In previous laboratory research work utilizing cotton leaf discs and mechanically isolated cells, PPG-1721 [1-(carboethoxy)ethyl-2,5-dichloro-6-methoxybenzoate] increased membrane permeability by inducing the crosslinking of certain membrane proteins. High rates of the chemical caused extensive membrane disruption. However, lower rates of the chemical influenced the membrane-dependent process of ethylene biosynthesis, and since PPG-1721 is an analog of a diphenylether herbicide, it may also influence photosynthesis and hormone reception. In field research conducted during 1985 and 1986, PPG-1721 significantly increased cotton yield by 13 and 17%, respectively, when applied 4 times at 14 g ai/A during reproductive growth. In 1986, the yield increase appeared to be from larger and more mature bolls and not from an increase in boll number. PGRIV is a fermentation broth of soil bacteria, yeast, and fungi and appears to contain a variety of biologically-active compounds. In field trials conducted during 1985 and 1986, PGRIV significantly increased yield by 12 and 16%, respectively, when applied as a 2-way split application during reproductive growth. The yield increase in 1965 was the result of more bolls, however, total boll weight tended to be decreased due to more upper boll development. Since PPG-1721 increased boll weight and PGRIV increased total bolls, these two materials were tested alone and in combination on field-grown cotton (cv. DPL 41).

In 1987,PGRIV and PPG-1721 were applied alone and tank-mixed in a 4-way split application with the first application made at match-headsquare (MHS), and the last at about early bloom (EB). Each time, PGRIV and PPG-1721 were applied at 2 oz/A and 14 g ai/A, respectively. During late reproductive growth, plants were sampled and the data indicated that both materials increased total bolls, however, both treatments tended to decrease total boll weight. When applied together, boll numbers were significantly increased but boll weight was again decreased. Yield data indicated that treatment did not influence first picking, however, second picking was Significantly increased by all treatments. Total yield was not significantly increased indicating carbohydrate and/or nutrient levels were inadequate to achieve higher yields.

In a separate test at the same location, PGRIV significantly increased cotton yield when applied at 4 oz/A, PHS followed by 4 oz/A, EB. This treatment significantly increased first picking by 12%, second picking by 65%, and total yield by 19%. However, although PGRIV significantly increased total yield, it appeared a greater increase could have been obtained since a significant quantity of unmatured bolls were left unpicked.

The cotton in these research plots were cultured under high N (150 lbs N/A applied in 6 applications), high water (irrigated 4 times during July and August for a total of 10 to 12 inches), and apparently adequate fertility (by soil test). The control plots averaged 4500 lbs/A seedcotton. We feel that due to an increased boll load induced by PGRIV and/or PPG-1721 and high water, nutrient deficiencies, especially k+, may have decreased the effectiveness of the bioregulant treatments. We are currently pursuing the concept of a mid- to late-season K+ (and perhaps other nutrients) fertilization coupled with selected bioregulants.