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Steven M. Borst, J. Scott McElroy, and Greg K. Breeden

, sodium carbonate peroxyhytests, and even dish detergent (Ultra Dawn®; Procter & Gamble, Cincinnati). These treatments are highly variable and often ineffective compared with the use of carfentrazone and mancozeb plus copper hydroxide, both labeled for the

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David Sugar, Kate A. Powers, and Sally R. Basile

Mancozeb (Manzate 200) and kaolin (Surround WP) were applied individually and in combination in a commercial pear (Pyrus communis) orchard by air-blast sprayer in two growing seasons and in a research orchard by handgun sprayer in four growing seasons. Mancozeb was applied at 50% bloom, petal fall (PF), PF + 2 weeks and PF + 4 weeks, while kaolin and mancozeb + kaolin were applied at PF, PF + 2 weeks and PF + 4 weeks. Both materials reduced russet in both years of the commercial orchard trial and in 2 years of the research orchard trial. In one trial, kaolin treatment reduced russet to a greater extent than did mancozeb, and in one trial the combination of mancozeb plus kaolin reduced russet to a greater extent than either material alone. The year with the greatest amount of russet was the year with the most rainfall, and the year with the least russet was the year with the least rainfall. Considering that mancozeb may be used in pear orchards for suppression of pear scab (Venturia pirina) and pear psylla (Cacopsylla pyricola), and kaolin may be used for suppression of pear psylla, russet reduction by each of these materials adds to their multipurpose utility.

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Cheryl R. Boyer*, Janet C. Cole, and Kenneth E. Conway

Plants of Euonymus fortunei `Emerald Gaiety', `Emerald 'n Gold' and `Canadale Gold' were sprayed to runoff weekly at two sites with one of three fungicide treatments or water (control) to determine fungicide effectiveness in controlling anthracnose caused by Colletotrichum gloeosporioides. Copper sulfate pentahydrate was applied at 0.4 or 0.6 g·L-1 a.i. or mancozeb was applied at 1.8 g·L-1 a.i.. Plants were rated for disease incidence approximately monthly. No interaction occurred between fungicide and cultivar. Differences among fungicide treatments were not apparent until weeks 18 or 20 depending on the site, when plants treated with mancozeb had lower disease ratings than plants receiving any other treatment. Cultivars differed at almost every rating date at both sites. Poison agar experiments were conducted to determine mycelial inhibition by copper sulfate pentahydrate or mancozeb.

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Stephanie L. Schupbach-Ningen, Janet C. Cole, James T. Cole, and Kenneth E. Conway

The effectiveness of chlorothalonil, mancozeb, and trifloxystrobin applied alone or in rotations of two or three fungicides to control anthracnose symptoms caused by Colletotrichum gloeosporioides was evaluated on three cultivars of field- and container-grown wintercreeper euonymus (Euonymus fortunei) during the 2001 growing season. Studies were conducted at Stillwater, Okla.; Fayetteville, Ark.; and Park Hill, Okla. Rooted cuttings of wintercreeper euonymus `Emerald Gaiety', `Emerald 'n Gold', and `Emerald Surprise' were transplanted from 1-gal plastic containers into field soil at the Oklahoma State University Nursery Research Station and at the University of Arkansas Horticulture Farm on 10 May 2001. In a parallel study, recently transplanted rooted cuttings of the same cultivars in 1-gal pots containing substrate consisting of pine bark and sand were placed in a shadehouse under 30% shade at Stillwater and Fayetteville and 73% shade at Park Hill on 11 May 2001. `Emerald Gaiety' had fewer disease symptoms than `Emerald 'n Gold' or `Emerald Surprise' in the field and in containers at Stillwater and Fayetteville. At Fayetteville, mancozeb applied alone or in rotation with chlorothalonil or trifloxystrobin provided better anthracnose control than treatments without mancozeb, but no fungicide eliminated anthracnose symptoms. Application of fungicides in rotations that include mancozeb and use of resistant cultivars can help decrease anthracnose symptoms.

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G.H. Neilsen and J. Yorston

In an apple (Malus domestica Borkh.) orchard with a severe replant problem, tree size was increased by the 2nd year and number of fruit by the 3rd year by treating the planting hole soil with formalin or mancozeb plus monoammonium phosphate (MAP) fertilizer. Growth increases were evident each year for 4 years only for the MAP + formalin treatment. In a second orchard, with a less severe replant problem, planting-hole treatment with formalin or dazomet + MAP increased tree size by year 2. Number of fruit in year 2 was increased by formalin and mancozeb + MAP treatments, although this effect persisted in year 3 only for mancozeb + MAP. Leaf P concentrations were increased to high values in the first year by MAP fertilization but declined in subsequent years. Leaf Mn concentration also increased in one orchard, a consequence of fertilizer-induced acidification of planting hole soil and Mn uptake from the fungicide mancozeb. Chemical names used: tetrahydro-3,5-dimethyl-2 H -l,3,5-thiadiazine-2-thione (dazomet); 37% aqueous solution formaldehyde (formalin); Zn, Mn ethylene dithiocarbamate (mancozeb).

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Mary C. Koelsch, Janet C. Cole, and Sharon L. von Broembsen

Common periwinkle and `Bowles' periwinkle production has declined in the southern United States due to foliar diseases caused by Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. and Phoma exigua Desmaz. var. inoxydabilis Boerema & Vegh in Vegh et al. Our study determined whether several labeled and experimental fungicides could control pathogens causing foliar diseases in common periwinkle in vitro and outdoors during two consecutive summers. Five concentrations of each of eight fungicides were used to test inhibition of mycelial growth of P. exigua var. inoxydabilis and two isolates of C. gloeosporioides on fungicide-amended agar. All concentrations of propiconazole inhibited growth of P. exigua var. inoxydabilis (100%) and both isolates of C. gloeosporioides (>96%). Cyproconazole completely inhibited mycelial growth of P. exigua var. inoxydabilis. Thiophanate methyl/mancozeb partially inhibited growth of C. gloeosporioides (50%). In outdoor trials, plants were sprayed weekly with the following fungicides and rates (in g a.i./liter): thiophanate methyl/mancozeb, 1.35; propiconazole, 0.14; thiophanate methyl, 0.84; triforine, 0.27; cyproconazole, 0.08; triforine–CC 17461, 0.27; or CGA 173506, 0.90. Thiophanate methyl/mancozeb was most effective at reducing foliar necrosis during both seasons. Shoot dry weights of plants treated with thiophanate methyl/mancozeb were significantly higher at the end of each growing season than those of plants treated with the other fungicides or the nontreated control plants. Chemical names used: dimethyl [(1,2-phenylene)-bis (iminocarbonothioyl)] bis [carbamate] and a combination of zinc ion and manganese ethylenebisdithiocarbamate (thiophanate methyl/mancozeb); 1-[2-(2′,4′-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl-methyl]-1H-1,2,4-triazole (propiconazole); dimethyl [(1,2-phenylene)-bis (iminocarbonothioyl)] bis [carbamate] (thiophanate methyl); N,N′-[1,4-piperazinediylbis (2,2,2-trichloroethylidene)] bis [formamide] (triforine); 2-(4-chlorophenyl)-1-(1H-1,2,4-triazol-l-yl)-butan-2-ol (cyproconazole); N,N′-[1,4-piperazinediylbis (2,2,2-trichloroethylidene)] bis [formamide] with micro emulsion (triforine–CC 17461); 4-(2-2-difluoro-1,3-benzodioxol-4-yl) pyrrole-3-carbonitrile (CGA 173506).

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D.A. Rosenberger, T.L. Robinson, J.R. Schupp, C.A. Engle-Ahlers, and F.W. Meyer

Effects of three sterol-demethylation inhibiting (DMI) fungicides and a contact fungicide were compared over two years at each of two locations to determine if fungicide treatments had differential effects on productivity, fruit size and shape, or gross returns for `Empire' apples (Malus ×domestica Borkh.). Treatments were applied four to five times per year during the primary apple scab season. Effects of treatments were assessed by comparing fruit set efficiencies, number of fruit per tree, total harvested fruit weight, and fruit length: diameter ratios at harvest. No significant differences were noted among individual treatments in any of the four trials. However, when treatments were contrasted by grouping individual treatments, significantly larger fruit size was noted for triflumizole treatments vs. combined fenarimol and myclobutanil treatments in one of the four trials and for captan or mancozeb compared to fenarimol and myclobutanil treatments in two trials. None of the DMI fungicides compared in these trials had any consistent adverse affect on fruit size, total yield, or estimated gross return per hectare. We conclude that the plant growth regulator effects of DMI fungicides are inconsistent and are unlikely to have significant economic impact on commercial apple production.

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G.H. Neilsen, J. Beulah, E.J. Hogue, and R. Utkhede

The effects of various nonfumigant planting-hole treatments on growth and yield of apple (Malus domestics Borkh.) trees were measured during the first 3 years after planting. Eight orchards diagnosed as having a replant problem were monitored. First-year shoot growth, the number of blossoms in the second year (inmost orchards), and first-year trunk cross-sectional area increment (TCAI) in 50% of test orchards were increased by monoammonium phosphate (MAP) fertilizer+ peat, MAP+ mancozeb, or MAP + peat + a bacterial antagonist. By the end of year 3, TCAI generally was not affected by treatments, but treatments resulted in more blossoms by the third season in two of seven orchards that blossomed in the second season. Cumulative yield after 3 years increased significantly in only three orchards, with the best treatment, MAP+ peat, resulting in cost recovery in only one orchard. Inadequate K or Cu nutrition may have reduced growth in some of the orchards, which were characterized by a wide range in yields, independent of planting-hole treatment.

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E.W. Stover, M. Myers, R.M. Sonoda, and Z. Guo

Stylar-end russetting (SER) is a cosmetic defect of Florida citrus fruit most frequently associated with navel orange. SER is evident as spots or streaks of corky tissue that often form a network of intersecting lines. Occurrence of SER is reported to vary widely from year to year, but some orchards have a history of severe SER, with fruit culled annually for this defect. Growers report that SER is typically first evident in August. The cause of SER has not been determined. Reports of yeast-like fungi inducing russet in pome fruit suggest that similar organisms may be implicated in SER. Yeast-like fungi were isolated on acid PDA from navel oranges in an orchard with frequent severe SER. Strains were selected with a wide range of colony morphology, but were not identified taxonomically. These strains, and strains of Aureobasidium pullulans and Rhodotorula glutinis that caused russetting in pome fruit, were grown in liquid suspension and sprayed on navel orange trees with three repeated applications during July and Aug. 1998. No increase in SER was observed on strain-inoculated trees compared to controls. Two broad-spectrum fungicides were sprayed on other navel orange trees to further explore the possibility that fungi may be involved in SER. GA (gibberellic acid) was also applied in this experiment because it can reduce russetting in apples. All applications were made five times at 3-week intervals in June through Sept 1998. SER was assessed in fruit harvested late Sept. 1998. The proportion of fruit with less than 10% of the surface exhibiting SER was 51% for controls, increased to 69% where myclobutanil was applied at 74 mg a.i./L and increased further to 93% where manganese ethylenebisdithiocarbamate was applied at 1775 mg a.i./L. GA did not significantly influence SER.

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Gary E. Vallad, Kenneth L. Pernezny, Botond Balogh, Aimin Wen, Jose Francisco L. Figueiredo, Jeffrey B. Jones, Timur Momol, Rosa M. Muchovej, Nikol Havranek, Nadia Abdallah, Steve Olson, and Pamela D. Roberts

ethylenebisdithiocarbamate (EBDC) such as maneb or mancozeb, which improves copper solubility and bacterial spot control ( Marco and Stall, 1983 ; Ritchie and Dittapongpitch, 1991 ). Despite frequent sprays, copper compounds with EBDCs still have limited efficacy, may cause