Herbicides in agronomic performance and chlorophyll indices of Enlist E3 and Roundup Ready soybean

Soybean DAS-44406-6 (Enlist E3) is tolerant to glyphosate, 2,4-D and glufosinate. However, more information is needed on selectivity of 2,4-D choline on Enlist E3 soybean, alone or in mixtures. The aim of this study was to evaluate herbicide effects on agronomic performance and chlorophyll indices of soybean. Glyphosate was applied at different stages of development of Enlist E3 and RR soybean. Furthermore, 2,4-D choline alone and in mixture with glyphosate or glufosinate were also applied on Enlist E3 soybean. Studies were conducted in 2016/17 and 2017/18 seasons. Experiment 1 consisted of application of glyphosate. The treatments were arranged in a 2x4 factorial (genotpes x growth stage). For genotypes, Enlist E3 and RR were used. For growth stage, control (without application), V4, V6 and R2 were used. Experiment 2 consisted of application of 2,4-D choline, glyphosate, glufosinate and associations, at V4 of Enlist E3 soybean. Crop injury, chlorophyll indices and agronomic performance were evaluated. The equivalent selectivity of glyphosate for Enlist E3 and RR soybean was verified, regardless of the stage. 2,4-D choline, alone or in mixtures, did not reduce chlorophyll indices and yield of Enlist E3 soybean after application at V4. Enlist E3 soybean was found to be tolerant to 2,4-D choline, glyphosate and glufosinate. The results showed that, in addition to glyphosate, Enlist E3 soybean may be an alternative for glyphosate resistant weeds

The Effective Role of Soil Indigenous Fungi on 2.4-D Herbicide Degradation

The normal field soil environment safeguarded, via indigenous microbes in a native manner, with the aim of turning herbicide waste into productive bio-resources, through fungi activities. This study aims to determine the effective role of soil indigenous fungi on 2,4-D herbicide degradation. The research was conducted over a period of six weeks, on Iraqi cereal field. A total of eight fungi species, belonging to six genera, (Aspergillus candidus L. ATCC 1002, A. niger T. ATCC 16888, Curvularia lunata W. B1933, Penicillium sp. L. 1809, Rhizopus stolonifer L. B9770, Stachybotrys atra C. 1837, Trichoderma harzianum R. IOC 3844, and T. lignorum T. Hartz 1872), were isolated from the soil. During the exposure periods, fungal populations were differently affected, upon treatments with herbicide. The applied herbicide treatments showed different effects on growth and development of the isolated fungi. The results showed that, five of the eight fungi species (C. lunata B1933, Penicillium sp. 1809, R. stolonifer B9770, T. harzianum IOC 3844, and T. lignorum Hartz 1872) were greatly enhanced by the treatment process. However, two fungi (S. atra 1837, and A. candidus ATCC 1002) were affected negatively by the herbicide, while one (A. niger ATCC 16888) remained unaffected. Once extracted from the soil of wheat fields in Iraq, the fungus S. atra 1837, was first isolated. The highest inhibitory effect was caused by 2,4-D herbicide, on the toxigenic fungus S. atra, causing its disappearance from the field at the last week of application. The laboratory experiments showed similar herbicide effects on the isolated fungi at low and moderate levels, while those at the high level (800 µg /ml) were toxic. These results showed that the herbicide 2,4-D treatments have substantial effects on microbial population in the field. When applied at recommended field rate, the herbicide causes transient impacts on fungal population growth and biodiversity, with the majority of the organism becoming responsible for 2,4-D mineralization in the soil. Therefore, the use of 2,4-D herbicide does not only control weed population, but it also affects microbial activities, especially indigenous fungi in the soil.

Cover crops are not affected by tobacco soil residual herbicides but also do not provide consistent weed management benefits

Winter cover crops (CCs) provide soil conservation benefits for strip-tillage tobacco producers, but soil-residual herbicides may interfere with their establishment and growth. Tobacco is planted later than many agronomic crops, but growers often terminate CCs early to minimize CC residue at planting, and this may reduce weed suppression potential. We examined residual herbicide effects on CCs across two seasons and the potential for CC-based weed suppression within strip-tilled tobacco. Mixtures of wheat plus crimson clover and cereal rye plus crimson clover were examined, with a no-CC control. Herbicides included two rates of PRE sulfentrazone (177 or 354 g ai ha–1) plus carfentrazone (20 or 40 g ai ha–1); the higher rate was also followed by POST clomazone (840 g ai ha–1) or mixed with PRE pendimethalin (1,400 g ai ha–1). Controls with no weed management and hand weeding were also included. CC density and biomass were not reduced by weed management (WM) treatments with residual herbicides. However, CCs did not reduce density of annual grasses, small-seeded broadleaves, or perennials in the tilled in-row or untilled between-row zones. Cereal rye plus crimson clover resulted in lower weed biomass at tobacco harvest in the untilled between-row zone in 2017. WM effects were variable between the years, weed groups, and zones. Adding clomazone or pendimethalin was more consistent for reducing weed density and biomass compared to the low rate of sulfentrazone plus carfentrazone. Tobacco yield was unaffected by CCs in 2017 but lower in some WM treatments in 2018. In this study, tobacco herbicides did not interfere with wheat, cereal rye, or crimson clover establishment, but additional research should determine if these results apply to other environments and soil types. However, when these CC species were terminated 5 to 6 wk before transplanting, they did not consistently contribute to weed control.