Weed control in organic vegetable production is a major challenge. During Summer 2004, we conducted field trials to manage weeds in organic sweet corn, carrots and onions. In sweet corn, we evaluated the efficacy of transplanting greenhouse-grown sweet corn seedlings. In carrots and onions, we tested vinegar and several concentrations of acetic acid. Studies were conducted in southwestern Minnesota at the Lamberton Research and Outreach Center and in eastern Minnesota at Foxtail Farm in Shaefer. Ten-day-old corn transplants were effective at both locations. Stand establishment was greater, less tillage was needed, and yield was greater than in the seeded plots. Straight vinegar was not very effective in controlling weed populations. Although there was greater damage to broadleaf weeds than grasses, straight vinegar did not reduce the need for tillage. Although 10% to 20% acetic acid did provide better weed control, it significantly damaged carrot and onion seedlings. These results suggest that using sweet corn transplants is time and cost effective for small acreage sweet corn production such as CSAs. Vinegar and acetic acid are problematic. Nonselectivity, potential danger in handling, and poor control at low concentrations were all considered significant disadvantages.
String impregnated with simazine, atrazine, and diuron (6.6%, 2.2%, and 2.2% by weight) controlled weeds in rows of 8 month-old peach (Prunus persica (L.) Batsch) and apricot (P. armeniaca L.) seedling nursery stock. A single strand of herbicide-impregnated string controlled all weed growth in a band 30.5 cm wide when placed at the base of the seedlings on the surface of a Fox sandy loam soil. Complete weed control was obtained from the fall of 1973 to the fall of 1974. Placement of the string at various heights above the soil surface gave less satisfactory weed control than surface placement, permitted less release of herbicide and caused injury to young leaves which came in constant contact with the string. A wheat bioassay of the nursery soil after seedling removal indicated no phytotoxic residues. Chemical analysis of the string at the end of the experiment showed that 88% of the herbicide was released when one strand of string was placed on the soil surface. This resulted in a concentration of 4.05, 1.35 and 1.35 kg/ha of simazine, atrazine and diuron, respectively, in the treated area. No phytotoxicity from the soil surface string placement was observed on peach or apricot nursery trees.
Four herbicides formulated as slow release tablets were evaluated for weed control on container grown nursery crops. These included alachlor (2-chloro-2, '6'-diethyl-N-(methox-ymethyl) acetanilide), metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-l-methylethyl) acetamide), oxadiazon (2-tertbutyl-4(2,4 dichloro-5-isopropoxyphenyl)-∆2-1,3,4-oxadiazoIin-one) and oryzalin (3,5-dinitro-N4,N4 dipropyl-sulfanilamide). Metolachlor tablets at 40 Kg/ha exhibited 120 days of excellent weed control. Less injury was evident on border forsythia (Forsythia intermedia Zab. “Spectasbilis’) and cranberry cotoneaster (Cotoneaster apiculatux Rhed. & E.H. Wils) when herbicide applications were made using tablets in comparison to equivalent rates of granular material.
Good broadleaf weed control was achieved in table beets (Beta vulgaris L.) with cycloate, CNP, pebulate, lenacil, pyrazon (preplant application = pre), IMC 3950, TCA + pyrazon and pebulate (preplant incorporation = ppi) followed by pyrazone (postplant incorporation = post), while fair to good weed control was achieved with EPTC, propachlor and solubor. Poor weed control was obtained from CDEC, chlorpropham, pyrazon (post) and TCA. Yields expressed as $/ha or tons/ha were reduced by chlorpropham, lenacil, CNP and TCA. Nitrate-N was significantly increased in blades of beets by lenacil, pyrazon (pre) and CNP. The herbicides cyloate, CNP, EPTC, pebulate (ppi) — pyrazon (post), and TCA + pyrazon increased NO3-N concentrations in petioles. TCA + pyrazon and CNP increased NO3-N in beet roots, while CDEC, chlorpropham, solubor and pyrazon (post) decreased NO3-N. Total N concentration in the leaf blades was not affected by any of the herbicide treatments. Total N in petioles increased when TCA, chlorpropham, lenacil and CNP were used. TCA, chlorpropham, lenacil and CNP increased root total N.
Weed management systems for Norway spruce (Picea abies L.) Christmas trees were investigated under field conditions. Potential alternative methods to replace the use of herbicides included the application of three different soil covers: plastic film (100% recoverable), biodegradable film 40-μ thick, and biodegradable film 70-μ thick. On another group, weed control was carried out mechanically (control plants). Each treatment consisted of 27 plants with three replications. At the time of the first growing season, the percentage of dead and survived plants in treated plants and in the control plants did not differ significantly. Data were recorded on plant height and quality during the second year of growth. Control plants always showed height increases shorter than other plants. Application of these films significantly affected growth and plant quality. In plastic film-treated plants, the average height increases were significantly higher than those observed on control plants mechanically treated (19 vs. 12 cm, respectively), and did not differ from biodegradable film-treated plants (17 cm). Plants responded similarly to the biodegradable films of varying thickness. The results indicate that all three films have potential for use in Christmas tree production. However, the use of biodegradable films would be preferable because they do not need to be removed at the end of the rotation (about 6–7 years). Furthermore, this culture system would be an efficient way to achieve three objectives: 1) to enhance weed control, avoiding the application of herbicides by many Christmas tree producers; 2) to improve quality and plant commercial value; and 3) to obtain a shorter rotation.
This study was undertaken to evaluate natural mulches for weed control in organic onion (Allium cepa) production where current practices rely on hand-weeding or plastic mulch. Three experiments were conducted over 2 years, with two experiments conducted on-farm in different years and one experiment conducted on-station. Treatments consisted of hand-weeding or mulches of wheat (Triticum aestivum) or oat (Avena sativa) straw, bermudagrass hay (Cynodon dactylon), compost, and needles of slash pine (Pinus elliottii) and longleaf pine (P. palustris). All of the mulches with the exception of compost tended to lodge in the onion tops due to their close spacing. Wheat straw and bermudagrass hay reduced plant stand and yield. Compost settled well around the onion plants and initially smothered weeds, but over time the compost treatment became very weedy. Pine needle mulch (referred to as pine straw in the southeastern U.S.) showed the most promise with less stand loss or yield reduction, but did tend to lodge in the tops. None of these mulches were acceptable compared to hand-weeding.
Field production of cannas in the United States is difficult to estimate ( Johnson et al., 1995 ), although in Texas it may be about 750 acres, primarily for rhizome seed stock production. Weed control in cannas and other ornamental crops is
Field plots of four production systems of `Tristar' dayneutral and `Earliglow' Junebearing strawberry (Fragaria xananassa Duch.) were established in 1993. Productions systems included conventional practices (CONV), best-management practices including integrated crop management (ICM), organic practices using corn gluten meal, a natural weed control product, (ORG-CGM), and organic practices using a natural turkey manure product (ORG-TM). `Earliglow' plants grown with ORG-CGM showed the highest number of runners and total vegetative biomass. Plots with CONV and ICM systems using standard herbicide treatments had lower total weed numbers (11 and 18, respectively) than ORG-CGM (63) and ORG-TM (58). `Tristar' plant growth, yield and berry number were reduced when plants were grown under straw mulch in ORG-CGM and ORG-TM compared to CONV and ICM plots with polyethylene mulch.
A three-year study determined the effect of winter cover crops on weeds and vegetable crops in a vegetable production system. Winter rye and hairy vetch were interseeded in the fall of 1990, 1991 and 1992 at 112 and 34-kg ha-1, respectively. The cover crops were killed by ether applying glyphosate at 1.1 kg a.i ha-1 [reduced tillage(RT)] or mowing and disking the cover crop (Disked). The conventional tillage (CT) was bare ground with a preplant incorporated application of 0.84 kg a.i ha-1 of trifluralin. During the three years, the greatest snap bean yields were in the CT; total yields of cabbage and tomato varied between the years; and were not affected by management systems. Weed control was similar in the RT and CT treatments during the three years. Disked cover crop treatments tended to have greater weed numbers than either RT or CT treatments.
Throughout the world, growers of horticultural crops employ a multitude of crop and pest management practices designed to reduce pests and minimize crop losses. Although weeds continue to afflict humans (65), host other pests (14), and cause appalling crop losses on a worldwide scale (66, 109, 110), certain weedy species may complement horticultural cropping systems. This paper reviews entomological, pathological, and crop-related literature where manipulation of a specific weed, a weed control practice, or a cropping system can suppress a crop pest. Perhaps horticulturists and colleagues will recognize an opportunity to improve our understanding and our ability to successfully manage one or more of the following examples, thereby improving production efficiencies within modern horticultural cropping systems.