– Cotton Physiology –

Early Fruit Retention May Not Affect Yield

By Craig Bednarz

Early-season fruit retention has been a subject of considerable debate across the U.S. Cotton Belt for many years. For some, early fruit retention is an integral component of early crop maturity and permeates every management decision made during the growing season.

For others, the destruction of beneficial insect populations and increased production costs associated with pre-bloom insecticide applications is believed to be riskier than reduced early-season square retention. Over the past 30 years, many studies have evaluated the ability of cotton to compensate for early season square loss.

For the past three growing seasons, we have conducted similar studies at the University of Georgia Coastal Plain Experiment Station in Tifton. This report provides a summary of our results. In our studies, square loss was simulated by manual removal of squares throughout the pre-bloom period. At harvest, each plot was hand picked by fruiting position. In this manner, the contribution of each fruiting position to final lint yield was determined.

When pre-bloom square retention remained high (85-95 percent), the probability of harvesting a first position boll at crop maturity increased from 10.4 percent at main stem node 5 to 66.3 percent at main stem node 11 and then decreased from main stem node 11 to the plant apex.

These values are similar to those reported by scientists in other regions of the Belt. Many producers are pleased to see scouting reports of greater than 85 percent square retention prior to flowering. It is interesting to note, however, that the probability of harvesting a boll on these fruiting positions is less than 70 percent. Hand removal of squares prior to flowering in our studies resulted in pre-bloom retention values of approximately 40 percent.

Yield mapping data at crop maturity showed the crop produced additional main stem nodes in these treatments as well as additional second and third fruiting positions. Thus, the crop fully compensated for early-season square removal by producing more bolls at apical and distal fruiting positions. It should be noted, however, these studies were conducted under high yield potential conditions.

Removal of early-season squares in our studies also resulted in additional vegetative growth (increased number of main stem nodes, plant leaf area, and root biomass). If a cotton crop will compensate for early-season square loss, it must produce additional fruiting positions, which will only occur through additional vegetative growth. In some situations, this may result in excessive vegetative growth.

It also has been suggested that early-season square retention could actually be too high in some instances. For example, a crop with very high early-season retention may lack sufficient pre-bloom vegetative growth, which may cause early cutout if the crop is stressed. Our current field studies are designed to address this hypothesis.

Thus, while there are many questions surrounding early-season fruit retention, it is becoming more apparent that a square on the ground prior to flowering does not necessarily translate into lost yield potential.

Craig Bednarz is assistant professor of crop physiology at the University of Georgia's Coastal Plain Experiment Station in Tifton, Ga. BASF sponsors this monthly column in Cotton Farming magazine through July. A guest cotton physiologist will address a different issue each month.