Host location and oviposition of lepidopteran herbivores in diversified broccoli cropping systems

1 Host location and oviposition are crucial steps in the life cycles of insect herbivores. A diversified cropping system may interfere with these processes, ultimately reducing pest colonization of crops and the need for chemical interventions. 2 In the present study, nonhost vegetation was added to a broccoli (Brassica oleracea var. italica) cropping system to determine the effect of plant diversification on host location and colonization of broccoli by Lepidopteran pests. The two diversification strategies applied consisted of a broccoli/potato (Solanum tuberosum) strip crop, made up of 1.65 m (tractor width) replications of two rows of potatoes and two rows of broccoli, and a cereal rye (Secale cereale) cover crop, which formed a sacrificial planting that was killed and rolled flat to minimize weed competition and improve the agronomic performance of the subsequent broccoli crop. 3 Diamondback moth Plutella xylostella eggs, and subsequent larvae and pupae, were less abundant on broccoli with the cover crop, probably due to interference with host location and oviposition processes. The strip crop had no effect. 4 Numbers of cabbage white butterflies Pieris rapae eggs and larvae did not differ among treatments, probably due to the superior ability of these Lepidoptera to visually locate hosts and their active egg‐dispersing behaviour. 5 These results of the present study indicate that the success of crop diversification strategies are contingent on the relative ability of the target herbivore to locate its host plant and the scale of diversity (e.g. the distance between the host and the nonhost plants), rather than diversity itself.     

Measuring host plant selection and retention of Halyomorpha halys by a trap crop

Trap cropping may exploit a pest's dispersal and host selection behavior in order to protect a desired crop. Here, we used a combination of visual sampling, immunomarking, and harmonic radar to assess host plant selection and retention time of the highly mobile and invasive Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), as it moves within and between a polyculture trap crop of sorghum and sunflower, and a bell pepper cash crop. Visual sampling demonstrated no significant differences in H. halys densities across crops, whereas dislodging stink bugs to collect for protein analysis revealed ca. 4× more bugs in the trap crop plants than in the peppers. In total 145 H. halys were collected and of these 6% were doubly marked with proteins, demonstrating that minimal movement occurred between the two planting systems. Tracking tagged H. halys with harmonic radar revealed that the trap crop retained adult H. halys within the plots 1.5× longer and reduced their movement by nearly half compared with bugs released in the pepper cash crop. The data suggest the trap crop of sunflower plus sorghum has the potential to attract and arrest the invasive H. halys, demonstrating that trap cropping may operate as an effective management tool.     

Interactions of maize and Italian ryegrass in a living mulch system: (1) Shoot growth and rooting patterns

It has been demonstrated that the use of living mulches solves some of the environmental problems associated with the conventional cropping of maize (Zea mays L.). However, plant growth and yield are often reduced in such a cropping system. Since shoot competition between the main crop and the cover crop can be avoided by regular cutting of the cover crop, it was hypothesized that decreases in maize growth and yield in a living Italian ryegrass (Lolium multiflorum Lam.) mulch must be related to below ground interactions between the two species and that these may be traced back to the characteristics of their root systems. Two cropping systems, maize grown alone in bare soil (conventional cropping, BS) or together with a living Italian ryegrass mulch (LM), were studied in lysimeters (1.0 m² surface area and 1.1 m depth) placed outdoors, near Zurich Switzerland, for a duration of three years. In the LM treatment a strip, 0.3 m wide, in the center of the plot around the maize row was free of grass. For comparison, an Italian ryegrass (RG) treatment, managed as the LM treatment but without maize plants, was also included in the study. Minirhizotrons (54 mm inner diameter) were horizontally installed at ten soil depths between 0.0 and 1.0 m, perpendicular to the orientation of the maize rows. The development of the maize shoot and the rooting patterns were observed non-destructively. LM strongly modified the maize crop by decreasing growth and duration of the leaf area, and thus biomass and grain yield at harvest by as much as 78 and 72%, respectively. Maximum root densities in the three treatments were observed around the time of maize anthesis. However, BS maize was unable to build up root densities similar to those observed in Italian ryegrass plots at the time of maize sowing. The root densities of the LM and the RG treatments were usually similar. The inability of the maize plants to establish a competitive root system in the LM limits the supply of nutrients and water and therefore reduces growth and yield. Improving the productivity of maize in living mulches will depend on the ability to achieve a better separation of the rooting volumes of the two species, so that specific steps to facilitate the main crop and control the living mulch can be taken.     

填闲种植及其在黄土高原旱作农业区的可行性分析

在主要粮食作物系统休闲期间种植填闲作物可兼顾环境与经济效益。综述了填闲种植对农田土壤水分、养分和后续粮食作物生产力形成等生态过程的影响及其具有的固碳减排、减少淋溶、控制侵蚀等环境与经济效益,并在此基础上从土壤水分限制、养分提高和产量经济效益等角度探讨了填闲种植在黄土高原旱作农业区的可行性,指出今后应重点加强填闲种植系统的水肥生产力形成机制、关键环境效益的形成机理、填闲作物与管理措施选择、生态经济效益评价以及气候变化背景下的填闲种植系统综合效益评估等方面展开定位观测与模型模拟研究,为填闲种植在黄土高原旱作农业区的推广提供科学依据。     

Recent cover crop adoption is associated with small maize and soybean yield losses in the United States

Cover crops are gaining traction in many agricultural regions, partly driven by increased public subsidies and by private markets for ecosystem services. These payments are motivated by environmental benefits, including improved soil health, reduced erosion, and increased soil organic carbon. However, previous work based on experimental plots or crop modeling indicates cover crops may reduce crop yields. It remains unclear, though, how recent cover crop adoption has affected productivity in commercial agricultural systems. Here we perform the first large-scale, field-level analysis of observed yield impacts from cover cropping as implemented across the US Corn Belt. We use validated satellite data products at sub-field scales to analyze maize and soybean yield outcomes for over 90,000 fields in 2019–2020. Because we lack data on cover crop species or timing, we seek to quantify the yield impacts of cover cropping as currently practiced in aggregate. Using causal forests analysis, we estimate an average maize yield loss of 5.5% on fields where cover crops were used for 3 or more years, compared with fields that did not adopt cover cropping. Maize yield losses were larger on fields with better soil ratings, cooler mid-season temperatures, and lower spring rainfall. For soybeans, average yield losses were 3.5%, with larger impacts on fields with warmer June temperatures, lower spring and late-season rainfall, and, to a lesser extent, better soils. Estimated impacts are consistent with multiple mechanisms indicated by experimental and simulation-based studies, including the effects of cover crops on nitrogen dynamics, water consumption, and soil oxygen depletion. Our results suggest a need to improve cover crop management to reduce yield penalties, and a potential need to target subsidies based on likely yield impacts. Ultimately, avoiding substantial yield penalties is important for realizing widespread adoption and associated benefits for water quality, erosion, soil carbon, and greenhouse gas emissions.     

Relative impact of spider predation and cover crop on population dynamics of Erythroneura variabilis in a raisin grape vineyard

Experimental and correlative evidence has steadily mounted over the past 30 years implicating spiders in the suppression of insect herbivore pests in crop fields. A large body of evidence has also shown that increasing agroecosystem vegetation diversity often influences the abundance of herbivores and their natural enemies. In previous experiments, the abundance of several species of spiders on grapevines in a raisin grape vineyard was twofold enhanced in vineyard plots vegetationally diversified with a cover crop. A concomitant reduction in the abundance of the leafhopper pest Erythroneura variabilis Beamer was observed on grapevines in the diversified plots, but a causal relationship was not established. In the present study, we simultaneously manipulated spider densities (in open‐vine spider exclusion and vine‐shoot enclosures) and ground cover to determine their relative impact on E. variabilis population dynamics. Open‐vine spider exclusion resulted in an average 35% increase in the density of E. variabilis the greatest effect with occurring during the first and second leafhopper generations. The negative impact of spiders on E. variabilis densities was corroborated with vine‐shoot enclosure experiments. Under the conditions of the present study, the cover crop per se did not affect the dynamics of E. variabilis populations on grapevines, despite a 1.6‐fold increase in spider densities on vines in cover crop plots, compared with vines in bare ground plots, probably due to insufficient spider enhancement and low overall E. variabilis abundance during the summer months. The cover crop had little effect on vine macronutrient status (and presumably vine water status). While this study provided further support for the hypothesis that vegetation diversity can enhance spider abundance, this enhancement does not always lead to lower pest densities, thus underscoring the complexity and variability that exists in interactions involving cover crop, spiders, and crop plants and their herbivore pests.     

Herbivore response to vegetational diversity: spatial interaction of resources and natural enemies

Vegetational diversity in agricultural systems is predicted to reduce herbivore populations, but we observed the opposite effect: higher nymph population densities of a functionally monophagous herbivore, the squash bug, Anasa tristis (Hemiptera: Coreidae) in a vegetationally diverse squash-bean-corn polyculture than in a squash monoculture. We examined spatial and temporal aspects of squash bug and predator populations in relation to vegetational diversity. Average colonization, oviposition, and mortality rates for the herbivore were similar in monocultures and polycultures. In the polyculture, however, we found that squash bugs eggs were highly aggregated on plants on the outer edges of plots. Predation was also lower on plants near the edges, allowing the large aggregations of eggs found in the polyculture to escape predation and ultimately produce more squash bugs. Spatial interactions between herbivores and natural enemies may underlie some of the general effects of vegetational diversity on herbivores.     

Browsing herbivores improve the state and functioning of savannas: A model assessment of alternative land‐use strategies

Changing climatic conditions and unsustainable land use are major threats to savannas worldwide. Historically, many African savannas were used intensively for livestock grazing, which contributed to widespread patterns of bush encroachment across savanna systems. To reverse bush encroachment, it has been proposed to change the cattle‐dominated land use to one dominated by comparatively specialized browsers and usually native herbivores. However, the consequences for ecosystem properties and processes remain largely unclear. We used the ecohydrological, spatially explicit model EcoHyD to assess the impacts of two contrasting, herbivore land‐use strategies on a Namibian savanna: grazer‐ versus browser‐dominated herbivore communities. We varied the densities of grazers and browsers and determined the resulting composition and diversity of the plant community, total vegetation cover, soil moisture, and water use by plants. Our results showed that plant types that are less palatable to herbivores were best adapted to grazing or browsing animals in all simulated densities. Also, plant types that had a competitive advantage under limited water availability were among the dominant ones irrespective of land‐use scenario. Overall, the results were in line with our expectations: under high grazer densities, we found heavy bush encroachment and the loss of the perennial grass matrix. Importantly, regardless of the density of browsers, grass cover and plant functional diversity were significantly higher in browsing scenarios. Browsing herbivores increased grass cover, and the higher total cover in turn improved water uptake by plants overall. We concluded that, in contrast to grazing‐dominated land‐use strategies, land‐use strategies dominated by browsing herbivores, even at high herbivore densities, sustain diverse vegetation communities with high cover of perennial grasses, resulting in lower erosion risk and bolstering ecosystem services.     

Explaining differences in flea beetle Phyllotreta cruciferae goeze densities in simple and mixed broccoli cropping systems as a function of individual behavior

Diversification of habitat has proved to be an efficient way to reduce insect pest levels in agroecosystems. Some general theories used to explain this fact, such as the natural enemies and the resource concentration hypotheses, do not always clearly apply because, in many cases, pest individuals and population response seem controlled by more specific insect-plant interactions. In non replicated plots, we found substantially lower flea beetle densities in mixed broccoli-Vicia cropping systems compared to broccoli monoculture. These results were consistent with those from controlled experiments reported in the literature. To investigate if beetle behavior was related to such population reduction, the movement behavior of marked individuals of Phyllotreta cruciferae Goeze released in plots composed solely of broccoli plants and of broccoli mixed with Vicia faba or Vicia sativa plants, was followed and analyzed. The mean tenure time of beetles was longer in simple than in mixed cultures. Also, more beetles tended to fly out and leave mixed cultures compared to monoculture. This resulted in faster reduction of artificially introduced flea beetle populations in the mixed systems.Flea beetles landing on cover crop plants spent considerable time entangled in Vicia sativa branches or attempting to reach the upper part of the tall Vicia faba plants from which they could fly away. It is possible that the beetles characteristic movement on these two species of cover crops increased their risk of predation and the time and energy expended before they reached suitable host plants. Nevertheless, it seems that the detected flea beetle emigration rates were more than sufficient to account for the population trends observed.     

Quantitative proteomics to study the response of wheat to contrasting fertilisation regimes

Negative environmental impacts from mineral fertilisers and pesticides used in conventional cropping have raised concern over the sustainability of arable crop production. Organic cropping uses alternatives that avoid many of these negative environmental effects; however, crop yields can be significantly reduced, possibly due to a lower proportion of plant-available nutrients. To gain insights into the molecular effects of organic compared to conventional cropping systems on plant utilisation of nutrients, we used proteomics to analyse winter wheat (Triticum aestivum). Our aim was to investigate the effects of contrasting fertility management and crop protection regimes in organic and conventional cropping systems on the wheat flag leaf proteome and the association between the proteome and physiological traits. Wheat flag leaves were flash-frozen, lyophilised and milled prior to protein extraction (TCA/acetone) and analysed using 2D gel electrophoresis and MALDI-TOF MS. The abundance of 111 protein spots varied significantly between fertilisation regimes. Flag leaf N and P composition were significant drivers of differences in protein spot abundance, including major proteins involved in nitrogen remobilisation, photosynthesis, metabolism and stress response. These results indicate that molecular-based mechanisms are involved in the effect of contrasting cropping systems on nutrient utilisation and wheat grain yield. Using a functional genomics approach, we were able to identify proteins that are linked to causal genes, enabling the potential development of functional molecular markers for crop improvement in nutrient use efficiency.     

Increased Productivity of a Cover Crop Mixture Is Not Associated with Enhanced Agroecosystem Services

Cover crops provide a variety of important agroecological services within cropping systems. Typically these crops are grown as monocultures or simple graminoid-legume bicultures; however, ecological theory and empirical evidence suggest that agroecosystem services could be enhanced by growing cover crops in species-rich mixtures. We examined cover crop productivity, weed suppression, stability, and carryover effects to a subsequent cash crop in an experiment involving a five-species annual cover crop mixture and the component species grown as monocultures in SE New Hampshire, USA in 2011 and 2012. The mean land equivalent ratio (LER) for the mixture exceeded 1.0 in both years, indicating that the mixture over-yielded relative to the monocultures. Despite the apparent over-yielding in the mixture, we observed no enhancement in weed suppression, biomass stability, or productivity of a subsequent oat (Avena sativa L.) cash crop when compared to the best monoculture component crop. These data are some of the first to include application of the LER to an analysis of a cover crop mixture and contribute to the growing literature on the agroecological effects of cover crop diversity in cropping systems.     

Arbuscular mycorrhizal fungi colonization and phosphorus nutrition in organic field pea and lentil

Phosphorus (P) can be low in soil under low input organic management; however, beneficial crop plant associations with arbuscular mycorrhizal fungi (AMF) are known to promote crop nutrition and increase phosphorus uptake. Thus, management strategies that promote AMF associations are particularly desirable for low-input cropping systems. The objectives of this study were to determine the impact of seeding rate on AMF colonization and the impact of AMF colonization on P concentration and uptake by organically grown field pea and lentil. Field experiments examined the impact of three seeding rates of field pea and lentil on P uptake and crop yield. Phosphorus accumulation was examined further in a controlled growth chamber experiment, in which field pea was sown at rates corresponding to those used in the field and harvested at 10-day intervals until 50 days after emergence. In the field, the level of AMF colonization of roots remained at 80% for field pea, while colonization of lentil increased with increasing seeding rates from 77% to 88%. The level of AMF colonization of field pea achieved in the growth chamber after 50 days was 80% for the two highest seeding rates and 60% for the low seeding rate. The rate at which AMF colonization occurred did not vary between treatments. Ultimately, AMF colonization level did not affect P accumulation. In contrast to several previous studies, both field and growth chamber experiments revealed that AMF colonization was not reduced at higher seeding rates. These results suggest that organic farmers may increase seeding rates without adversely affecting P nutrition.     

Control of western tarnished plant bug Lygus hesperus Knight (Hemiptera: Miridae) in California organic strawberries using alfalfa trap crops and tractor-mounted vacuums

A key economic pest of strawberries in California is the western tarnished plant bug, Lygus hesperus Knight (Hemiptera:Miridae). Alfalfa (Medicago sativa L.) is a highly attractive plant host to western tarnished plant bug, and we hypothesized that it can be successfully managed as a trap crop for pest suppression in strawberries. Completely randomized design trap cropping experiments were established on an organic strawberry farm from 2002 to 2004. Western tarnished plant bug adults and nymphs were significantly more abundant in alfalfa trap crops than in comparable edge strawberry rows. Over 3 experimental yr, twice-weekly summer vacuuming of alfalfa trap crops with a tractor-mounted vacuuming device reduced adult and nymph abundance by 72 and 90%, respectively, in trap crops. This summer vacuuming of alfalfa trap crops also significantly reduced damage caused by western tarnished plant bug in associated unvacuumed organic strawberries (June and July 2002, June 2003, and June and July 2004) compared with either an untreated control (2003) or the organic strawberry grower's standard whole field vacuuming treatment. Vacuuming of alfalfa trap crops reduces an organic grower's costs (tractor, tractor fuel, and driver time) by 78% compared with current whole field vacuuming practices. An economic analysis of a whole hectare model indicates that a positive return from the use of vacuumed trap crops could be realized in 2004. The overall potential positive net return for the 3 mo of vacuumed alfalfa trap crop treatments in 2004 was calculated at +$1,829/ha.     

Attraction of Trialeurodes vaporariorum and Bemisia argentifolii to eggplant, and its potential as a trap crop for whitefly management on greenhouse poinsettia

Trap cropping, though promising, has had little evaluation in greenhouses. This study evaluated eggplant, Solanum melongena L. (Solanaceae), as a trap crop for two whitefly species, Trialeurodes vaporariorum (Westwood) and Bemisia argentifolii Bellows & Perring (both Hemiptera: Aleyrodidae), on greenhouse poinsettia, Euphorbia pulcherrima Willd. ex Koltz (Euphorbiaceae). Because the two whitefly species co‐occur in greenhouses, a common trap crop for both whiteflies is desirable. When adults were provided a choice between eggplant and poinsettia in a cage, 60% of B. argentifolii and 98% of T. vaporariorum were observed on eggplant after 3 days. However, when adults were given eggplant after first settling on poinsettia, only 38% of B. argentifolii were later found on eggplant, whereas 95% of T. vaporariorum moved to eggplant. In a greenhouse experiment, eggplant did not affect either the spatial distribution or density of adult B. argentifolii on poinsettias. In contrast, eggplant changed the spatial distribution of T. vaporariorum within 3 days by attracting and retaining the adults. However, the attractiveness of eggplant did not result in a reduced number of T. vaporariorum on poinsettias compared with poinsettias in monoculture. Adult T. vaporariorum mortality was high on poinsettias and this likely caused adult density on poinsettias in monoculture to decrease as fast as that under trap cropping. A simulation model was developed to examine how adult whitefly mortality on poinsettia influences trap cropping effectiveness. When whitefly mortality was high, simulated densities were similar to the experimental data. This reveals an unexpected factor, pest mortality on the main crop, that can influence the relative effectiveness of trap cropping. Our results indicate that eggplant will not work unilaterally as a trap crop for B. argentifolii. For T. vaporariorum, attraction to eggplant might be useful as a trap crop system when whitefly mortality on the main crop is not high.     

Avoidance of natural enemies by adult whiteflies, Bemisia argentifolii, and effects on host plant choice

In this study we asked whether, in the context of a trap crop system, differential predation risks among plants influence host choice patterns of adult whiteflies, Bemisia argentifolii. We investigated whether adult whiteflies avoid natural enemies inhabiting poinsettia (a cash crop) and whether this behavior can be used to increase the movement of whiteflies to cucumber (a trap crop). The potential of cucumber as a trap crop was first evaluated and we found that significantly more whiteflies were attracted to cucumber when the whiteflies were released between the two plants. However, the accumulation of whiteflies on cucumber substantially diminished if the insects had first settled on poinsettia. Under such circumstances, we investigated whether movement of adult whiteflies to cucumber could be increased by creating conditions that would cause the whiteflies that had settled on poinsettia to leave the plant. A mechanical disturbance, consisting of shaking the plant, was first used to test this hypothesis. The shaking caused more whiteflies to leave poinsettia and move onto the trap crop, compared to undisturbed whiteflies. We then asked whether the presence of natural enemies on the cash crop could induce whiteflies to leave the cash crop and move onto the trap crop. Three natural enemies were tested: two predators, Amblyseius swirskii and Delphastus catalinae, and a parasitoid Encarsia formosa. The presence of D. catalinae on poinsettia induced significantly more whiteflies to disperse to cucumber compared to poinsettia with no natural enemies, whereas A. swirskii and E. formosa did not result in a significant increase. Predator avoidance behavior by adult whiteflies should be investigated further in the context of trap cropping and other crop-habitat alterations designed to help manage whitefly abundance.     

Evaluating legume species as alternative trap crops to chickpea for management of Helicoverpa spp. (Lepidoptera: Noctuidae) in central Queensland cotton cropping systems

Mounting levels of insecticide resistance within Australian Helicoverpa spp. populations have resulted in the adoption of non-chemical IPM control practices such as trap cropping with chickpea, Cicer arietinum (L.). However, a new leaf blight disease affecting chickpea in Australia has the potential to limit its use as a trap crop. Therefore this paper evaluates the potential of a variety of winter-active legume crops for use as an alternative spring trap crop to chickpea as part of an effort to improve the area-wide management strategy for Helicoverpa spp. in central Queensland's cotton production region. The densities of Helicoverpa eggs and larvae were compared over three seasons on replicated plantings of chickpea, Cicer arietinum (L.), field pea Pisum sativum (L), vetch, Vicia sativa (L.) and faba bean, Vicia faba (L.). Of these treatments, field pea was found to harbour the highest densities of eggs. A partial life table study of the fate of eggs oviposited on field pea and chickpea suggested that large proportions of the eggs laid on field pea suffered mortality due to dislodgment from the plants after oviposition. Plantings of field pea as a replacement trap crop for chickpea under commercial conditions confirmed the high level of attractiveness of this crop to ovipositing moths. The use of field pea as a trap crop as part of an area-wide management programme for Helicoverpa spp. is discussed.     

Aggregating fields of annual crops to form larger-scale monocultures can suppress dispersal-limited herbivores

An important part of landscape ecology is determining how the arrangement (aggregation or fragmentation) of patches in space influences the population dynamics of foraging organisms. One hypothesis in agricultural ecology is that fine-grain spatial heterogeneity in cropping (many small agricultural fields) should provide better pest control than coarse-grain heterogeneity (few large agricultural fields); this hypothesis has been proposed as an explanation for the increased pest abundance associated with agricultural intensification. However, empirical studies have found mixed support for this hypothesis, and some, surprisingly, demonstrate a strong decrease in pest abundance with increased crop aggregation. We developed a spatially explicit simulation model of pest movement across an agricultural landscape to uncover basic processes that could reduce pest abundance in landscapes with fewer, larger fields. This model focuses on herbivore movement and does not include predation effects or other biological interactions. We found that field aggregation in the model led to severely reduced pest densities and further discovered that this relationship was due to an increased distance between fields and a decreased “target area” in more aggregated landscapes. The features that create a negative relationship between aggregation and pest densities rely on crop rotation and limited dispersal capabilities of the pests. These findings help to explain seemingly counter-intuitive empirical studies and provide an expectation for when field aggregation may reduce pest populations in agro-ecosystems.     

Comparison of management strategies for squash bugs (Hemiptera: Coreidae) in watermelon

Two watermelon pest management practices, a squash trap crop and a standard recommendation using soil-applied carbofuran, were compared using large-scale field plots to assess trap crop suitability as a replacement for the standard in 2000, 2001, and 2002. In both systems, foliar insecticide applications were used to control squash bugs when populations exceeded threshold levels. During 2001 and 2002, a treatment of untreated watermelon was used. Early season adult insects, from seedling to fruit set, are most critical for watermelon. Significantly fewer early adult bugs were found on watermelon in the trap crop than in the standard recommended practice in 1 of 3 yr. In both years, significantly fewer adult squash bugs were found in watermelon in the trap crop than in untreated fields. The standard recommended practice significantly reduced adult squash bugs in watermelon compared with the untreated in 1 of 2 yr. There was no significant correlation of watermelon yield and squash bug density, indicating that squash bug densities were too low to impact yield. Although squash bugs were reduced significantly by the trap crop, marketable watermelon yields were lower in the squash trap crop than in untreated watermelon, suggesting that pest management treatments may interfere with crop productivity factors other than squash bug colonization. Results suggest that mid-season production squash bug should be managed by monitoring populations and using insecticides as needed rather than using at-plant treatment. Further research is needed to compare treatments during early-season production.     

Assessing the performance of pea and lentil at different seeding densities as trap crops for the management of wireworms in spring wheat

Wireworms, the larvae of click beetles (Elateridae), are difficult to manage due to their habitats and behaviour. Wireworms pose a major threat to the wheat crop in the north‐western USA. Seed treatment with neonicotinoids, biological control management and some cultural controls are recommended to manage these pests. Trap cropping is an emerging way to manage wireworms. In strawberry and potato crops, trap cropping has been found effective at attracting wireworms away from the principal crop. An earlier study in the Golden Triangle area of Montana found that pea and lentil could be effective trap crops for managing wireworms in spring wheat. In the present study, experiments were conducted at two locations. The effectiveness of peas and lentils as trap crops with wheat at different seeding densities was assessed [pea at 0, 4, 8, 16 seeds/sq.ft. or 0, 43, 86, 172 seeds/sq.m.; lentil at 0, 6, 12, 18 OR 0, 65, 130, 194 seeds/sq.m.; both with wheat at 0, 11, 22, or 28 seeds/sq.ft. or 0, 120, 230, 300 seeds/sq.m.] in a randomized design where all three crops were intercropped. Both trap crops were found to be effective in protecting wheat at standard seeding rates of 8 seeds/sq.ft. for pea and 12 seeds/sq.ft. for lentils. At these seeding rates, higher numbers of wireworms were found to be attracted to the trap crop, resulting in higher yield (7%–10%) of the associated spring wheat plant stands at 22 seeds/sq.ft. To develop an effective trap crop strategy, the pea–wheat and lentil–wheat spatial patterns that are possible need to be assessed in further field trials. Proper design and evaluation of the cost–benefit ratio of pea and lentil as trap crops are likely to produce good results for wheat crops in Montana.     

Soil Microbial Community Response to Corn Stover Harvesting Under Rain-Fed,No-Till Conditions at Multiple US Locations

Harvesting of corn stover (plant residues) for cellulosic ethanol production must be balanced with the requirement for returning plant residues to agricultural fields to maintain soil structure, fertility, crop protection, and other ecosystem services. High rates of corn stover removal can be associated with decreased soil organic matter (SOM) quantity and quality and increased highly erodible soil aggregate fractions. Limited data are available on the impact of stover harvesting on soil microbial communities which are critical because of their fundamental relationships with C and N cycles, soil fertility, crop protection, and stresses that might be imposed by climate change. Using fatty acid and DNA analyses, we evaluated relative changes in soil fungal and bacterial densities and fungal-to-bacterial (F:B) ratios in response to corn stover removal under no-till, rain-fed management. These studies were performed at four different US locations with contrasting soil-climatic conditions. At one location, residue removal significantly decreased F:B ratios. At this location, cover cropping significantly increased F:B ratios at the highest level of residue removal and thus may be an important practice to minimize changes in soil microbial communities where corn stover is harvested. We also found that in these no-till systems, the 0- to 5-cm depth interval is most likely to experience changes, and detectable effects of stover removal on soil microbial community structure will depend on the duration of stover removal, sampling time, soil type, and annual weather patterns. No-till practices may have limited the rate of change in soil properties associated with stover removal compared to more extensive changes reported at a limited number of tilled sites. Documenting changes in soil microbial communities with stover removal under differing soil-climatic and management conditions will guide threshold levels of stover removal and identify practices (e.g., no-till, cover cropping) that may mitigate undesirable changes in soil properties.