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James E. Klett, David Staats, and Matt Rogoyski

Poster Session 18–Weed Management 19 July 2005, 12:00–12:45 p.m., Poster Hall–Ballroom E/F

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S. Alan Walters, Bryan G. Young, and Ronald F. Krausz

A field study was conducted in 2002, 2003, and 2004 to evaluate various pre-emergence herbicides (ethafluralin & clomazone, ethafluralin & clomazone + halosulfuron, and ethafluralin & clomazone + imazamox) with or without a winter rye (Secale cereale L.) cover crop in tillage and no-tillage `Appalachian' pumpkin (Cucurbita pepo L.) production. All herbicides were applied within two days of seeding, and no injury was observed with any of the herbicides evaluated at any time during the three growing seasons. Early- and late-season control of all weed species [giant foxtail (Setaria faberi Herrm.), common cocklebur (Xanthium strumarium L.), redroot pigweed (Amaranthus retroflexus L.), and common waterhemp (Amaranthus rudis Sauer)] were highly correlated (0.47 ≤ r ≥ 0.86, P ≤ 0.01) with pumpkin yield and fruit size. The winter rye + no-tillage system provided greater weed control compared to the tillage systems and the no cover crop + no-tillage production system. Although winter rye alone had little influence on pumpkin yield, the no-tillage system improved pumpkin yield and fruit size compared to the tillage system. The two herbicide combinations (ethafluralin & clomazone + halosulfuron and ethafluralin & clomazone + imazamox) improved weed control and pumpkin yields compared to only ethafluralin & clomazone. Although this study indicated that the use of a high-residue winter rye cover crop in no-tillage pumpkin production will provide some weed control, the choice of pre-emergence herbicides is critical to maximize pumpkin productivity. No-tillage pumpkin production is feasible with proper herbicide use and timing, although current herbicide options will not provide optimal weed control.

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Calvin Chong

The first weed disc (Weed Guard) was introduced to Ontario in the early 1980s. They were made of semirigid plastic similar to 45-rpm records. Small holes allow water to penetrate but weeds germinating on the substrate often grow through them. In the 1990s, we obtained 85% reduction of container weeds using discs made from geotextile fabric (Mori Guard) or foam (similar to polyfoam used for container winter protection). The foam disc tended to curl upward at the edges, become easily windblown, and tended to partially expose the surface of the container mix. During the past 15 years, we have annually reused the same fabric discs (now unavailable due to high unit cost), and have tested various other weed discs, including several new-generation types and also the Mori Weed Bag. The new-generation discs are fabricated from materials such as fabric (Tex-R Geodisc), pressed peat moss (Biodisc), corrugated cardboard (Corrudisc), and plastic (Enviro LID). Both Tex-R Geodisc and Enviro LID were as effective or better in controlling weeds than weekly hand-weeding, herbicides, or the Mori Guard fabric disc. The Mori Weed Bag, a patented black polyethylene sleeve with prepunched holes fitted around the container like a florist's plant prepared for market, is used effectively and almost exclusively by one Ontario nursery. We also tested two types of insulated blanket covers, which when placed around the ball of above-ground container-grown trees, prevented weed growth during the summer and also protected the root ball against cold during the winter. We introduced the garbage bag sleeve, the ultimate no-weed method for pot-in-pot tree culture, which also reduces water use and frequency of irrigation. Due to factors such as under-performance, insufficient demand, and/or high costs, only certain discs are currently manufactured: Weed Guard, Tex-R Geodisc, Biodisc, and Enviro LID. The Mori Weed Bag is available but not the insulated blankets.

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D. W. Wells, R. J. Constantin, and J. W. Wells

Six prodiamine treatments, three applied alone and three applied in combination with methazole, were compared with oxyfluorfen/oryzalin, oxadiazon, and controls (weeded and non-weeded) on ornamental and weed species. Ornamentals included green liriope, Asiatic jasmine, serissa, gardenia, `Needlepoint' holly, Japanese yew, `Prostrata' juniper, and `Carror' azalea. Weeds grown in separate containers were goosegrass, crabgrass, pigweed, and prostrate spurge. At 13 days after treatment (DAT), oxadiazon and oxyfluorfen/oryzalin caused some contact burn on liriope, and the injury persisted until the 81 DAT rating. Methazole/prodiamine treatments caused chlorosis on gardenia leaf tips, with plants recovering by 61 DAT. These combinations also resulted in slight injury to azalea at the first rating, but the injury disappeared by the second rating. Control of goosegrass, crabgrass, and pigweed was good to excellent with all chemical treatments. Control of spurge using oxadiazon and oxyfluorfen/oryzalin decreased at 81 and 100 DAT.

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D. W. Wells, R. J. Constantin, and J. W. Wells

Six prodiamine treatments, three applied alone and three applied in combination with methazole, were compared with oxyfluorfen/oryzalin, oxadiazon, and controls (weeded and non-weeded) on ornamental and weed species. Ornamentals included green liriope, Asiatic jasmine, serissa, gardenia, `Needlepoint' holly, Japanese yew, `Prostrata' juniper, and `Carror' azalea. Weeds grown in separate containers were goosegrass, crabgrass, pigweed, and prostrate spurge. At 13 days after treatment (DAT), oxadiazon and oxyfluorfen/oryzalin caused some contact burn on liriope, and the injury persisted until the 81 DAT rating. Methazole/prodiamine treatments caused chlorosis on gardenia leaf tips, with plants recovering by 61 DAT. These combinations also resulted in slight injury to azalea at the first rating, but the injury disappeared by the second rating. Control of goosegrass, crabgrass, and pigweed was good to excellent with all chemical treatments. Control of spurge using oxadiazon and oxyfluorfen/oryzalin decreased at 81 and 100 DAT.

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Brian A. Kahn, Raymond Joe Schatzer, and Wendy A. Nelson

The herbicides trifluralin, metolachlor, and paraquat were compared for efficacy of weed control in cowpea with and without cultivation as a supplemental strategy for two years. Herbicides also were compared against a no-herbicide control (with and without cultivation). Cultivation had no significant effect on seed yield, biological yield, or harvest index of cowpea. Paraquat, used in a “stale seedbed” system, was ineffective for weed control and did not change cowpea yield from that of the no-herbicide control. Trifluralin and metolachlor more then tripled cowpea seed yield compared to that of the no-herbicide control in 1988, when potential weed pressure was 886 g m-2 (dry wt.). Trifluralin and metolachlor did not significantly increase cowpea seed yield compared to that of the no-herbicide control in 1989, when potential weed pressure was 319 g m-2 (dry wt.). However, in 1989, these two herbicides each still increased net farm income by $206 per hectare compared to the income obtained without an herbicide.

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Bert T. Swanson and James B. Calkins

Fourteen herbicides or herbicide combinations, a wood chip mulch, a chipped rubber tire mulch, and a newspaper mulch were evaluated for weed control efficacy and potential phytotoxicity using 12 species of herbaceous perennials under field-growing conditions. Nineteen herbicides or herbicide combinations were similarly evaluated under container-growing conditions using 11 species of herbaceous perennials. The effect of herbicide application time also was monitored through application of herbicides to dormant and actively growing plants. Herbicides and mulch treatments were compared to weeded and nonweeded controls. Herbicide phytotoxicity effects were dependent on the age and species of the herbaceous perennial and herbicide application timing. Herbicide injury was generally greater for newly established plants compared to established plants. Although injury was usually reduced when herbicides were applied to dormant plants, injury was sometimes greater when herbicides were applied in early spring compared to applications made in late spring after complete herbaceous perennial emergence. This effect resulted in injury to young shoots that had emerged before the earliest possible time that herbicides could be applied in early spring. A wood chip mulch provided the most effective weed control and highest quality plants under field growing conditions. Several of the herbicides evaluated demonstrated potential for weed control in both field and container herbaceous perennial production systems and landscape plantings.

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Efren C. Celaya and Brenda S. Smith

A field experiment was conducted on broccoli (Taki Marathon variety) at California Polytechnic State University, San Luis Obispo to evaluate three rates of AN-20 for weed control and crop phytotoxicity. The rates were: low-40 gal./A, standard-60 gal./A, high-80 gal./A, and untreated control. Each treatment was applied to the base of the broccoli plant to avoid crop injury. Each treatment had four replications. Data collected included hoe time/plot and percent visual control. Broccoli was not injured at any rate of AN-20. It was noticed that the older weeds, greater than five-leaf stage, managed to pull through, so size of weed is crucial. On a cost-per-acre basis, the money saved on the high rate is half that of the low rate and one third that of the control. Weed control was not adequately controlled at the standard and low rates. An economic analysis was conducted, and it was found there was a savings as less labor was required to hoe the field when AN-20 had been applied.

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James E. Klett and David Staats

During the 1999 season, preemergent herbicides were applied to container-grown herbaceous perennials and evaluated on the basis of weed control, phytotoxicity, and effect on plant growth. The herbicides and rates were: Oxyfluorfen + Pendimethalin (Scotts Ornamental Herbicide II) 3 and 6 lb ai/A, Napropamide (G) (Devrinol) 3 and 6 lb ai/A, Oryzalin (Surflan) 2 and 4 lb ai/A, Oxadiazon (Ronstar) 4 and 8 lb ai/A, Oxyfluorfen + Oryzalin (Rout) 3 and 6 lb ai/A, Prodiamine (Barricade) 0.65 and 1.3 lb ai/A, Pendimethalin (Scotts Ornamental Weedgrass Control) 2 and 4 lb ai/A, Trifluralin (Treflan) 4 and 8 lb ai/A. Herbicides were applied to Penstemon mexicali `Red Rocks'™, Osteospermum barberiae compactum `Purple Mountain'™, Gazania linearis `Colorado Gold'™, Agastache rupestris, Diascia integerrima `Coral Canyon'™, and Zauschneria arizonica. All plant and herbicide combinations did not result in any significant decline in plant growth. All herbicides provided good weed control.

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Warren Roberts, Jim Shrefler, Jim Duthie, and Jonathan Edelson

A study was conducted in southeastern Oklahoma to determine treatments or combinations of treatments that provided the best weed control and crop yield for watermelon. `Allsweet' watermelons were grown with different combinations of mechanical and chemical weed control. Treatments included naptalam, clomazone, naptalam + clomazone, bensulide, naptalam + bensulide, napropamide, trifluralin, dcpa, ethalfluralin, sethoxydim, paraquat, glyphosate, cultivation, cultivation + hoeing, cultivation + paraquat, cultivation + glyphosate, and one treatment with no weed control. Glyphosate and paraquat were applied as wipe-on when weeds were taller than watermelons. The five treatments with greatest yields were (in descending order) cultivation + hoeing, trifluralin, cultivation + paraquat, cultivation, and dcpa. The treatments with lowest yield were the control, paraquat, glyphosate, and naptalam. A visual rating (0–10, 0 is poor, 10 is ideal) was taken about 5 weeks after seeding. Treatments with a visual rating of 6 or more were trifluralin (9.4), cultivation + hoeing (9.3), napropamide (9.3), cultivation + glyphosate (7.5), cultivation + paraquat (6.8), dcpa (6.7), and cultivation (6.5). With the exception of the cultivation + hoeing, all plots were weedy at harvest time. Suppression of selected weeds by a herbicide usually allowed rapid growth of the remaining weeds.