Indirect measurement of insect defoliation

Leaf area index (LAI) after insect defoliation injury is closely related to yield, so measuring the LAI of defoliated plant canopies is of considerabl e importance. Unfortunately, direct measurement of LAI is laborious and tim e-consuming. This study was conducted to evaluate the LAI-2000. a commercia lly available instrument for rapidly and accurately measuring LAI of insect -defoliated soybeans, Glycine mar (L.) Merr. The instrument's indirect meas urements of LAI were compared with direct measurement of LAI. Measurements were made in 2 fields, one with approximate to 50% defoliation and the othe r with approximate to 30% defoliation. The LAI range for direct measurement was 2.47-4.24. The instrument's indirect LAI measurements exceeded the dir ect measurements, but by <15%. With respect to plant response to insect def oliation, an error rate of approximate to 15% is acceptable for most applie d and research purposes. Additional comparison of LAI-2000 estimates to act ual LAIs from 3 experiments revealed a linear relationship with a slope not significantly different from 1. Therefore, our work indicates the LAI-2000 provides accurate estimates of LAIs for insect defoliated soybeans, and wo uld likely perform comparably in other crops.