There are two primary methods for harvesting a cotton crop. The first is by spindle picking where only relatively mature cotton (e.g., at least 60% open boll) is harvested in one or more pickings. Because cotton fibers are generally best at full maturity, spindle picking may harvest some fibers before they have achieved the desired fineness and length. The second is by strip picking where everything is stripped from the plant in a single picking. Strip picking occurs at 100% open boll, i.e., all bolls on the plants in a field are open. Fiber properties are generally at their peak at 100% open boll if only they can be harvested without reducing the crop value.
The presence of leaves on the cotton plants is a major source of crop value reduction. Both spindle and strip picking require that the cotton plants be free of leaves and other vegetative matter at the time of picking. The presence of green leaves can stain the cotton fibers and significantly reduce the crop value since cotton fibers are more difficult if not impossible to dye once stained by chlorophyll. The value of a cotton crop can be reduced as much as 5-10% by staining.
In addition to staining, because its is difficult to avoid harvesting leaves by the strip picking method. A precleaner separation stage can remove most of the burrs and many, but not all, of the leaves. If leaves or pieces thereof enter the gin, the leaves are broken down into very fine pieces that become mixed with the cotton fibers. Even 1 wt % of such vegetative fines may reduce the crop value by as much as 50%. Higher levels make the crop valueless.
The market has responded to the concerns over vegetative contamination of cotton with a variety of harvest aids. There are products available for defoliating cotton plants, enhancing the effects of defoliants, surfactants for assuring adequate contact, and boll openers for accelerating the maturation rate of cotton bolls.
Harvest aids are generally applied as a mixture about two weeks before the cotton is planned to be picked. This two week period may require some careful coordination because some cotton fields may take six weeks to harvest and, depending on the type of picking method used, may require two passes to complete the harvest. Unexpected events, rain or other weather delays, or a lack of adequate planning for the harvest may permit the cotton plants to begin to grow new vegetative matter as well as produce immature squares.
Fruiting sites in cotton are referred to as "squares." Each fruit bearing branch will form three fruiting sites ("squares") with approximately six days between square formations on each branch. New squares and the beginning of reproductive growth in cotton plants are referred to as "pinhead" squares due to their barely visible size. After about three days, the square has grown to about the size of a match head and is a period in the plant cycle referred to as a "match head square." The match head square continues to grow to about the size of an average adult fingernail before blooming ("early bloom"). Three days later, a boll has formed beneath the bloom. Roughly thirty days after early bloom, the product boll is fully mature and ready for harvest.
Regrowth and the production of immature squares pose a problem in effective harvesting and crop management. Regrowth is young, vital vegetative matter that cannot be effectively treated with defoliants. The tissue is too vigorous to succumb to the chemical effects. The conventional method for responding to regrowth is to apply a desiccant (to avoid fiber staining) and pick the cotton despite the dry vegetation accumulated with the cotton. The immature squares are also where weevils overwinter to infest the next crop and reduce its yield.
It would be desirable to have a way of preventing cotton plant regrowth after defoliation that did not materially affect yield or cotton fiber quality.
It would also be desirable to have a means for preventing the development of immature squares to reduce weevil infestation by eliminating sites for overwintering.
In some planting practices, cotton seeds from the harvested cotton are recovered and used for the next crop. It is desirable, therefore, that any treatment to deter regrowth not adversely affect the vigor of seeds from the treated plants.