(Fields 5A, 5F and 6G)
Megha N. Parajulee, Ram B. Shrestha, Stanley C. Carroll, and James P. Bordovsky
Objective: The objective was to evaluate the effect of three irrigation application methods on the population dynamics of cotton insect pests and predators.
Methodology: Experimental plots of Paymaster 2379RR cotton were planted on May 7, 2002 at the Helms Research Farm located near Halfway, Texas. The experiment had a completely randomized design (CRD) with three treatments and four replications. The three treatments included low energy precision application (LEPA), overhead spray irrigation and drip irrigation. Cotton was planted (approximately 56,000 seeds per acre) in 30-inch rows and 100 lbs of nitrogen per acre was applied through irrigation systems to all treatment plots. Insect pests and predators were sampled at weekly intervals by a vacuum sampling method from June 17 to September 19, 2002. The two-cycle backpack aspirator equipped with a 21.2 cc engine (Model 1612, John W. Hock Company, Gainesville, FL) was used for 30 seconds per plot to vacuum insects from an estimated 500 cotton plants per plot. Cotton aphids were sampled weekly from July 22 to September 26, 2002 by visually inspecting 5 top and 5 bottom leaves from each plot. Cotton aphid data were converted to average numbers per leaf and the predator data were reported as total numbers per 500 plants.
Results: Significantly higher (p=0.023) number of aphids per leaf (seasonal average/leaf=0.93) were found in overhead spray plots compared to LEPA and drip irrigated plots (Fig.1). Average number of aphids per leaf was comparatively higher in overhead spray plots throughout the season, except in the first two weeks of June.
Similarly, total predator abundance was highest in overhead spray plots (seasonal average/500 plant=10.5) followed by LEPA and drip irrigation (Fig.2).
Summary: Preliminary results of this on-going study suggest that higher populations of cotton pests and predators may be favored by overhead irrigation when compared to LEPA and drip irrigation. The study will be repeated in 2003 to further investigate these population dynamics as affected by irrigation type.
