Economic analyses compared the returns of weed control methods for drip and sprinkler irrigated celery (Apium graveolens L. `Sonora'). The nine treatments included an untreated control, cultivation as needed for weed control, a pre-emergent herbicide (trifluralin), and six post-emergent herbicides. The effect of each treatment on weed control, yield, crop value, cost of control, costs for additional hand-weeding, net return, and dollar investment (marginal rate of return) was determined. The treatments that reduced weed populations under drip and sprinkler irrigation also increased yield, net returns, and rate of returns. Effective weed control reduced the additional costs of hand-hoeing the weeds not killed by herbicides, resulting in greater net return. The net returns of weed control were even greater when celery was drip irrigated than when sprinklers were used. In 1998, the sprinkler irrigated field returned $1148 to $3921/ha, compared with -$5984 for the untreated control. Net returns for drip irrigation were much higher, ranging from $3904 to $9187/ha compared with -$8320 for the untreated control. Net returns were also higher in 1999, ranging from $2466 to $5389 when weeds were controlled compared with a net loss of $5710 for the untreated control in the sprinkler irrigated field. The returns on the drip-irrigated field were much higher, from $6481 to $8920 when weeds were controlled, compared with -$8046 for the untreated control. The associated returns for every dollar invested (marginal rate of return) in the non-dominated treatment (more return and lower cost) ranged from 52% to 156% for sprinkler irrigation, and 59% to 144% for drip irrigation in 1998. In 1999, the rate of return for each dollar invested ranged from 104% to 324% for sprinkler and 2.4% to 321% for drip irrigated fields.
A 2-year field project was conducted in Thermal, Calif., to investigate cowpea [Vigna unguiculata (L.) Walp.] mulch as an alternative weed control option in pepper (Capsicum annuum L.) production. Treatments included: bare ground (BG) with hand weeding, BG with no weeding, cowpea mulch (CM) with hand weeding, and CM with no weeding. Cowpea was seeded in July on 76-cm beds and irrigated with buried drip line. Two weeks prior to transplanting peppers, irrigation water was turned off to desiccate the cowpea plants. In September, cowpea was cut at the soil line, mulch was returned to the top of the bed, and pepper plants were transplanted into the mulch and fertilized through the drip line. Every 2 weeks, the number of weeds emerged and pepper plant height were recorded. Fruit production, pepper plant dry weight, and weed dry weight were recorded at harvest in December. Fewer weeds emerged in CM than in BG. The final weed population in nonweeded CM was reduced 80% and 90% in comparison with nonweeded BG in 1997 and 1998, respectively. Weed dry weights in nonweeded CM were 67% and 90% less than those in nonweeded BG over the same period. In 1997 and 1998, respectively, pepper plants produced 202% and 156% more dry weight, as well as greater fruit weight, in CM than in BG. There were no differences in mean fruit weight. Cowpea mulch provided season-long weed control without herbicides while promoting plant growth and fruit production.
Combinations of seeding rate, spacing, and weed control treatments were evaluated for their effect on the performance of the Virginia Tech transplanted meadow technique. The treatments consisted of seeding at 112 or 56 g·90 m−2; within-row transplant spacing of 30, 45, or 60 cm; and mulching, oryzalin application, or no weed control measures. Plant competition alone was insufficient, whereas oryzalin was the most effective for weed control but also reduced the plant stand and floral display. Mulch provided effective weed control with maximum floral display. Close transplant spacing within rows resulted in quick site coverage initially, but this advantage disappeared after 8 weeks compared to wider spacing. Seeding rate did not affect site coverage until the meadow reached maturity at 12 weeks. The lower seed rate allowed more lodging, resulting in a more open appearance and greater canopy light transmission. Chemical name used: 4-(dipropylamino)-3,5-dinitrobenzenesulfonamide (oryzalin).
During 1978 and 1979, oxadiazon [2-ferf-butyl-4-(2-,4-dichloro-5-isopropoxyphenyl)-1,3,4-oxadiazolin-5-one] and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] were evaluated on 7 species of container-grown ornamentals for full season weed control, phytotoxicity, and final plant size. Based on these experiments, both herbicides provided 75% or better weed control for a 4 month period when applied at recommended and higher rates. Neither herbicide caused any significant plant injury to the 7 species when applied at 4 times the recommended rate. The largest plants were produced in containers treated with the herbicide rates providing the best weed control, and also in the weeded controls.
A 3-step method for weed control in onion seed fields is described which involves early spring tillage to kill winter-annual weeds; mid-spring tillage plus a preemergence herbicide to kill spring-annual weeds and a directed herbicide spray at layby time to kill the summer-annual weeds. The method gave nearly complete season-long weed control on experimental plots as well as commercial onion seed fields.
This experiment was conducted to determine temporal weed management parameters for tart cherry (Prunus cerasus L.) orchards. Annual ryegrass (Lolium multiflorum L.) and lambsquarter (Chenopodium album L.) were planted in tree rows of a 4-year-old tart cherry orchard. Weeds either were not controlled or controlled with nonresidual herbicides during the following intervals: all-summer; May, June, July, or August; preharvest (April-July); or postharvest (late July to frost). Trees in all-summer, June, and preharvest weed-free plots had more shoot growth, more nodes, longer internodes, greater leaf area, and higher concentrations of leaf nitrogen than did those in the weedy control and postharvest, July, or August treatments. A larger increase in trunk circumference was observed in all-summer and preharvest weed-free plots than in postharvest and weedy plots. Early-summer weed control was important for tree vegetative growth. Tree yield (fruit weight and number) was greater on trees without weed competition postharvest than in those treated in May, June, July, or in weedy controls. Late-season (after late July) weed control is therefore important for fruit yield.
Growth of 2-year-old tart cherry (Prunus cerasus L.) trees as measured by trunk circumference increase or total shoot elongation was significantly greater in plots receiving chemical or mechanical weed control within the tree row than in plots receiving between-row cultivation only. Shoot growth of one-year-old apple (Malus domestica Borkh. ‘Delicious’) trees responded similarly to weed control. Tart cherry trees in hand weeded and dinoseb or glyphosate treated plots had greater growth than those in paraquat treated plots. Tart cherry trees in plots receiving chemical or mechanical weed control out-yielded trees in unweeded plots during the first year of production. ‘Delicious’ apple trees in plots treated with dinoseb (6.7 and 10.1 kg/ha), the high rate of glyphosate (1.7 kg/ha), or mechanical weed control also outyielded trees in unweeded plots during the first year of production. Effects of weed control on growth and yield were less distinct during the 2nd year of production. Trees from treated plots came into production one year earlier than trees in the unweeded plots. Chemical names used: 2-(1-methylpropyl)-4,6-dinitrophenol (dinoseb); N-(phosphonomethyl)glycine (glyphosate); 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat).
The economics of pesticide production and registration has limited the number of pesticides registered for use in minor crops relative to agronomic crops. Current regulations such as the Food Quality Protection Act may further reduce the number of efficacious compounds registered for use on minor crops. Traditionally, the lack of registered pesticides for minor crops has been offset by soil fumigation. However, methyl bromide use is scheduled for phase-out in the United States by 2005, leaving a pest control vacuum in some crops. Loss of methyl bromide has stimulated research into the use of other soil fumigants for weed control. Methyl bromide, methyl iodide, propargyl bromide, 1,3-dichloropropene, and metham sodium have been tested alone and in combination with chloropicrin in laboratory experiments to determine their efficacy against Cyperus esculentus L (yellow nutsedge) tubers. All the fumigants controlled nutsedge equal to or better than methyl bromide and resulted in synergistic control when combined with chloropicrin. Although excellent weed control can be achieved with all the fumigants in the laboratory, weed control in the field with the same fumigant may result in poor or no control. Further research is necessary to optimize the field application of the remaining fumigants to maximize pest control. In the near future, to achieve the broad-spectrum pest control obtained with methyl bromide, growers will need to rely on multiple control strategies. The most promising replacement program for broad-spectrum pest control includes dichloropropene/chloropicrin fumigation followed by a herbicide program or mechanical weed control. To control problem weeds that are not controlled with the in-season herbicide program, a chemical fallow program should be instituted in the off-season to reduce weed pressure during the cropping season.
Alternative approaches to strawberry production that rely on cultural practices, biological controls, or natural products to reduce or replace off-farm chemical inputs are needed. Driving this growing interest are environmental concerns and rising production costs. Corn gluten meal (CGM), a byproduct of corn wet-milling, has weed-control properties and is a N source. The weed control properties of CGM have been identified in previous studies. The hydrolysate is a water-soluble, concentrated extract of CGM that contains between 10% to 14% N. Our objective was to investigate corn gluten hydrolysate as a weed control product and N source in `Jewel' strawberry production. The field experiment was a randomized complete block with a factorial arrangement of treatments and four replications. Treatments included application of granular CGM, CGM hydrolysate, urea, urea, and DCPA (Dacthal), and a control (no application). Granular CGM and urea were incorporated into the soil at a depth of 2.5 cm at rates of 0, 29, 59, and 88 g N/plot. Plot size was 1 × 3 m. The field experiment was conducted from 1995-1998. The source of nitrogen showed few effects for all variables measuring yield and weed control for all years. In general, the rate of nitrogen had little or no effect on total yield. However, the rate of nitrogen at 88 g N/plot showed an increase in average berry weight, leaf area, leaf dry weight, and weed control.
Five weed-control treatments (unweeded; hand-weeded; bensulide and naptalam; bensulide, naptalam, and paraquat; black polyethylene mulch) were combined factorially with three row-cover treatments (no cover, spun-bonded polyester, highly perforated polyethylene) in a 2-year experiment. Slicing cucumbers (Cucumis sativus L.) were transplanted 26 (1985) or 23 (1986) days after application of the bensulide-naptalam. This combination of herbicides provided weed control for up to 4 weeks after transplanting, but was less effective in 1986 than in 1985. Row covers reduced herbicide efficacy. Spraying paraquat through the covers 2 to 3 days before setting transplants significantly improved weed control and cucumber yield. Soil crusting was reduced, and earliness and total yield were enhanced by mulch and row covers. Greatest yields and estimated net economic return in both years occurred with row covers with mulch followed by mulch alone in 1986 and by mulch alone or hand-weeding with row covers in 1985. Weed control, earliness, and yield were not affected significantly by type of row cover in either year. Chemical names used: O,O-bis(1-methylethyl)-S-[2-(phenylsulfonyl)amino]ethyl]phosphorodithioate (bensulide); 2-[(1-napthalenylamino)carbonyl]benzoic acid (naptalam); 1,1′-dimethyl-4,4′-bipyridinium salts (paraquat).