Identification Of The Last Effective Boll Population For Basing End Of Season Management Decisions

COTMAN™ is a decision-aid tool developed in Arkansas for managing cotton production.  Nodes above white flower (NAWF) is an informative measure of crop growth status, and allows for better precision in making harvest aid decisions at the end of the season.  Through monitoring NAWF, COTMAN can more accurately identify the last effective boll (LEB) population.  It has been proposed that the LEB population occurs when there are five nodes above the uppermost first position white flower (NAWF=5), which is purportedly known as cutout.  This assumption is derived from previous research in Arkansas showing that the boll population which contributes 95% of yield is set when the crop stage is at NAWF=5 (Bourland et al., 1992).  The objective of this study was to determine if LEB population occurs at NAWF=5 in other parts of the Cotton Belt.

Field studies were conducted in College Station and Corpus Christi, Texas.  Studies were designed in a randomized complete block design with four replications.  Treatments consisted of three nodal positions (NAWF=5, 4, and 3).  NAWF counts were made on weekly basis until the three nodal positions were reached.  Once each nodal position was reached, 20 plants per plot were tagged denoting the respective nodal position.  Each treatment was defoliated at 850 accumulated heat units beyond each corresponding nodal position.  Evaluations of percent open boll and nodes above cracked boll were assessed at defoliation to obtain a relative evaluation of other commonly used methods to determine crop termination. Fourteen days after defoliation, treatments were harvested to compare lint yield, percent open boll, and fiber quality.  Tagged plants were hand-harvested to determine the percentage of yield above and below each nodal position.