CCN-98-10A

Selecting Cotton Varieties Considering Roundup Ready Problems

Keith Edmisten - Extension Cotton Specialist

Several weeks ago I posted the Carolina Cotton Note
CCN-98-9A -  "More Thoughts on Defoliation and Roundup Ready Cotton". Having seen more fields and talked to other specialists in other states I would like to go back over how prevent or reduce the likelihood of having problems next year. You will notice that the main difference in my observations now is that I am not convinced that fruit abortion problems will not occur on stacked varieties sometimes.

1. One option is to go back to conventional varieties. Some growers have already indicated that this is what they plan to do at this time. I realize that everyone will not be able to or want to do that. If a grower can at least not grow all Roundup Ready cotton he doesn't have all his eggs in one basket.

2. We have seen problems or heard of problems in almost every Roundup Ready variety. I said earlier I I have not heard of any severe problems in stacked varieties. The only stacked variety I have seen enough to form any conclusion at all is 1220 stacked. I have not seen a field of stacked 1220 that has a problem. However there are several complaints on 1220 stacked in Mississippi. Mississippi got a lot more experience this year with some Delta and Pine Land stacked varieties. I rely heavily on their observations as we had very little in the state. They have had several complaints on Delta and Pine Land stacked varieties, primarily on 458. DPL 458 is the stacked version of 5415. The problems in Mississippi included both poor retention and cavitation. I no longer feel increasing the portion of their crop devoted to stacked varieties is a safe way to avoid problems.

3. I stated earlier that so far the problems I have seen that are severe enough that the plant will not likely be able to compensate for have been in fields with 2 or more applications of Roundup. Sometimes both were over-the-top and some times one was post-directed. One way to reduce the likelihood of having problems is to use Roundup only one time over-the-top as early as possible followed by post-direct application of traditional herbicides. However I recently saw one field in Hoke county that had severe problems that only had one application of roundup so this approach may not be perfectly safe.

4. Severe cavitation has been mostly in DPL5690RR and to a lesser extent DPL5415RR. I don't think limiting Roundup applications as mentioned above will help prevent cavitation. Cavitation has been worse on anything that has 90 in its background. This includes 5690RR 5415RR, 90RR, DPL 458, DPL 655, and DPL 688. If you have poor fruit retention in addition to cavitation you will not be a happy camper. I would limit the amount of acres I put into these varieties if I grew them at all..

5. Where the weed spectrum fits the BXN system growers should consider that system to "spread their risk". In fields with sicklepod a half rate of MSMA will help slow down sicklepod so that post-direct sprays can control it. I would rather take the potential delayed maturity from a half rate of MSMA than to have cotton that looks like some of the Roundup Ready cotton this year.

6. There is another problem with some varieties that is not related to the Roundup system but to genetic predisposition. In some other cotton producing states including LA, MS, GA and SC growers have seen what is called bronze wilt, copper top or red wilt. It is believed that varieties with TAMCOT-SP37 are susceptible to this malady. The disease has been seen in the 1200 Paymaster series and in Stoneville 132 and 373. Some fields have been disced and abandoned due to this problem. Dr. William McCarty, Extension Cotton Specialist in Mississippi has some pictures and description of the disease at:

http://ext.msstate.edu/anr/plantsoil/cotton/csbw.html

He also has some pictures and explanations of potential fruit retention and cavitation problems with Roundup Ready Cotton at:

http://ext.msstate.edu/anr/plantsoil/cotton/csrr.html

7. I know that growers don't want to hear the next point but I think it is important. There is only one way I can think of to know if you are paying a penalty for growing Roundup Ready cotton. That is to grow some traditional varieties. A way to know if roundup is causing abnormal fruit abortion is to grow some Roundup Ready cotton in a traditional herbicide program with no Roundup applications.

For growers who feel they cannot do without Roundup Ready cotton and want to reduce the risk of problems associated with Roundup Ready cotton in some fields:

Change to a modified Roundup system that utilizes only one application of Roundup as early as feasible. In this system you will be more likely to need pre or pre-plant incorporated herbicides. You will need to be timely with Roundup applications and to utilize traditional herbicides for all post-direct applications.