In the last few years we have been seeing the need for foliar thrips applications in cotton, even though seed was treated with an Insecticide Seed Treatment (IST). Growers and consultants have been frustrated with the need for foliar applications to protect cotton from thrips after spending $15 per acre for a seed treatment and then having to make one or two foliar applications. The cost for controlling this tiny pest is getting to be too much and impacting profitability. We felt like there were several issues that might be involved with this situation.
Obviously poor growing conditions in the spring the last couple of years have been part of the problem. Cold and wet conditions don’t allow the cotton to grow fast enough to out run the thrips. When cotton isn’t growing, it’s a perfect situation for thrips as well as diseases and nematodes, to rear their “ugly heads” and cause problems. Also, the increase in the use of pre-emerge herbicides to combat problematic weeds like Roundup-resistant pigweeds, can slow down cotton growth causing thrips to become a problem.
Simply put, whatever the reason, it appears like the Insecticide Seed Treatments (IST’s), particularly Cruiser, have not been providing the same level of protection for thrips control that they have in the past. This year thrips were collected early in the season and sent for testing. These preliminary studies indicate that tobacco thrips, the most predominant species in Arkansas and the Mid-South, are resistant/ tolerant to Cruiser (thiamethoxam). The source of the thrips from Arkansas was Marianna, AR. The tests and our observations also indicated that there appears to be no cross resistance to imidacloprid (Gaucho), at least at the current time. As both of these insecticides are in the same class, neonicotinoids, it may be just a matter of time before we start seeing issues with imidacloprid too. These preliminary results certainly have implications to our growers for the future. If you plan to grow cotton in 2014 you have a few choices:
- Continue to use Cruiser. If that is your choice, you should be prepared to make at least one foliar application for thrips, and depending on thrips levels it may take two applications. Based on our observations the last few years, we can’t recommend the use of Cruiser in cotton for thrips control. However, remember those seed treatments control more than thrips. There are nematodes and diseases to consider.
- Switch to imidacloprid. While this is no “silver bullet”, it may be enough to provide the level of protection needed, and if thrips levels are high, will be better than the alternative. That is not to say you won’t have to make a foliar application(s) if thrips numbers are high.
- Don’t use an IST and go strictly with foliar application(s) only. That may sound good to some and if you can be timely with the application(s) you can get by with it. But, as we all know, sometimes it’s very difficult in the spring to make a timely application. That’s a busy time of year for growers with planting, fertilizing, weed control, etc. and sometimes it’s hard to get around to everything. The problem is, if you are a day or two late with the application, you can get in trouble quickly with thrips. Weather is also a big concern—rain at the wrong time can cause a delay in that foliar application which can be problematic. I will tell you it is very difficult to be as timely as you need to be with foliar applications. If you go this route be prepared and make it a priority. Also, remember some thrips insecticides can flare secondary insects such as aphids and mites, so choose wisely. The other issue is tank mixing the insecticide with a herbicide. Organophosphates like acephate and bidrin mixed with post emerge herbicides such as Dual and Warrant have been observed at times to cause burn on the cotton.
- Acephate Seed Treatment. This is a viable option if it is available. Acephate seed treatment has been used for a long time. Before the new seed treatments came on board, it was a standard recommendation and worked fairly well. Again, in high thrips populations it may not keep you from needing a foliar application but will provide early protection which is the most important.
That earliest spray, when thrips are on the cotton as the stand becomes established from emergence to first true leaf, is the most critical timing. To maximize potential yield and earliness, it is vital to keep thrips numbers down on cotton at this time. One or two days can make a big difference.
It’s important to realize that this resistance/ tolerance issue is only about tobacco thrips in cotton—we have no information on other thrips species. We’ve always had a hard time with western flower thrips with all seed treatments, and in those years when western flower thrips are bad, like 2012, the potential for foliar applications being needed is high regardless of the IST used.
As far as thiamethoxam on other crops such as rice, soybeans, and grain crops, the seed treatment appears to be working well. We saw good results this year in rice with CruiserMaxx Rice as well as the other IST’s labeled for rice, as we have in the past. Different situations and different pests.
Many growers are making variety selections right now on all their crops for next year and deciding what treatments they will be adding to their seed, and we want to make sure you can make the right choices for a successful crop in 2014.
- Preliminary studies indicate that tobacco thrips (predominant species in AR) are tolerant or resistant to thiamethoxam (Cruiser, Avicta Complete Pack, all trade names associated with thiamethoxam). The level and extent of tolerance/resistance across the state is yet to be determined. Rest assured we will be looking at that this next year. However, knowing that this tolerance/ resistance was found in all states around us including MS, TN, and LA, indicates the problem is widespread in the Mid-South
- For now, this situation appears to be only in the Mid-South
- Consider your options for thrips control; make a game plan for next year
- This is not an indication of performance on other pests or other crops
If you have any questions contact your local county agent for help.
Information provided by Dr. Gus Lorenz and Dr. Glenn Studebaker-Entomologists-University of Arkansas Division of Agriculture