Cotton Production in Mississippi
Cavitation
Xylem Cavitation: There are many questions about young bolls turning brown and hanging on the plant. There are two schools of thought about the cause of this. Some Plant Pathologists have described this as "Phomopsis." This organism has been isolated from the petiole wound. Whether it is the cause or is secondary is still up for debate.
This
has also been described by some Physiologists as a form of "xylem
cavitation" or "vascular cavitation." This occurs when
the plant has a burst of elongation, or growth, after a period of stress.
Actually, when the flower opens there is a corresponding increase in
transpiration rates of the fruiting structure. This is due to several
factors which include a sharp increase in surface area, development of
the ovule, and the beginning of fiber elongation. This rapid increase
in transpiration puts a tremendous demand on the xylem tissue. If conductive
tissue secondary cell wall (thickness) development has not been able
to keep pace with elongation and transport demand, stress may cause a
rupture. When this happens the fruiting form basically dies before an
abscission layer forms and the dry fruiting form hangs on the plant by
a dangling piece of tissue. This is where we get the term "boll
dangle."
This cavitation injury has been seen before, especially in 1998, and was observed to occur on some varieties at a higher frequency than others. The fact that it is physiological in nature and related to a plant may account for why it may be more pronounced on some varieties than others.
There is no "cure" for this problem. After it has occurred the grower should be prepared to manage the crop as a "later maturing" crop. This is because the first position fruit on the lower and central fruiting branches are gone. When this happens, the plant may tend to produce rapid vegetative growth and a PGR such as mepaquat chloride (PIX) may be in order. Insect control will need to be continued longer in order to mature the fruiting forms on the upper fruiting nodes.