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P. R. Johnstone, T. K. Hartz, E. M. Miyao, and R. M. Davis

Mustard cover crop residue has been reported to have a “biofumigant” action when incorporated into the soil, potentially providing significant disease suppression and yield improvement for the succeeding crop. Such activity could be particularly useful in processing tomato rotations, where consecutive cropping invariably results in yield decline. Agronomic and environmental effects of growing over-winter mustard cover crops preceding tomato production were investigated in three field trials between 2002 and 2004. Two mustard cover crops [`Pacific Gold', a brown mustard (Brassica juncea), and `Caliente', a blend of brown and white mustard (Sinapis alba)] were compared to a legume cover crop mix, a fallow bed treatment (the standard grower practice in this region), and, in two of the three trials, a fumigation treatment using metam sodium. No suppression of soil populations of Verticillium dahliae or Fusarium spp. was observed with the mustard cover crops, nor was there any visual evidence of disease suppression on subsequent tomato crops. In these fields, the mustard either had no effect, or reduced tomato yield, when compared to the fallow treatment. At one of two sites, metam sodium fumigation significantly increased tomato yield. The presence of a cover crop, whether mustard or legume, reduced winter runoff by an average of 50% over two years of trials. No benefit of mustard cover cropping beyond this reduction in winter runoff was observed.

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Francis X. Mangan and Stephen J. Herbert

Field research was conducted in Deerfield, Mass. to study the effects of leguminous cover crops on sweet corn yield. Oat was planted alone and in combination with four leguminous cover crops August 8, 1990. Cover crop residue was disked once and sweet corn seeded April 23, 1991. Each cover crop combination had three rates of nitrogen added in two applications. Sweet corn seeded into stands of hairy vetch (Vicia villosa) yielded the highest of the cover crop combinations. All leguminous cover crop treatments yielded higher than oat alone or no cover crop when no synthetic nitrogen was added. Cover crop combinations were seeded again in the same field plots August 12, 1991. Oat biomass in November was greater where there had been leguminous cover crops or high rates of synthetic nitrogen. Legume growth was retarded in the plots that had previously received high nitrogen. It is thought that legume growth was reduced in the high nitrogen treatments due to increased oat growth and higher soil nitrogen levels which could inhibit root nodulation.

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Victor W. Winkler

A U.S. Environmental Protection Agency (EPA) voluntary program encourages the registration of pesticides that represent reduced risk to human health and the environment. A “reduced risk” designation for a pesticide depends on how its use will affect human health and the environment, pesticide resistance, and pesticide management. Prohexadione-Ca is a bioregulator being developed by BASF Corporation to control vegetative growth in apples with the effect of improving fruit production. BASF will petition the EPA to register prohexadione-Ca as a reduced risk pesticide in 1997 based on the following properties associated with its use: Prohexadione-Ca exhibits a very low mammalian toxicity and a low propensity for crop residues. Prohexadione-Ca rapidly dissipates in soil as a result of microbial metabolism and causes no detrimental ecological effects. There is no other hazard associated with the compound and no health risk for user or consumer is indicated. The use of prohexadione-Ca reduces the incidence of fireblight (and helps control this disease). The use of prohexadione-Ca reduces tree row spray volumes of other pesticides up to 25%. With these beneficial characteristics, prohexadione-Ca will fit exceptionally well into an Integrated Pest Management (IPM) program, providing another “reduced risk” justification for the registration of prohexadione-Ca. The current situation of accepting prohexadione-Ca as a reduced risk pesticide and its registration status will be discussed.

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Alvin D. Rutledge

Research yields of conservation tillage (CT) snap beans (Phaseolus vulgaris L.) and sweet corn (Zea mays L. var. rugosa Bonaf.) have been less than those produced under conventional tillage. This has been due to soil conditions at planting, the cover crop used, weed control and a lack of proper design in equipment for CT. However, some growers have been successful with CT for sweet corn using hairy vetch (Vicia villosa Roth.) as the cover crop. On-farm demonstrations of CT with cabbage (Brassica oleracea L. Capitata Group), pumpkins (Cucurbita pepo L.), tomatoes (Lycopersicon esculentum Mill.) and watermelons [Citrullus lanatus (Thunb) Matsum. & Nak.] have been successful and with good management it is commercially feasible under Tennessee conditions. Advantages include reduced soil erosion, cleaner products, more efficient application of crop protection chemicals, quicker planting after rainfall, lower energy costs and facilitation of harvest in wet weather. Disadvantages include reduced weed control, modifications of existing equipment, less uniformity in seed coverage and problems with transplanting, cover crop residue in mechanically harvested crops, possible delays in early harvest of fresh market crops due to delayed maturity and limited application of soil protective chemicals.

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C.D. Stanley, A.A. Csizinszky, G.A. Clark, and J.W. Prevatt

Combinations ofvarious vegetable crop species grown in multiple-cropping sequences using microirrigation on a sandy soil were evaluated for production potential and changes in normal cultural management An initial fall-season fresh-market tomato crop was followed immediately by a winter-season crucifer crop (cauliflower, broccoli, or cabbage), which was followed by a spring-season cucurbit crop (cucumber, zucchini squash, or muskmelon). Studies were conducted over a 3-year period in southwestem Florida. Results showed that when cropping sequences were compared on a basis of a derived relative value index (RVI), the sequence of tomato-cauliflower-zucchini squash significantly outperformed other sequences. Several management concerns particular to the production system (crop residue removal and interference, plastic mulch deterioration and damage, and weed control) were identified and discussed. The potential savings when cropping sequences are compared to individual crop production resulted in net savings (dollar savings less additional production costs) that ranged from $565 to $1212/acre ($1396 to $2993/ha) and $614 to $1316/acre ($1516 to $3251/ha) for the 1986-87 and 1988-89 seasons, respectively.

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James E. Altland, Leslie Morris, Jennifer Boldt, Paul Fisher, and Rosa Raudales

Paclobutrazol is a plant growth retardant commonly used on greenhouse crops. Residues from paclobutrazol applications can accumulate in recirculated irrigation water. Given that paclobutrazol has a long half-life and potential biological activity in parts per billion concentrations, it would be desirable to measure paclobutrazol concentration in captured irrigation supplies. However, there are no standard protocols for collecting this type of sample. The objective of this research was to determine if sample container material or storage temperature affect paclobutrazol stability over time. In two experiments, paclobutrazol was mixed in concentrations ranging from 0.04 to 0.2 mg·L−1 and stored in polyethylene, clear glass, or amber glass containers at temperatures of either 4 or 20 °C. Paclobutrazol concentration was measured at 3, 14, and 30 days after the start of each experiment. Across the two experiments, there were no consistent trends in reduction of paclobutrazol concentration with respect to container material or storage temperature. In the first experiment, there was an average of 5% reduction across all treatments from day 0 to 30, whereas in the second experiment, concentration did not decrease over the 30-day time period. These data suggest that paclobutrazol is stable in collected water samples for at least 30 days, and that either glass or polyethylene containers are suitable for collecting greenhouse water samples for analysis of paclobutrazol concentration. A minimum volume of 100 mL was determined to be the optimum to analyze water samples with diverse paclobutrazol concentrations.

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T.K. Hartz, P.R. Johnstone, E.M. Miyao, and R.M. Davis

Mustard (Brassica spp.) cover crop residue has been reported to have significant `biofumigant' action when incorporated into soil, potentially providing disease suppression and yield improvement for the succeeding crop. The effects of growing over-winter mustard cover crops preceding processing tomato (Lycopersicon escultentum Mill.) production were investigated in six field trials in the Sacramento Valley of California from 2002–04. A selection of mustard cover crops were compared to a legume cover crop mix, a fallow-bed treatment (the current grower practice in the region), and in two of the six trials, fumigation treatments using metam sodium. Mustard cover crops removed 115 to 350 kg·ha–1 N from the soil profile, reducing NO3-N leaching potential. Soil populations of Verticillium dahliae Kleb. and Fusarium spp. were unaffected by the cover crops, and there was no evidence of soilborne disease suppression on subsequent tomato crops. Mustard cover crops increased tomato yield in one field, and reduced yield in two fields. In one of two fields, metam sodium fumigation significantly increased tomato yield. We conclude that, while environmental benefits may be achieved, mustard cover cropping offers no immediate agronomic benefit for processing tomato production.

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John M. Luna and Mary L. Staben

Two strip tillage systems for sweet corn production were compared to conventional tillage systems in western Oregon. A power take-off rotary tiller configured to till six rows per pass was used in 1997 and 1998; a shank/coulter strip tillage machine was used in 1999 and 2000. A paired t test experimental design was used in field-scale, on-farm research with eight replications in 1997-98 and 12 replications in 1999-2000. Sweet corn was harvested using the participating growers' corn pickers and yield was determined. A subset of the participating growers recorded types of machinery and labor for tillage operations and total costs were computed for each tillage system. The rotary strip tillage system produced 900 kg·ha-1 greater corn yields (P = 0.11) than conventional tillage. The shank/coulter strip tillage system produced yields comparable to conventional tillage (P = 0.95). The rotary strip tillage system reduced total tillage costs by an average of $38.50/ha compared to conventional tillage (P = 0.03) and reduced machinery operating time by 0.59 h·ha-1 (P = 0.01). The shank/coulter strip tillage system reduced tillage costs by $36.50/ha compared to conventional tillage (P = 0.003) and reduced machinery operating time by 0.47 h·ha-1(P = 0.001). Slugs damaged corn in several strip tillage fields requiring the use of slug bait to prevent economic damage. Herbicides used in conventional tillage systems were generally effective in the strip tillage systems. Mechanical cultivation with standard cultivating equipment was more difficult in some of the strip tillage fields with heavy cover crop residue.

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Erin C. Hill, Mathieu Ngouajio, and Muraleedharan G. Nair

Laboratory experiments were conducted to study the effect of aqueous extracts of hairy vetch (Vicia villosa Roth) and cowpea (Vigna unguiculata (L.) Walp) cover crops on germination and radicle elongation in seven vegetable and six weed species. Lyophilized aqueous extracts of the cover crops were dissolved in reverse osmosis (RO) water to produce seven concentrations: 0.00, 0.25, 0.50, 1.00, 2.00, 4.00, and 8.00 g·L–1. Each treatment had 4 replications and the full experiment was repeated. Experiment 1 (E1) and Experiment (E2) were conducted under similar conditions. In general, seed germination was not affected by extracts of both cover crops. However, radicle growth of all species tested (except common milkweed exposed to cowpea extract) was affected by the cover crop residue extracts. Low concentrations of hairy vetch extract stimulated the radicle growth of carrot, pepper, barnyardgrass, common milkweed, and velvetleaf. Likewise, low concentrations of cowpea extract stimulated the growth of corn, barnyardgrass, and velvetleaf. At higher concentrations all species tested were negatively affected. The order of species sensitivity to the hairy vetch extract, as determined by the IC50 (concentration required to produce 50% radicle inhibition) values, was common chickweed > redroot pigweed> barnyardgrass E1 > carrot E1 > wild carrot > corn > carrot E2 > lettuce > common milkweed > tomato > onion > barnyardgrass E2 > velvetleaf > pepper > cucumber (most sensitive to least sensitive). For cowpea the order was common chickweed > redroot pigweed > corn > tomato > lettuce > wild carrot > pepper > carrot > cucumber > onion> barnyardgrass and velvetleaf. Results suggest that the susceptibility of weeds and vegetable crops to aqueous extracts of hairy vetch and cowpea is dependent on both species and extract concentration.

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Leslie A. Weston

Allelopathy can be defined as an important mechanism of plant interference mediated by the addition of plant-produced secondary products to the soil rhizosphere. Allelochemicals are present in all types of plants and tissues and are released into the soil rhizosphere by a variety of mechanisms, including decomposition of residues, volatilization and root exudation. Allelochemical structures and modes of action are diverse, and may offer potential for development of future herbicides. In the past, allelopathy was described by the Romans as a process resulting in the “sickening” of the soil; in particular, chickpea (Cicer arietinum) was described as problematic when successively cropped with other species. Other early plant scientists, such as De Candolle in the 1800s, first described the ability of plant roots to produce toxic exudates. More recently, research has focused on development of weed management strategies using allelopathic crop residues, mechanism of allelochemical action, and gene regulation of allelochemical production. This paper briefly describes a variety of weed and crop species that establishes some form of potent allelopathic interference, either with other crops or weeds, in agricultural settings, in the managed landscape, or in naturalized settings. Recent research suggests that allelopathic properties can render one species more invasive to native species and thus potentially detrimental to both agricultural and naturalized settings. In contrast, allelopathic crops offer strong potential for the development of cultivars that are more highly weed suppressive in managed settings. A new challenge that exists for plant scientists is to generate additional information on allelochemical mechanisms of release, selectivity and persistence, mode of action, and genetic regulation. Armed with this specific information, we can further protect plant biodiversity and enhance weed management strategies in a variety of ecosystems.