Many cotton fields are maturing rapidly which means we have reached the final phase of cotton development, leading to cotton defoliation. The last thing we need now is a tropical system with rain and wind! One important fact is that the maturity of the seed and fiber cannot be hastened through the use of harvest-aid chemicals. Only time and favorable growing conditions mature cotton. Harvest aids can only promote defoliation, more rapid boll opening and desiccation, and thus prepare the crop for timely harvest.
Deciding when to apply harvest aids is a compromise between slowing or halting further development of green bolls and minimizing weathering of open bolls so that yield is maximized. If applied too early, the plant may not properly defoliate, fiber quality and yield may be reduced, re-application may be necessary, and planting seed quality may be lowered. If applied too late, yield and quality may be reduced by weathering.
There are several techniques for determining when to begin applying harvest aids. Using a combination of methods will improve timing. Most harvest-aid chemical labels recommend that the products be applied when the crop attains a certain percentage of open bolls, generally 50 to 70 percent. Cotton with excessive growth should have at least 80 percent of the bolls open to reduce regrowth. If there was a “skip” in the fruit set on the plant, using the percent open bolls method may not fully evaluate the maturity of the remaining green bolls compared to the mature bolls.
Seed development is also a good indicator of boll maturity. Cutting across mature bolls with a sharp knife will split seed so their maturity can be evaluated. The seed coats of mature seed will be tan to brown in color. There will not be any clear “jelly” in mature seed. The cotyledonary leaves will be completely formed and the embryo will be dry. Mature fiber rolled between the thumb and forefinger will feel moist but not watery.
The location of the uppermost harvestable green boll in relation to the uppermost first position-cracked boll also can be used to assess crop maturity and time harvest aid applications. This technique, known as Nodes Above Cracked Boll (NACB), takes into account the relationship between the age (and consequently the maturity) of bolls at adjacent fruiting branches. When using this technique one must count nodes above the uppermost cracked boll and not bolls above cracked bolls to determine the age of bolls above the cracked boll. A cracked boll is used as a reference point because it denotes the uppermost boll that has attained 100 percent of its yield and quality potential.
It seems that every year is a little different when it comes to defoliating cotton. The recent rains should have relieved the cotton moisture stress conditions in some cases, and the cotton leaves should now be more receptive to harvest-aids. However, plants that are severely moisture stressed, with tough, leathery leaves, are difficult to defoliate.
Good spray coverage is essential for effective cotton harvest-aid work, because most of the materials are not readily translocated within the plant. Some research indicates that cone-type spray nozzles provide better coverage of cotton foliage than flat-fan or floodjet tips.
Many factors are involved in obtaining good results from a defoliant or desiccant. Good results are obtained when applications are made under the following conditions:
- warm, calm, sunny weather
- low soil moisture but sufficient to maintain plant activity without drought stress
- low soil and plant nitrogen levels
- few new or active leaves
- mature, cutout plants that have at least 70 percent open bolls
Several products are available for use as cotton harvest aids. These products differ in type of activity (boll opener vs. defoliant vs. desiccant and herbicide vs. PGR). Their effectiveness can be altered by environmental conditions and cotton plant health. To help determine what products might be working well this year, I have established two Cotton Harvest-Aid Test Plots in the County. One is located on the Thomas Busenlehner Farm, southeast of Robstown at the intersection of FM 2826 and FM 1694, and the other plot is located on the Scott Frazier Farm, southwest of Driscoll on the east side of CR 95, north of CR 14. I will publish results and post them on the Nueces County Extension web site; http://nueces-tx.tamu.edu/
At the web site, select the Publications Tab, the select the link for Cotton Result Demonstrations.
Jeffrey Stapper is the Agricultural and Natural Resources Agent for Nueces County. Readers may contact him at (361) 767-5223