Effect of Tillage on Cotton Plant Populations and Seedling Diseases

Abstract

Tillage practices can affect the growth of plants and the development of plant diseases. This study was conducted to evaluate the effect of tillage on cotton (Gossypium hirsutum L.) stand establishment, seed cotton yield, and seedling diseases. Three tillage practices (conservation, moldboard, and conventional) were evaluated for their effects on plant populations and the development of cotton seedling diseases on a Norwood fine sandy loam soil (fine-silty, mixed, calcareous, thermic Typic Udifluvent). Each tillage plot was divided into two subplots, with and without the application of Temik (2-Methyl-2-(methylthio)propanal O-[(methylamino)carbonyl]oxime) + Terraclor Super X (10% pentachloronitrobenzene [PCNB] + 2.5% etridiazol) (TSX). Plant populations were determined at 4 wk. Seedling disease was assessed at 4 wk by rating 20 surviving seedlings for root/hypocotyl necrosis. Yield of seed cotton was determined at plant maturity. Tillage practice significantly affected plant population 3 yr., while application of Temik + TSX affected populations in 1 yr. Generally, plant populations were lowest in the conservation tillage plots. Disease index was influenced by both tillage and application of Temik + TSX. Infurrow application of Temik + TSX resulted in lower disease indices all 4 yr. The conservation tillage plots had the highest disease index in 1990; however, disease indices were not significantly different in 1989 and 1991. Application of Temik + TSX resulted in higher yield every year except 1990. The influence of tillage practices on yield of seed cotton was variable each year and no trend was observed. Research Question Cotton farmers have become more interested in conservation tillage cotton production. Conservation tillage, however, can increase the incidence and severity of some diseases. The objective of this research was to evaluate the effect of three tillage practices, conservation, conventional, and moldboard, with and without the application of an in-furrow fungicide + nematocide/insecticide on plant populations and root necrosis. Literature Summary Several studies on conservation tillage of cotton have been published. Most of these reports involve reduced tillage following cover crops. These reports describe variable results on yield and little information on the incidence and severity of cotton seedling diseases. Study Description The study was conducted in northwestern Louisiana on a Norwood very fine sandy loam soil (fine-silty, mixed, calcareous, thermic Typic Udifluvent) from 1988 to 1991. Applied Question What is the effect of conservation tillage on cotton seedling diseases and production? Stand establishment and the severity of seedling diseases as determined by a root and hypocotyl disease index is influenced by tillage; however, in some years environmental conditions may negate the effect of tillage. Generally, seedling diseases are more severe under cool, wet conditions. In 1988 and 1990, plant populations were reduced and disease index was greater under conservation tillage than conventional tillage and moldboard plowing. Plant population and disease index among tillage practices were not significantly different in 1989, a dry year. In 1991, a wet year, plant population, but not root and hypocotyl disease index, was significantly different among tillage practices. Yield among tillage practices was variable, and is probably related to chemical and physical properties of the soil that were not measured in this study. What was the effect of the fungicide + insecticide/nematocide? Application of Temik + TSX improved plant population 1 yr, reduced root disease index all 4 yr, and improved yield of seed cotton 3 of 4 yr. The application of a fungicide + insecticide/nematocide is recommended for conservation tillage in cotton to reduce seedling diseases and improve yields. Table 1. Four-year average of plant population, disease index, and yield of seed cotton. Plant Disease Seed cotton population† index‡ (lb/acre) Tillage practice +§ −§ + − + − Conventional 129 121 1.3 2.0 2004 1626 Moldboard 115 109 1.4 1.8 2089 1736 Conservation 82 72 1.5 2.2 1938 1579 † Number of plants per 50 ft of row. ‡ On a scale of 0–4, where 0 = no necrosis, 1 = <33%, 2 = 33–66%, 3 = 67–100% necrosis, 4 = dead taproot. § + = with Temik + TSX; − = without Temik + TSX.