Perennial Cropping Systems Research Articles

Interactions Between the Augmentatively Released Predaceous MiteGalendromus occidentalis(Acari: Phytoseiidae) and Naturally Occurring Generalist Predators

Predatory mite releases can be an effective means of managing spider mites in many perennial cropping systems, yet little research has been performed in annual cropping systems. Herein we evaluate the compatibility of predaceous mite releases with the conservation of resident natural enemies in an annual agroecosystem. We quantify the impact of naturally occurring generalist predators, Geocoris spp. and Orius tristicolor White, and the omnivore Frankliniella occidentalis (Pergande), on the establishment of the western predatory mite Galendromus occidentalis (Nesbitt) and how these predator-predator interactions influence spider mite control. Field experiments showed that in the absence of generalist predators, released predatory mites can establish populations on cotton, increase in abundance through reproductive recruitment, and suppress spider mite populations. Hemipteran predators had a negative impact on predatory mite populations but generally improved spider mite suppression. The presence of F. occidentalis had no impact on predatory mite performance.

United States Department of Agriculture-Agricultural Research Service research on alternatives to methyl bromide: pre-plant and post-harvest.

Methyl bromide is a widely used fumigant for both pre-plant and post-harvest pest and pathogen control. The Montreal Protocol and the US Clean Air Act mandate a phase-out of the import and manufacture of methyl bromide, beginning in 2001 and culminating with a complete ban, except for quarantine and certain pre-shipment uses and exempted critical uses, in January 2005. In 1995, ARS built on its existing programs in soil-borne plant pathology and post-harvest entomology and plant pathology to initiate a national research program to develop alternatives to methyl bromide. The focus has been on strawberry, pepper, tomato, perennial and nursery cropping systems for pre-plant methyl bromide use and fresh and durable commodities for post-harvest use. Recently the program has been expanded to include research on alternatives for the ornamental and cut flower cropping systems. An overview of the national research program is presented. Results from four specific research trials are presented, ranging from organic to conventional systems. Good progress on short-term alternatives is being made. These will be used as the foundation of integrated management systems which begin with pre-plant management decisions and continue through post-harvest processing.

Effects of organic mulches on soil microfauna in the root zone of apple: implications for nutrient fluxes and functional diversity of the soil food web

A variety of organic materials (e.g. composts, paper recycling wastes, hay) can be used as in-row mulches in perennial horticultural cropping systems such as high density apple orchards. As organic materials with variable properties, such mulches can be expected to have variable effects on structure of the soil food web and mineralisation of N and P in the root zone. The overall objectives of this study were to: (1) assess the effects of a selection of organic mulches on the abundance of protozoa and nematode trophic groups; (2) use the model of Hunt et al. [Biol. Fertil. Soils 3 (1987) 393] to assess the implications of changes in microfaunal abundance for microbial turnover and N mineralisation; and (3) determine effects of the mulches on nematode indicators of increased microbial production/turnover and functional diversity of the soil food web. Organic mulch treatments commenced in 1994 and included shredded office paper, municipal biosolids, shredded paper applied over municipal biosolids, shredded paper applied over municipal compost, alfalfa hay, and black polyethylene fabric. The control was conventional tree-row weed management with glyphosate. Biosolids and municipal compost treatments were re-applied in 1997. Protozoan abundance was determined in 1998, 1999 and 2000. Nematode community structure was assessed in 1998, 1999, and twice in 2000. Nematode community parameters evaluated included: abundance of bacterivorous, fungivorous, omnivorous and predacious nematodes; abundance of the root-lesion nematode, Pratylenchus penetrans; absolute and relative abundances of enrichment opportunist nematodes ( Rhabditidae+ Diplogasteridae+ Panagrolaimidae); Simpson’s diversity; evenness; and the indices of nematode community enrichment (EI) and structure (SI) described by Ferris et al. [Appl. Soil Ecol. 18 (2001) 13]. Measurements of the abundance of enrichment opportunists and the EI were evaluated as indicators of enhanced nutrient fluxes. Diversity and the SI were evaluated as indicators of changes in functional diversity of the soil food web. The abundance of protozoa and bacterivorous nematodes, and estimated fluxes of N and P through the microfauna, were greater under all combinations of biosolids or municipal compost and shredded paper than under the control and plastic mulch. The abundance of enrichment opportunist nematodes and the EI were also consistently greater under combinations of biosolids or municipal compost and shredded paper. The abundance of enrichment opportunists and EI were both also correlated with leaf P, providing additional evidence to support the use of these parameters as indicators of enhanced turnover of microbial biomass and nutrients. The SI was greatest under shredded paper and shredded paper applied over municipal compost, and least under municipal biosolids and alfalfa hay. Population densities of P. penetrans were reduced under shredded paper mulch relative to the control and biosolids alone.

Perennial Wheat Germ Plasm Lines Resistant to Eyespot, Cephalosporium Stripe, and Wheat Streak Mosaic.

A perennial wheat cropping system on the Palouse Prairie of eastern Washington may provide an alternative to the Federal Conservation Reserve Program and reduce soil erosion while providing a harvestable crop for growers. Twenty-four perennial wheat germ plasm lines resulting from crosses between wheat and wheatgrass were evaluated under controlled environment conditions for resistance to Wheat streak mosaic virus (WSMV), Cephalosporium gramineum, and Tapesia yallundae (anamorph Pseudocercosporella herpotrichoides var. herpotrichoides). Perennial wheat lines SS452, SS103, SS237, MT-2, and PI 550713 were resistant to all three pathogens. Eight lines (33%) were resistant to WSMV at 21°C and 25°C; AT3425 was resistant to WSMV at 21°C but not at 25°C. Thirteen lines (54%) were highly to moderately resistant to C. gramineum. Thirteen lines (54%) were resistant to T. yallundae in each experiment, but the reactions of four lines differed between experiments. The wheatgrasses Thinopyrum intermedium (PI 264770) and Thinopyrum ponticum (PI 206624) are reported as new sources of resistance to T. yallundae. Perennial wheat must have resistance to these diseases in order to be feasible as a crop in the Pacific Northwest.

Habitats and Management Associated with Common Ground Beetles (Coleoptera: Carabidae) in a Michigan Agricultural Landscape

The associations between common ground beetles and habitat and management characteristics were studied in an agricultural landscape that comprised part of the Long-Term Ecological Research site in southwestern Michigan. The 42-ha area included 7 habitat treatments, which represented 4 annual cropping systems in wheat, Triticum aestivum L., corn, Zea mays L., soybean, Glycine max (L.) Merr., rotation; 2 perennial crop systems (alfalfa, Medicago sativa L., and Populus ); and a native succession habitat. Pitfall traps were used to sample adult ground beetles during the growing seasons of 1994 and 1995. Four species numerically dominated the trap catches and together accounted for 87% of the total specimens collected: Cyclotrachelus sodalis (LeConte), Poecilus lucublandus (Say), Pterostichus melanarius (Illiger), and Agonum placidum (Say). Differences in representation of these common species were most pronounced between perennial and annual plant systems. However, tillage also influenced the relative abundance of these species. The adult-overwintering, spring-breeding species, P. lucublandus and A. placidum , were most common in the annual crop habitats, particularly those under conventional tillage. Catch numbers of these 2 species were correlated positively, suggesting similar habitat preferences or responses to management practices. In contrast, C. sodalis , a larval-overwintering, autumn breeder, was most common in the perennial crop systems and the annual crop system receiving no tillage. The exotic species P. melanarius showed the least response to the agricultural habitat treatments but was more abundant in managed crop habitats compared with the unmanaged succession habitat. Cluster analysis based on these 4 species indicated that plant type and tillage were important in distiniquishing the carabids of these habitats. The potential implications of these findings for conserving or enhancing ground beetle populations in agricultural systems are discussed.

Soil Aggregation and Fungal and Bacterial Biomass under Annual and Perennial Cropping Systems

AbstractUnderstanding the mechanisms controlling crop effects on soil aggregation is necessary to develop sustainable soil management practices. Changes in soil aggregation, carbohydrates, and fungal vs. bacterial biomass were monitored following a shift from fallow (bare soil) to various cropping systems. Faba bean (Vicia faba L.) and wheat (Triticum aestivum L.) were used as annual cropping systems, while alfalfa (Medicago sativa L.), timothy (Phleum pratense L.), bromegrass (Bromus inermis L.), and reed canarygrass (Phalaris arundinacea L.) were used as perennial cropping systems. Crops were established in spring 1989, on a silty clay loam (fine, mixed, frigid Typic Dystro‐chrept) and a clay loam (fine‐loamy, mixed, frigid Typic Humaquept) near Québec City (Canada). After three growing seasons, the mean‐weight diameter of water‐stable aggregates (MWD) was higher under reed canarygrass (2.26 mm in the clay loam and 2.45 mm in the silty clay loam) and timothy (2.13 and 2.26 mm) than under faba bean (1.92 and 1.89 mm) or wheat (2.06 and 1.57 mm). Intermediate values were found under alfalfa and bromegrass. Changes in MWD were not correlated with microbial biomass C. Acid‐hydrolyzable carbohydrates correlated with MWD in the silty clay loam (r2 = 0.42**) but the relationship decreased with higher carbohydrate levels in the clay loam (r2 = 0.05). Close correlations were found between MWD and both fungal glucosamine (r2 = 0.68***, soils combined) and bacterial muramic acid (r2 = 0.48***). Changes in MWD were mostly reflected in aggregates >2 mm, and the close relationship with fungal glucosamine suggests that fungi played a dominant role in soil macroaggregation. Measurement of muramic acid and glucosamine is proposed as a potential approach to compare bacterial vs. fungal contributions to soil aggregation.

Economic Thresholds for Phytophthora Foot Rot of Citrus Using Estimates of Value of Tree Loss and Chemical Control Costs

Economic thresholds (ET) for Phytophthora foot rot of young citrus trees planted at three tree spacing densities were calculated as the number of trees/acre/year that must be lost to offset the costs of fungicide treatment. Thresholds were based on the present value of lost trees during the first four years of orchard establishment and the cost of annual and cumulative annual fungicide applications of fosetyl Al or metalaxyl. Economic thresholds for the first two years after orchard establishment ranged from 1.5% to 2.6% and 0.6% to 2.4% annual tree losses/acre to offset treatment costs of metalaxyl and fosetyl Al, respectively. Tree losses/acre had to exceed 2.2% to 3.9% and 1.9% to 5.2% to offset treatment costs of metalaxyl and fosetyl Al, respectively, in yr 3 and 4. Routine treatment programs for foot rot were not recommended because annual economic tree losses to foot rot rarely exceed fungicide treatment costs on a cumulative annual basis. The adaptibility of ET determination to a perennial cropping system where pest population densities and pest aggressiveness can be substituted for with a spatial unit (tree or whole plant) is discussed.