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- Author or Editor: D. R. Evert x
Nonterminal cuttings were taken just after leaf fall (November) from nongirdled shoots and from shoots girdled 7 weeks previously on `Flordaking', `Junegold', and `Harvester' peach trees [Prunus persica (L.) Batsch.]. Cuttings from nongirdled shoots rooted (85%) and survived (72%) better than did cuttings from girdled shoots on the same trees (64% rooting, 49% survival). Total sugar averaged across cultivars was 68 mg·g-1 dry weight in cuttings from nongirdled shoots and 82 mg·g-1 dry weight in cuttings from girdled shoots. Starch averaged 26 mg·g-1 dry weight and was independent of shoot girdling. `Flordaking' had the lowest starch concentration and the highest” percentage of cuttings that rooted and survived. Rooting and survival percentages differed by as much as 90% among trees within each cultivar.
Normalized electrical impedance and cold hardiness were measured for internodal sections of ‘Delicious’ apple (Malus domestica Borkh.) during fall and winter for 2 years. Each year, the normalized impedance for the August date was significantly higher than on later dates. The relationship between normalized impedance and cold hardiness was inconsistent; r2=0.03 and P>5%, first year and r2=0.4 and P<1%, second year. The relationship between cold hardiness and the mean temperature for the 7 days before the sample date was consistent; r2=0.85 and P<1%, first year and r2=0.81 and P<1%, second year. The slope of the line relating sample diameter and normalized impedance changed from plus to minus each year.
Normalized electrical impedance measured cold injury to stem sections of ‘Delicious’ apple (Malus domestica Borkh). The measurements did not alter later visual ratings of browning on the same sample. Normalized electrical impedance estimates of injury and visual ratings of browning agreed in 87% of the samples in the first year and 95% of the samples in the second year. In 29 of the 30 adjacent sampling temperatures that produced intermediate injury, as determined by visual browning, normalized impedance values had a higher probability of distinguishing between temperatures than did visual browning. Linear interpolation of the temperatures, which were needed to produce equal injury for the two methods, yielded a mean difference of 0.8°C.
Midshoot peach [Prunus persica (L.) Batsch.] leaves were collected in 1984 and 1985 from phony-diseased [presumably infected with Xylella fastidiosa (Wells et al.)] and healthy trees of several cultivars at intervals during the summer. Leaves were evaluated for specific chlorophyll content, specific leaf weight, and color (lightness, hue, and saturation). The darker green of diseased trees reported previously could not be attributed to the quantitative changes in the leaf characteristics measured in this study. Midshoot leaves from diseased trees were more yellow and less green than midshoot leaves from healthy trees.
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.
A precise temp control apparatus is described which is useful for studying plant responses between +50° and -100°C.