Effects of Fenamiphos on Pratylenchus penetrans and Growth of Apple

A 3-year study was conducted to evaluate fenamiphos at 20.2 kg a.i./ha applied in both fall and spring or in spring only for the control of Pratylenchus penetrans on apple, Malus domestica cv. Granny Smith on M7a rootstock. The initial population densities of P. penetrans within the plot area were 89/250 cm(3) soil and 268/g root dry weight. Fenamiphos increased (P < 0.05) trunk diameter in years 2 and 3 and shoot length in years 1 and 2. Yield data obtained in year 3 showed that the spring only and the fall plus spring fenamiphos treatments increased (P < 0.05) yields by 36 and 80% with a net gain of $2,352 and $5,456/ha, respectively. Results suggest that P. penetrans may be of economic importance in Washington state.