Measuring Maturity of Cotton Using Nodes above White Flower

Due to its indeterminate growth habit, maturation of cotton (Gossypium hirsutum L.) is affected by many environmental and cultural factors. An easy and reliable measure of its progression toward maturity that can be attained during crop development is needed for both production and research programs. As a cotton plant develops, first-position flowers progress toward the plant apex, and their relative position can be determined by counting the number of main-stem nodes above the uppermost white flower. After plants attain nodes above white flower = 5.0 (physiological cutout date; i.e., flowering date of the last effective boll population), subsequent flowers have a low probability of producing bolls of adequate size and quality. The objective of this study was to evaluate physiological cutout date (days from planting to physiological cutout) as a measure of maturity in cotton by comparing it with two established harvestbased methods: mean maturity date and percentage of crop harvested in the first of two harvests (% first F.M. Bourland, N.R. Benson, and E.D. Vories, Northeast Research & Extension Center, P.O. Box 48, Keiser, AR 72351; N.P. Tugwell, Department of Entomology, and D.M. Danforth, Department of Agricultural Economics and Agribusiness, University of Arkansas, Fayetteville, AR 72701. Received 17 Aug. 2000. *Corresponding author ([email protected]). 2 BOURLAND ET AL.: MEASURING COTTON MATURITY WITH NODES ABOVE WHITE FLOWER pick). Comparisons were made in three tests: (i) evaluation of varying treatments for thrips (Frankliniella spp.), (ii) nitrogen rate on three cultivars, (iii) cultivar evaluation at different locations in Arkansas. Within each test, sequential nodes above white flower counts were used to determine physiological cutout date, while mean maturity date (days from planting until 50% yield can be harvested), and % first pick were determined from sequential harvests. Significant variation was found within each test for all of the maturity measurements. Physiological cutout date tended to be closely related to mean maturity date and % first pick. Exceptions occurred when values of % first pick exceeded 90% (variation in maturity was not expressed) and when Verticillium wilt (caused by Verticillium dahliae Kleb.) affected crop maturity after physiological cutout. Thus, physiological cutout date provides a precise, easy, and reliable measurement of the accumulated effects of environmental and cultural factors on crop development that occurs before the flowering of the last effective boll population. E crop maturation and harvest of cotton can enhance production efficiency by alleviating late-season risks associated with insect problems and adverse weather (Anderson et al., 1976). Various measurements have been used to evaluate earliness of cotton. Richmond and Radwan (1962) found that phenological (first square, flower, and open boll) and product-quantity measurements (ratios of fractions relative to total yield) of earliness were significantly correlated. They suggested that the most practical method by which to measure maturity involved examining the ratio of weights in early harvests to total seedcotton harvested. Although percentage of total crop yield harvested in the first of two harvests (% first pick) has been the most frequently used measurement of earliness, it has disadvantages. First, data from different tests cannot be compared directly because values depend on when the first harvest was made. Second, variation in maturity may be masked by delayed harvests, such as when average first pick exceeds 90%. Third, the use of boll-openers (e.g., ethephon [2-chloroethylphosphonic acid]) has frequently led to once-over harvesting, thus negating the time and expense of second-harvest as well as eliminating the possible use of % first pick as a measure of maturity. Richmond and Ray (1966) found that mean maturity date provided a more exact measurement of earliness than did percentages of total harvest in multiple harvests. Mean maturity date is determined by multiplying sequential yield weights by days from planting, then dividing by total yield. Thus, mean maturity date directly measures realized maturity of the crop and quantifies maturity in a meaningful, comparable unit; i.e., number of days from planting to harvest. However, mean maturity date requires multiple harvests with its accuracy enhanced as number of harvests increases, and it cannot be calculated until after harvests are completed. As boll load increases, maturation of cotton plants is signaled by slowed development of new main-stem nodes, which causes first-position white flowers to appear progressively closer to the plant apex (Oosterhuis et al.,1992). Waddle (1974) was the first to report the use of node number of firstposition white flower relative to the plant apex as an indicator of maturity in cotton. Comparing cultivars that differed in maturation time, he observed that earlier maturing cultivars had fewer nodes above the last white flower during the third and fourth weeks of flowering than did later maturing cultivars. Furthermore, he indicated that “it is reasonable to expect that the number of nodes above the last white bloom will be an excellent herald for cutout and a general growth indicator for any one variety.” Sequential measurements of this plant parameter, now referred to as nodes above white flower, can be used to monitor the development and maturation of cotton (Bourland et al., 1992). Within the COTMAN expert system, physiological cutout has been defined as the flowering date of the last effective flower population, as determined by an average nodes above white flower of 5.0 (Oosterhuis et al., 1996). Flower retention and subsequent boll size decline rapidly when flowers occur five nodes (and closer) from the plant terminal. If nodes above white flower = 5.0 is attained after the latest possible cutout date (based on historical weather data, the latest date from which sufficient heat likely will be available to mature a population of bolls), seasonal cutout is indicated. Maturity is then determined by weather limitations rather than crop maturation, because late-developing flowers (even those that occur at nodes above white flower > 5.0) will not have time to develop into economically viable bolls. 3 JOURNAL OF COTTON SCIENCE, Volume 5, Issue 1, 2001 Crop maturity, as defined by the date that physiological cutout occurs, can be determined from multiple measurements of nodes above white flower and expressed as days from planting to nodes above white flower = 5.0 (physiological cutout date). Like mean maturity date, physiological cutout date may provide a temporal measure of maturity that can be compared among diverse environments, but it does not require multiple harvests. Determination of maturity based on harvest data, as done with % first pick or mean maturity date, precludes in-season management that is based on crop maturation. To utilize early maturation effectively, a simple and reliable in-season measure of maturity is needed. The relation of physiological cutout date (an in-season measurement of maturity) to mean maturity date and % first pick (harvestbased measurements of maturity) has not been established. The objective of this study was to determine whether physiological cutout date provides an accurate in-season measure of maturity. MATERIALS AND METHODS Comparisons of physiological cutout date with harvest-based measures of maturity were made using data from three data sets. These data, which evaluated treatments that would likely affect crop maturity, were selected because they included measurements of nodes above white flower, sequential harvests, and yield. The three experiments were established to evaluate: (i) thrips c o n t r o l b y a l d i c a r b ( 2 m e t h y l 2 [methlythio]propionaldehyde O-[methylcarbamoyl] oxime) treatments in 1986 and 1988; (ii) effects of N-application rates on different cultivars in 1994; (iii) cultivar performance at three locations of the Arkansas Cotton Variety Test in 1989 and 1990.