Because the use of synthetic agrochemicals is generally not allowed in organic crop production systems, growers rely on natural substances and processes, such as microbial control, to suppress insect pests. Reduced tillage practices are associated with beneficial soil organisms, such as entomopathogenic fungi, that can contribute to the natural control of insect pests. The impacts of management, such as tillage, in a cropping system can affect soil biota in the current season and can also persist over time as legacy effects. We investigated the in-season and legacy effects of soil management in four, three-year organic feed grain and forage production systems that varied in number and intensity of soil disturbances on the relative prevalence of the entomopathogenic fungus, Metarhizium robertsii. Employing sentinel bait assays with Tenebrio molitor and Galleria mellonella, we found that relative prevalence, measured as infection rate of sentinel insects, was lowest in systems utilizing a shallow high-speed disk (G. mellonella: 14%; T. molitor: 23%) in the current and previous seasons compared to systems that included inversion and non-inversion tillage (G. mellonella: 22%; T. molitor: 34%) or no-till planting (G. mellonella: 21%; T. molitor: 30%,). There was no difference in prevalence in systems that included the use of a high-speed disk compared to a perennial hay crop (G. mellonella: 16%; T. molitor: 28%). There were no negative legacy effects of inversion tillage on the prevalence of M. robertsii in subsequent crops. Sentinel assays with G. mellonella (19%) produced overall lower estimates of relative prevalence of M. robertsii than T. molitor (29%) but the association of relative prevalence with environmental variables was greater in assays with G. mellonella. We suggest that the use of occasional inversion tillage is not damaging to populations of M. robertsii in soil and that surveys using assays with multiple sentinel insect species will improve our ability to understand the effects of agricultural practices on entomopathogenic fungi.

Organic growers rely largely on cultural and biological control to manage pest populations and often use soil disturbance with inversion tillage to manage pests and weeds, incorporate crop residues and fertility amendments, and create seedbeds. Reduced-tillage systems are often associated with greater populations of insect generalist predators, as tillage can directly and indirectly disrupt predators and their activity. We investigated the in-season and legacy effects of soil disturbance in three organic feed grain and one forage production systems that varied in frequency and intensity of disturbance on epigeal predation rates on larval waxworms, Galleria mellonella L., and foliar predation rates on eggs of the western bean cutworm, Striacosta albicosta Smith, and European corn borer, Ostrinia nubilalis (Hübner), by arthropod natural enemies. The experimental site included three annual feed grain production systems comprised of a corn, Zea mays L., soybean, Glycine max (L.) Merr., and wheat Triticum aestivum L. sequence and one forage production system represented by a biculture of alfalfa, Medicago sativa L. and orchardgrass, Dactylis glomerata L. We also measured damage to corn ears from naturally occurring lepidopteran pests and corn yield. The epigeal predation rate on sentinel waxworms in the system managed predominantly with reduced tillage (64 ± 6.4%) was significantly greater than in the systems managed predominantly with inversion tillage (44 ± 5.5%) or with a shallow high-speed disk (48 ± 5.1%). There was no effect of intensity or frequency of soil disturbance on foliar predation or foliar predator community composition in corn. Damage to corn ears from lepidopteran pests was greater in the system managed predominantly with a shallow high-speed disk (51 ± 4.4% damaged ears) compared to systems predominantly managed with inversion tillage (35 ± 4.3%) or no-till planting (31 ± 1.4%). There was no difference in corn yield across systems, but corn yield variability was greatest in the reduced tillage system. We suggest that the occasional use of inversion tillage with a moldboard plow may not have lasting detrimental effects on foliar or epigeal predation rates on arthropod pests in annual organic grain production systems.

Cover crop mixtures provide ecosystem services, but species' relative abundance in mixtures is challenging to manage. We report on an 11-year experiment where our main objective was to use species selection and seeding rate adjustments over time to increase the evenness of mixtures. Replacing rye with triticale and red clover with crimson clover while adjusting seeding rates resulted in mixtures that were more even and closer to the desired composition (greater legume biomass) than the original communities. For example, the first version of a six-species mixture produced biomass composed of 81% grass, 5% brassica, and 14% legume, but after adjustments, subsequent versions contained 25% grass, 10% brassica, and 65% legume biomass. Substituting a less aggressive grass for a dominant grass and a more aggressive legume for a weaker legume better balanced the mixture to meet farmers' ecosystem service goals, as did reducing the proportion of grass seed in the mixtures.

Seedcorn maggot, Delia platura (Meigen) (Diptera: Anthomyiidae), is an economically important early-season pest of corn and soybean in the United States. Adult seedcorn maggot is attracted to decomposing plant residues for oviposition, creating potential management issues where growers typically use tillage to incorporate fertility amendments and to create a seedbed. The use of growing degree-day models to time planting dates is an important tool for effectively managing this pest, but their use has not been examined in organic crop production. Here, we report the results of experiments to determine the effects of cover crops, tillage, and relative planting date on seedcorn maggot in corn and soybean in 2 experiments: The first during the transition to organic from conventional management and the second during the 3 yr following organic certification in central Pennsylvania, United States. Overall, delaying the planting date by 1-2 wk reduced fly emergence in corn, but not in soybean in both experiments. Seedcorn maggot emergence was also consistently greater in corn than in soybean, with 6 times more flies in corn than in soy. About 15 times more seedcorn maggot flies emerged from corn in treatments in which cover crops were managed with tillage compared to treatments in which cover crops were terminated with a roller-crimper followed by no-till planting of corn. Fly emergence was negatively related to the proportion of legumes in the cover crop mixture preceding corn. These results can help inform soil, cover crop, and crop decisions for organic growers in the Mid-Atlantic United States.

Plants face many environmental challenges and have evolved different strategies to defend against stress. One strategy is the establishment of mutualistic associations with endophytic microorganisms which contribute to plant defense and promote plant growth. The fungal entomopathogen Metarhizium robertsii is also an endophyte that can provide plant-protective and growth-promoting benefits to the host plant. We conducted a greenhouse experiment in which we imposed stress from deficit and excess soil moisture and feeding by larval black cutworm (BCW), Agrotis ipsilon, to maize plants that were either inoculated or not inoculated with M. robertsii (Mr). We evaluated plant growth and defense indicators to determine the effects of the interaction between Mr, maize, BCW feeding, and water stress. There was a significant effect of water treatment, but no effect of Mr treatment, on plant chlorophyl, height, and dry biomass. There was no effect of water or Mr treatment on damage caused by BCW feeding. There was a significant effect of water treatment, but not Mr treatment, on the expression of bx7 and rip2 genes and on foliar content of abscisic acid (ABA), 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), and gibberellin 19 (GA19), whereas GA53 was modulated by Mr treatment. Foliar content of GA19 and cis-Zeatin (cZ) was modulated by BCW feeding. In a redundancy analysis, plant phenology, plant nutrient content, and foliar DIMBOA and ABA content were most closely associated with water treatments. This study contributes toward understanding the sophisticated stress response signaling and endophytic mutualisms in crops.

To defend against damage from environmental stress, plants have evolved strategies to respond to stress efficiently. One such strategy includes forming mutualist relationships with endophytes which confer stress-alleviating plant defensive and growth promoting effects. Metarhizium robertsii is an entomopathogen and plant-protective and growth-promoting endophyte. To determine the context dependency of the relationship between M. robertsii and maize, we conducted a greenhouse experiment that imposed stress as deficit and excess soil moisture on maize plants which were inoculated or not inoculated with M. robertsii and measured plant growth and defense indicators. Maize height and endophytic root colonization by M. robertsii were positively correlated in the deficit water treatment, but not in the adequate or excess water treatments. The relative expression of ZmLOX1 in the jasmonic acid (JA) biosynthesis pathway was significantly greater in M. robertsii-inoculated than in non-inoculated plants, but water treatment had no effect. There was significant interaction between M. robertsii and water treatments on foliar concentrations of JA and jasmonoyl isoleucine (JA-ILE), suggesting that water stress impacts M. robertsii as a modulator of plant defense. Water stress, but not inoculation with M. robertsii, had a significant effect on the expression of MYB (p = 0.021) and foliar concentrations of abscisic acid (p<0.001), two signaling molecules associated with abiotic stress response. This study contributes toward understanding the highly sophisticated stress response signaling network and context dependency of endophytic mutualisms in crops.

Fungi in the genus Metarhizium (Hypocreales: Clavicipitaceae) are insect-pathogens and endophytes that can benefit their host plant through growth promotion and protection against stresses. Cochliobolus heterostrophus (Drechsler) Drechsler (Pleosporales: Pleosporaceae) is an economically-significant phytopathogenic fungus that causes Southern Corn Leaf Blight (SCLB) in maize. We conducted greenhouse and lab-based experiments to determine the effects of endophytic M. robertsii J.F. Bisch., Rehner & Humber on growth and defense in maize (Zea mays L.) infected with C. heterostrophus. We inoculated maize seeds with spores of M. robertsii and, at the 3 to 4-leaf stage, the youngest true leaf of M. robertsii-treated and untreated control plants with spores of C. heterostrophus. After 96 h, we measured maize height, above-ground biomass, endophytic colonization by M. robertsii, severity of SCLB, and expression of plant defense genes and phytohormone content. We recovered M. robertsii from 74% of plants grown from treated seed. The severity of SCLB in M. robertsii-treated maize plants was lower than in plants inoculated only with C. heterostrophus. M. robertsii-treated maize inoculated or not inoculated with C. heterostrophus showed greater height and above-ground biomass compared with untreated control plants. Height and above-ground biomass of maize co-inoculated with M. robertsii and C. heterostrophus were not different from M. robertsii-treated maize. M. robertsii modulated the expression of defense genes and the phytohormone content in maize inoculated with C. heterostrophus compared with plants not inoculated with C. heterostrophus and control plants. These results suggest that endophytic M. robertsii can promote maize growth and reduce development of SCLB, possibly by induced systemic resistance mediated by modulation of phytohormones and expression of defense and growth-related genes in maize.

Reducing the intensity and frequency of tillage in organic grain production systems is likely to produce several agronomic, economic, and environmental tradeoffs. We evaluated four organic corn (Zea mays L.) sequences in a 3-yr, full-entry organic cropping systems experiment. Two sequences included a hairy vetch (Vicia villosa Roth)/triticale (Triticale hexaploide Lart.) mixture sown after spelt harvest that differed in tillage practices (no-till [NT], conventional) before corn and corn harvest management (silage, grain). Two sequences included a red clover (Trifolium pretense L.)/timothy (Phleum pretense L.) mixture frost-seeded into spelt in late winter followed by conventional tillage preceding corn and either silage or grain harvest. Our results showed that late-season weed biomass did not differ across alternative sequences, although both tillage and NT corn production resulted in high in-row weed pressure in different years. Cover crop management prior to tillage-based corn production did not affect grain yields, but NT silage production resulted in lower yields compared with the tilled sequence. Corn silage yields were positively correlated with corn populations in both tilled and NT systems. The NT sequence lowered tillage frequency and intensity by 39 and 52%, respectively, compared with tillage-based corn production as measured using established metrics, including the soil disturbance rating, but did not significantly influence labile carbon pools. Sequences using underseeded red clover resulted in higher net returns compared with hairy vetch sequences due to additional income from fall forage harvests.

Fungi in the genus Metarhizium are entomopathogens that can establish endophytically inside plants and benefit them through growth promotion and pest suppression. Lab- and greenhouse-based experiments were conducted to examine the effects of endophytic M. robertsii colonization in maize (Zea mays) on fall armyworm (FAW) (Spodoptera frugiperda). Maize seeds were inoculated with M. robertsii conidia, plants were evaluated for endophytic colonization, and then relative growth rate (RGR) and feeding behavior of larval FAW fed leaves from inoculated and uninoculated maize were measured. Endophytic M. robertsii was recovered from 60.5% of inoculated maize. In feeding bioassays, the RGR of larval FAW fed leaves of inoculated maize was no different than the RGR of larvae fed leaves from uninoculated maize. The RGR of larval FAW was positively correlated with the proportion of endophytic colonization of maize leaf and root tissues; however, in feeding assays, FAW larvae demonstrated no preference for consuming leaf tissue from inoculated or uninoculated maize. The proportion of leaf tissue consumed was unrelated to the proportion of M. robertsii-colonization of leaf or root tissue from source plants. We discuss possible reasons why FAW were not affected by endophytic M. robertsii in the context of assay methodology, FAW physiology, and induced maize defenses.

Agricultural production is increasingly viewed as more than a source of food, feed, fiber and fuel, but also as a system of interdependent biotic and abiotic components that interact to produce ecosystem services and disservices. Weeds and insects are commonly viewed as non-desirable components of agroecosystems that should be managed. However, weeds can also provide benefits to cropping systems, such as providing resources and habitat to pollinators and other beneficial arthropods. This review on weed-insect interactions in annual cropping systems focuses on functional interactions within the context of regulating and supporting ecosystem services and disservices. Regulating services are those that act as regulators of the environment, such as weed-insect interactions that contribute to the regulating services of pollination and biological control, but also contribute to the disservices of crop and cover crop seed predation, and maintenance of insect pests and insect-transmitted phytopathogens. Supporting services include habitat and biodiversity that are necessary for the production and maintenance of the other types of ecosystem services. Here we review the impacts of weed-insect interactions as a component of biodiversity. We conclude by identifying some knowledge gaps that hinder our understanding of trade-offs when seeking to improve net positive ecosystem services in annual cropping systems. [GRAPHICS]

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.

Organic grain producers are interested in interseeding cover crops into corn (Zea mays L.) in regions that have a narrow growing season window for post-harvest establishment of cover crops. A field experiment was replicated across 2 years on three commercial organic farms in Pennsylvania to compare the effects of drill- and broadcast-interseeding to standard grower practices, which included post-harvest seeding cereal rye (Secale cereale L.) at the more southern location and winter fallow at the more northern locations. Drill- and broadcast-interseeding treatments occurred just after last cultivation and used a cover crop mixture of annual ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] + orchardgrass (Dactylis glomerata L.) + forage radish (Raphanus sativus L. ssp. longipinnatus). Higher mean fall cover crop biomass and forage radish abundance (% of total) was observed in drill-interseeding treatments compared with broadcast-interseeding. However, corn grain yield and weed suppression and N retention in late-fall and spring were similar among interseeding treatments, which suggests that broadcast-interseeding at last cultivation has the potential to produce similar production and conservation benefits at lower labor and equipment costs in organic systems. Post-harvest seeding cereal rye resulted in greater spring biomass production and N retention compared with interseeded cover crops at the southern location, whereas variable interseeding establishment success and dominance of winter-killed forage radish produced conditions that increased the likelihood of N loss at more northern locations. Additional research is needed to contrast conservation benefits and management tradeoffs between interseeding and post-harvest establishment methods.

Reducing the intensityand frequency of tillage in an organic grain system requires an emphasis on utilizing ecological processes to manage pests and fertility. Cover crop-based, organic rotational no-till (CCORNT) corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production systems utilize cover crop surface mulch as the primary within-season weed control tactic. Winter-sown cereal rye (Secale cereale L.) was grown preceding soybean and hairy vetch (Vicia villosa Roth) mixtures before corn. We conducted a 3-yr cropping systems experiment in Delaware, Maryland, and Pennsylvania to evaluate crop management (planting date) and integrated weed management (IWM) tactics for CCORNT corn and soybean production in a corn-soybean-winter wheat (Triticum aestivum L.) rotation during the transition to organic. Corn and soybean yields were sensitive to planting date, but optimal planting dates differed among locations. Delayed cover crop termination did not consistently increase total cover crop biomass production or reduce weed biomass levels. High-residue cultivation reduced total weed biomass across locations, but this IWM tactic produced variable results on cash crop yields. Total weed biomass was negatively correlated to soybean yields but did not influence corn yields. At the Pennsylvania location, delaying corn planting dates was positively correlated with predatory athropod activity-density, which was positively correlated with corn populations. Assessment of CCORNT practices on short-term soil health indicators (labile carbon, aggregate stability, entomopathogenic fungi) at the Pennsylvania location produced variable results. Adaptive pest management strategies will need to be used in CCORNT systems within the Mid-Atlantic United States.

Fungi in the genus Metarhizium (Hypocreales: Clavicipitaceae) are entomopathogens that can establish as endophytes and benefit their host plant through growth promotion and suppression of insect pests. This study focuses on the Metarhizium-insect-plant interactions in greenhouse- and lab-based experiments. We inoculated seeds of maize (Zea mays L.) with spores of Metarhizium robertsii and evaluated V4 maize for endophytic colonization of leaves and roots, measured plant height, chlorophyll content and above-ground biomass, and relative growth rate of black cutworm, Agrotis ipsilon (Hufnagel). In addition, we studied the expression of selected plant defense genes. We recovered M. robertsii from 91% of plants grown from inoculated seeds. We detected M. robertsii more frequently in roots compared with leaves. Colonized plants were greater in plant height and above-ground biomass compared to control plants. Leaf tissue from colonized plants showed changes in the expression of genes involved in plant defense. In feeding bioassays, the relative growth rate of black cutworm was lower on leaves from endophytic plants compared to control plants. Few other studies have examined the defense response of plants to colonization by Metarhizium spp. Endophytic colonization of maize plants by M. robertsii promoted plant growth and altered defense gene expression in maize, and suppressed growth rate of black cutworm larvae.

Frequent and intensive tillage can have negative effects on soil, including increasing risk of erosion, oxidizing organic matter, and disrupting life cycles of soil organisms. Even though tillage can negatively affect soil, this practice is still used across much of the world to prepare fields for planting and to manage pests. Farmers who have adopted reduced-tillage systems can struggle with a suite of insect and mollusc pests; however, reducing the frequency and intensity of tillage may increase predator populations and improve biological control. To better evaluate the effects of reduced-tillage practices (e.g., no-fill, harrowing, shallow disking) on the abundance of invertebrate pests and natural enemies relative to high-disturbance tillage practices (e.g., moldboard plowing), we conducted a meta-analysis of studies published between 1983 and 2017. We tested the hypotheses that 1) pest herbivore and arthropod predator abundances are greater where tillage is reduced, 2) soil-associated invertebrates are more responsive to tillage compared with foliar invertebrates, and 3) medium-disturbance tillage practices would have an intermediate effect on pests and arthropod predators relative to high- and no-disturbance practices. We found that insect and slug pests were not more abundant in reduced-tillage systems than in high-disturbance tillage systems. Pest herbivores that spend part of their life-cycle in the soil followed this pattern, but foliar pests were more abundant in systems with more intense tillage practices. The abundance of arthropod predators that spend part of their life-cycle in the soil was significantly lower in high-disturbance tillage systems compared with no-disturbance tillage systems, regardless of the intensity of the disturbance, though predators in general were similar in abundance across tillage intensifies.

In organic agronomic cropping systems, the use of synthetic insecticides and transgenic varieties are prohibited and producers rely mainly on biological control, tillage, crop rotation, and other cultural practices to manage pests. We measured damage to organic corn (Zea mays L.) from multiple invertebrate pests, including slugs (Gastropoda: Mollusca), European corn borer (Ostrinia nubilalis Hübner), corn earworm (Helicoverpa zea Boddie), and fall armyworm (Spodoptera frugiperda Smith), early and late in the growing season in four cropping systems that varied in tillage frequency and intensity and in winter cover crop species. Specific management tactics included two cover crop mixtures preceding corn, the use of a roller-crimper or tillage to terminate cover crops preceding corn, and the establishment of interseeded cover crops after corn emergence. Prevalence of early-season damage was high, but severity of damage was very low and unrelated to corn yield. The proportion of corn plants affected by chewing pests early in the season was lower in plots in which tillage compared to a roller-crimper was used to terminate cover crops. Cropping system did not affect the numbers of late-season caterpillar pests or corn yield. Predation by natural enemies appeared to effectively maintain damage from chewing pests below yield-damaging levels. These results support the inclusion of winter and interseeded cover crops in organic agronomic crop rotations to gain environmental benefits without increasing risks of damage by insect pests.

Cover crop mixtures can provide multiple ecosystem services but provisioning of these services is contingent upon the expression of component species in the mixture. From the same seed mixture, cover crop mixture expression varied greatly across farms and we hypothesized that this variation was correlated with soil inorganic nitrogen (N) concentrations and growing degree days. We measured fall and spring biomass of a standard five-species mixture of canola (Brassica napus L.), Austrian winter pea (Pisum sativum L), triticale (x Triticosecale Wittm.), red clover (Trifolium pratense L.) and crimson clover (Trifolium incarnatum L.) seeded at a research station and on 8 farms across Pennsylvania and New York in two consecutive years. At the research station, soil inorganic N (soil iN) availablity and cumulative fall growing degree days (GDD) were experimentally manipulated through fertilizer additions and planting date. Farmers seeded the standard mixture and a "farm-tuned" mixture of the same five species with component seeding rates adjusted to achieve farmer-desired services. We used Structural Equation Modeling to parse out the effects of soil iN and GDD on cover crop mixture expression. When soil iN and fall GDD were high, canola dominated the mixture, especially in the fall. Low soil iN favored legume species while a shorter growing season favored triticale. Changes in seeding rates influenced mixture composition in fall and spring but interacted with GDD to determine the final expression of the mixture. Our results show that when soil iN availability is high at the time of cover crop planting, highly competitive species can dominate mixtures which could potentially decrease services provided by other species, especially legumes. Early planting dates can exacerbate the dominance of aggressive species. Managers should choose cover crop species and seeding rates according to their soil iN and GDD to ensure the provision of desired services.

Cover cropping is proposed to enhance soil microbial diversity and activity, with cover crop type affecting microbial groups in different ways. We compared fungal community compositions of bulk soils differing by cover crop treatment, season, and edaphic properties in the third year of an organic, conventionally tilled rotation of corn-soybean-wheat planted with winter cover crops. We used Illumina amplicon sequencing fungal assemblages to evaluate effects of nine treatments, each replicated four times, consisting of six single winter cover crop species, a three-species mixture, a six-species mixture, and fallow. Alpha-diversity of fungal communities was not affected by cover crop species identity, function, or diversity. Sampling season influenced community composition as well as genus-level abundances of arbuscular mycorrhizal (AM) fungi. Cover crop mixtures, specifically the three-species mixture, had distinct AM fungal community compositions, while cereal rye and forage radish monocultures had unique Core OTU compositions. Soil texture, pH, permanganate oxidizable carbon, and chemical properties including Cu, and P were important variables in models of fungal OTU distributions across groupings. These results showed how fungal composition and potential functions were shaped by cover crop treatment as well as soil heterogeneity.