Interest in planting mixtures of cover crop species has grown in recent years as farmers seek to increase the breadth of ecosystem services cover crops provide. As part of a multidisciplinary project, we quantified the degree to which monocultures and mixtures of cover crops suppress weeds during the fall-to-spring cover crop growing period. Weed-suppressive cover crop stands can limit weed seed rain from summer- and winter-annual species, reducing weed population growth and ultimately weed pressure in future cash crop stands. We established monocultures and mixtures of two legumes (medium red clover and Austrian winter pea), two grasses (cereal rye and oats), and two brassicas (forage radish and canola) in a long fall growing window following winter wheat harvest and in a shorter window following silage corn harvest. In fall of the long window, grass cover crops and mixtures were the most weed suppressive, whereas legume cover crops were the least weed suppressive. All mixtures also effectively suppressed weeds. This was likely primarily due to the presence of fast-growing grass species, which were effective even when they were seeded at only 20% of their monoculture rate. In spring, weed biomass was low in all treatments due to winter kill of summer-annual weeds and low germination of winter annuals. In the short window following silage corn, biomass accumulation by cover crops and weeds in the fall was more than an order of magnitude lower than in the longer window. However, there was substantial weed seed production in the spring in all treatments not containing cereal rye (monoculture or mixture). Our results suggest that cover crop mixtures require only low seeding rates of aggressive grass species to provide weed suppression. This creates an opportunity for other species to deliver additional ecosystem services, though careful species selection may be required to maintain mixture diversity and avoid dominance of winter-hardy cover crop grasses in the spring.

Yellow starthistle, spotted knapweed, and meadow hawkweed are three competitive noxious weeds that collectively infest about 640,000 ha of range and noncropland in Idaho. The purpose of this study was to determine the control of these three noxious weeds and undesirable annual grasses with imazapic applied at different rates and growth stages. Imazapic applied fall preemergence, spring postemergence (POST), or fall plus spring POST and picloram applied fall and spring POST reduced yellow starthistle plant density 75 to 100% compared with the untreated control, at about 100 d after spring treatment (DAST). However, by 440 DAST, yellow starthistle plant density did not differ from the untreated control in plots treated with imazapic, whereas picloram reduced plant density 82 to 99%. Imazapic did not control meadow hawkweed or spotted knapweed, whereas picloram reduced plant density of both species 91 to 100% 60 DAST compared with the untreated control and 71 to 100% 440 DAST. Imazapic did not affect weedy annual grass plant density compared with the untreated control at the yellow starthistle or the spotted knapweed sites. However, at the meadow hawkweed sites, imazapic applied spring POST at 210 g/ha and fall plus spring POST at 70 plus 140 g/ha reduced grass plant density 77 to 84% 60 DAST. All treatments that contained spring-applied imazapic reduced grass plant density 46 to 92%, 440 DAST at the meadow hawkweed site. At all locations, picloram increased weedy annual grass plant density two- to eightfold 440 DAST compared with the untreated control. Imazapic offers only moderate control of weedy annual grasses for a brief period after application and does not provide control of these three major noxious weed species in the West. Unfortunately, it eliminates a fairly new rangeland herbicide from the list of potential tank mix partners for control of auxinic herbicide–resistant weed species.

Research to understand and manage ecosystems to supply services has recently spurred a functional view of their biodiversity. In particular, approaches based on functional traits rather than species diversity are increasingly used to reflect interactions between organisms and their environment. These approaches bring a functional perspective to the study of community structure responses to disturbances and resources, and of their effects on ecosystem functioning and services. From an academic perspective, we propose a conceptual framework based on species functional traits to better infer how grassland management practices (fertilization, defoliation regime) along with abiotic factors influence plant, animal and microbial community composition and a range of services in grassland ecosystems. The core of the framework relies on combinations of plant functional traits and associated microbial features that specifically respond to environmental and management factors and influence ecosystem services. To overcome stakeholders’ difficulty in applying the concept of functional traits, we propose an operational approach implying the mapping of plant communities distributed into five plant functional types (PFTs). The approach was used for fields in grassland-based livestock farms from two French grassland networks. We evaluated its ability to predict a range of services including forage provision and non-market services according to environmental and management drivers. PFT-based plant community composition predicted forage services reasonably well but responded weakly to environmental gradients. To cope with the observed limitations of current predictive approaches, we suggest including soil microbial functional types and adaptive management rather than using a prescriptive scheme.

At 25°C and 70% r.h. larvae of Spodoptera exempta develop faster and pass through five instars on star grass, Cynodon dactylon (L.); Pers. maize, Zea mais L.; and Kikuyu grass, Pennisetum clandestinum Chiov. whereas on guinea grass, Panicum maximum Jacq.; and Setaria plicatilis (Hochst.) Hack, the development is not only slower, but the larvae pass through six and seven instars, respectively. Samples of larvae reared on the former grass species suffer high mortality only at the first and the last instar stages so that the distribution of per cent mortality is U-shaped. On the latter host plants, the mortality during the first instar stage is equally high and continues through the subsequent instars with no obvious peak towards the end of the larval life. The samples on C. dactylon and Z. mais had much higher growth indices than those on P. maximum and S. plicatilis. C. dactylon is a preferred natural food plant of S. exempta in the field, and these investigations demonstrate its value and importance.