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 considerable importance. Unfortunately, direct measurement of LAI is laborious and time-consuming. This study was conducted to evaluate the LAI-2000, a commercially available instrument for rapidly and accurately measuring LAI of insect-defoliated soybeans, Glycine max (L.) Merr. The instrument’s indirect measurements of LAI were compared with direct measurement of LAI. Measurements were made in 2 fields, one with a50% defoliation and the other with a30% defoliation. The LAI range for direct measurement was 2.47–4.24. The instrument’s indirect LAI measurements exceeded the direct measurements, but by <15%. With respect to plant response to insect defoliation, an error rate of a15% is acceptable for most applied and research purposes. Additional comparison of LAI-2000 estimates to actual 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 would likely perform comparably in other crops.