Eric B. Brennan

Stale Seedbed Techniques for Organic Vegetable Production

Weed control in organic vegetable production systems is challenging and accounts for a large portion of production costs. Six methods to prepare a stale seedbed were compared on certified and transitional organic land in Salinas, CA, in 2004. Weed control operations occurred on raised beds 2 to 3 d before planting baby spinach or a simulated vegetable planting. A flamer and an herbicide application of 10% v/v of a clove oil mixture (45% v/v clove oil) at 280 L/ha (iteration 1) or 15% v/v of a clove oil mixture (45% clove oil) at 467 L/ha (iterations 2 and 3) were used to control weeds without disturbing the soil. Top knives on a sled, a rolling cultivator, and a rotary hoe were used to control weeds while tilling the bed top. A bed shaper–rototiller combination was also used, which tilled the entire bed. Broadleaf weed control was 36% with clove oil, 63% with the rotary hoe, and significantly higher (87 to 100% control) with the remaining treatments in iteration 1. Broadleaf weed control was consistently lower (72 to 86% control) with the flamer than all other treatments (95 to 100% control) in iterations 2 and 3. The difference between sites can probably be attributed to differences in weed size. The flamer and the clove oil herbicide had the lowest number of weeds emerging with the crop following stale seedbed formation. The most expensive technique was clove oil at

Characterization and Epidemiology of Outbreaks of Impatiens necrotic spot virus on Lettuce in Coastal California

1,372/ha. The estimated cost of forming the stale seedbed with the remaining weed management tools ranged from

Weed Management in a Legume-Cereal Cover Crop with the Rotary Hoe1

10 to

Can We Grow Organic or Conventional Vegetables Sustainably Without Cover Crops

43/ha. Nomenclature: Spinach, Spinacia oleracea L. #3 SPQOL. Additional index words: Flaming, cultivation, weed emergence, irrigation, stale seedbeds, vegetables. Abbreviations: USDA-ARS, U.S. Department of Agriculture–Agricultural Research Service.

Soil microbial biomass and enzyme data after six years of cover crop and compost treatments in organic vegetable production

California is the leading producer of lettuce (Lactuca sativa) for the United States and grows 77% of the countrys supply. Prior to 2006, coastal California lettuce was only periodically and incidentally infected by a single tospoviruses species: Tomato spotted wilt virus (TSWV). However, beginning in 2006 and continuing through 2012, severe outbreaks of disease caused by Impatiens necrotic spot virus (INSV) have affected the coastal lettuce crop, though TSWV was also present. In contrast, TSWV was the only tospovirus associated with disease outbreaks in Central Valley lettuce during this period. Disease surveys conducted over two seasons (2008 and 2009) in 10 commercial fields (acreage of 6 to 20 ha) indicated that INSV was the only tospovirus associated with economically damaging disease outbreaks in lettuce in the coastal region, with incidences of 0.5 to 27% (mean = 5.7%). Molecular characterization of INSV isolates associated with these disease outbreaks revealed little genetic diversity and indicated that lettuce-infecting INSV isolates were nearly identical to those previously characterized from ornamental or other hosts from different locations in the United States and the world. Monitoring of thrips revealed moderate to large populations in all surveyed lettuce fields, and the majority of thrips identified from these fields were western flower thrips, Frankliniella occidentalis. There was significant positive correlation (r2 = 0.91, P = 0.003) between thrips populations and INSV incidence in the most commonly encountered type of commercial lettuce (romaine, direct seeded, conventional) included in this study. A reverse-transcription polymerase chain reaction assay developed for detection of INSV in thrips showed promise as a monitoring tool in the field. Surveys for INSV reservoir hosts in the coastal production area revealed that the weeds little mallow (Malva parvifolia) and shepherds purse (Capsella bursa-pastoris) were commonly infected. M. parvifolia plants infected in the field did not show obvious symptoms, whereas plants of this species inoculated in the laboratory with INSV by sap transmission developed necrotic spots and chlorosis. Eleven other weed species growing in the lettuce production areas were found to be hosts of INSV. Coastal crops found to be infected with INSV included basil (Ocimum basilicum), bell pepper (Capsicum annuum), calla lily (Zantedeschia aethiopica), faba bean (Vicia faba), radicchio (Cichorium intybus), and spinach (Spinacia oleracea). Thus, it is likely that INSV was introduced into coastal California lettuce fields via viruliferous thrips that initially acquired the virus from other local susceptible plant species. Results of this study provide a better understanding of INSV epidemiology in coastal California and may help growers devise appropriate disease management strategies.

Winter Cover Crop Seeding Rate and Variety Affects during Eight Years of Organic Vegetables: I. Cover Crop Biomass Production

Substantial weed growth often occurs in legume-cereal cover-crop mixes commonly grown on organic vegetable farms. A 2-yr study at the USDA-ARS in Salinas, CA, was conducted to test the effect of zero, one, and two passes with a rotary hoe on weed control in a mixed cover crop of 10% rye, 15% common vetch, 15% purple vetch, 25% peas, and 35% bell bean. Rotary hoeing occurred 14–15 days after planting (DAP) in the one-pass treatment, and 14 and 28 DAP in the two-pass treatment. Rotary hoeing did not affect total cover-crop density or biomass in either year, but reduced rye density and biomass in year 2. One pass reduced total weed density by 69% in year 1 and 49% in year 2. A second pass did not affect weed density in year 1 but reduced weed density an additional 33% in year 2. One pass decreased weed biomass in year 1, whereas two passes were required to reduce weed biomass in year 2. Rotary hoeing reduced seed shed by chickweed and shepherds-purse seeds, the two predominant weed species, by 80 to 95% in both years. Rotary hoe efficacy depended on weather conditions directly before and after cultivation. The decision to repeat rotary hoeing should be based upon field scouting and weather conditions following the initial pass with the rotary hoe. Nomenclature: Chickweed, Stellaria media (L.) Vill. #3 STEME; shepherds purse, Capsella bursa-pastoris (L.) Medic. # CAPBP; rye, ‘Merced’ Secale Cereale L.; common vetch, Vicia sativa L.; purple vetch, Vicia benghalensis L.; peas ‘magnus’, Pisum sativum L.; bell bean, Vicia faba L. Additional index words: Weed seed, organic, Senecio vulgaris, Lamium amplexicaule, Solanum sarrachoides, Poa annua. Abbreviations: GDD, growing degree days

Effect of Seeding Rate and Planting Arrangement on Rye Cover Crop and Weed Growth

Vegetable and fruit consumption patterns in the United States indicate that most people need to eat far more fruits and vegetables to meet the current nutritional guidelines for a healthy diet. Following these guidelines would require more than doubling the harvested acreage for fruits and vegetables and could have serious environmental implications if unsustainable production practices were used. This situation will likely intensify with population growth and climate change.

Seeding Rate and Planting Arrangement Effects on Growth and Weed Suppression of a Legume–Oat Cover Crop for Organic Vegetable Systems

Cover crops and compost are organic matter inputs that can impact soil health in tillage-intensive, high-input, organic vegetable production systems in the central coast region of California. Data are presented on soil microbial biomass (carbon and nitrogen) and soil enzymes (β-glucosidase, β-glucosaminidase, alkaline phosphatase, aspartase and L-asparaginase and dehydrogenase) from a relatively long-term organic systems experiment in Salinas, California that was focused on lettuce and broccoli production and included eight different certified organic systems. These systems differed in compost inputs, cover cropping frequency, cover crop type, and cover cropping seeding rate. The compost was made from urban yard waste, and the cover crops included rye, a legume-rye mixture, and a mustard mixture planted at two seeding rates (standard rate 1× versus high rate 3×). There were three legume-rye 3× systems that differed in compost inputs (0 versus 15 Mg ha-1 year-1 and cover cropping frequency (every winter versus every fourth winter). The data in this article support and augment information presented in the research articles “Cover cropping frequency is the main driver of soil microbial changes during six years of organic vegetable production” (Brennan and Acosta-Martinez, 2017) and “Cover crops and compost influence soil enzymes during 6 years of tillage-intensive, organic vegetable production” (Brennan and Acosta-Martinez, 2018).