Yield response of indeterminate potato (Solanum tuberosum L.) to simulated insect defoliation

Yield response to insect defoliation is primarily a function of light interception. A series of leaf removal experiments were conducted on an indeterminate chipping variety of Irish potato, Solanum tuberosum L., to simulate late-season insect defoliation injuries. Leaf removal was conducted following a computer simulation model for growing insect populations. Across 2 yr, 50 to 75% of the canopy leaf area was removed during a 10-d period. In 2001, 75% leaf removal resulted in a 14% yield loss (in total potato weight) while in 2002, 50% defoliation resulted in 15% yield loss and 75% leaf removal resulted in 22% yield loss. In addition to yield differences, high defoliation reduced number and weight of large (65-100 mm diam.) tubers and increased the number of small tubers (47-64 mm diam.). Yield loss was significant when defoliated canopies remained below a leaf area index (LAI) of 4.0. Percentage light interception was a better predictor of potato yield than was percentage defoliation. These data are consistent with the light interception hypothesis and show that remaining leaf area is a better predictor of yield potential than percentage defoliation. Thus, treatment decisions based on light interception and LAIs rather than estimates of percentage defoliation should be applicable to indeterminate varieties of potato.