COTTON PLANT STRESSORS IMPACTING BOLL DEVELOPMENT
June 11, 2021
Cotton bolls can shed from cotton plants due to many stresses beyond a farm manager’s control, such as insects and weather events. Even some agronomic management practices can cause stresses that influence the ability of plants to hold bolls.
A few days after bloom, the developing seeds in a cotton boll begin to draw significant amounts of energy from the plant. If that needed energy is not available, those bolls often shed so the plant can concentrate its available resources on bolls that have been retained to fill the seed and develop the associated lint inside.
Therefore, bolls three to five days after bloom are most likely to shed. Deeper levels of stress on the plant increase the likelihood that larger and older bolls can shed. Several factors can cause energy limitations in newly bloomed bolls.
Environmental Limitations
Extreme drought, waterlogging, cloudy days and high heat indexes all serve to limit the productivity of the plant because they limit its ability to manufacture sugar. We have little to no control over this, other than drainage and irrigation.
Oftentimes, allowing plants to get too far into drought stress will trigger this type of shed upon irrigation. For this reason, timely rainfall and/or early irrigation combined with appropriate plant growth management can aid in limiting boll shed.
Boll Load
Normally, in good conditions, squares will turn into bolls, and the demand for more energy to fill the fruit increases. This is the cause of the typical fruit shed in most cotton fields. We accumulate a good/adequate fruit load and have a cloudy afternoon, and the large shed of late July occurs because the plant cannot support more fruit with energy.
Although perfectly normal (and often the sign of a very good crop), it can be disturbing when this happens.
Vegetative State of the Field
Sugar made by the plants could be going into excess vegetative development. Plant growth regulators (PGR) are used to redirect energy from vegetation and make it available to other parts of the plant, including developing fruit.
This serves the dual purpose of reducing vegetative development and increasing fruit load, which is the ultimate goal.
Varietal Background
To optimize PGR use, we must understand how the variety planted reacts to PGRs when applied. Some Deltapine® cotton varieties are much more determinate and thus are typically more sensitive to PGR applications than others.
When growing less-sensitive varieties, many systems require very aggressive approaches to growth control if adequate results are to be obtained.
The Production System
Generally, the most aggressive system would be described as indeterminate varieties, behind corn, on strong soil, with high levels of fertility and planted at a relative high population. Each of these factors requires different consideration, but often they add up to an extremely high vegetative potential. This would almost certainly require a very aggressive approach to growth control.
Without this approach, these fields often end up too growthy and have difficulty in accumulating adequate fruit loads. In less-productive dryland systems, the approach can be modified as weather and plant development dictates.
Many factors should be considered during the development of bolls on a cotton plant, including adequate fertility and irrigation to aid in helping bolls develop to maximum potential. To optimize the performance of cotton varieties, a sound scouting/insect management plan, timely PGR use and appropriate defoliation timings can all contribute to the ultimate success of any given field. Each field of Deltapine cotton should be considered as its own case and be managed accordingly.
By Jay Mahaffey, Scott learning center manager and Bayer Science fellow
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.
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