Weekly in-season Updates
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INFORMATION |
August 28, 2006 Talkin’ Cotton TIMING AND SCHEDULING OF HARVEST AIDS J.C. Banks Oklahoma Cooperative Extension Service Harvesting cotton as early as possible increases the likelihood of more ideal weather conditions and higher lint quality during the first part of the harvest season. It is important to apply harvest aids early enough to take advantage of the benefits of early harvest, while avoiding application so early that it decreases yield and quality of the cotton. Timing of harvest-aid applications is not exact. There is a relationship between maturation of later-developing bolls and degradation of the earlier bolls that already are open. The correct decision is a compromise between these two factors. Timing of harvest-aid application varies with the area of the country, harvest-aid materials used, type of harvest, and individual preferences. When harvest aids first were introduced. They were applied according to historical harvest dates; however, factors such as weather, heat unit accumulation, and cotton varieties made this technique largely undependable. Currently, timing is determined by the combination of techniques, each of which further confirms and verifies the others. These techniques are Percent Open Bolls, Cut Boll Technique, and Nodes Above Cracked Boll (NACB). Percent Open Bolls Percent Open Bolls was one of the earliest techniques developed; it was used extensively prior to the introduction of hormonal boll openers. Decisions for timing of defoliation were made by counting the total number of bolls on the plant that would contribute to harvest and calculating the percentage of these bolls that were open. The primary problem with this technique when used alone is that it does not allow for differences in boll development throughout the plant. If there is a gap in the fruiting pattern, some harvestable bolls may not be allowed to mature. Recommendations vary, but, for timing of defoliants, 65 to 90 percent of bolls should be open; for timing of desiccants in stripper cotton, 80 percent or more of bolls should be open. This technique should not be used alone, but rather in support of the other techniques described below. Cut Boll Technique The Cut Boll Technique is used to determine the maturity of the seed inside of the boll. This technique has been used extensively since development of hormonal defoliants and boll openers. Cutting a mature green boll is roughly equivalent to cutting a one-inch diameter, wet cotton rope, and the knife must be sharp to obtain usable results. Be careful with this technique: Immature green bolls are sliced easily and lack of resistance may cause an accident! Mature green bolls are difficult to slice; when sliced, the seed inside the mature boll will have a dark seedcoat and a fully developed pale green embryo inside. Seeds that are not yet mature will have a light-colored seedcoat and will contain a gelatin-like substance. The Cut Boll Technique is straightforward, but the difficulty in making a timing decision involves determining the uppermost harvestable boll. If the cotton has experienced a definite cutout, normally the top large-sized green boll is the uppermost harvestable boll. There will be a definite gap between this boll and the smaller bolls on the top of the plant. If the cotton plant does not have this gap in fruiting, a realistic top harvestable boll must be selected and monitored, and recommendations should be based on this boll. Slight changes might need to be made as the time for defoliation approaches. Nodes Above Cracked Boll Nodes Above Cracked Boll (NACB) is a relatively new technique that uses the principles of plant monitoring to determine the proper time for harvest-aid application. This technique can use average heat unit accumulations to determine whether the plant is ready for harvest-aid application or approximately how long it will be until the plant is ready. Square initiation, flowering, and boll development proceed up the main stem in an orderly manner during the life of the cotton plant. At first-position fruiting sites, the difference in age of each node is approximately three days, or 55 heat units. This relationship occurs in theory throughout boll development in the plant. As the end of the season approaches and daily heat unit accumulation declines, allowance will need to be made for the three-day rule. The difference between nodes may be four – even five – days as the season end nears and cooler temperatures are present. The NACB technique was developed from data generated in a Cotton Foundation-supported project. Field tests were conducted in California, Oklahoma, Texas, and Mississippi. These data show that, as node number at the top of the plant increases, the percentage contribution of each position decreases dramatically. Programs have been developed to calculate potential yield and micronaire loss using data for fruiting-site contribution under specific conditions. When these data were summarized, it was determined that defoliation of cotton when the top harvestable boll is within four nodes of the top first position cracked boll, there was no yield loss and no reduction in fiber quality. Defoliating at an NACB of greater than 4 may allow more immature fibers to be harvested, decreasing micronaire. In may cotton production regions. Producers may need to lower micronaire values to avoid high micronaire discounts. Under these conditions, defoliation at 5 or 6 NACB might be desirable. Timing of harvest aids is best accomplished by combination of the three methods of percent open boll, cut boll technique, and nodes above cracked boll.
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