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James E. Klett, Laurel Potts and David Staats

During the 1998 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: Napropamide (Devrinol 10G), 0.72 and 1.44 kg a.i./ha; Oryzalin (Surflan 40AS), 0.36 and 0.72 kg a.i./ha; Oxadiazon (Ronstar 2G), 0.72 and 1.44 kg a.i./ha; Oxyfluorfen + Oryzalin (Rout 3G), 0.54 and 2.16 kg a.i./ha; Oxyfluorfen + Pendimethalin (Scott's OH II), 0.54 and 1.09 kg a.i./ha; and Trifluralin (Treflan 5G), 0.72 and 1.44 kg a.i./ha. Herbicides were applied to Phalaris arundinacea `Picta', Scabiosa caucasica, Sedum × `Autumn Joy', Pennisetum setaceum `Rubrum', Salvia argentea, Penstemon × mexicali `Red Rocks', Osteospermum barberiae v. compactum `Purple Mountain', and Gazania linearis `Colorado Gold'. Phytotoxicity symptoms (visual defects) were apparent with Napropamide on Phalaris (at both rates) but recovered by the end of season. All herbicides provided good weed control.

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John F. Karlik and Martha P. Gonzalez

Roses are likely the most popular garden plant in the United States, and cultivars are also used as landscape plant materials. Three herbicide trials with two main objectives were conducted with rose plants. The first objective was to evaluate injury to the roses when over-sprayed at various stages of growth. The second objective was to evaluate the efficacy of the herbicides. All herbicides were used at label rates and applied over the top of rose plants. In the first trial, the pre-emergent herbicides pendimethalin, oryzalin, trifluralin, metolachlor, napropamide, and oxyfluorfen were applied to plots containing dormant roses with ≈1-cm shoots just pushing. Evaluations of shoot length taken over the next 6 weeks showed no differences in growth of rose plants, but weed populations were reduced. In the second trial, five post-emergent herbicides were applied to plots containing dormant roses. Herbicides evaluated included the grass herbicides fluazifop-p-butyl, sethoxydim, and clethodim. The nonselective herbicide glyphosate was included in the trial, as was a combination herbicide containing 2,4-D, mecoprop, and dicamba. There was no visible injury to rose plants until 6 weeks after treatment. At that time, roses treated with glyphosate had shorter shoots. Recovery from glyphosate appeared more rapidly than recovery from the combination herbicide. Weed control varied with each herbicide. The third trial evaluated the same five herbicides for control of bermudagrass in late spring. Injury to roses was noted immediately from the combination herbicide and glyphosate. All the grass herbicides and glyphosate were effective in controlling bermudagrass.

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James E. Klett, David Hillock and David Staats

Herbicides were applied to container-grown herbaceous perennials and evaluated on the basis of weed control, phytotoxicity, and effect on plant growth. During the 1995 season six preemergent herbicides [(in kg·ha–1) Napropamide (Devrinol 10G), 4.5 and 9.1; Isoxaben (Gallery 75DF), 1.1 and 2.3; Oxadiazon (Ronstar 2G), 4.5 and 9.1; Oxyfluorfen + Oryzalin (Rout 3G), 3.4 and 13.6; Oryzalin (Surflan AS), 2.8 and 4.5; and Trifluralin (Treflan 5G) 4.5 and 9.1, were tested on Callirhoe involucrata, Delosperma nubigenum, Dendranthemum ×morifolium `Jennifer', Festuca cinerea `Sea Urchin', and Gypsophila paniculata `Fairy's Pink'. Isoxaben (both rates) resulted in visual phytotoxicity symptoms and sometimes death to Dendranthemum. Oxadiazon (9.1 kg·ha–1) and Oxyfluorfen + Oryzalin (both rates) resulted in plant chlorosis and necrosis to Delosperma soon after herbicide application, but plants outgrew herbicide damage. Napropamide (both rates), applied to Delosperma, resulted in less dry weight when compared to some of the other herbicide treatments. Oryzalin (4.5 kg·ha–1) resulted in visual phytotoxicity and less plant dry weight to Festuca. Data analysis revealed no significant differences in Callirhoe and Gypsophila. In general, most herbicides controlled weeds effectively.

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Randy Smith, Darin Lickfeldt, Dan Loughner, Mike Melichar and James Breuninger

In 2003 and 2004, a new herbicide containing three active ingredients was evaluated for efficacy on important weed species and the tolerance of popular ornamental plant species. Currently available ornamental herbicides differ greatly in the weeds they control and tolerance of ornamental plants grown in production nurseries. This new granular product, trade name Showcase, also known by its experimental number, GF-1162, contains 2% trifluralin, 0.25% isoxaben, and 0.25% oxyfluorfen. With preemergent applications applied to pots artificially infested with weed seed, GF-1162 demonstrated exceptional control of many difficult to control species, such as spurge, groundsel, bittercress, oxalis, and crabgrass. When applied preemergence at 150 lb/acre, GF-1162 was as efficacious as current standards. At 200 lb/acre, weed control was exceptional, exceeding all products included in the trials. Ornamental tolerance to GF-1162 was comparable to that of Snapshot TG, with the exception of whorled plants. On whorled plants, such as daylily and hosta, where granular products can be retained on leaf surfaces, products containing oxyfluorfen must be applied with special precautions to immediately shake or wash granules from leaf surfaces. Even when whorled plants were injured by GF-1162, they did eventually recover. GF-1162 received a federal registration in 2004 and state registrations may be complete as early as Spring 2005, at which time this new herbicide would be made available to ornamental nurseries and lawn care companies as an alternative to current herbicide options.

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David Staats, James Klett, Teri Howlett and Matt Rogoyski

During the 2005 season, three preemergence herbicides were applied to four container-grown herbaceous perennials and evaluated for weed control, phytotoxicity, and effect on plant growth. The herbicides and application rates were: 1) Pendimethalin (Pendulum 2G) 2.24, 4.48, and 8.96 kg/ha; 2) Trifluralin and Isoxaben (Snapshot 2.5 TG) 2.8, 5.6, and 11.2 kg/ha; and 3) S-metolachlor (Pennant Magnum 7.6 EC) 2.8, 5.6, and 11.2 kg/ha. Herbicides were applied to Coral Bells (Heuchera sanguinea), Hopflower Oregano (Origanum libanoticum), CORONADO™ Hyssop (Agastache aurantiaca), and SPANISH PEAKS™ Foxglove (Digitalis thapsi). Treatments were applied twice with 30 days between applications. Plants were evaluated for phytotoxicity after 1, 2, and 4 weeks after applying herbicide treatments. No phytotoxicity symptoms were apparent on any of the plants treated with Pendulum, and plant size (dry mass) was not affected. Snapshot resulted in visual phytotoxicity with Digitalis and Heuchera at the higher rates and also resulted in smaller plants. Pennant Magnum caused phytotoxicity at all rates in all plants and resulted in significantly smaller plants than the control. Weed control was very good with all herbicides, but did not control every weed.

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James E. Klett and David Hillock

Herbicides were applied to container-grown herbaceous perennials and evaluated on the basis of weed control and phytotoxicity. During the 1994 season, seven preemergent herbicides, napropamide (Devrinol) at 4.5 and 9.1 kg·ha–1, metolachlor (Pennant) at 4.5 and 9.1 kg·ha–1, isoxaben (Gallery) at 1.1 and 2.3 kg·ha–1, oxadiazon (Ronstar) at 4.5 and 9.1 kg·ha–1, oxyfluorfen + oryzalin (Rout) at 3.4 and 13.6 kg·ha–1, oryzalin (Surflan) at 2.8 and 4.5 kg·ha–1, and trifluralin (Treflan) at 4.5 and 9.1 kg·ha–1, were tested on Aquilegia caerulea `McKana's Giant', Digitalis purpurea, Gaillardia aristata, Limonium latifolium, and Veronica spicata. Isoxaben (both rates) resulted in visual phytotoxicity symptoms and death to Digitalis. Metolachlor (both rates) resulted in plant death to Veronica. Pennant (both rates), when applied to Limonium, resulted in stunted growth. Aquilegia and Gaillardia were not adversely affected. Most herbicides controlled both dicot and monocot weeds effectively.

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Pat Bowen

Research was conducted to determine whether tillage in the fall rather than spring could be used to prepare fields for transplanting broccoli and cauliflower crops. Because fall-tilled soils are prone to erosion by winter rains, the effects of a fall-planted barley cover crop were also determined. Trifluralin was applied to the spring-tilled plots, according to grower practice. Herbicide treatments applied to fall-tilled plots were early and/or late applications of glyphosate and napropamide following early and late glyphosate applications. Weed emergence was generally increased by the barley cover crop, but the species depended on which herbicides were applied. Napropamide reduced the emergence of some weed species, whether or not a cover crop was grown. Yield of broccoli was reduced by the cover crop, and was highest in fall-tilled plots that received two glyphosate treatments. Yield of cauliflower was highest in spring-tilled plots that were cover-cropped. In fall-tilled plots, cauliflower response to the cover crop and herbicide treatments was inconsistent.

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Glenn B. Fain, Charles H. Gilliam and Gary J. Keever

Hardy ferns are widely grown for use in the landscape. The 1998 National Agricultural Statistics Services census of horticulture reported production of hardy/garden ferns at 3,107,000 containers from over 1200 nurseries. There is little research on herbicide use in hardy ferns, and herbicides that are labeled for container production are not labeled for use on hardy ferns. Studies were conducted to evaluate the tolerance of variegated east indian holly fern (Arachniodes simplicior `Variegata'), tassel fern (Polystichum polyblepharum), autumn fern (Dryopteris erythrosora), rochford's japanese holly fern (Cyrtomium falcatum `Rochfordianum'), and southern wood fern (Dryopteris ludoviciana), to applications of selected preemergence applied herbicides. Herbicides evaluated included selected granular or liquid applied preemergence herbicides. Spray-applied herbicides were pendimethalin at 3.0 or 6.0 lb/acre, prodiamine at 1.0 or 2.0 lb/acre, isoxaben at 1.0 or 2.0 lb/acre, and prodiamine + isoxaben at 1.0 + 1.0 lb/acre. Granular-applied herbicides were pendimethalin at 3.0 or 6.0 lb/acre, prodiamine at 1.0 or 2.0 lb/acre, oxadiazon + prodiamine at 1.0 + 0.2 or 2.0 + 0.4 lb/acre, oxyfluorfen + oryzalin at 2.0 + 1.0 or 4.0 + 2.0 lb/acre, trifluralin + isoxaben at 2.0 + 0.5 or 4.0 + 1.0 lb/acre, oxadiazon at 4.0 or 8.0 lb/acre, and oxadiazon + pendimethalin at 2.0 + 1.25 or 4.0 + 2.5 lb/acre. The greatest reduction in growth of autumn fern was observed with the high rates of oxadiazon, oxadiazon + pendimethalin, and oxadiazon + prodiamine. Reductions in rochford's japanese holly fern growth were most severe when plants were treated with the high rate of trifluralin + isoxaben resulting in a 66% and 72% decrease in frond length and frond number, respectively. There were also reductions in frond length and number of fronds when treated with the high rate of oxadiazon + pendimethalin. There were no reductions in frond numbers on tassel fern with any herbicides tested. However, there were reductions in frond length from four of the 10 herbicides evaluated. The most sensitive fern to herbicides evaluated in 2004 was variegated east indian holly fern with reductions in frond length and number of fronds with four of the 10 herbicides tested. Southern wood fern appeared to be quite tolerant of the herbicides tested with the exception of the high rate of oxadiazon. Granular prodiamine proved to be a safe herbicide for all species tested in both 2004 and 2005. In 2005 all plants from all treatments were considered marketable by the end of the study. The durations of both studies were over 120 days giving adequate time for any visual injury to be masked by new growth. However, there was significant visual injury observed on the rochford's japanese holly fern treated with isoxaben at 60 and 90 days after treatment, which might reduce their early marketability.

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Hannah M. Mathers, Luke T. Case* and Jennifer A. Pope

DNA herbicides are the most commonly used preemergents in container nursery crops. The objectives of this study were: 1) to investigate differences between DNA herbicide applied as granulars, directed sprays, or in combination with mulch (pine nuggets and cypress) on Taxus, Azalea and and Ilex root development; and, 2) to compare efficacy of the above treatments on common groundsel (Senecio vulgaris), large crabgrass (Digitaria sanguinalis), and annual bluegrass (Poa annua). The granular formulations tested were Barricade 65 WG (prodiamine) at 2.0 lbs active ingredient per acre (a.i./ac) and Treflan TR10 (trifluralin) at 2.0 lbs a.i./ac. The liquid formulations that were used as direct sprays and to treat the mulches were Surflan 4 AS (oryzalin) at 2.0 lbs ai/ac and Pendulum 3.8 CS (pendimethalin) at 3.0 lbs a.i./ac. Evaluations of phytotoxicity and efficacy were taken as rated scores, dry weights, and leaf area measures. Evaluations were taken at 30, 60, 90, and 120 days after treatment (DAT). Efficacy ratings were based on a 0-10 scale with zero being no control, 10 perfect control and 7 commercially acceptable. By 120 DAT, none of the treatments were commercially acceptable. Root (1.52 g) and shoot (3.75 g) weights indicate that Ilex was stunted the most vs. the control (2.42 g roots and 4.87 g shoots) by the direct spray of Pendulum 2X. The Azalea was most effected by the granular application of Barricade at the 2X rate (1.72 g for roots, 4.44 g for shoots) vs. the control (2.23 g for roots, 5.83 g for shoots). Taxus roots were most stunted by Treflan 1X (0.81 g) vs. control (1.01 g). Shoot weights were the lowest with Cypress+1X Pendulum (0.90 g), vs. the control (0.96 g); however, the Treflan 1X treatment gave the second lowest shoot weight for Taxus (0.91 g).

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Charles L. Webber, Vincent M. Russo and James W. Shrefler

Non-pungent jalapeño peppers are used for making commercial picante sauces (salsas) and have a potential for outstanding yields in Oklahoma. There is incomplete information on the crop safety of certain herbicides that may not specifically address their use with non-pungent jalapeño peppers. The objective of this research was to determine the weed control efficacy and safety of a combination of preplant incorporated herbicides on transplanted non-pungent jalapeño pepper production. A field study was conducted during the Summer 2005 on 91-cm-wide raised beds at Lane, Okla. The herbicides in the study included napropramide (2.2 kg a.i./ha), clomazone (1.1 kg a.i./ha), bensulide (6.7 kg a.i./ha), and trifluralin (1.1 kg a.i./ha) used separately and in combination with one of the other herbicides. All herbicides were applied preplant-incorporated just prior to transplanting `Pace 105' non-pungent jalapeño peppers on 6 May 2005. Fruit were harvested on 21 July 2005, 76 days after transplanting. Plants treated with clomazone used by itself produced the greatest yields (16.4 t/ha) compared to plants treated with the other herbicides used individually, although it was not significantly greater than napropramide, 9.2 t/ha. Four of the five top-yielding herbicide treatments included the use of clomazone. The tank mixture of napropramide and bensulide produced the second greatest yield (16.2 t/ha). The weed-free treatment produced 17.5 t/ha compared to 86% yield reduction for the weedy check. These results demonstrated that clomazone, used individually or in combination with certain other herbicides, can maintain non-pungent jalapeño yields equivalent to weed-free levels.