Effect of Potato Leafhopper Control on Yield and Protein Content of Alfalfa, 1980

Efficacy of three insecticides in controlling potato leafhopper was evaluated on 3rd cutting, 4-year old alfalfa at Harrisonburg, VA. Insecticide treatments and an unsprayed check were arranged in a four-replicate, randomized block design within a 10-acre alfalfa field. Replicate blocks were 40 x 40 ft. A 6 ft border of Furadan at 1.0 lb al/acre was sprayed around the perimeter of the experimental block. Insecticides were applied July 10 in 30 gal water/acre at 22 psi using a hand-carried, CO2-powered boom sprayer. Insect densities were estimated using a 15-in dia sweep net, with 10 pendular sweeps/sample and 8 samples/treatment/date. Insect densities were also estimated in the remaining field outside the experimental block, and these density estimates are indicated in Table 1 as “control (OUT)”. To estimate yields and protein content, twelve 0,1m2 quadrats per treatment were randomly selected. All alfalfa stems within a quadrat were clipped at ground level and counted, and 5 stem lengths/quadrat were randomly selected, measured and recorded. Each quadrat sample was bagged and returned to the laboratory where they were dried at 43°C for five days and dry weights per quadrat then measured. To reduce sources of variance in yield due to stem density, yields per stem/ quadrat were calculated by dividing dry weight by total number of stems per quadrat. Protein analyses were performed by the Virginia Tech Forage Testing Laboratory using a kjeldahl nitrogen method. Yield and protein samples were taken only within the experimental block.