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Abstract

Ethrel (Amchem 66-329, 2-chloro-ethylphosphonic acid) is a water soluble plant growth regulator thought to be degraded within plant cells resulting in the liberation of ethylene (1, 2). The eth-lene released within the plant is probably responsible for the subsequently observed biological activity.

Open Access
Authors: and

Abstract

Growth of 2-year-old tart cherry (Prunus cerasus L.) trees as measured by trunk circumference increase or total shoot elongation was significantly greater in plots receiving chemical or mechanical weed control within the tree row than in plots receiving between-row cultivation only. Shoot growth of one-year-old apple (Malus domestica Borkh. ‘Delicious’) trees responded similarly to weed control. Tart cherry trees in hand weeded and dinoseb or glyphosate treated plots had greater growth than those in paraquat treated plots. Tart cherry trees in plots receiving chemical or mechanical weed control out-yielded trees in unweeded plots during the first year of production. ‘Delicious’ apple trees in plots treated with dinoseb (6.7 and 10.1 kg/ha), the high rate of glyphosate (1.7 kg/ha), or mechanical weed control also outyielded trees in unweeded plots during the first year of production. Effects of weed control on growth and yield were less distinct during the 2nd year of production. Trees from treated plots came into production one year earlier than trees in the unweeded plots. Chemical names used: 2-(1-methylpropyl)-4,6-dinitrophenol (dinoseb); N-(phosphonomethyl)glycine (glyphosate); 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat).

Open Access

Abstract

Carrot roots (Daucus carota L.) and onion bulbs (Allium cepa L.) were planted in Kidman silt loam immediately after DCPA (dimethyl tetrachloroterephthalate), ethofumesate (2-ethoxy-2,3-dmydro-3,3-dimethyl-5-benzofuranol methanesulfonate), linuron (3-(3,4-dichlo-rophyenyl)-l-methoxy-l-methylurea), napropamide (2-(a-naphthoxy)N,N-diethylpropiona-mide), or trifluralin (a,a,a-trifluoro-2,6 dinitro-N,N-dipropyl-p-toluidine) had been soil incorporated. In a second experiment, carrot roots and onion bulbs were planted in a conventionally-prepared seed bed or among vigorously growing wheat plants (7 to 10 cm tall). DCPA, linuron, and oryzalin (3,5-dinitro-N 4,N 4-dipropylsulfanilamide) plus glyphosate (N-(phos-phonomethyl)glycine) were surface applied to these seedbeds after planting but prior to crop emergence. Methazole (2-(3,4-dichlorophenyl)-4-methyl-l,2,4-oxadiazolidine-3,5-dione) and nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) were applied postemergence. Chemical treatments significantly altered the seed yields within the no-tillage method. Carrots grown in the tilled plots exhibited no effect of chemical treatments on seed yield. Comparison of tillage methods indicated a highly significant reduction in carrot seed yield relative to the no-tillage plots. Those on the non-weeded control and no-tillage plots showed a highly significant reduction in seed yield. Many of the onion bulbs from male-fertile lines failed to develop seedstalks in the plots sprayed with linuron and napropamide and those that did were delayed in development. Linuron and ethofumesate reduced the numbers of onion flowers per umbel. Onions grown in the tilled plots exhibited no effect of chemical treatments on seed yield. Those on the non-weeded control and no-tillage plots showed a highly significant reduction in onion seed yield. Comparison of tillage methods indicated a highly significant reduction in onion seed yield relative to the no-tillage plots.

Open Access

Rowcovers were placed over `Himrod' grapes during the 1992 and 1993 growing seasons to test the feasibility of manipulating the microclimate temperature sufficiently to bring the covered grapes into full bloom and harvest earlier. The rowcovers were removed from the grapes after fruit set each year. In 1992, the covered grapes bloomed 18 May, 6 days earlier than the open blocks. In 1993, full bloom in the covered grapes occurred on 29 May, 9 days earlier than the controls. However, the advanced bloom of the covered grapes did not result in the expected earlier maturity when compared to the uncovered grapes. Covered grapes did attain a soluble solids maturity index of 18 two to three days earlier than uncovered grapes.

Free access

`Crimson Sweet' watermelon plants grown under various mulches and rowcovers were harvested weekly and analyzed for absolute growth rate (AGR), relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), specific leaf area (SLA), specific leaf weight (SLW), leaf weight ratio (LWR), leaf area duration (LAD), biomass duration (BMD), and runner growth. Hourly air and soil temperatures were monitored inside the rowcovers. Vispore and Reemay rowcovers generally showed greater mean AGR, LAR, SLA, LAD, and BMD than Agronet black-clear and black mulches. No significant differences in LWR were found between mulched and rowcovered plants. Plants under mulches and rowcovers showed significant increases in AGR, RGR, NAR, LAR, SLA, LAD, and BMD over noncovered (bare ground) plants. Longest runner length was highly correlated with total runner length. Growth analyses depicted decreased growth rate inside the rowcovers during the hottest weeks of the summer, and generally correlated well with the earliness and total yield of the crop.

Free access

A `Montmorency' sour cherry planting was established on 20 clonal rootstocks in April, 1987, as part of the NC-140 cherry rootstock trial. After 5 seasons scion/rootstock combinations showed a 2.5-fold range in trunk circumference. During the fifth season there was a 6-day range in bloom date, a 4-fold range in growth rate, a 7.5-fold range in yield and a 3-fold range in yield efficiency as influenced by rootstock. Trees on GM 9 were the smallest, had the lowest yields, smallest fruit and were among the lowest in yield efficiency. Mahaleb has been the standard cherry rootstock in Utah. Rootstocks whose trees were comparable or exceeded those on mahaleb in both yield and yield efficiency during the fifth season included 148-1, 196-13 and M×M 2. Differences were also observed in root sucker tendency.

Free access

Calcium chloride (CaCl2) enhances turgidity and quality of postharvest sour cherry, Prunus cerasus L., fruit. Mechanisms by which plasma membrane (PM) ATPase maintains the electrochemical gradient in cell turgor were studied in isolated PM vesicles isolated from tapwater-, CaCl2- and chelated amino acid-calcium-treated Montmorency sour cherry fruit. Electron microscopy and periodic-chromicphosphotungstic acid staining indicated 85-90% closed PM vesicles. Protein activity associated with the PM was four times higher in both Ca treatments than in untreated cherries. ATPase activity was insensitive to NO3 and NaN3, but inhibited by vanadate, indicating absence or low levels of tonoplast and mitochondrial ATPases. PM vesicles exhibited a pH jump in the presence of acridine orange (A493-530nm). Cherry fruit appeared to have a PM ATPase similar to that of other plant species. Generation of a positive membrane potential across the PM was dependent upon ATP.

Free access

In the production of fresh-market vegetables, off-farm inputs, such as, plastic, nitrogen fertilizer, fungicides, insecticides, and herbicides are routinely used. One aim of the sustainable agriculture program at the Beltsville Agricultural Research Center is to develop systems that reduce these inputs. We have completed the second year of a study designed to examine foliar disease progress, foliar disease management, and marketable fruit yield in staked fresh-market tomatoes grown in low- and high-input production systems. Specifically, four culture practices (black plastic mulch, hairy vetch mulch, dairy manure compost, and bare ground) were compared in conjunction with three foliar disease management treatments (no fungicide, weekly fungicide, and a foliar disease forecasting model, TOMCAST). Within all culture practices, use of the TOMCAST model reduced fungicide input nearly 50%, compared with the weekly fungicide treatment, without compromising productivity or disease management. With regard to disease level, a significant reduction of early blight disease severity within the hairy vetch mulch was observed in 1997 in relation to the other culture practices. Early blight disease severity within the black plastic and hairy vetch mulches was significantly less than that observed in the bare ground and compost treatments in 1998. In addition, despite a 50 % reduction in synthetic nitrogen input, the hairy vetch mulch generated yields of marketable fruit comparable to or greater than the other culture practices. It appears that low-input, sustainable, production systems can be developed that reduce the dependence on off-farm inputs of plastic, nitrogen fertilizer, and pesticides, yet generate competitive yields.

Free access

Abstract

Leaves of cold-acclimated lemon [Citrus limon (L.) Burm. f.], grapefruit (C. paradisi Macf.), orange [C. sinensis (L.) Osbeck], and mandarin (C. unshiu Marc.) trees ranged in cold hardiness from −4 to −11°C. No significant differences in water content (g H2O/g dry weight) or melting point depression were observed. Plots of liquid water content during freezing (g H2O/g dry weight) vs. temperature were similar for the 4 citrus species. The tissues apparently deviated from ideal freezing behavior because less ice was formed. The reduced ice formation could not be accounted for by osmotic effects. Negative pressure potential developed during freezing is hypothesized to play a role in tissue water potential in frozen systems. It was concluded that hardier Citrus leaves survive freezing of a larger fraction of their tissue water.

Open Access

Abstract

Mature ‘Red Delicious’ apple trees (Malus pumila Mill) were sprinkled intermittently with an overhead irrigation system after completion of winter rest. A 2-minute sprinkling cycle operated automatically whenever the ambient air temperature of the orchard exceeded 7°C until the control trees reached full bloom. Evaporative cooling of the treated trees reduced bud temperatures to within 2°C of the wet bulb temperature. Treated trees reached full bloom 17 days after the untreated controls.

Open Access