Critical Light Interception during Seed Filling for Insecticide Application and Optimum Soybean Grain Yield

Abstract

Relationships between defoliation, light interception, and grain yield for soybean [Glycine max (L.) Merr.] during the last half of the seed filling period are not fully understood. Because defoliating insect pests in the southeastern USA frequently attack soybean during this period, knowledge of such relationships would aid development of criteria for economic insecticide application. Our first objective was to determine the efficacy of using light interception and leaf area index as criteria for economic insecticide application to manage defoliating insect pests. The second objective was to determine the effects of partial and total defoliations during seed filling on grain yield and grain yield formation. ‘Centennial’ soybean (Maturity Group VI) was planted in 1993 and 1994 near St. Gabriel, LA. Experimental design was a randomized complete block in a split‐plot arrangement. Main plots were the temporal midpoint and 3/4‐point seed‐filling stages. Split plots were four defoliation treatments: 0% leaf removal (control), 37 to 41% leaf removal, 56 to 61% leaf removal, and 100% leaf removal. At the temporal midpoint, grain yield declined linearly as light interception fell from 93 to 50%. Thus, for a crop achieving near‐maximal light interception, insecticide application would be recommended whenever light interception at the midpoint seed‐filling stage fell below 93%. Yield and light interception were not closely related at the 3/4‐point seed‐filling stage. Maintenance of maximal grain yield (yield at 0% defoliation) required retention of at least 39% of the leaf area at this time. In conclusion, light interception potentially could be used as an insecticide application criterion at midpoint seed‐filling stage, but not the 3/4‐point. Partial defoliation at the midpoint will affect grain yield if it reduces light interception below 93%, whereas at the 3/4‐point total defoliation is required to affect grain yield.

Soybean Yield Formation: What Controls It and How It Can Be Improved

“…Browde et al (1994) using a combination of defoliating insects, nematodes, and herbicide damage, concluded that light interception was the "unifying explanation for yield losses". Similar conclusions were reached by Board et al (1997) who reported a linear relationship between yield and LI at the temporal midpoint of the seed filling period.…”

“…5.4 to 5.5 or 6.2 to 6.3) resulted in a 5% reduction in yield loss caused by 100% defoliation. Throughout early and mid seed filling (R5 to R6.2), defoliation had to be sufficient to reduce light interception by about 20% to decrease yield (Board et al, 2010;Ingram et al, 1981;Board et al, 1997 Table 6. Summary of row spacing and plant population effects on soybean physiology, growth, yield components, and yield.…”

“…passes into the last half of the seed filling period, defoliation must be at or close to 100% (resulting in a 50% relative LI reduction) to cause yield loss (Board et al, 2010;Board et al, 1997). The effects of defoliation stress on yield formation are summarized in Table 7.…”

Simulated insect defoliation and duration of weed interference affected soybean growth

“…Others reported that a soybean LAI of 3.5 was the critical LAI needed for 90% light interception, and for achieving the best rate of dry matter accumulation (Shibles and Weber 1965) and maximum crop yield (Board et al 1997). A soybean crop that reaches this critical LAI earlier in the season is expected to accumulate more biomass and provide greater yield.…”

Efeitos De Níveis E Épocas De Desfolhamento Sobre O Rendimento E Os Componentes Do Rendimento De Grãos Da Soja

“…A redução do peso do grão ocorre principalmente quando o desfolhamento se dá no período reprodutivo tardio, ou seja, durante o período efetivo de enchimento de grãos [17]; [3,5]). …”