Intensified cover cropping practices are increasingly viewed as an herbicide resistance management tool but clear distinction between reactive and proactive resistance management performance targets is needed. We evaluated two proactive performance targets for integrating cover cropping tactics, including (1) facilitation of reduced herbicide inputs, and (2) reduced herbicide selection pressure. We conducted corn (Zea mays L.) and soybean [Glycine max (L.) Merr] field experiments in Pennsylvania and Delaware using synthetic weed seedbanks of horseweed [Conyza canadensis (L.) Cronquist] and smooth pigweed (Amaranthus hybridus L.) to assess winter- and summer- annual population dynamics, respectively. The effect of alternative cover crops was evaluated across a range of herbicide inputs. Cover crop biomass production ranged from 2,000 to 8,500 kg ha-1 in corn and 3,000 to 5,500 kg ha-1 in soybean. Experimental results demonstrated that herbicide-based tactics were the primary drivers of total weed biomass production with cover cropping tactics providing an additive weed suppression benefit. Substitution of cover crops for PRE or POST herbicide programs did not reduce total weed control levels or cash crop yields but did result in lower net returns due to higher input costs. Cover cropping tactics significantly reduced C. canadensis populations in three of four cover crop treatments and decreased the number of large rosettes (> 7.6 cm diameter) at the time of pre-plant herbicide exposure. Substitution of cover crops for PRE herbicides resulted in increased selection pressure on POST herbicides, but reduced the number of large individuals (> 10 cm) at POST applications. Collectively, our findings suggest that cover crops can reduce the intensity of selection pressure on POST herbicides but the magnitude of the effect varies based on weed life-history traits. Additional work is needed to describe proactive resistance management concepts and performance targets for integrating cover crops so producers can apply these concepts in site-specific, within-field management practices.

Cover crops are increasingly being adopted to provide multiple ecosystem services, including weed suppression. Understanding what drives weed biomass in cover crops can help growers make the appropriate management decisions to effectively limit weed pressure. In this paper, we use a unique dataset of 1764 measurements from seven cover crop research experiments in Pennsylvania (USA) to predict, for the first time, weed biomass in winter cover crops in the fall and spring. We assessed the following predictors: cover crop biomass in the fall and spring, fall and spring growing degree days between planting and cover crop termination, cover crop type (grass, brassica, legume monocultures, and mixtures), system management (organic, conventional), and tillage before cover crop seeding (no-till, tillage). We used random forests to develop the predictive models and identify the most important variables explaining weed biomass in cover crops. Growing degree days, cover crop type, and cover crop biomass were the most important predictor variables in both the fall (r 2 = 0.65) and spring (r 2 = 0.47). In the fall, weed biomass increased as accumulated growing degree days increased, which was mainly related to early planting dates. Fall weed biomass was greater in legume and brassica monocultures compared to grass monocultures and mixtures. Cover crop and weed biomass were positively correlated in the fall, as early planting of cover crops led to high cover crop biomass but also to high weed biomass. In contrast, high spring cover crop biomass suppressed weeds, especially as spring growing degree days increased. Grass and brassica monocultures and mixtures were more weed-suppressive than legumes. This study is the first to be able to predict weed biomass in winter cover crops using a random forest approach. Results show that weed suppression by winter cover crops can be enhanced with optimal cover crop species selection and seeding time.

Bioregenerative life-support systems for space have been investigated for 60 years, and plants and other photosynthetic organisms are central to this concept for their ability to produce food and O2, remove CO2, and help recycle wastewater. Many of the studies targeted larger scale systems that might be used for planetary surface missions, with estimates ranging from about 40 to 50 m2 (or more) of crop growing area needed per person. But early space missions will not have these volumes available for crop growth. How can plants be used in the interim, where perhaps <5 m2 of growing area might be available? One option is to grow plants as supplemental, fresh foods. This could improve the quality and diversity of the meals on the International Space Station or on the Lunar surface, and supply important nutrients to the astronauts for missions like Mars transit, and longer duration Martian surface missions. Although plant chambers for supplemental food production would be relatively small, they could provide the bioregenerative research community with platforms for testing different crops in a space environment and serve as a stepping stone to build larger bioregenerative systems for future missions. Here we review some of NASA’s research and development (ground and spaceflight) targeting fresh food production systems for space. We encourage readers to also look into the extensive work by other space agencies and universities around the world on this same topic.

Cover crops are increasingly being adopted to provide multiple ecosystem services such as improving soil health, managing nutrients, and decreasing soil erosion. It is not uncommon for weeds to emerge in and become a part of a cover crop plant community. Since the role of cover cropping is to supplement ecosystem service provisioning, we were interested in assessing the impacts of weeds on such provisioning. To our knowledge, no research has examined how weeds in cover crops may impact the provision of ecosystem services and disservices. Here, we review services and disservices associated with weeds in annual agroecosystems and present two case studies from the United States to illustrate how weeds growing in fall-planted cover crops can provide ground cover, decrease potential soil losses, and effectively manage nitrogen. We argue that in certain circumstances, weeds in cover crops can enhance ecosystem service provisioning. In other circumstances, such as in the case of herbicide-resistant weeds, cover crops should be managed to limit weed biomass and fecundity. Based on our case studies and review of the current literature, we conclude that the extent to which weeds should be allowed to grow in a cover crop is largely context-dependent.