THE USE OF PLANT MONITORING TECHNIQUES AS AN AID IN DETERMINING MEPIQUAT CHLORIDE RATES IN RAIN-FED COTTON

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Five Pix treatments were applied at seven locations across the Coastal Plain. The five treatments consisted of a check receiving no Pix, a low rate multiple approach receiving four applications of 292 ml ha-1 of Pix at 10-14 day intervals beginning at first square (LRM), a low rate multiple approach with Pix application based on a plant monitoring point system (LRM-PM), an early bloom approach receiving eight ounces at early bloom (EB) and a modified early bloom approach based on a plant monitoring point system (EB-PM). No yield responses were observed due to Pix at any locations due to the drought, the lack of value associated with earliness this year due to the drought and lack of excessive moisture at any location. All locations had good plant growth until about two weeks prior to early bloom. One location received almost no rainfall for the remainder of the season and the other six locations had limited rainfall capable of producing 800 to 1500 kg of lint ha-1. No location received what might be considered any where close to excessive rainfall. The LRM-PM system seemed to do a good job of recognizing the change in the crop prior to early bloom and called for lower Pix rates than the standard LRM. The EB-PM system appeared to be too aggressive and called for higher rates of Pix at than the standard EB approach at some locations. No significant yield reductions due to Pix treatments were observed.

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USE OF GROWTH REGULATORS IN COTTON PRODUCTION

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Considerable interest exists for the use of plant growth regulators (PGRs) in cotton production.  Plant growth regulators are organic compounds, other than nutrients, that affect physiological processes of plants when applied in small concentrations.  These compounds represent diverse chemistries and modes of action and provide numerous possibilities for altering crop growth and development.  Their time of use extends from early season when they are applied in-furrow or as seed treatments at planting to late season in preparing the crop for harvest.  Overall benefits from plant growth regulator use in cotton include yield enhancement, improved fiber quality, and greater ease of harvest.  More specific responses include alteration of C partitioning, greater root:shoot ratios, enhanced photosynthesis, altered nutrient uptake, improved water status, and altered crop canopy.  These responses are a reflection of the interaction of heritable characteristics, cultural inputs, and environment.  Because of this complex interaction, crop response to PGRs is not always predictable.  Techniques have been developed to monitor the growth and development of the crop, with specific emphasis on the fruiting characteristics.  One such technique, plant mapping, provides detailed information on fruiting rates and potential, fruit retention, and distribution of fruit set relative to PGR treatment.  Since over 80% of the yield is produced on first position fruiting sites, retention and maturation of these bolls is critical.  Increased boll retention at the early fruiting sites enhances crop maturity, allowing quicker harvest and improved lint quality.  In summary, strategies for using PGRs in cotton production include numerous options for beneficially modifying crop response to improve yield and management of the crop.

Conclusion

A review of the recent literature indicates that plant growth regulator use in cotton remains a viable option for effectively modifying plant growth and development.  Success with growth retardants, yield enhancers, and crop terminating compounds makes managing the crop an easier task.  Suppressing excessive vegetative growth allows for better control of insects and assists with harvest.  Identification of compounds that enhance photosynthetic activity and greater partitioning of carbon to developing fruit remains as one of the primary focuses of research.  However, compounds that increase root activity, ion uptake, and water use efficiency are equally important.  Consistency of PGR performance is complicated by the interaction with heritable characteristics of the crop and environment.

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