The "Cotton leaf burn" syndrome was first documented in 1990 (Chu et al., 1990). In 1989 and 1990, the "leaf burn" syndrome began to appear in med-July. In most cases the symptoms occurred at the proximal part (palm) of the leaf blade. The interveinal green leaf tissue turned a pale yellowish color, which intensified to a brown necrotic condition designated as "leaf burn." The major vein tissues and the part of the leaf blade distal to the necrotic area also appeared normal and remained green. In the late stage of development, the necrotic leaf area was surrounded by a silvery ring, and flower buds and young green bolls were shed. The leaves most affected occurred at the exterior of the plant canopy. cotton plants adjacent to fallow fields and at field borders appeared to have more leaves with the symptoms than those in the interior of cotton fields. The new plant growth that developed in early August from apical buds did not express "leaf burn" symptoms.

The symptoms occurred again late in July 1991 in a few commercial cotton fields in the Imperial Valley, CA. Most of the commercial cotton fields in the Valley were Temik^®(aldicarb) [2-methyl-2-(methylthio) propionaodihydeO-(methylcarbamoyl) oxime] treated for insect control, and as a precaution against recurrence of "leaf burn", as we suggested earlier (Chu et al. 1990).

The Objectives of this study were to further investigate potential cause(s) of the plant disorder.