, weeds can harbor pathogens and insects that could affect the crop. All but a few fumigant-tolerant weed seed species such as California burclover ( Medicago polymorpha L.) and common mallow ( Malva neglecta Wallr.) are controlled by MB and Pic mixtures
) are registered in strawberry and vegetables, but none are effective on nutsedge species, and as a result, growers tend to rely on fumigants for weed control. However, fumigants are found to be more effective for long-term weed control when used in
Weed control is a major challenge confronting growers transitioning to organic vegetable production. Organic standards require that growers manage weeds without synthetic herbicides while maintaining or enhancing soil quality. In 2005, we evaluated the effects of two seedbed preparation methods and six weed management tactics, compatible with organic standards, on soil quality indicators, weed pressure, and yield of edamame soybean [Glycine max (L.) Merrill]. Seedbed preparation was conducted with either a moldboard plow and roto-tiller or a spading machine. Weeds were managed by a) regular hand weeding, b) pre-emergent flaming, c) post-emergent incorporation of 100 g of corn gluten meal/m2, or weekly passes from crop emergence until row closure with d) a spring-tine weeder, e) a rolling cultivator, or f) a between-row flame weeder. Dominant weeds were smooth pigweed [Amaranthus hybridus (L.)], goosegrass [Eleusine indica (L.) Gaertn.], and giant crabgrass [Digitaria sanguinalis (L.) Scop.]. Smooth pigweed dominated in the corn gluten meal and spring-tine weeder treatments; goosegrass and giant crabgrass dominated in the two flamed treatments. Weed pressure was lowest, and crop yield highest, in the hand-weeded control and rolling cultivator treatments. Relative to these, crop yield was severely depressed by weed pressure in other treatments. The labile carbon concentration and enzymatic activity of soils was tested midseason, and at harvest, showed no significant treatment effects. Results suggest that the rolling cultivator offered the best weed control among the tactics tested, without adversely affecting soil quality.
Container production has increased rapidly in many parts of the U.S. over the past 15 years. Container production has been the fastest growing sector in the nursery industry and the growth is expected to continue. Weed growth in container-grown nursery stock is a particularly serious problem, because the nutrients, air, and water available are limited to the volume of the container. The extent of damage caused by weeds is often underestimated and effective control is essential. Various researchers have found that as little as one weed in a small (1 gal) pot affects the growth of a crop. However, even if weeds did not reduce growth, a container plant with weeds is a less marketable product than a weed-free product. Managing weeds in a container nursery involves eliminating weeds and preventing their spread in the nursery, and this usually requires chemical controls. However, chemical controls should never be the only management tools implemented. Maximizing cultural and mechanical controls through proper sanitation and hand weeding are two important means to prevent the spread and regeneration of troublesome weeds. Cultural controls include mulching, irrigation methods (subirrigation), and mix type. Nursery growers estimate that they spend $500 to $4000/acre of containers for manual removal of weeds, depending on weed species being removed. Economic losses due to weed infestations have been estimated at approximately $7000/acre. Reduction of this expense with improved weed control methodologies and understanding weed control would have a significant impact on the industry. Problems associated with herbicide use in container production include proper calibration, herbicide runoff concerns from plastic or gravel (especially when chemicals fall between containers) and the need for multiple applications. As with other crops, off-site movement of pesticides through herbicide leaching, runoff, spray drift, and non-uniformity of application are concerns facing nursery growers. This article reviews some current weed control methods, problems associated with these methods, and possible strategies that could be useful for container nursery growers.
Novel and standard herbicides were applied alone, sequentially, or tank-mixed to determine weed control efficacies and tolerances in 15 species of field-grown herbaceous perennials. Autumn applications provided excellent but short-term broadleaf (BL) and annual grass (AG) weed control. Early spring applications were equally effective and of longer duration. Mid- and late spring treatments provided moderate to poor control of AG and poor control of winter perennial BL. Single applications of prodiamine provided season-long control of AG and of spring germinating BL. Greatest number of weed species were controlled by DCPA. Increased duration occurred with tank-mixes of DCPA + pendlimethalin, DCPA + quinclorac. Quinclorac provided excellent pre/post control of AG and some BL. Crop injury was minimized with directed applications. Isoxaben provided excellent preemergent control of BL. Tank-mixes improved AG control. Treatments applied prior to, or at the same time as mulch applications increased weed control and lessened drought stress. Treatments applied over mulch were less effective, suppressed fewer weed species, were of shortened duration, and increased the likelihood of crop injury.
A rapid increase in municipal solid waste (MSW) production (2 kg/person per day), combined with a decreasing number of operating landfills, has increased waste disposal costs. Composting MSW can be an alternative method of waste disposal to traditional landfilling or incineration. Weed control methods using waste materials such as bark, straw, and sawdust were used in commercial crop production for many years before the advent of chemical weed control. Weed growth suppression by mulching can often be almost as effective as conventional herbicides. A 10 to 15 cm-deep mulch layer is needed to completely discourage weed growth in these systems, and best results are obtained with composted materials. In recent years, composts made from a large variety of waste materials have become available on a commercial scale. Preliminary investigations into the use of MSW compost as a weed control agent have shown that compost, especially in an immature state, applied to row crop middles reduced weed growth due to its high concentration of acetic, propionic, and butyric acids. Subsequently, compost can be incorporated into the soil for the following growing season to potentially improve soil physical and chemical properties. Integrated pest management programs that incorporate biological control should be adopted wherever possible because some weed species with persistent seeds can escape chemical control.
A set of studies was established in Summer 1998 to determine the tolerance of field-grown cut flower species to specific preemergence herbicides, the effectiveness of weed control by those materials, and to determine if productivity of cut flowers is affected either by the herbicides or by colored mulches. Pendimethalin provided excellent early season weed control, but poor late-season control. It consistently caused injury at 4 lb a.i./A and sometimes at the 2 lb a.i./A rate. Oryzalin provided good to excellent weed control, but slightly injured celosia and zinnia when applied at 4 lb a.i./A. Napropamide provided excellent early season weed control, but marginally acceptable weed control later in the season. Though napropamide caused some injury to celosia early in the season when applied at the high rate, no injury to any of the plants was observed later in the season. Prodiamine and trifluralin were the overall safest of the herbicides, but they provided the weakest weed control. OH-2 was very effective when placed on the soil surface, but was less effective when placed on an organic mulch. The organic mulch was designed to keep the OH-2 particles from splashing on to the crop plant and injuring the plants. OH-2 tended to be safer placed on a mulch than on the soil surface, but statice was slightly injured even when a mulch was used.
Four herbicides, alone and/or in combination, were evaluated for weed control in beds of leatherleaf fern [Rumohra adiantiformis (G. Forst) Ching]. Fair winter weed, predominantly chick weed [Stellaria media (L.) Cyr.], control was obtained with simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] at 2 kg active ingredient (a.i.)/ha, simazine + metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 1.1 + 2.2 kg a.i./ha and oxadiazon [2-terf-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] + simazine at 1.1 + 1.1 kg a.i./ha. Oxadiazon + simazine, oxadiazon + metolachlor at 1.1 + 2.2 kg a.i./ha, and simazine + metolachlor controlled spring weeds. All herbicide treatments gave fair weed control in summer. Except for simazine applied alone, none of the treatments injured leatherleaf fern visibly. Oxadiazon + metolachlor, oxadiazon + simazine, and simazine + metolachlor reduced winter weeding times. All combination treatments reduced spring weeding times, but none of the treatments reduced summer weeding times. No treatment reduced fern yield or affected average frond weights. Frond length and frond weight were positively correlated (r = 0.74).
Pejibaye (Bactris gasipaes Kunth, Palmae) is being evaluated for production of fresh heart of palm in Hawaii. Precocity, yields, and weed control were evaluated in response to woven black polypropylene mat (control), oryzalin, oxyfluorfen, and paraquat. Control plots attained 100% of plants harvested by 26 months, followed by oxyfluorfen (97.5%), oryzalin (77.5%), and paraquat (60%). Estimated heart of palm yields (3731 plants/ha) were similar with oxyfluorfen 1.2 kg a.i./ha (707 kg·ha–1), polypropylene mat (612 kg·ha–1), oxyfluorfen 0.6 kg a.i./ha (600 kg·ha–1), and oryzalin 4.5 kg a.i./ha (478 kg·ha–1). Based on precocity, yields, and weed control efficiency, the performance rating of these weed control treatments was mat ≈ oxyfluorfen > oryzalin > paraquat. Chemical names used: 4-(dipropylamino)-3,5-dinitrobenzenesulfonamide (oryzalin); 2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene (oxyfluorfen); 1,1′-dimethyl-4-4′-bibyridinium ion (paraquat).
Poster Session 18–Weed Management 19 July 2005, 12:00–12:45 p.m., Poster Hall–Ballroom E/F