We have had some unusual weather so far in 2019, with repeated cool spells, thunderstorms and rain, and within the past week (from 5/24), some widespread locations pelted by hail. While hail damage can be a fairly common late-spring and early-summer occurrence in many cotton production regions across the U.S., it is an infrequent problem here in the San Joaquin Valley.
In addition, cotton has been growing slower than usual this year due to cloudy and generally cool conditions that prevailed well into May. So, a further set-back is not at all welcome. In trying to decide what to consider after a hail storm hits your field, here are some recommendations to consider:
FIRST – After a hail storm, it is likely best to wait 3 to 5 days before assessing damage and potential impact. That gives the plants a chance to recover a little and the damaged leaves will have fallen off. You can also more accurately assess overall damage — what portion of the plants were only lightly damaged compared to those that were severely injured.
Once you initially look over the field, start determining the following 6 criteria:
#1. Is the hail damage severe in some areas but much less in other parts of the field?
Hail sometimes comes through as a “band” that affects a limited zone within the field, with severe plant damage limited to a small portion of the field and lesser damage in the remainder of the field. Damage can include stem breakage, heavy leaf loss and severe terminal damage.
Severity of damage can be evaluated according to the discussions below, but if the percentageof field affected is relatively small, then decisions to abandon, replant, or modify management practices going forward can be directed just to those limited areas.
Early-season light to moderate hail damage in other field areas mibht be limited to some shredded leaves,without much stem or terminal damage. That will have limited impact on your yield potential when compared to the effects of insect pressure or cold or hot weather problems.
#2. What percentage of plants in the field have significant or severe terminal damage?
The “terminal” is the plant’s newest forming small leaves at the top of the plant stem. It is the new growth on the main stem as well as where future vegetative and fruiting branches are initiated.
Damage to terminals can be light (just breaking of small, developing leaves) all the way to complete terminal loss, with the upper stem breaking off or killed. Loss of the terminal part of the plant will have the greatest impact on yield potential when plants are very small (at the 2 to 4 leaf stage). At that point, leaf area is limited, and there will only be a couple of nodes where new vegetative branches can start to develop.
Severe terminal damage – and especially terminal loss – will definitely delay maturity and will at least moderately reduce yield potential. Plants will recover and regrow by pushing out vegetative buds, but they will typically produce multiple vegetative branches which will have delayed fruit production.
Reduced yield potential and growth management problems associated with delayed fruiting can be a problem, but not necessarily a reason to terminate the crop.
#3. What percentage of plants have main stems that are broken off at the cotyledon or below the first main stem leaf?
These plants will likely die or will have very delayed production and low yields. If the stems aren’t completely broken, are they bent and damaged enough that they might fall over later in the season when the fruit loads up?
Again, if that level of damage is widely seen, yield effects will be significant and potential for plant recovery is greatly reduced.
#4. What percentageof plants have major leaf loss?
While the impacts of leaf damage and leaf loss can look terrible and give the appearance that your field was shredded, damage to or loss of even 50% to 75% of leaf area can be tolerated quite well when plants are young, like in the 3-leaf to 7- or 8-leaf stage. That’s particularly the case if the terminal is only lightly damaged and can restart leaf growth quickly.
Again, if the terminal is present to provide new sites for leaves to develop, recovery can be pretty quick with good weather, since root systems are decently established by that time.
In some ways, impacts of early leaf damage or loss with hail can be similar to those seen with early thrips damage, where we often witness good recovery, with not a lot of lasting impact on growth and only slightly reduced yield potentials.
#5. Is replanting a viable option at this time of year?
Since most of the hail damage reported recently has occurred in the third week of May, replanting would not generally be a good option for the currently-available Pima cultivars, since they were developed with full-season production in mind.
Under “typical” fall weather conditions in the SJV, you will likely run out of heat units to mature out the later-season bolls, or you will have to take a chance on very late harvests for replanted fields.
Many Upland varieties can potentially set and mature out a decent crop in a significantly shorter growing season than most Pimas, but you may have to settle for lower yields and employ practices to terminate the crop earlier to avoid late-season insect pest control costs and losses.
Another consideration with replantings in May or early June is that seedlings developing during warm to hot weather often exhibit very fast vegetative growth and delayed timing of first fruiting branches. With late plantings, you are even more likely to produce late-maturing fruit.
#6. What about management practice changes with hail-damaged plants?
Particularly with small plants with fewer than 7 to 8 leaves at the time of the hail damage, plants will produce multiple (sometimes many) vegetative branches in response to main stem damage. If weather conditions are decent, vegetative growth can be very vigorous following this type of damage.
Vegetative branches have potential to produce flowers and bolls, but bolls set on the plants will be delayed. Under this combination of conditions, plant growth regulators may be very beneficial in helping manage growth while trying to get acceptable fruit set.