Beneficial and Pest Arthropod Responses to Tillage and Cover Crop Residues in Organic Cucurbits

Reduced tillage methods such as strip tillage are often combined with cover crop mixtures to provide agronomic benefits which can support crop and soil health. However, reduced tillage and cover crop species/arrangements effects on arthropods is less understood and results of previous studies have varied. In this study, we examined how agriculturally relevant pest and beneficial arthropod species were impacted by tillage and cover crop methods in USDA-certified organic Cucurbita (L.) (Cucurbitales: Cucurbitaceae). Aphididae were the most observed foliar pests and abundance was highest in full tillage treatment plots while foliar herbivores overall, excluding Aphididae, were more abundant in strip tillage treatment plots regardless of cover crop arrangement. Formicidae was also observed more on foliage, flowers, and in pitfall traps in full tillage, similarly to Aphididae. Parasitica were the most observed foliar natural enemies with increased abundance in strip tillage treatments. Activity densities of several epigeal natural enemies were also higher in strip tillage compared to full tillage. No significant effects of tillage and cover crop treatments were observed on flower visitation rates of Eucera pruinosa (Say) (Hymenoptera: Apidae), an important pollinator of Cucurbita, while the highest visitation rates of Apis mellifera (L.) (Hymenoptera: Apidae) and Bombus spp. (Latreille) (Hymenoptera: Apidae) were in strip tillage treatments. These results suggest that reduced tillage methods can support greater abundances of natural enemies and possibly pollinators. This may lead to enhanced biological control and pollination, but impacts may vary for different arthropod species and crops.

Weed germinable seedbanks of rice-wheat systems in the Eastern Indo-Gangetic Plains: Do tillage and edaphic factors explain community variation?

Zero tillage (ZT) is widely promoted throughout India's Eastern Indo-Gangetic Plains (IGP) because of its potential to increase wheat productivity and resilience to abiotic stresses. Weeds remain a major barrier to ZT adoption, yet it remains unclear how ZT will influence weed communities in the Eastern-IGP. The primary objective of this study was to characterise the composition of the germinable weed seedbank sampled just prior to the wheat phase of rice-wheat farms in Bihar and Eastern Uttar Pradesh, and examine whether adoption of ZT wheat has shifted weed community composition compared to conventional tillage (CT). Additionally, we examined whether edaphic properties and topography (upland vs. lowland) explain variation in germinable weed seedbank communities. In December 2014, we evaluated the germinable seedbank from 72 fields differing in their historic (>=3 year) tillage practices (ZT vs. CT) in three regions: Samastipur-Vaishali-Muzaffarpur (SVM), Ara-Buxar and Maharajgunj-Kushinagar. Weed community composition and species richness varied by region and topography. ZT adoption was associated with lower relative density of Chenopodium album in the germinable seedbank and lower emergence of Phalaris minor seedlings within farmers' fields. In upland topographies of the SVM region, ZT adoption was also associated with greater relative abundance of Solanum nigrum in the weed seedbank. However, differences between tillage systems in individual species were not large enough to result in detection of differences at the whole-community level. Variation in edaphic properties, most notably soil texture and pH, explained 51% of the variation in the weed seedbank community. Our work suggests several frequent but poorly understood species (e.g. Mazus pumilus and Grangea maderaspatana) in Eastern IGP for which future research should quantify their effects on crop yields. Finally, future work surveying weed species abundance at harvest could further determine the dominant problematic species in these regions.

Floral Strips Attract Beneficial Insects but Do Not Enhance Yield in Cucumber Fields

Natural enemies and pollinators require nutritional and habitat resources that are often not found in conventional agricultural fields. The addition of flowering plants within agroecosystems may provide the resources necessary to support beneficial insects at the local scale. We hypothesized that insect pollinator and natural enemy abundance would increase in cucumber (Cucumis sativus) plots containing flower strips and that the effect would be greatest in the crop rows closest to the flower strips. Three flower treatments were tested: 1) buckwheat (Fagopyrum esculentum), 2) yellow mustard (Brassica hirta), 3) sweet alyssum (Lobularia maritima), and cucumbers as a control. Flowers were planted within a commercial cucumber field in 20-m-long strips in a randomized complete block design with six replications in the 2014 and 2015 growing seasons. Some floral treatments successfully attracted more beneficial insects than others, but the beneficials did not disperse out to the cucumber plants. Cucumber yield was unaffected by flowers with one exception: in 2015, cucumber yield in the sweet alyssum plots were greater than those in plots with no flowers. Our research indicates that adding flowers to cucumber fields to increase services from beneficial insects needs to be further investigated to better understand the effect of factors such as relative flowering strip size.

Effects of Cover Crops on Pratylenchus penetrans and the Nematode Community in Carrot Production

Cover cropping is a common practice in U.S. Midwest carrot production for soil conservation, and may affect soil ecology and plant-parasitic nematodes-to which carrots are very susceptible. This study assessed the impact of cover crops-oats (Avena sativa), radish (Raphanus sativus) cv. Defender, rape (Brassica napus) cv. Dwarf Essex, and a mixture of oats and radish-on plant-parasitic nematodes and soil ecology based on the nematode community in Michigan carrot production systems. Research was conducted at two field sites where cover crops were grown in Fall 2014 preceding Summer 2015 carrot production. At Site 1, root-lesion (Pratylenchus penetrans) and stunt (Tylenchorhynchus sp.) nematodes were present at low population densities (less than 25 nematodes/100 cm3 soil), but were not significantly affected (P > 0.05) by cover crops. At Site 2, P. penetrans population densities were increased (P ≤ 0.05) by 'Defender' radish compared to other cover crops or fallow control during cover crop growth and midseason carrot production. At both sites, there were few short-term impacts of cover cropping on soil ecology based on the nematode community. At Site 1, only at carrot harvest, radish-oats mixture and 'Dwarf Essex' rape alone enriched the soil food web based on the enrichment index (P ≤ 0.05) while rape and radish increased structure index values. At Site 2, bacterivore abundance was increased by oats or radish cover crops compared to control, but only during carrot production. In general, cover crops did not affect the nematode community until nearly a year after cover crop growth suggesting that changes in the soil community following cover cropping may be gradual.

The Effect of Conservation Tillage and Cover Crop Residue on Beneficial Arthropods and Weed Seed Predation in Acorn Squash

Conservation tillage combined with cover crops or mulching may enhance natural enemy activity in agroecosystems by reducing soil disturbance and increasing habitat structural complexity. In particular, weed seed predation can increase with vegetation cover and reduced tillage, indicating that mulches may improve the quality of the habitat for weed seed foraging. The purpose of this study was to quantify the effects of tillage and mulching for conservation biological control in cucurbit fields. The effects of mulch and reduced tillage on arthropods and rates of weed seed loss from arenas were examined in field trials on sandy soils in 2014 and 2015. Experimental factors included tillage and cover crop, each with two levels: strip-tillage or full-tillage, and cover crop mulch (rye residue) or no cover crop mulch (unmulched). Arthropod abundance on the crop foliage was not affected by tillage or cover crops. Contrary to expectations, epigeal natural enemies of insects and rates of weed seed removal either did not respond to treatments or were greater in full-tilled plots and plots without mulch. Our study demonstrates the potential importance of weed seed predators in reducing weed seedbanks in vegetable agroecosystems, and suggests that early-season tillage may not be detrimental to epigeal predator assemblages.

Cover crop mulch and weed management influence arthropod communities in strip-tilled cabbage

Cover crop mulch and weeds create habitat complexity in agricultural fields that may influence arthropods. Under strip-tillage systems, planting rows are tilled and preestablished cover crops can remain between rows. In field experiments conducted in Michigan in 2010 and 2011, a preestablished oat (Avena sativa L.) cover crop was allowed to grow between rows of strip-tilled cabbage and killed at 0, 9-14, or 21-27 d after transplanting (DAT). The effects of herbicide intensity and oat kill date on arthropods, weeds, and crop yield were examined. Two levels of herbicide intensity (low or high) were used to manipulate habitat vegetational complexity, with low weed management intensity resulting in more weeds, particularly in 2010. Oat kill date manipulated the amount of cover crop mulch on the soil surface. Later oat kill dates were associated with higher natural enemy abundance. Reduced herbicide intensity was associated with (1) lower abundance of several key cabbage (Brassica oleraceae L.) pests, and (2) greater abundance of important natural enemy species. Habitats with both later oat kill dates and reduced herbicide intensity contained (1) fewer herbivores with chewing feeding guilds and more specialized diet breadths, and (2) greater abundance of active hunting natural enemies. Oats reduced cabbage yield when oat kill was delayed past 9-14 DAT. Yields were reduced under low herbicide intensity treatments in 2010 when weed pressure was greatest. We suspect that increased habitat complexity associated with oat mulches and reduced herbicide intensity enhances biological control in cabbage, although caution should be taken to avoid reducing yields or enhancing hyperparasitism.

Occurrence of the new invasive insect Contarinia nasturtii (Diptera: Cecidomyiidae) on cruciferous weeds

Contarinia nasturtii (Kieffer) (Diptera: Cecidomyiidae), a common insect pest in Europe and a new invasive pest in North America, causes severe damage to cruciferous crops. In the United States, C. nasturtii was first reported in western New York in 2004. From 2005 to 2007, field surveys were conducted in western New York to investigate the occurrence of C. nasturtii in weeds that might serve as a reservoir for this pest. The results indicate that 12 cruciferous weed species were found in and around commercial vegetable crucifer plantings, and C. nasturtii emergence was detected from most of them. The number of C. nasturtii that emerged from the weeds was low and varied by species, year, and the timing of sampling. Peak emergence from weeds in fallow fields occurred in June. Nonchoice tests in the laboratory showed that significantly fewer larvae were found on cruciferous weeds than on cauliflower plants, although C. nasturtii could lay eggs on the weeds. When weeds and cauliflower plants were simultaneously exposed to C. nasturtii adults for egg laying (choice tests), 97.3% of the C. nasturtii larvae were found on the cauliflower plants 8 d after oviposition, 2.7% on Sinapis arvensis L., and none on the other five weed species tested. Our results suggest that cruciferous weeds can serve as alternative host plants of C. nasturtii but are less suitable than cauliflower. A method of detecting C. nasturtii on weeds and control of C. nasturtii through weed management are discussed.

Survival and performance of the invasive vine Vincetoxicum rossicum (Apocynaceae) from seeds of different embryo number under two light environments

The nonnative vine Vincetoxicum rossicum threatens several ecosystems in the Lower Great Lakes Basin of North America. One feature that may contribute to its invasiveness is the production of some seeds with multiple embryos (polyembryony), which may be beneficial as a bet-hedging strategy in variable environments. However, lower seed reserves per embryo in polyembryonic seeds may entail costs in low-light environments. The effect of seed from three embryonic classes (1, 2, or 3 embryos/seed) on V. rossicum survival and growth was studied under two forest understory light environments: full canopy (shade) or canopy gaps (light) in New York state. Two seedling cohorts were planted, in May 2004 and in May 2005. The survival and growth of seedlings was monitored biweekly for two (2005 cohort) or three (2004 cohort) seasons. For both cohorts, plants grown in canopy shade had reduced survival and growth compared with those grown in gaps. Contrary to expectations, seed embryo number had no effect on the final height, survival, or dry mass of plants in either habitat. Our results suggest that any fitness advantage provided by polyembryony may be habitat (light) dependent and not a general trait that affords V. rossicum a benefit in all habitats colonized.

Seed characteristics of the invasive alien vine Vincetoxicum rossicum are affected by site, harvest date, and storage duration

The alien vine Vincetoxicum rossicum (Kleopow) Barbar. (Asclepiadaceae) is a major concern in natural areas of the Lower Great Lakes Basin. Reproduction in this perennial occurs largely by polyembryonic seeds that mature from August to November. Many seeds produced in autumn germinate the following spring, but the germinability of seeds produced in late summer is unknown. The influence of parent plant light environment on seed characteristics in this species is also poorly understood. We examined the characteristics of V. rossicum seeds harvested in late August and early November 2002 from three habitats in central New York State, USA, differing in light availability. Site had a significant effect on seed weight and germination percentage, but not on the number of embryos germinating per seed or radicle length. Seeds produced in the shaded habitat in August weighed significantly more and had lower germin ability than seeds produced in an adjacent open habitat, but this was not observed in a second open habitat. The probability of germination decreased with seed size for seeds ranging from 2 to 8 mg. For the open sites, fresh seeds produced in August had approximately double the germination percentages of those produced in November. However, for all sites, germination following 18 weeks of cold storage was greatest for seeds harvested in November. The probability of multiple embryos germinating was influenced by seed weight. The nature of this relationship varied by site, but not by harvest date or storage duration. Larger seed size resulted in longer total radicle length after 7 d, regardless of site.Key words: Cynanchum rossicum, maternal environment, pale swallowwort, polyembryony, resource allocation, seed dormancy.