The influence of `Elbon', `Maton', and `Wheeler' winter rye (Secale cereale) with or without herbicide treatments on weed control in no-tillage (NT) zucchini squash (Cucurbita pepo) was determined. `Elbon' or `Maton' produced higher residue biomass, greater soil coverage, and higher weed control compared with `Wheeler'. Although winter rye alone did not provide sufficient weed control (generally <70%), it provided substantially greater redroot pigweed (Amaranthus retroflexus) and smooth crabgrass (Digitaria ischaemum) control (regardless of cultivar used) compared with no winter rye at both 28 and 56 days after transplanting (DAT). No effect (P > 0.05) of winter rye cultivar on early or total squash yield was detected. Although applying clomazone + ethalfluralin to winter rye residues improved redroot pigweed control compared with no herbicide, the level of control was generally not adequate (<85% control) by 56 DAT. Treatments that included halosulfuron provided greater control of redroot pigweed than clomazone + ethalfluralin, and redroot pigweed control from halosulfuron treatments was similar to the weed-free control. However, regardless of year or cover crop, any treatment with halosulfuron caused unacceptable injury to zucchini squash plants which lead to reduced squash yield (primarily early yields). Insignificant amounts of squash injury (<10% due to stunting) resulted from clomazone + ethalfluralin in no-tillage plots during either year. Treatments with clomazone + ethalfluralin had early and total yields that were similar to those of the weed-free control, although this herbicide combination provided less weed control compared with the weed-free 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).
Five field experiments compared weed control systems for snap bean (Phaseolus vulgaris L.) production in 25-cm rows including herbicides, but no cultivation, to systems for conventional 91-cm rows including both herbicides and cultivation. Herbicide combinations of EPTC + dinoseb each at 3.4 kg/ha, EPTC at 3.4 kg/ha + bentazon at 0.8 kg/ha, and trifluralin at 0.6 kg/ha + bentazon at 0.8 kg/ha provided excellent control of annual weeds and yellow nutsedge in most experiments. With the most effective herbicide treatments, weed control was similar in 25-cm and 91-cm rows. However, when herbicide treatments failed to control all weed species, weed control in 91-cm rows was better than that in 25-cm rows, because 91-cm rows were cultivated. Snap beans in 25-cm rows yielded an average of 25% higher than snap beans in 91-cm rows (plant density was equivalent at both row spacings). As weed control improved, the magnitude of the yield difference between 25-cm and 91-cm row spacings increased.
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 study in Lexington, Ky., evaluated weed control efficacy and influence on yields of several organic mulches in two organically managed bell pepper (Capsicum annuum) production systems. Five weed control treatments [straw, compost, wood chips, undersown white dutch clover (Trifolium repens) “living mulch,” and the organically approved herbicide corn gluten] were applied to two production systems consisting of peppers planted in double rows in either flat, bare ground or on black polyethylene-covered raised beds. In the first year, treatments were applied at transplanting and no treatment was found to provide acceptable season-long weed control. As a result, bell pepper yields in both production systems were very low due to extensive weed competition. First year failures in weed control required a modification of the experimental protocol in the second year such that treatment application was delayed for 6 weeks, during which time three shallow cultivations were used to reduce early weed pressure and extend the control provided by the mulches. This approach increased the average weed control rating provided by the mulches from 45% in 2003 to 86% in 2004, and resulted in greatly improved yields. In both years, polyethylene-covered raised beds produced higher yields than the flat, bare ground system (8310 lb/acre compared to 1012 lb/acre in 2003 and 42,900 lb/acre compared to 29,700 lb/acre in 2004). In the second year, the polyethylene-covered bed system coupled with mulching in-between beds with compost or wood chips provided excellent weed control and yields. When using the wood chip mulch, which was obtained at no cost, net returns were $5587/acre, which is similar to typical returns for conventionally grown peppers in Kentucky. Net returns were substantially decreased when using compost due to the purchase cost. Results from this study indicate that shallow cultivation following transplanting, combined with midseason mulch application, resulted in high yields in an organically managed bell pepper system that were comparable to yields of most varieties grown conventionally in a variety trial conducted on the same farm.
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.
Application of linuron was compared with hand-weeding and a nontreated control (= control) for weed control in carrots. Linuron, applied pre- or postemergent, was slightly less effective than the 100% weed control obtained by hand-weeding. Carrot yields were similar for all treatments, and were at least six times as great as in the control. In 1996, linuron treatments returned net profits ranging from $980 to $1887 per ha, compared to $740 for hand-weeding and -$2975 for the control. In 1997, return on linuron treatments was greater, ranging from $5326 to $6426, compared with $2852 for hand-weeding. Marginal rates of return ranged from 21% to 86% in 1996. In 1997, rates of return for every dollar invested in linuron were over 59%. Chemical name used: N′-(3,4-dichlorophenyl)-N-methoxy-N-methylurea (linuron).
Application of linuron was compared with hand-weeding and a nontreated control (= control) for weed control in carrots. Linuron, applied pre- or postemergent, was slightly less effective than the 100% weed control obtained by hand-weeding. Carrot yields were similar for all treatments, and were at least six times as great as in the control. In 1996, linuron treatments returned net profits ranging from $980 to $1887 per ha, compared to $740 for hand-weeding and - $2975 for the control. In 1997, return on linuron treatments was greater, ranging from $5326 to $6426, compared with $2852 for hand-weeding. Marginal rates of return ranged from 21% to 86% in 1996. In 1997, rates of return for every dollar invested in linuron were over 59%. Chemical name used: N′-(3,4-dichlorophenyl)-N-methoxy-N-methylurea (linuron).
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.
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.