CCN-98-8B

More Thoughts on Roundup Ready Cotton Problems

Keith Edmisten - Extension Cotton Specialist

Industry representatives have offered some of the following explanations for the problems we are seeing on Roundup Ready Cotton

1. Plant bugs -

a. Most of the scars on the fields I have seen are too large to have been caused by plant bugs.

b. If plant bugs took all the fruit off from the first fruiting branch all the way up the plant to where it is blooming you would expect to see a great deal of crazy cotton with terminals taken out earlier.

c. If plant bugs are causing this damage why are there small bolls all over the ground in these fields. These bolls do not have insect damage. These bolls should not be aborting as there is essentially no boll load and good moisture. Plant bugs are not making these bolls abort.

d. We have found some flowers with very few anthers and therefore little or no pollen. This indicates a potential pollination problem.

e. If plant bugs caused this much damage why are some fields very close by showing absolutely no problem.

f. The abortion in most fields is too evenly distributed across the field.

g. Some of the fields with problems were sprayed in June for second generation budworms which should have limited plant bug damage.

2. High night time temperatures -

a. High night time temperatures can cause pollination problems. I have reviewed temperature data and there are no nights that the temperature did not get down into the 60's or 70's. One of the differences in North Carolina's climate versus many other areas of the belt is that we have lower night time temperatures.

b. It would take a lot of hit nights (over 80 degrees) to cause pollination problems with fruit set over such a long period of time. We are not talking about a narrow zone of abortion.

3. Abortion due to Roundup only occurs on one or two fruiting branches (a narrow zone)

a. This perception is based on Alan York's data that shows that cotton sprayed over-the-top of say 10 leaf cotton may abort fruit on the 6^th and 7^th node. None of the cotton I looked at was sprayed over-the-top anywhere near that late. I think the difference is that Alan was working with "normal" Roundup Ready cotton that works. For some reason the Roundup Ready cotton in these fields is not behaving like other Roundup Ready cotton.

b. The problems seen in Mississippi last year were not limited to a narrow zone on the plant.