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Defoliation during reproductive growth of soybean [Glycine max(L.) Merr.] may significantly reduce yields. The objective of this study was to elucidate the relationships among organism‐induced defoliation, CO2exchange rates, and reproductive growth in fieldgrown soybean. Soybean (‘Bragg’) plots were sprayed a factorial design with diflubenzuron (0.035 kg a.i./ha) and a benomyl‐maneb mixture (1.12 a.i./ha) on two dates, first at early flowering (5 August) and again at early pod set (19 August). Diflubenzuron application prevented defoliation by velvetbean caterpillar (Anticarsia gemmatalisHubner). By 12 September, LAI was reduced from 5.5 to 2.8, leaf dry weight from 185 to 110 g/m2, and midday light interception from 94 to 72% in defoliated as compared to non‐defoliated plots. While canopy specific leaf weight (SLW) increased in all treatments during the experimental period, SLW was 1.0 mg/cm2higher in defoliated than non‐defoliated plots. On 4 September defoliated plots were sprayed with diflubenzuron (0.035 kg a.i./ha) and carbaryl (0.56 kg a.i./ha) prevent further leaf loss. Canopy CO2exchange was measured at various photosynthetic photon flux densities (PPFD) to develop photosynthesis light response curves. Net canopy photosynthesis at 1,500 μE·m−2·sec−1PPFD (PN1500) declined steadily in all treatments during seed growth. PN1500 and plant dark respiration, respectively, were reduced by 6.8 and 3.3 mg CO2·dm−2·hour−1in defoliated compared to non‐defoliated plots. Soil CO2efflux rates did not differ significantly (P < 0.05) between treatments. Differences in pod growth rates (7.6 and 9.21 g·m−2·day−1and yields (434 and 502 g·m−2) between defoliated and non‐defoliated plots, respectively, were attributed to differences in canopy photosynthetic capacity. There was no apparent effect of defoliation on seed growth duration or seed abortion. Rather, yield reduction in defoliated plots was related primarily to slowing of the individual seed growth rate. Balance of carbon flux to seeds showed relationships between instantaneous canopy CO2exchange measurements and sequential harvest data.

The southern green stink bug [Nezara viridula(L.)] is a pest soybean [Glycine max(L.) Merr.] in many areas of the Southern U.S., particularly in Louisiana and other Gulf Coast states, as well as in other countries where soybeans are grown. To identify resistance to the southern green stink bug, 894 plant introductions and 26 cultivars of Maturity Groups V through VIII were evaluated in replicated single row field plots during 1975 to 1979 at Baton Rouge, LA. Damage ratings were made by classifying 100 seeds selected at random from each sample into four categories (none, light, medium, and severe) on the basis of visual damage. Stink bug damage was associated with plant maturity, with earlier maturing genotypes generally having less damage than later maturing genotypes. Significant differences in stink bug damage were detected among cultivars within Maturity Group VI. There were no differences in damage among cultlvars within Groups V, VII, or VIII. However, all cultivars had in excess of 60% damage and were highly susceptible to stink bug feeding. Highly significant differences in damage were obtained among plant introductions. Of the 894 strains evaluated, 67 had significantly less damage than the most resistant cultivar of similar maturity, and appeared to have resistance. These strains were from fairly diverse geographical locations and may represent different sources of resistance. There were no differences in damage among the more resistant strains within Maturity Groups V, VII, or VIII. However, the Group VI strain PI 171444 had significantly less damage than the other more resistant Group VI strains. This strain had the lowest stink bug damage rating in the test during all years, and appeared to have a high level of southern green stink bug resistance.