We began visually inspecting cotton fields for BMSB on July 17, 2013. As of August 22, we have made 76 visits to cotton fields in Dinwiddie, Greensville, Isle of Wight, Southampton, Suffolk, Surry, and Sussex Counties. No BMSB have been found during our cotton surveys, to date.

We had a request to develop a list of the insecticides available for managing bollworm and stink bugs in cotton—sprays that will go out over the next few weeks. The reason is that with the many products, both single and mixed active ingredients (ai) and different amounts of ai per gallon, it is very confusing and hard for growers to make good selections. Making the best product choice means knowing what the active ingredients are, what they are designed to kill, and how much product is needed to apply enough ai per acre to achieve good results. The attached table provides that information. It was a collaborative effort and included input from Jack Bacheler and Dominic Reisig at NCSU. Please note that not all products are included and that the rates on the table are from the product labels. Hopefully this information will be useful.
Additional information: bw-sb-cotton-insecticides-2013-herbert-docx

Things are pretty quiet in cotton pest-wise with the exception of scattered fields with spider mites and reports (mostly from northeast North Carolina) of pockets of plant bug activity. We are not used to seeing spider mites in wet years and do not really understand the ‘why’. I have seen this in the past and have a couple of observations. One is that under these conditions it is very hard to achieve perfect control of spider mites regardless of the products used, but, mite injury is not a great concern since plants are vigorously growing. My recommendation is to hold off on treating unless 1) rainfall amounts decrease and we begin to see some drought stress, or 2) mite injury gets so bad that otherwise healthy leaves (mid and upper canopy) start to drop due to intense feeding. Injury to and dropping of lower leaves is not really to concerning as these lower leaves are not as important to overall plant health and will be shed in the natural maturing process.

We are not seeing much evidence of plant bugs in the fields we are checking, and not hearing about much from others. We assess plant bug activity by checking for bugs and determining percent square retention. Plant bugs target squares and feeding results in shed. The danger point is reached if retention drops below 80-85 percent—and the fields we have checked have greater than 90% retention.

At this point most cotton in Virginia is into the flowering stage. Once flowering begins, we shift our emphasis to boll protection. We will follow with more specific advice in the next few weeks.

Most cotton in Virginia planted before mid May has blooms at the tops of plants, has mature bolls and is safe from further damage by stink bugs or bollworms. Local estimates are that this describes about 75% of the acreage. The remaining 25% planted after May 15 has not cut out yet and still has some insect-susceptible bolls, but percentage of susceptible bolls on a plant goes down each day as more bolls mature. Most fields, whether BG2 or WideStrike, have been treated one time for bollworms/stink bugs. In most years, this single treatment is sufficient for protection until harvest. But each year is different. This year summer rainfall patterns and some relatively cooler temperatures in recent days have slowed maturity a bit, especially the later planted fields. Whereas in most years by this time we can find some open bottom bolls, few are visible this week. So, early planted cotton is safe, but late planted cotton needs to be scouted for another few weeks, and may require a second treatment.

What about top-crop growth? We are not expecting a lot of new top-crop growth but it can happen. Late season top-crop growth is most common in summers when cotton is heat/drought stressed during the summer and cuts out early, then begins regrowth as a response to late August early September rain. This was the case in a lot of fields last year. This top-crop presents a new set of insect susceptible bolls that is very attractive to the final season’s generation or worms and stink bugs. But in most cases, the top-crop does not have enough lint potential to warrant another insecticide treatment.

In cotton, we are beginning to find corn earworm (=bollworm) eggs in fields. This fits what we would expect given the increase in moth activity. This is a little earlier than normal. Over the past several years, we have seen egg lay start during the first week of August. I suggest that any sprays from this time forward should be directed to bollworm and stink bug. In the past, we have been able to get good control of bollworms in BG2 or Widestrike cotton varieties with a single application of a pyrethroid at the highest labeled rate for that product. Pyrethroids are also picking up most of any stink bugs that could be present. We time the application to coincide with what used to be the second spray in the old (pre-BG cotton days) egg threshold two-spray system (first app at egg threshold, the second in 5-7 days). A treatment 5-7 days after the old egg threshold is designed to target any worms that have escaped the Bt toxins, but would still be small enough to kill with the pyrethroids before doing any significant boll damage. Up until now (at least based on data up to 2011), the single high rate pyrethroid treatment has remained effective in cotton because (in my opinion), if timed correctly they are directed to a small number of small larvae—easier to kill and fewer to kill. We have field trials in place to continue monitoring this.

Most of our cotton is about 10 days to 2 weeks in to the blooming period. This is the perfect time to begin scouting for stink bug damaged bolls. We just completed 5 cotton field scouting clinics across our cotton region and it was not hard to find stink bug damaged bolls, and a couple of fields had high levels—30-40 percent internal stink bug damage. By the 3rd week of bloom, the threshold drops to 10 percent new damage and remains at 10 percent through the 5th week of bloom. These next three weeks (3rd, 4th and 5th weeks of blooming) are the most import time to scout and treat, if needed, cotton for stink bugs. Use the new cotton stink bug scouting card which provides the thresholds, scouting procedures and a template for determining the proper size of the bolls that should be used to make any treatment decision. If you don’t have one, contact your local Virginia Cooperative Extension Ag Agent—we will see that you get one.

We call this ‘Thrips Season’ for a good reason. Although we seem to be coming down from last weeks peak numbers of immatures (about 120-150 per 5 plant sample), we are still getting about 35-40 per 5 plants. The insecticide seed treatments, regardless of source, which were providing decent levels of control last week have broken and now have immature counts as high as or higher than untreated controls. We did not apply any additional foliar sprays to these seed treatments as we wanted to evaluate what levels of control they provide, but we recommend that growers do…and suggested that last week was the right week to pull that trigger. With this kind of heavy thrips pressure, no products are perfect and few are really good to excellent. There are a couple of pretty decent treatments but we will share more details at our tour next week (June 5, 9 am EST till noon), and more at winter meetings. We plan to take these trials to yield…data that tell you what worked and how well.

The corn earworm (bollworm) flight out of corn started over the past weekend. A few cotton fields have reached what we use as the egg threshold in conventional varieties (10 eggs in 100 terminals). Our long-standing recommendation is to treat BGll and Widestrike varieties with a single application of the pyrethroid of choice at the highest labeled rate, 5 to 7 days after the egg threshold. In most areas, that should happen next week. Even with the potential for corn earworm/bollworm pyrethroid resistance/tolerance (see the other July 28 advisory), I think a high rate of pyrethroid is still a good choice for cotton, as it has performed very well in past years. The difference compared with soybean (where we do recommend non-pyrethroids) is that in cotton, we only have to control the few worms that have escaped the Bollgard/Widestrike insect toxins. Are these escapes easier to control because they have been exposed to the Bt toxins? There are also some stink bug hangers-on in some fields, and we are seeing a shift from predominantly brown stink bugs to predominately green stink bugs, which are easily controlled with normal pyrethroids. So, for the money, consider a single high rate treatment of your pyrethroid of choice. There is a lot of confusion about some of the pyrethroid products, especially those combining bifenthrin and zeta-cypermethrin (e.g., Steed, Hero). We have attached a table that provides the amounts of active ingredient of each insecticide, for the recommended lowest and highest labeled rates for cotton bollworm/stink bug contorl. In general, you can get more active ingredient per acre if you fall back to the single-insecticide products (e.g., Brigade, Mustang). Additional information: hero-steed-mustang-brigade-table-july-28-2011-docx

As cotton enters the blooming period, we should begin transitioning from plant bug management strategies to protect squares–to stink bug management strategies to protect developing bolls. Stink bug populations seem to be on the rise and we are already hearing of a few fields with upwards of 30% internal boll damage.

In Virginia we are faced with a large variation in the maturity stage of cotton fields. Early planted fields (end of April to 1st week of May) have been blooming for 3 weeks or so with a few of the oldest bolls almost at the stink-bug-safe stage (25 days or older, 1.25 inch-diameter or larger). The majority of their bolls are still stink-bug-susceptible (5-24 days old, 0.5-1.24 inch-diameter). Later planted fields (2nd and 3rd weeks of May) are just beginning to bloom. This means that no single recommendation can cover all cases, except that we are firm in the belief that when making stink bug control decisions, following the new Dynamic Threshold will fit. Basically, with this new threshold the allowable percent of bolls with internal stink bug damage changes with crop age. This threshold is based on two concepts: that cotton plants can compensate for relatively high levels of early season boll damage, and that the number of stink bug susceptible bolls changes as plants mature. These concepts were thoroughly evaluated in a cooperative multiple-state project (VA, NC, SC, GA, AL) resulting in the development of the Dynamic Threshold (1st week of bloom-50%; 2nd week-30%; 3rd, 4th and 5th weeks-10%; 6th week-20%; 7th week-30%; 8th week-50%). The many field evaluations also showed that applying the new threshold consistently resulted in higher profit ($) per acre.

If an insecticide treatment is needed for controlling stink bugs, there is a lot of misinformation being passed around as to the best choices. Although the neonicotinoid insecticides are effective against plant bugs, they are not as effective against stink bugs as products like Bidrin or high rates of the pyrethroids. Green stink bugs are easily controlled with most any pyrethroid. Brown stink bugs, if the dominant species in the field, are a bit more difficult to control and products containing bifenthrin seem to have a better track record. Another misconception is that a single treatment will provide ‘weeks of residual control’. Not so. Although they provide a good kill of existing adults and nymphs, none provide residual control against newly invading adult stink bugs. If they do continue to invade fields, especially if they invade several days to weeks after initial sprays, additional treatments would be needed. This has not been common in Virginia, but each year is different so the best defense is careful and consistent crop scouting and applying the threshold until all ‘harvestable’ bolls are safe from bug damage.