Masters Theses

Date of Award

12-1993

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

Thomas C. Mueller

Committee Members

Thomas C. Mueller, Robert M. Hayes

Abstract

Field research was conducted at Jackson in 1991 and Milan in 1992 to compare the effect of MSMA and DPX-PE350 on cotton development, yield and quality. "Deltapine 50" cotton was planted in rows spaced 1 m apart. Individual plots were four rows by 9 m in length. Treatments were replicated four times in a randomized complete block design. MSMA at 2.24 kg ai ha-1 and DPX-PE350 at 0.14 kg ai ha-1 were applied to 15 to 25 cm (early) and 45 to 55 cm (late) cotton. Early treatments coincided with first square, while late applications were just prior to first flower. An untreated check was included for comparison. Experiments were hand-hoed to maintain weedfree conditions. Plant growth regulators and harvest aids were not used in these experiments to prevent interactive effects. A plant mapping procedure developed by Jenkins et al. 1990 was used to describe plant development. Terms include; 1. monopodium - vegetative branch; 2. sympodium - fruiting branch; 3. node - place on the main stem where sympodia or monopodia arise, nodes begin with the cotyledonary node as zero; 4. position - refers to the order in which fruit is produced on a sympodium branch; 5. fruiting site - any specific node and position combination. Plants were mapped at 5 weeks after treatment (WAT)2, 12 WAT and at harvest. Mapping data measured plant internode, height, number of sympodia, number of open bolls / closed bolls and yield by fruiting site. Data was collected from seven consecutive plants in 1 m of a middle row. Two center rows of each plot were machine harvested. A 1.14 kg sample of seed cotton from each plot was composited by treatment and ginned. Generally, DPX-PE350 did not affect development, yield and quality of cotton. However at 5 WAT, DPX-PE350-late increased square production and decreased boll production for sympodia position two, which could cause delayed plant development under extreme adverse growing conditions. MSMA decreased cotton plant internode length and height at 5 WAT for both years. However, only MSMA-late decreased plant height in 1992 and further observations revealed that no other plant characteristics were different for the 1992 growing season which could be a result of more favorable growing conditions. In 1991, MSMA generally increased squares and decreased blooms and bolls for monopodia and sympodia position one and two which suggests a delay in plant development. However, the delayed plant development response was more pronounced for MSMA-late which was still prevalent late season. At 12 WAT, MSMA-late reduced plant height, number of sympodia and number of open bolls, while increasing number of closed bolls.In 1991, mechanical harvest and plant mapping lint yields were decreased by MSMA-late. Mechanical harvest lint yields were decreased by MSMA at first harvest while increasing lint yields second harvest. However, only MSMA-late decreased total harvest lint yield. Plant mapping data determined that the yield decrease was a result of decreased yields at sympodia positions one and two. A trend developed for sympodia 8,9,10 and 11 where yield at positions one and two were generally decreased and position three was increased. This coincides with late applications made during sympodia 8 development. Fiber properties: length, strength and % trash were not different but, micronaire readings were decreased by MSMA-late in both years. Cotton seed arsenic analysis in 1991 indicates that MSMA-late increased arsenic levels for sympodia at position one and two compared to the untreated check, while position two contained the highest level. Therefore, arsenic movement in the plant may follow a source to sink relationship. In summary, DPX-PE350 had no measurable adverse affects on development, yield and quality of cotton. MSMA-late decreased plant internode and height, number of sympodia, number of open bolls, yield, and micronaire. MSMA-late also increased arsenic levels in cotton seed for sympodia at positions one and two.

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