Soybean Yield and Pest Management as Influenced by Nematodes, Herbicides, and Defoliating Insects

Abstract

Pest management strategies based on crop losses from single stress factors may be inadequate where multiple stresses occur. Consequently, experiments were conducted in 1989, 1990, and 1991 to quantify interactive effects of stresses from soybean cyst nematode (Heterodera glycines Ichinohe), acifluorfen (5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2‐nitrobenzoic acid) plus bentazon [3‐(1‐methylethyl)‐(1H)‐2,1,3‐benzothiadiazin‐4(3H)‐one 2,2‐dioxide] herbicides, and green cloverworm [Plathypena scabra (F.)] on seed yield of soybean [Glycine max (L.) Merr.]. Treatments were combinations of at‐planting soybean cyst nematode soil density, acifluorfen plus bentazon rate, and green cloverworm defoliation level. Herbicides were applied at V6 soybean development, while green cloverworm feeding was simulated during R2 to R4 soybean development. Plot yield and yield components (pods per plant, seeds per pod, and weight per seed) were determined. Herbicide injury and defoliation independently reduced yield in 1990 and 1991. Yield reductions from defoliation were attributed to fewer pods per plant, while herbicide injury decreased pods per plant (1990) and weight per seed (1990 and 1991). Moreover, herbicide injury and defoliation interacted over 1990 and 1991 to decrease yield. Although stress from soybean cyst nematode alone never affected yield, interactions with herbicides and with defoliation reduced yield in 1990. No treatment effects on yield were found in 1989, probably due to uncontrolled environmental factors. Because of the 2‐yr herbicides × defoliation effect, lower economic injury levels for green cloverworm were developed for soybean treated with acifluorfen plus bentazon. To account for potential interactions involving soybean cyst nematode, growers will be advised to consider adjusting weed and insect management strategies for soybean fields infested with soybean cyst nematode.

Soybean Cultivar Differences on Light Interception and Leaf Area Index during Seed Filling

“…Yield is affected by defoliation through a combination of reduced LI resulting in decreased canopy photosynthesis, loss of leaf storage material, and/or shortening of the effective grain filling period (Ingram et al, 1981; Hinson et al, 1978). Other research has reported that among these factors, yield losses result primarily from reduced LI of defoliated canopies (Browde et al, 1994; Higley, 1992). Haile et al (1998a) reported that among three cultivars, defoliation‐induced yield losses were directly related to LI.…”

Relationship Between Leaf Area Index and Yield in Double-Crop and Full-Season Soybean Systems

“…Reductions in leaf area index below this critical region due to insect defoliators may reduce yield (Board et al 1997). Browde et al (1994) reported both linear and quadratic relationships between soybean defoliation and leaf area index, and between defoliation and yield. Therefore, soybean leaf area index becomes an important factor in making management decisions regarding defoliating insects.…”

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

“…Thus, leaves remaining after defoliation cannot compensate photosynthetically for lost leaf material and the reduced LI directly decreases the photosynthetic rate and yield. 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.…”