BEAN LEAF BEETLE INJURY TO SEEDLING SOYBEAN - CONSUMPTION, EFFECTS OFLEAF EXPANSION, AND ECONOMIC INJURY LEVELS

The bean leaf beetle (BLB) [Cerotoma trifurcata (Forster)] is a major pest of seedling soybean [Glycine max (L.) Merr.], but little is known of the effects of seedling leaf expansion on final leaf tissue loss r esulting from BLB injury. This field study was conducted to (i) determ ine a precise daily consumption rate of BLB on seedling soybean; (ii) determine the direct and indirect reduction of leaf area resulting fro m BLB injury and soybean leaf expansion; and (iii) develop economic in jury levels for BLB on seedling soybean. The study was conducted on a Sharpsburg silty clay loam in an 'Elgin 87' soybean field near Mead, N E. Experimental designs were completely random. Consumption rate treat ments consisted of 2 beetles leaflet(-1), in the field and laboratory. Leaf expansion treatments consisted of an uninjured check and three l evels of injury. Injury (gross removal of leaf tissue) was imposed at Vegetative Stage V3 on a lateral leaflet of the fourth trifoliate leaf . Mean BLB consumption of soybean was 0.31 cm(2) d(-1). An injury expa nsion coefficient matrix was developed to estimate final leaf tissue l oss at late V3. Final estimated tissue loss resulting from one BLB fee ding for 1 d on an unexpanded leaf was 2.74 cm(2). Final estimated tis sue loss caused by one BLB feeding from Stage V1 through V3 (14 d) was 13.93 cm(2). Seedling soybean yield-loss relationships were used to c alculate economic injury levels (EILs) for VC, V1, and V2 soybean. The se EILs were more than twice the value of the current EIL of 1.33 beet les plant(-1).