We finally got a much-needed break from the triple digit temperatures, and some areas even received some rain although it was much less than what is needed. Area crops are starting to show the impact of the prolonged period of triple digit temperatures and no rain. Corn in the area is drying down fast with some areas of corn dying prematurely from either stalk rot or lack of moisture.
Cotton across the area is starting to shed fruiting positions as it adjusts its fruit load to the resources it has available. Pest issues in area cotton is relatively quiet currently, but stink bugs and their damage are starting to increase across the area and grasshoppers are starting to move into some area fields. Aphids are present in a handful of fields across the area, but currently they are still below the economic threshold thanks to a decent beneficial insect population.
Cotton has weathered the drought and high temperatures okay, but is finally starting to show some of the impacts including fruit shed and nutrient deficiencies. Pest activity across the area is light thankfully, but there are some pest present that we need to keep our eye on. Current pest issues include stink bugs, grasshoppers, and aphids. Spider mites at this time have not been found in area cotton fields since a few months ago.
Fruit shed is very common in cotton and can be caused by issues such as insect damage, temperature, and soil moisture levels. Currently, most of the fruit shed I have seen is a result of both the drought and high temperatures. Cotton is a perennial plant and does not know that we will be killing it later in the year to harvest the fiber and seed it produced.
Due to it perennial growth habit, when faced with stressful growing conditions it will utilize it resources to survive itself an produce only the amount of seed and fiber that it can, which causes the plant to start shedding fruit. Nutrient deficiencies can also lead to fruit shed, as if the plant does not have enough Nitrogen, Phosphorous, or Potassium in the plan to fully develop that boll it will shed that fruiting position.
The recent spell of high temperatures can also be blamed for some of the fruit shed, especially the small bolls. The two weeks leading up to a square opening as a flower, it the most susceptible to heat stress. If the temperatures during this time frame averages 86F or higher, it can cause issues will pollen release, size of the boll, number of seeds per ovule/lock.
These bolls that are produced from heat stressed squares will stay on the plant, and may be shed from the plant in 3 to 5 days after pollination but could remain on the plant. If the boll is retained on the plant it will have fiber quality issues, and may become misshapen as some locks may not produce seed and lint. Hopefully, we can keep these cooler temperatures and get some beneficial moisture, to hopefully off set the fruit loss.
Grasshoppers are starting to move into area cotton fields, and in most cases are causing damage but not enough at this time to justify treatment. Most of the grasshopper issues I am seeing are on the western side of Hill County, or in fields that are surrounded by pastures that are dried up. Grasshoppers prefer to breed in areas of undisturbed soil like our pastures, and road side ditches. The nymphs are not very mobile as they lack wings for movement, and most grasshopper issues in cotton are caused by adults migrating into the field to eat.
Because of it being adults moving into cotton and causing damage it can happen in waves over periods of weeks. Grasshoppers damage cotton by removing the leaf tissue that is need for the plant to produce energy to grow and produce cotton seeds and fibers, and they can even clip the terminal off from the plant which essentially stops growth of the plant.
The sooner you catch the grasshopper migration the less damaging they can be to the crop and typically if they are caught early treating one or two passes along the field margins can be sufficient to limit them from spreading across the entire field. There are a wide range of insecticide available for grasshopper management in cotton including Mustang, Mustang Maxx, Bidrin 8, Baythroid XL, Besiege, Elevest, and Vantacor (formerly Prevathon).
While it may be tempting to choose the cheaper products like Mustang Maxx, Baythroid XL, Mustang, and Bidrin 8 it may not be the smartest choice. These products can lead to a second grasshopper application soon, or even cause issues with other pests like aphids and spider mites. The products Besiege, Vantacor, and Elevest will provide residual activity against the grasshopper populations moving into the field, however, both Elevest and Besiege will also kill the beneficial insect population and potentially flare either spider mites or aphids.
Stink bugs and their damage is starting to increase across the area, and some fields in the western portions of Hill County actually had treatable levels of damage. Stink bugs pierce the boll to feed on the developing seeds inside. This feeding can lead to boll rots, stained lint, hard lock (lint not fluffing out when boll opens), and potentially boll shed. Stink bugs can have a significant impact on the profitability of a crop because they can impact the amount of lint produced per acre, but they can also reduce the fiber quality which can impact the value of the lint.
Currently, I am finding mostly brown stink bugs, but there are a few green stink bugs floating around area cotton fields. It is important to know the type of stink bug brown or green that you have in the field, as our pyrethroid based insecticide options are not as effective against the brown stink bug populations we see in cotton. Treatment for stink bugs is justified when boll sampling indicates that the percentage of bolls with internal damage is at or above the economic threshold for that week of bloom.
Once the crop has accumulated 450 GDD60s past cutout (5 nodes above white flower) treatment for stink bugs is no longer justified. Thankfully, we are accumulating Growing Degree Days quickly and fields may only need to be treated once this year. Insecticides we can use to manage stink bugs in cotton include bifenthrin (Baythroid 2EC), Bidrin 8, zeta-cypermethrin (Mustang and Mustang Maxx), lamba -cyhalothrin (multiple generics), and gamma-cyhalothrin (multiple generics).
If you are in a situation where you need to manage stink bugs and grasshoppers at the same time Elevest is a product that will control the stink bugs and grasshoppers and give residual activity against the grasshopper populations that may try to reinfest the field after application. Once treating the field for stink bugs, we need to be very cautious and keep an eye on our aphid and spider mite populations, as these products can flare both pest quickly in our current weather conditions.
Aphids are present in a handful of fields across Hill County, but at this time there are no fields with enough aphids that would justify an insecticide application. In these fields with the aphids there is a good level of beneficial insects to keep the populations for exploding quickly. However, we are up against a bollworm egg lay event that may move the beneficials from feeding on the aphids to feed on the bollworm eggs and young larvae.
Currently the economic threshold is around 50 aphids per true leaf, and hopefully we do not see fields approach this level so we can avoid have to treat for them. If we are going to treat a field for stink bugs that also has aphids in the field, it could be beneficial to include few ounces of an imidacloprid product to suppress the aphids as we kill off the beneficial insects in the field. If we have aphids at the economic threshold within a field the product recommendation would change because imidacloprid is not very effective at controlling aphids populations.
Products recommended for aphids that have reached the economic threshold include Sefina, Sivanto, Transform, PQZ, and many others. If you have any questions on if you need to spray, or what to spray to manage aphids please do not hesitate to contact me.