Cotton fruits over a long period of time compared to most other crops and attracts many species of insects, many beneficial, but a few damaging ones. When cotton reaches the fourth or fifth week of bloom, the few bad insects such as escape bollworms, plant bugs, or especially stink bugs, in the southern cotton growing areas of the US, often overwhelm the good insects. At this time many fruit, especially bolls, are at risk. Unfortunately, a decision has to be made to control the harmful bugs. Most of the bad bugs, such as stink bugs, cannot be controlled with selective insecticides. As a general rule, if a grower can get to this point in the season without using hard insecticides, beneficial insects have carried it as far as they can and a decision has to be made to protect the fruit rather than conserve beneficials. This is a difficult decision since there may be millions of lady beetles, pirate bugs and other species present per acre. However, when we get to the gin in the fall, they will only weigh the cotton and not the beneficial insects. Beneficials are a great resource but they are just NOT any help against plant bugs and stink bugs.
We have very good thresholds for these damaging bugs, based on many years of research conducted throughout the cotton belt. When the damage threshold is exceeded, controls must be applied in order to protect the fruit and make cotton production economical. When cotton is planted during our desired planting window of late April to mid May, cotton reaches this fourth or fifth week of bloom about the last 10 days of July. This is the time we have to make the decision to either conserve beneficials or protect the fruit. In order to maximize yields and profits we should choose to protect the fruit. Beneficials are a cost free resource in cotton but they can only take us so far.
Wednesday, July 18, 2018
Extension Entomologist, Auburn University
We are entering the most critical period of bollworm presence during the next 20 days (July 15-Aug 1). This increase in bollworm activity began last week (July 9-13) along the Gulf Coast and the Mobile/Santa Rosa County (Jay) FL area. By July 20th, we should see an increased bollworm egg lay in Central AL (Montgomery, Prattville, Selma areas). By the 25th this increase may reach Cherokee County in the northeast, and by August 1st the Tennessee Valley area of northern AL.
Increased bollworm moth presence was noted last week as far north as Pike and Barber County (Troy) area. This increased moth activity will be influenced by the planting date and acreage of corn planted in a given region of the state. Most all bollworm were corn earworms in corn previous generation. This life cycle is about 30 days and the eggs in corn were deposited during the white or pink silk stge. About 30 days later these moths that emerged from corn are looking for their next host. Cotton is the best host they will find in AL (not soybeans or peanuts).
Many (but not all) fields in all areas of the state had more worm damaged bolls in 2017 than we had seen since 1995. If we want to prevent this from happening again, the next 2 weeks are critical.
I assume that most realize now that our 2 gene cotton has lost some level of effectiveness against the bollworm species. When resistance is a factor, the problem usually gets worse over time—it seldom gets better.
Now, what should fieldmen be looking for?
1. Eggs in terminals or on the fruiting structures: square bracts, white or red blooms (threshold on 2 gene cotton is 20 eggs/100 plants)
2. Damaged squares in the upper canopy – may find more damage to small squares near the terminal in Phytogen varieties (5% damage is threshold).
3. Newly hatched larvae
May find in small squares in Phytogen varieties
May find more in open white blooms or underneath red or dried blooms in Delta Pine and other varieties
(5% of plants with small larvae is threshold)
These small larvae are white when they have just hatched and will turn pale green within a day or so.
One thing that makes them stand out in a white bloom is they will have a black or dark brown head. Often the head is the best thing to look for since being dark stands out from the white bloom petals. (See Picture)
Once a significant increase in eggs or small larvae are detected—do not waste more time in the field. Get the word to the grower and get the sprayer loaded. Every 24 hour period that passes from detection to treating means less effectiveness with your insecticide. Also note that these bollworm moths will likely seek out our oldest and most promising cotton to deposit eggs in.
Now what treatment options do we have? Basically two. We can try the older chemistry, pyrethroids, or we can go to the newer chemistry, Besiege and Prevathon.
Things to consider here: bollworms have shown levels of resistance to pyrethroids in many areas of the cotton belt. However, the pyrethroid chemistry is much less expensive. Pyrethroids have about a 4-5 day residual on bollworms, where they are still active.
The newer chemistry Beseige and Prevathon have about 10+ days of residual on bollworms, depending on the rate applied.
If using pyrethroids, I suggest the highest labeled rate. If using Beseige, I suggest 8-9 oz/ac. If using Prevathon, I suggest 16-18 oz/ac. Besiege contains a low rate of Karate pyrethroid in the mixture. If you need tarnished plant bug or stink bug control, you will need to add about 1 oz of additional Karate, or equivalent pyrethroid, to the tank mixture. Prevathon has no activity on plant bugs or stink bugs.
In summary, this is the time to be ready to react to bollworms in 2 gene cotton. I will be tweeting as I hear of increased pressure in a region, county, or area.
I will be conducting tests on thresholds, timing, and chemical choices at our research farm at Prattville in Central AL, so will be in the field a lot within the next 2 weeks or so.
Stay in touch with the Syngenta Pest Patrol reports for up to date observations on bollworms. To sign up for the Syngenta Pest Patrol Updates for Alabama, register online at syngentaus.com/pestpatrol or register via text by texting pestpat11 to 97063.
My Syngenta 800 line:
o Call 1-877-285-8525: when prompted, press 1, then 2, then 4
Weekly email newsletter from Tim Reed containing moth trap data
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