Carolina Cotton Notes

As I mentioned earlier, this year is a lot like last year in terms of mepiquat use in early July: http://www.cotton.ncsu.edu/ccn/2007/july13.html

I have rarely seen yield responses to mepiquat following a dry June. Keep in mind that mepiquat is a tool to use to control plant growth if needed prior to boll load. The recent rain will cause the plant to grow but many fields are blooming or close to bloom. One of the possible effects of mepiquat is to reduce the number of nodes on the plant. Right now we have a lot cotton that is either blooming or close to blooming with less nodes than we would like to see at this point. Less nodes means less fruiting sites. I would be hesitant to do anything now that might reduce the number of potential fruiting sites should the weather turn dry again.

For example: I looked at cotton that had 10 nodes and was already blooming. Of these 10 nodes slightly less than 5 were fruiting branches. We would like to have 10 fruiting branches. If it turns dry, applying mepiquat now could reduce the chance of getting these extra 5+ fruiting branches we would like to see. In this example the NAWB is almost down to 4. Normally you read that cotton is cut out at NAWB of 4 and that all the harvestable cotton is on the plant. Hopefully this is not true for us. Having all the harvestable cotton on the plant at NAWB = 4 is based on a cut out due to boll load. When we see this in cotton that has been drought stressed in June we are looking at a stress based cut out rather than a boll load based cut out. If rains continue what we often see is that we stay in a “suspended cut out” where the plant is not really cut out at all. It is simply adding nodes at about the same rate the flowers are moving up the plant. This is one of the reasons why using “cut out” as a basis for timing defoliation for us is not recommended in NC.

Remember that we do not recommend applications of mepiquat on cotton with a NAWB of 5 or less. A lot of cotton in the state would fall into this category at this point. I would be hesitant about applying mepiquat to cotton with a NAWB of 5 to 6.

One thing that may be different about cotton this year compared to cotton in the past few years is that a lot of the cotton is Flex cotton. In the past we often lost some of the lower fruit in Roundup Ready cotton due to pollination problems. This should not be a problem in Flex cotton and we should see early boll load have more effect on plant growth control than in the past. The retention on the Flex fields I have been in is very high with no signs of pollination problems on the lower crop.