Catherine Eastman

The influence of organic transition systems on beneficial ground-dwelling arthropods and predation of insects and weed seeds

The influence of farm management practices on ground-dwelling natural enemy communities and predation of insects and weed seeds was investigated over the first 2 years of the transition from conventional to organic production. Three transition strategies were selected that differed in their management and input intensities, and were characteristic of pasture/ley systems (low intensity), cash grain systems (intermediate intensity), and vegetable production (high intensity). Beneficial arthropods (insectivores and granivores) were monitored using pitfall (arthropod activity) and quadrat (arthropod density) samples. The frequency of predation on restrained larvae of Galleria mellonella and the species observed feeding were recorded. Weekly removal rates of weed seeds representative of abundant species at our site were monitored over a 3-week period during fall. Management intensity affected the activity and abundance of biological control agents. In year two of the transition, biological control agent densities were higher in the low-intensity treatment than in the other two treatments, but activity of insectivores and granivores was reduced in this treatment relative to the higher intensity systems. The patterns in the abundances of biological control agents may be explained by habitat stability within the different cropping systems. Quadrat samples were strongly correlated with the insectivory index, although pitfall samples were not. Insectivory rates were highest (>80% of G. mellonella larvae) in the low-intensity treatment. Predation patterns over a 17-h period differed substantially among the management treatments, indicating behaviorally distinct insectivore communities. Seed removal was also highest in the low-intensity treatment. We conclude that low-intensity cropping systems are most favorable to the abundance and function of beneficial ground-dwelling arthropod communities (insectivores and granivores) during the transition process.

Yield and Quality Constraints of Cabbage Planted in Rye Mulch

ABSTRACT The impact of cereal rye (Secale cereale L.) mulch or a mixture of rye mulch and red clover (Trifolium pratense L.) on weeds, insect pests and diseases of cabbage (Brassica oleracea var. capitata L. cv. ‘Market Prize’) was investigated. Autumn-planted rye was killed the following spring either with glyphosate and then mowed and left as a plant residue, or by mowing the rye and then seeding red clover into the rye residue. Initial suppression of most weed species by rye or rye/clover mulch was similar to that resulting from conventional tillage where trifluralin was used. Supplemental weed control was necessary in the rye plots later in the season. Early dandelion (Taraxacum officinale Weber) infestation from windblown seeds was a problem in rye mulch in 1995. Redroot pigweed (Amaranthus retroflexus L.) and velvetleaf (Abutilon theophrasti Medicus) were significantly reduced by the rye mulch. Cabbage grown in rye mulch had lower insect pest populations than cabbage under conventional tillage. The ...

Translocation and multiplication ofSpiroplasma citri in turnip (Brassica rapa)

Following inoculation of designated leaves of turnip plants withSpiroplasma citri byCirculifer tenellus, spiroplasmas were cultured first from roots (four days) and then from youngest leaves (eight days), but almost never from oldest leaves. In experiments using enzyme-linked immunosorbent assay to monitor changes in titer in turnip leaves during the course of plant infection,S. citri was detected seven days after inoculation and reached peak titers of 1010–1011 colony-forming units/g 12–20 days after inoculation, declining thereafter. Spiroplasmas were detected 5–9 days before symptoms appeared.