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B.J. Johnson

A field experiment was conducted for 2 years to determine the effects of rate and time interval for repeated applications of the plant growth regulators (PGR) flurprimidol and paclobutrazol on vegetative suppression of `Tifway' bermudagrass [Cynodon transvaalensis Burtt-Davy × C. dactylon (L.) Pers.]. Suppression of vegetative growth of this grass was generally the same when either flurprimidol or paclobutrazol was applied twice after a 2-, 3-, or 4-week interval. The duration of growth suppression was also similar after initial application with flurprimidol at 0.84 kg·ha-l and repeated at 0.28 to 0.84 kg·ha-1 or with paclobutrazol applied initially at 1.1 kg·ha-1 an d repeated at 0.56 to 1.1 kg·ha-1. Both PGRs caused slight to moderate turfgrass injury at these rates, but the injury was temporary and the grass had fully recovered by 10 weeks. Chemical names used: α -(1-methylethyl)- α -[4-(trifluoromethoxy)-phenyl]-5-pyrimidinemethanol (flurprimidol); (±)-(R*R*) β -[(4-chlorophenyl)-methyl]- α -(1,1-dimethylethyl)-1H-1,2,4-triazole-l-ethanol (paclobutrazol).

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B.J. Johnson

Pendimethalin and oxadiazon are used commonly to control crabgrasses (Digitaria spp.) in tall fescue (Festuca arundinacea Schreb.) and common bermudagrass [Cynodon dactylon (L.) Pers.]. A field experiment was conducted for 2 years to determine if reduced pendimethalin and oxadiazon application rates would control large crabgrass [D. sanguinalis (L.) Sco.] effectively in tall fescue and common bermudagrass. Oxadiazon applied at 1.1 kg a.i./ha in each of two applications at a 60-day interval (less than recommended rate) effectively controlled large crabgrass (≥93%), regardless of turfgrass species. Pendimethalin applied at 1.1 kg a.i./ha in each of two applications controlled large crabgrass in common bermudagrass effectively (≥90%) but not large crabgrass in tall fescue (47%). The difference in pendimethalin performance between the two species was attributed to the ability of common bermudagrass to compete more successfully than tall fescue with large crabgrass during late summer. Chemical names used: 3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethy1)-l,3,4-oxadiazol-2-(3 H)-one (oxadiazon); N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin).

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B.J. Johnson

A field experiment was conducted over 2 years to determine the effects of treatment dates with plant growth regulators (PGRs) on performance of `Tifway' bermudagrass [Cynodon transvaalensis Burtt-Davy] × [C. dactylon (L.) Pers.]. For flurprimidol at 0.84 kg·ha-1, the highest injury occurred from 16 or 28 June application in 1987 and from 17 May or June application in 1988. The injury was similar from treatment dates with flurprimidol + mefluidide or paclobutrazol + mefluidide. The PGRs were applied over a longer period in 1987 than 1988 without affecting vegetative suppression of `Tifway' bermudagrass. However, in 1988, the suppression from the 17 May treatment was equal to or better than that obtained when treatment dates were delayed until 1 June or later. Chemical names: α-(1 -methylethyl)- α -[4-(trifluoromethoxy)phenyl]-5-pyrimidinemethanol (flurprimidol); N -[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl]amino]phenyl]acetamide (mefluidide); (±)-(R*R*) β -[(4-chlorophenyl)-methyl]- α -(1,1-dimethylethyl)- 1H -1,2,4-triazole- 1-ethanol (paclobutrazol).

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Sang Ryul Shim and B.J. Johnson

Creeping bentgrass (Agrostis palustris Huds.) putting greens are commonly infested with crabgrass (Digitaria spp.) and goosegrass [Eleusine india (L.) Gaertn.]; however, many herbicides have the potential to severely injure this turfgrass species. A field investigation was conducted over 2 years to determine the tolerance of creeping bentgrass to various herbicides. Trifluralin plus benefin (2.2 to 6.7 kg·ha-1), dithiopyr (0.37 to 1.1 kg·ha-1), and prodiamine (0.5 to 1.7 kg·ha-1) did not injure creeping bentgrass. Pendimethalin caused only slight injury when applied at 3.4 kg·ha-1, but injury increased in 1 of 2 years when applied at ≥6.7 kg·ha-1. Creeping bentgrass was severely injured when treated with benefin plus oryzalin (≥4.5 kg·ha-1), fenoxaprop (0.07 kg·ha-1), and oxadiazon (3.4 kg·ha-1) granular and WP formulations and, therefore, should not be applied to the turf. Chemical names used: N -butyl-N -ethyl-2, 6-dinitro-4-(trifluoromethyl) benzenamine (benefin); S,S -dimethyl 2-(difluoromethyl-4-(2-methylpropyl)-6-(trifluoromethyl-3, 5-pyridinedicarbothioate (dithiopyr); (±) 2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoic acid (fenoxaprop); 4-(dipropylamino)-3,5-dinitrobenzenesulfonamide (oryzalin); 3-[2,4-dichloro-5-(l-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one (oxadiazon); N -(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin); 2,4-dinitro N,N -dipropyl-6-(trifluoromethyl)-1,3-benzenediamine (prodiamine); 2,6-dinitro-N-N -dipropyl-4-(trifluoromethyl)benzenamine (trifluralin).

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R.N. Carrow and B.J. Johnson

A turfgrass wear injury study was conducted at Griffin, Ga., on `Tifway' bermudagrass (Cynodon dactylon × C. transvaalensis) using two golf car tires and three golf car types driven in a semicircular pattern to deliver 85 passes over the tread path plot area. Wear injury for the 14 days after wear was applied was assessed by visual quality, percent green coverage, leaf bruising, and verdure. Golf tire × car interactions occurred, but more wear occurred with the low pressure (48 × 103 Pa), dimpled tread tire with flexible sidewalls than the commonly used bias ply (4-ply), V-shaped tread tire with more rigid sidewalls. Significant differences in wear damage occurred for golf car type but were influenced by tire design. Thus, selection of golf car tire and golf car type can influence the degree of wear injury on turfgrass sites.

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Heidi J. Johnson, Jed B. Colquhoun and Alvin J. Bussan

There is significant interest from vegetable processors, growers, and consumers in organic sweet corn (Zea mays) production. Organic nitrogen (N) management is particularly challenging in high N consuming crops such as sweet corn because of the low N content and low N to phosphorus (P) ratios of organic soil amendments. Various management programs were compared to determine the optimal combination of soil amendments and green manure crops for organic sweet corn production. Alfalfa (Medicago sativa), rye (Secale cereale), and field pea (Pisum sativum) were used as green manure crops. Composted poultry manure and a high N content organic fertilizer were used as organic amendments. Ammonium nitrate was used in a conventional management program for comparison. Treatments were designed to deliver a full rate of N (150 lb/acre), a half rate of N (75 lb/acre), and to limit the amount of P applied. Phosphorus can become a source of pollution when applied to erodible soils, particularly when soils already contain excessive P. Sweet corn yield in many of the organic programs was highly variable among years while the yield was more consistent in the conventional program. This was attributed to differences in organic N mineralization in both the green manure crops and the amendments. The most stable yield from an organic treatment, among years, was achieved using the commercially available organic N fertilizer. Commercially available amendments were costly, and although organic sweet corn received a premium price in years when organic yields were lower, profit was reduced by the high cost of N management.

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Heidi J. Johnson, Jed B. Colquhoun, Alvin J. Bussan and Carrie A.M. Laboski

Organic sweet corn (Zea mays) production is challenging for growers because of the high nitrogen (N) requirements of sweet corn and the relatively low N content of organic soil amendments. Total N supplied and rate of mineralization throughout the growing season are two important aspects in determining the optimal N management program. Green manure (GrM) crops, composted manures, and commercially available organic fertilizers are used to manage N in organic production systems. Using a combination of these tactics can optimize N while minimizing cost. In this study, we used combinations of composted poultry manure (CPM) and two organic fertilizers (one high N and one with a balance of nutrients) with three GrM crops [rye (Secale cereale), alfalfa (Medicago sativa), and pea (Pisum sativum)] in a loamy sand soil for a 112-day laboratory incubation study. Total plant available N (PAN) was quantified at six times throughout the 16 weeks to determine total N mineralized and rate of N release from each of the management programs. The CPM and the high N organic fertilizer mineralized completely within the first 6 weeks of the study, while only 65% of the other organic fertilizer mineralized by the end of the study. Total N mineralized from pea grown as a GrM for 48 days was comparable to the amount of N mineralized from rye suggesting that pea as a GrM crop should not receive an N credit in field production on a sandy soil. Significant quantities of PAN were mineralized from alfalfa residue, the equivalent of 80 lb/acre, although this is not sufficient for sweet corn production. The combination of alfalfa and the high N organic fertilizer provided sufficient N for sweet corn production and the mineralization rate closely matched sweet corn need. The release of N from CPM, even in combination with GrM crops, was asynchronous with sweet corn crop need.

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C.J. Coyne, D.C. Smith, S.A. Mehlenbacher, K.B. Johnson and J.N. Pinkerton

Resistant cultivars are a promising disease control method for eastern filbert blight, which is devastating hazelnut production in Oregon. In 1990, two studies were begun to evaluate the relative resistance of European hazelnut (Coyhls avellana) genotypes to the causal fungus, Anisogramma anomala. A randomized block design of 40 genotypes was planted using inoculated trees planted in the borders as the disease source. The first- and second-year disease incidence (percent) were compared to the published disease incidence (percent) based on exposing potted trees of 44 genotypes to high doses of inoculum. Disease incidence was significantly correlated between the two studies in 1991 (r =0.41, P = 0.02) and in 1992 (r =0.64, P = 0.001; rs = 0.35, 0.025 < P < 0.050). Three genotypes, however, showed no disease in the field, but they had disease in >70% of the potted tree study. A plot of disease incidence in the field planting indicates that the inoculum was present throughout the blocks.

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B. G. Cobb, D. L. Andrews, D. M. MacAlpine, J. R. Johnson and M. C. Drew

We have been examining the response of maize seedling roots to oxygen stress. Previously, we have shown that maize seedlings with primary root lengths of 10cm or greater require a pretreatment with low oxygen (hypoxia) for survival of greater than 12 hours of anoxia. During the pretreatment there is induction of mRNA and increase in enzymatic activity of alcohol dehydrogenase (ADH) and other enzymes that are necessary for alcoholic fermentation. However, we have found that younger seedlings do not need a pretreatment to survive anoxia. They appear to have high levels of ADH and other enzymes that are needed for anaerobic survival at levels equivalent to those that are induced in older seedlings. These results suggest that, at the time of seedling emergence, seedlings may be more adapted to oxygen stress than during later stages of growth.

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H. Friedrich, C.R. Rom, D. Johnson, J. Popp, B. Bellows, M. Savin and D. Miller

A multidisciplinary effort has been initiated between the University of Arkansas and the National Center for Appropriate Technology to identify production barriers, research and outreach needs, and market opportunities for sustainable and organic fruit in the Southern region. The goals of the project are to identify barriers of the organic system through focus group meetings with producers, processors and marketers, and to develop regional research and outreach projects to overcome these obstacles. Market development, organic fertilizer knowledge and organic pest management have been identified as areas that need research and outreach activities. Long-term outcomes are expected to increase sustainable and organic fruit production, provide opportunities for growers and consumers, and encourage local economic development in the Southern region.