It’s not unusual for cotton grown in the Southeastern U.S. to experience early season injury from hail storms, with damage ranging from seedling death and stand loss to little to no leaf removal.
The big question for growers is when is the damage severe enough to warrant replanting?
Experiments conducted in Tifton, Ga., this past year attempted to address the issue of cotton plant leaf removal and its effect on plant growth, maturity and yield.
“Hail damage is not necessarily uncommon throughout the Southeast,” says Guy Collins, University of Georgia Extension cotton agronomist.
“We typically experience some form of that on some portion of our cotton acreage in Georgia, enough to raise concerns. In most cases, when we receive significant hail damage, replanting is required.”
The end of the normal planting window is approximately June 15 in southwest Georgia, said Collins at the 2012 Beltwide Cotton Conferences held in Orlando.
“Events that may be occurring during that time might prevent us from replanting. Also, there have been reports of decent yields despite injured fields that were left alone and not replanted.”
Collins says his research focused on leaf removal and leaf matter remaining on the plant and did not account for stem damage or stand loss.
“If stands that remain after a hail event are acceptable, do we really need to replant? I don’t think so, because we have seen several reports, even with substantial injury, where cotton made a good yield.
“Recovery is possible if stands are not influenced below a critical level.
“We wanted to quantify the effects of certain amounts of leaf removal, and we wanted to try and find the least amount of leaf material needed to sustain normal growth and development of cotton,” he says.
For this trial, Phytogen 499 was planted in a dryland environment on June 8, near the end of the planting window for the Tifton, Ga., region.
“We did not kill the terminal bud, but any distinguishable true leaf in the bud was removed. Treatments consisted of factorial arrangements of true-leaf removal (none, and all true leaves removed) and cotyledon removal (none, one-half cotyledon removed, two one-half cotyledons removed, one cotyledon removed, one and one-half cotyledons removed, and two cotyledons removed).
“All leaf removal treatments were applied to two-leaf cotton using hand scissors and were arranged in a randomized complete block design containing four replications.”
Plant growth was monitored throughout the season, with the cotton being carried through to test yield and quality.
“This was conducted on two to three-leaf cotton,” says Collins.
“Results may be different if this test is conducted on four-leaf cotton or just cotyledon cotton where the first true leaf is barely distinguishable.”
At four weeks after planting, when the terminal remained intact, there was no real effect on plant height whether or not the cotyledons were removed, he says.
“When the terminal was removed, we did have an effect of cotyledon removal on plant height, especially when we get down to only one-half cotyledon remaining or both cotyledons removed.”
At 55 days after planting, there’s no effect on plant height when the terminal is intact, he adds. There is a small effect with the most severe treatments.
“At cut-out, when we got to the end of the season, we did see some numerical differences. However, the effect on plant height is not significant. This shows that recovery is possible throughout the season, and some of this injury may just be transient,” he says.
In addition, says Collins, there was no distinguishable difference in nodes above white bloom throughout the season. None of the leaf removal treatments alone had a significant effect on seed cotton yields, he says.
“When the terminal and cotyledon were removed, we saw significant effect, especially when we got to our most severe treatment.”
In conclusion, says Collins, the loss of the terminal alone and terminal and cotyledon can have an effect on plant height and plant growth in the early part of the season.
But, he says, much of this may be transient, depending on the environment. There was no effect on maturity or plant mapping characteristics.
“Lint yield appeared to be affected only when terminal and entire two cotyledons were removed.
In future research, we’d like to look at something similar but in more stressful environments. We did not account for bruising or stand loss, and that is important as well.”