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Mathieu Ngouajio

Over the last century, climate change, adoption of new regulations, and changes in cropping systems have significantly impacted weed and pest management in horticultural crops. The objective of this workshop was to provide a critical review of major changes and discuss current and future trends for weed and pest management. Speakers touched on a broad range of topics including climate change and disease dynamics, the use of disease resistance inducers, soil management for pest management, and the role of allelopathy in weed management. Major recommendations included 1) increased grower education related to the impact of climate change on plant diseases; 2) more research directed towards a better understanding of the interaction of plant–pathogen–inducer; 3) use of organic soil amendments, cover crops, crop rotations, and resistant cultivars to enhance the weed and disease suppressive effect of soils; and 4) enhancement of allelochemical production and subsequent weed suppression through conventional breeding and molecular techniques.

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Henry G. Taber

Black, clear, and wavelength-selective IRT 76 plastic mulches with or without clear, slitted, hooped rowcovers were evaluated for early muskmelon production in 1991 and 1992. Clear and IRT 76 plastic mulches tripled early yield, compared with bare ground, 130 and 45 cwt/acre, respectively. Highest yields both years were from the combination of rowcover with either clear plastic or IRT 76 mulch-181 cwt/acre in 1991 and 379 cwt/acre in 1992. Yield from clear plastic was superior to that from IRT 76 by 41 cwt/acre in 1991, but not in 1992. The minimum soil temperature for IRT 76 compared with clear plastic was +0. 5F and -2F for 1991 and 1992, respectively. Crop rotation and herbicides were used to provide adequate weed control both years. The best cost-effective early muskmelon production system tested involved clear plastic, rowcovers, and trickle irrigation.

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Laura K. Paine and Helen Harrison

Since the domestication of the first crop species, farmers have dealt with the problem of soil depletion and declining crop yields. Fallowing of land was the first approach to restoring soil fertility, and is still the most commonly used method among indigenous farmers. Alternatives to fallow, such as crop rotation and green manures, developed in a number of areas. The earliest record of their use is in Chinese writings from ca. 500 B.C. Discussion of these practices is found in European agricultural publications dating from the 16th century. While these ancient techniques have proven value for soil conservation, their use in modern agriculture is quite limited. Renewed interest within the agriculture community in recent decades has resulted in a greater research effort in the areas of green manures, cover crops, and living-mulch cropping systems.

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Lynn Marie Sosnoskie*, John Cardina, Catherine Papp Herms and Matthew Kleinhenz

Community composition of the soil seedbank were characterized 35 years after the implementation of a long-term study involving cropping sequences (continuous corn, corn-soybean, corn-oat-hay) and tillage systems (conventional-, minimum- and no-tillage). Germinable seeds within the top 10 cm of soil in early spring were identified and enumerated in 1997, 1998 and 1999. Species diversity, which was characterized by richness (S), evenness (E) and the Shannon-Weiner index (H'), was significantly influenced by crop rotation rather than tillage. Generally, diversity measures were greatest in the corn-oat-hay sequences as compared to the corn-soybean rotations and the corn monoculture. Species richness and H' typically declined with increasing soil disturbance (no-tillage > minimum-tillage > conventional-tillage), whereas E increased with more intense tillage. A synthetic importance value (RI), incorporating both density and frequency measures, was generated for each species in each plot. Multiresponse permutation procedures (MRPP) were used to examine differences in weed community composition with respect to management system for all three years. Results suggest that the weed seed community in a corn-oat-hay rotational system differs substantially, in structure and composition, from communities associated with continuous corn and corn-soybean systems. No tillage systems were significantly different in composition as compared to conventional tillage and minimum tillage treatments. Crop sequence and tillage system are important cultural methods of shifting weed species number and diversity, and therefore, community structure. Manipulation of these factors could help to reduce the negative impact of weeds on crop production.

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Frank J. Coale, Russell T. Naqata and Lawrence E. Datnoff

Corky root (CR) of lettuce (Lactuca sativa L.) is caused by the bacterium Rhizomonas suberifaciens. Current management strategies involve the use of resistant cultivars and crop rotation. The use of transplants as a method to grow CR-susceptible cultivars in CR-infested fields was recently demonstrated. The objective of this study was to evaluate corky root destruction of root systems of direct-seeded and transplanted lettuce. Direct seeded, and three and five week old transplants of CR susceptible `Shawnee' and CR resistant `South Bay' crisphead lettuce were grown in a naturally CR-infested field. Root systems were evaluated at head harvest maturity. When direct seeded, South Bay developed 104% more total lateral root length than did Shawnee. When transplanted at three and five weeks, South Bay developed 50% and 61% more total lateral root length than Shawnee, respectively. Total lateral root length for Shawnee transplanted at five weeks was 100% greater than direct seeded Shawnee. Comparatively, total lateral root length for South Bay transplanted at five weeks was 58% greater than direct seeded South Bay. Tap root lengths and dry weights were not different among planting systems. Transplanting is a possible method for reducing the impact of CR on lettuce lateral root development.

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Reid Torrance, David Langston and Don Sumner

Metam sodium has been evaluated on onions in Georgia since the mid-1980s for control of various soil pathogens in the production of transplants. Observations also indicated excellent weed control activity. Further work showed significant growth response of transplants, 90% or better weed control, and efficacy of Phoma terrestris, Fusarium, and Pythium. Results were better in comparison studies than found with methyl bromide, chloropicrin, and other fumigation combinations. This led to use of the product in field production of dry bulb onions. Seven years of studies revealed an average yield increase of 190 bushels per acre over the control, even where Phoma terrestris levels were minimal. Today, almost all transplant production includes the use of metam sodium and field use is beginning to be used by growers. With limited crop rotation being practiced in the Vidalia onion belt, metam sodium will continue to play a major role in controlling the ever-increasing levels of Phoma terrestris and maintaining profitability in onion production in Georgia.

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V.M. Russo

Crop rotations can reduce problems that occur in monoculture planting systems. In 1990, at Lane, Okla., 0.5 ha of Bernow fine-loamy soil was planted to peanut (Arachis hypogaea L.). In the following 5 years, bell pepper (Capsicum annuum var. annuum L.), cucumber (Cucumis sativas L.), navy bean (Phaseolus vulgaris L.), and cabbage (Brassica oleracea L. Capitata group) were planted in one of four rotations after 1, 2, or 3 years of peanut. The first vegetable planting in each annual rotation was followed by either vegetables or peanut in following years. In 3 of the 6 years, peanut or vegetables were planted in each rotation. Peanut yields in the first year averaged 6.6 Mg·ha-1, but were <1.9 Mg·ha-1 thereafter. Yields of the first vegetable planting, which followed 1 or 2 years of peanut, were normal for this location, but were significantly lower after 3 years of peanut. For second or third plantings of vegetables in rotations, yields were reduced up to 50% compared to the first vegetable planting. For most crops, the rotation that had 3 years of peanut followed by 3 years of vegetables generally produced the least cumulative yield. Numbers of sclerotia produced by soilborne plant pathogenic fungi fluctuated over the years, but were the same in the spring of the second and sixth years. Rotating these crops appears to have limited applicability for maintaining high vegetable or peanut yields.

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K. Delate

Sales of organic products reached $8 billion in the U.S. in 2000, continuing the nearly decade-long trend of 20% annual growth. In Iowa alone, organic production for all crops was 5265 ha (13,000 acres) in 1995 but 60,750 ha (150,000 acres) in 1999. Despite the growth in organic agriculture, our knowledge of organic farming systems remains limited. We have adopted a systems theory approach in our current research program at Iowa State University (ISU) to help address this gap in understanding. Systems theory holds that biological systems, such as agroecosystems, consist of integrated units of people, plants, animals, soil, insects and microorganisms, and each subsystem provides feedback to the other. In order to obtain input on research questions and experimental design, the Leopold Center for Sustainable Agriculture and ISU held six focus groups across Iowa in 1998 before long-term site establishment. Producers and agricultural professionals at the focus groups supported the need for long-term agroecological research (LTAR) sites in four distinct agroecological zones in Iowa. The goal of each LTAR is to examine the short- and long-term physical, biological, and socioeconomic effects of organic and conventional farming systems. By establishing long-term experiments, we are testing the hypothesis that longer crop rotations, typical of organic farms, provide yield stability, improve plant protection, and enhance soil health and economic benefits compared to conventional systems with shorter rotations and greater off-farm inputs. Examples of research results from two LTAR experiments in Iowa include similar pepper (Capsicum annuum) and soybean (Glycine max) yields in the conventional and organic systems. Organic systems used mechanical weed control and locally produced compost in place of synthetic fertilizers. Feedback from the local farm associations that are responsible for farm stewardship and farm finances is inherent in the LTAR process.

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Gladis M. Zinati

Conventional agricultural systems increase per-area food production, but deplete natural resources and degrade both crop and environmental quality. Many of these concerns are addressed by sustainable agricultural systems, integrated pest management, biocontrol, and other alternative systems. Environmental and social concerns have escalated the need for alternative agricultural systems in the last decade. One alternative, the organic farming system, substitutes cultural and biological inputs for synthetically made fertilizers and chemicals for crop nutrition and pest management. Practices used for crop and pest management are similar during transition from conventional to organic farming systems, but produce is not certified to be organic during the transition period. During the transition from conventional to organic farming, growers may face pest control difficulties and lower yields when conventional practices are abandoned. The objectives of this paper are to 1) give an overview of the reasons for converting to organic farming and the challenges that growers face during the transition period, 2) outline some potential strategies for crop, soil, and pest management, and 3) list guidelines and recommendations for pest management during the transition to organic farming. Implementation of crop and pest management practices depends on geographical location, climate, available onsite resources, and history of the land. During transition, growers rely on cultural mechanisms and on organic and mineral sources to improve soil fertility, to build a population of natural enemies to suppress pest populations. Pest management practices during the transition period that reduce pest populations to economically manageable levels include crop rotation, cultivation, cover crops, mulches, crop diversification, resistant varieties, and insect traps. These practices also enrich the soil biota and increase crop yields before produce is certified organically grown.

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Sean M. Westerveld, Alan W. McKeown and Mary Ruth McDonald

An understanding of nitrogen (N) uptake and the partitioning of N during the season by the carrot crop (Daucus carota subsp. sativus [Hoffm.] Arkang.) is required to develop more efficient N fertilization practices. Experiments were conducted on both organic and mineral soils to track the accumulation of dry matter (DM) and N over the growing season and to develop an N budget of the crop. Treatments included two carrot cultivars (`Idaho' and `Fontana') and 5 N rates ranging from 0% to 200% of the provincial recommendations in Ontario. Foliage and root samples were collected biweekly from selected treatments during the growing season and assessed for total N concentration. Harvest samples were used to calculate N uptake, N in debris, and net N removal values. Accumulation of DM and N in the roots was low until 50 to 60 days after seeding (DAS) and then increased linearly until harvest for all 3 years regardless of the soil type, cultivar, and N rate. Foliage dry weight and N accumulation were more significant by 50 to 60 DAS, increased linearly between 50 and 100 DAS, and reached a maximum or declined slightly beyond 100 DAS in most cases. The N application rates required to maximize yield on mineral soil resulted in a net loss of N from the system, except when sufficient N was available from the soil to produce optimal yield. On organic soil, a net removal of N occurred at all N application rates in all years. Carrots could be used as an N catch crop to reduce N losses in a vegetable rotation in conditions of high soil residual N, thereby improving the N use efficiency (NUE) of the crop rotation.