Industrial hemp (Cannabis sativa L.) has a wide array of end uses which, when coupled with regulatory reductions in the United States, has spurred renewed interest in its production. Best management practices, including weed control, need to be evaluated. Since little is known about herbicide tolerance of hemp, studies were conducted to identify suitable options for grain or dual‐purpose (fiber and grain) production. Greenhouse experiments with pre‐emergence and postemergence herbicides were conducted to identify herbicide choices for subsequent field trials. In field studies, S‐metolachlor was the safest pre‐emergence herbicide, resulting in 0 and ≤ 15% injury in 2017 and 2018, respectively, and a hemp stand count that was 97% of the nontreated check (pooled across years). All other pre‐emergence herbicides tested in the field resulted in ≥ 25% visible injury in at least one of the years and ≥ 24% stand reduction relative to the nontreated check (pooled across years). However, no grain yield differences were observed due to pre‐emergence herbicides relative to the nontreated check. Postemergence herbicides sethoxydim, quizalofop, bromoxynil, and clopyralid caused < 20% injury across rating timings and years and had similar grain yield as the nontreated check (588 kg ha−1). Our results indicate that S‐metolachlor applied pre‐emergence or sethoxydim, quizalofop, bromoxynil, and clopyralid applied postemergence are suitable for hemp production, but some of these treatments caused transient visible injury. Future research should be conducted to corroborate results across cultivars, soil types (for pre‐emergence herbicides), and environments.

Residual herbicides applied to summer cash crops have the potential to injure subsequent winter annual cover crops, yet little information is available to guide growers’ choices. Field studies were conducted in 2016 and 2017 in Blacksburg and Suffolk, Virginia, to determine carryover of 30 herbicides commonly used in corn, soybean, or cotton on wheat, barley, cereal rye, oats, annual ryegrass, forage radish, Austrian winter pea, crimson clover, hairy vetch, and rapeseed cover crops. Herbicides were applied to bare ground either 14 wk before cover crop planting for a PRE timing or 10 wk for a POST timing. Visible injury was recorded 3 and 6 wk after planting (WAP), and cover crop biomass was collected 6 WAP. There were no differences observed in cover crop biomass among herbicide treatments, despite visible injury that suggested some residual herbicides have the potential to effect cover crop establishment. Visible injury on grass cover crop species did not exceed 20% from any herbicide. Fomesafen resulted in the greatest injury recorded on forage radish, with greater than 50% injury in 1 site-year. Trifloxysulfuron and atrazine resulted in greater than 20% visible injury on forage radish. Trifloxysulfuron resulted in the greatest injury (30%) observed on crimson clover in 1 site-year. Prosulfuron and isoxaflutole significantly injured rapeseed (17% to 21%). Results indicate that commonly used residual herbicides applied in the previous cash crop growing season result in little injury on grass cover crop species, and only a few residual herbicides could potentially affect the establishment of a forage radish, crimson clover, or rapeseed cover crop.

Cover crops provide a number of agronomic benefits, including weed suppression, which is important as cases of herbicide resistance continue to rise. To effectively suppress weeds, high cover crop biomass is needed, which necessitates later termination timing. Cover crop termination is important to mitigate potential planting issues and prevent surviving cover crop competition with cash crops. Field studies were conducted in Virginia to determine the most effective herbicide options alone or combined with glyphosate or paraquat to terminate a range of cover crop species. Results revealed that grass cover crop species were controlled (94% to 98%) by glyphosate alone 4 wk after application (WAA). Overall, legume species varied in response to the single active-ingredient treatments, and control increased with the addition of glyphosate or paraquat. Mixes with glyphosate provided better control of crimson clover and hairy vetch by 7% to 8% compared with mixes containing paraquat 4 WAA. Mix partner did not influence control of Austrian winter pea. No treatment adequately controlled rapeseed in this study, with a maximum of 58% control observed with single active-ingredient treatments and 62% control with mixes. Height reduction for all cover crop species supports visible rating data. Rapeseed should be terminated when smaller, which could negate weed suppressive benefits from this cover crop species. Growers should consider herbicide selection and termination timing in their cover crop plan to ensure effective termination.

No abstract

Core Ideas Coarse soil texture should not restrict fall biosolids application to winter wheat. Grain yield from biosolids is greater than or equal to that from urea. Nitrogen recovery from biosolids is greater than or equal to that from urea. Environmental concerns and regulatory guidelines about winter N leaching limit fall biosolids applications to winter wheat (Triticum aestivum L.) in Virginia to a plant‐available N (PAN) rate of ≤50 kg PAN ha−1. Ten field studies were established in 2012 to 2014 in Virginia to determine the agronomic and environmental feasibility of fall biosolids applications to soft red winter wheat at the agronomic N rate (100 kg PAN ha−1). Anaerobically digested and lime‐stabilized biosolids were fall applied at rates of 100 and 50 kg PAN ha−1. The 50 kg PAN ha−1 biosolids treatments received 50 kg N ha−1 as urea in spring. Urea‐N was split applied at 0, 50, 100, and 150 kg N ha−1, with 1/3 applied in fall and 2/3 in spring. Biosolids increased N use efficiency (NUE) by 0 to 27%, grain yield by 0 to 1.1 Mg ha−1, and N recovery by 0 to 38% compared with agronomic N rate urea in coarse‐textured soils, especially when lime‐stabilized biosolids were used. Biosolids and agronomic rate urea typically resulted in equal NUE, grain yield, and N recovery in fine‐textured soils, regardless of biosolids type or application strategy. Therefore, biosolids can be fall applied at the full agronomic N rate to winter wheat in coarse‐ and fine‐textured soils in Virginia.

Harvest weed seed control (HWSC) methods destroy, remove, or concentrate weed seeds collected during harvest. Depending on the method of HWSC, chaff and straw fractions may also be destroyed, removed, or concentrated. Observations at soybean (Glycine max (L.) Merr.) harvest in this study estimated the distribution of aboveground biomass between seed, straw, and chaff fractions and the nutrient composition of straw and chaff. Measurements were combined to predict nutrient consequences of HWSC, which have not been documented. The average harvest index of soybean was 0.57:1. Soybean biomass that enters the combine partitions into 7.25 ± 0.37% chaff, 36.05 ± 1.2% straw, and 56.7 ± 1.2% seed. Chaff and straw residues equal 13.4% and 68.5% of the seed weight, respectively. In a soybean crop yielding 3368 kg ha−1 (50 bu a−1), chaff yields 9.4, 0.8, 5.0, and 0.6 kg ha−1 and straw 31.6, 2.1, 1.1, and 2.0 kg ha−1 of N, P, K, and S, respectively. Using 5-year average fertilizer prices ending in 2021, the cost to replace chaff, straw, and the combination of both residues is USD 1.58, USD 5.88, and USD 7.46, respectively. These results give insight into the nutrient consequences and replacement costs of HWSC.

The data presented in this article are those from the second year of a two‐year biosolids‐wheat study conducted in the Virginia Coastal Plain. Researchers identified soil types to which biosolids could safely be applied at full agronomic N rates in the fall for wheat without incurring nitrogen leaching problems. Earn 0.5 CEUs in Nutrient Management by reading this article and taking the quiz at http://www.certifiedcropadviser.org/education/classroom/classes/517.

Core Ideas• Japanese stiltgrass is an increasingly problematic weed in forages.• Japanese stiltgrass can be selectively controlled in cool-season grass forages.• Aminopyralid and aminopyralid + metsulfuron resulted in 68 to 88% control.• Glyphosate should be applied after the germination period.• Aminocyclopyrachlor is also an option for control, where labeled. AbstractJapanese stiltgrass [Microstegium vimineum (Trin.) A. (Camus)] is an invasive annual grass that is problematic in pastures and hayfields along the United States' Eastern Seaboard. It is particularly aggressive in shaded areas where it outcompetes desirable grasses. Since little research has examined Japanese stiltgrass control in coolseason grass forages, field studies were conducted in 2015 to 2018 to evaluate various herbicide options labeled for such use. Of the treatments evaluated, only aminopyralid alone and aminopyralid + metsulfuron controlled Japanese stiltgrass (70 to 90%), are registered for use in cool-season grass forages and are safe to desirable grass species. Weed control was improved when metsulfuron was added to aminopyralid and applied when five to eight true leaves are present (June in this study) but not earlier than when one to five true leaves are present (May in this study). Other effective treatments for control included glyphosate alone or with pendimethalin and aminocyclopyrachlor. Studies suggest that applying glyphosate shortly after the germination period ceases (June in this study) results in better control than earlier in the season (May in this study). Application timing should be carefully considered.