application will make management more difficult and expensive in the long run. I would encourage everyone to read the two publications below. The first provides detailed instructions on how to scout whiteflies and use thresholds. The second explains the biology of SLWF and describes environments which are at greatest risk of whitefly infestation.
1. Sampling and Managing Whiteflies in Georgia Cotton:
https://extension.uga.edu/publications/detail.html?number=C1184
2. Cross-Commodity Management of Silverleaf Whitefly in Georgia:
https://extension.uga.edu/publications/detail.html?number=C1141
Insecticides recommended for SLWF include Knack, Courier, Assail, Sivanto, PQZ, Venom, and Oberon. Knack and Courier are insect growth regulators (IGR) and have good residual activity and minimal impact on beneficial insects. In general, these IGRs are slow acting but perform well when applied in a timely manner. Conservation and the presence of beneficial insects are an important part of the IGR program. Knack is active on large nymphs and eggs (eggs will not hatch) Courier is active on nymphs only. Neither Knack nor Courier will control adults. Knack has a 24(c) Special Local Need label for a split application of whitefly on vegetative cotton. Knack should be applied at 5 ozs followed by an additional application of 5 ozs 14 days later. This split application allows for treatment of new plant growth which occurs after the first application. If cotton is no longer vegetative or “cut out”, the rate of knack is 8-10 ozs per acre. Courier is labeled at 9-12.5 ozs per acre. We would expect 2+ weeks of residual activity of the IGRs. If you are late with the initial application an IGR is not the most appropriate insecticide.
Assail and Sivanto are active on all stages, immatures and adults. Sivanto provides more consistent control of adults when compared with Assail. Assail or Sivanto would be a preferred choice over an IGR if you are late with the initial whitefly application. We would expect 2+ weeks of residual activity with Assail and Sivanto. PQZ is a relatively new product which provides good control of adults and is also active on immatures. Residual activity of PQZ is less than that observed with Assail and Sivanto. Venom and Oberonare also labeled for whiteflies but are rarely used.
It is extremely important that we as an industry manage SLWF on all fields. In addition to reducing yield, honeydew accumulation on lint can negatively impact fiber quality and spinning efficiency at mills. Yield
loss can be devastating if high populations are not controlled.
My cotton is yellow!! The last two weeks, I have received a lot of questions about yellow cotton. Nutrient deficiencies and water logged soils has been common around the Colquitt County. Below is information from Dr. Glenn Harris, UGA Soils Agronomist, about nutrient issues that we are currently seeing.
Post-bloom Nutrient Deficiencies, Waterlogging, and Foliar Feeding (Glen Harris): Most Georgia
cotton has been blooming for a while now and is starting to show some classic post-bloom nutrient deficiencies. Some areas of the state have gotten significant rainfall also and are showing symptoms of
waterlogging or “wet feet”. Sometimes these symptoms, usually involving yellowing or bronzing of leaves, can be confusing and hard to diagnose. Knowing which problem you are dealing with is critical to knowing how or even if you can remedy the problem. Taking soil and tissue samples from “good” and “bad” areas of a field can go a long way toward deciding which nutrient problem you have if any. Petiole sampling is a good way to determine N and K status and needs postbloom but will not pick up
problems such as sulfur and magnesium deficiency (have to take tissue or “leaf blade” samples), Also, once cotton has been blooming for a full 3 weeks, it is not recommended to soil-apply nitrogen (and definitely not K) with ground rigs or through center pivots since root systems are declining and uptake from the soil will be very inefficient. It is at this point (after 3 weeks of bloom) that foliar feeding things like N and K should be considered.
Here is a quick look at symptoms of some of the post-bloom problems occurring in Georgia cotton right now:
Nitrogen – A pale yellowish leaf color should start on older leaves toward the bottom of the plant since nitrogen is mobile and can move to the younger leaves at the top of the plant. Early on plants can also be stunted and younger leaves may be reduced in size. Post-bloom and if nitrogen deficiency gets severe enough the bottom leaves will turn bright yellow or red. This is a sure sign of nitrogen deficiency.
Potassium – The early signs of potassium deficiency are interveinal chlorosis or yellowing between the veins, more in a “window paning” pattern than the whole area between the vein (like in peanuts). This symptom can progress to the point where it is often confused with nematode damage. Severe potassium deficiency in cotton are very distinct with sever yellowing and also chlorosis or browning around the margins of the leaves. Leafspots, particularly Stemphylium are also often present on sever potassium deficient cotton leaves.
Waterlogging – while not a nutrient deficiency, this symptom is often confused with potassium deficiency. Waterlogging usually results in a bronzing and drooping of the upper leaves giving the cotton “rust” color. While potassium deficiency can show bronzing sometimes, if the yellowing of the leaves between the veins is not also present then waterlogging is likely your only issue.
Sulfur – Sulfur deficiency is becoming more prevalent. It also causes a yellowing of the leaves, more on the whole leaf not just between the veins (like K) and will be on the whole plant including in the top or older leaves (unlike N). Sometimes the leaves on the lower part of the plant will remain green while leaves on the upper part of the plant are yellow.
Foliar Feeding – Once cotton starts blooming foliar feeding of things like N and K should be the focus. Unfortunately, once you get well into the bloom period it is too late to easily fix deficiencies such as sulfur and magnesium, that should be caught pre-bloom with tissue sampling. Petiole sampling can be very useful to help determine N and K needs and maybe boron too, to help move some nitrogen from leaves into bolls, once the cotton starts blooming. General foliar feeding guidelines can be found in the fertilization section of the UGA Cotton Production Guide. There are a lot of foliar feeding products available so it is important to look at how much N and K you are getting at the recommended rate…and how much it costs!
Red Banded Stinkbugs: Last week I got a question or two about red banded stinkbug in soybean. According to Dr. Phillip Roberts, the Redbanded Stink Bugs (RBSB) are more damaging to soybean compared with stink bugs we normally encounter in Georgia soybeans. Redbanded stink bug is a major pest of soybean in the Mid-South especially following mild winters. Redbanded stink bugs feed on legumes and are NOT a pest of cotton.
Unfortunately, we are observing redbanded stink bugs in south Georgia soybeans. The threshold for RBSB is lower than that we use for commonly encountered stink bugs in Georgia. Insecticides needed for good control are also different for RBSB. Redbanded stink bugs are about half the size of southern green stink bugs. Adult RBSB are light green with a reddish band near the thorax. Older RBSB nymphs are green and somewhat flattened with black and red markings on the top of the abdomen. The
primary characteristic to identify RBSB adults is a long spine that arises from the abdomen and protrudes between its hind legs.
Proper identification of stink bugs will be important. Southern green, green, and brown stink bugs are the most common stink bugs observed infesting soybeans in Georgia (photos by Herb Pilcher, ipmimages.org).
Thresholds: Since RBSB is more damaging than other stink bugs infesting soybean, the threshold is lower. Southern green, green, and brown stink bugs: 9 stink bugs per 25 sweeps or 1 per row foot.
Redbanded stink bug: 4 RBSB per 25 sweeps or 2 per six row feet using a drop cloth.
It is likely that fields which have RBSB will also have southern green stink bugs and potentially green and brown stink bugs. These mixed populations can be accounted for by counting RBSB twice and adding to
other stink bugs present and using the 9 per 25 sweeps threshold.
The information below is from the 2022 Insect Control Guide from Mississippi State University
Extension, found online at http://extension.msstate.edu/publications/publications/insect-control-guidefor-agronomic-crops#soybeans.
Note that RBSB can damage soybeans much later than other stink bugs.
A pdf of this information is here