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  • Author or Editor: Edward F. Durner x
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Abstract

The number of replicates (sample size) and the size of replicates (plot size) are important considerations in the design of plant science experiments. Sample size has recently been addressed by several authors (Snedecor and Cochran, 1980; Trout and Marini, 1984). Plot size is also important since smaller plots allow greater replication in a given area, but larger plots often have lower variances and are thus more statistically desirable.

Open Access

Two- to three-week-old `Sweet Charlie' strawberry (Fragaria ×ananassa Duch.) plug plants were conditioned [seven 9-hour short days without chilling (21 °C day/21 °C night) followed by seven 9-hour short days with chilling during the nyctoperiod (21 °C/12 °C night)] in September, then planted in a vertical hydroponic system for winter greenhouse production. Conditioned plugs produced significantly more fruit than did nonconditioned control plugs in January and February, but the difference was nonsignificant in March and April. Fruit yield increased linearly with height in the column (≈40 g/plant for every 30-cm increase in column height), probably because of increasing light level. When productivity is considered on an area basis (kg·m–2) and the column height effect on yield is accounted for, productivity over a 4.5-month period was 4.8 kg·m–2 for controls and 7.8 kg·m–2 for conditioned plugs. Conditioned plug plants offer the potential for increasing strawberry productivity and therefore the profitability of a winter greenhouse production system.

Free access

`Redhaven' peach trees [Prunus persica (L.) Batsch.] on their own roots or budded to seven rootstock [`Bailey', `Siberian C', `Lovell', `Halford' (seedlings), GF 655.2, GF 677 (`Amandier'), or `Damas' (GF 1869) (clonal)] were evaluated for rootstock influence on flower bud hardiness, live pistils at bloom, thinning requirements, marketable yield, and production efficiency after exposure to temperatures lower than – 23C in 1987 and to - 26C in 1988. In 1987, flower bud hardiness was as great on `Siberian C' as on own-rooted `Redhaven' and greater than on the other rootstock. Fewer live pistils were observed during bloom on GF 677 than on `Siberian C', `Lovell', `Damas', or self-rooted trees in 1987. In 1988, flower bud hardiness was greater on `Siberian C' and `Bailey' than on GF 677. At bloom, `Lovell' and `Siberian C' rootstock carried more flowers with live pistils than `Damas'.`Siberian C' and `Lovell' required significantly greater fruit thinning than all other rootstock and self-rooted trees. GF 677 produced a larger marketable crop than GF 655.2 or `Damas'. In addition, `Bailey', `Lovell', and self-rooted trees produced a significantly larger crop than `Damas'. No significant rootstock effect on production efficiency was detected in either year. Tree vigor during the growing season preceding each freeze did not significantly influence flower bud survival or productivity.

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Ethephon (100 mg·liter-1) was applied to mature peach trees [Prunus persica (L.) Batsch. cv Redhaven] on 13 Oct. 1989. Ethephon-treated and non-treated trees were pruned on 12 Dec. 1989, or left not pruned. Flower bud hardiness was assessed via exotherm analysis from Dec. through Mar. on buds taken directly from the orchard and on buds deacclimated / reacclimated under controlled conditions. Buds from ethephon-treated trees were consistently hardier than buds from non-treated trees. After a warm spell in Jan., buds from pruned trees not previously treated with ethephon were less hardy than those from non-pruned trees. Hardiness of buds from ethephon-treated trees after the warm spell was not affected by pruning. All buds rehardened with the return of low temperatures. Under controlled conditions, buds from pruned trees were less hardy than those from non-pruned trees. Pruning resulted in a rapid loss of hardiness at warm temperatures (21C). If trees had been treated with ethephon the previous fall, significant rehardening of dehardened buds from pruned trees occurred at 5 or -1C. Buds from pruned, non-treated trees did not reharden.

Free access

Flower bud hardiness of ethephon-treated (100 mg·liter-1 in October), dormant pruned (in December) `Redhaven' peach (Prunus persica L. Batsch.) trees was studied from December through March using exotherm analysis. In early December, buds not treated with ethephon were 0.5C hardier than ethephon-treated buds. From mid-December through March, ethephon-treated buds were 0.5 to 2.1C hardier than nontreated buds. When a main effect of pruning was detected, buds from pruned trees were 0.8 to 2.8C less hardy than buds from nonpruned trees. On several dates, a significant interaction on flower bud hardiness between ethephon treatment and pruning was detected. For trees not treated with ethephon, buds from pruned trees were 1.8 to 2.2C less hardy than those from nonpruned trees. Pruning did not affect hardiness of buds from ethephon-treated trees. Ethephon delayed bloom to the 75% fully open stage by 9 days. Pruning accelerated bloom to the 75% fully open stage by 3 days compared to nonpruned trees. Flower bud dehardening under controlled conditions was also studied. As field chilling accumulated, flower buds dehardened more rapidly and to a greater extent when exposed to heat. Pruning accelerated and intensified dehardening. Ethephon reduced the pruning effect. The percentage of buds supercooling from any ethephon or pruning treatment did not change as chilling accumulated. In trees not treated with ethepbon, fewer buds supercooled as heat accumulated, and pruning intensified this effect. In pruned, ethephon-treated trees, fewer buds supercooled after exposure to heat. The number of buds supercooling in nonpruned trees did not change with heat accumulation. Flower bud rehardening after controlled dehardening was also evaluated. After dehardening in early February, there was no difference in the bud hardiness of pruned or nonpruned trees. Buds from ethepbon-treated trees were hardier than those from nontreated trees. With reacclimation, buds from pruned trees were not as hardy as those from nonpruned trees. The percentage of buds supercooling from ethephon-treated trees did not change with deacclimation or reacclimation treatments. After deacclimation in late February, buds from pruned trees were 2.2C less hardy than those from nonpruned trees. After reacclimation, buds from pruned, ethephon-treated trees rehardened 2.6C while buds from all other treatments remained at deacclimated hardiness levels or continued to deharden. Ethephon-treated pistils were shorter than nontreated pistils. Pistils from pruned trees were longer than those from nonpruned trees. Deacclimated pistils were longer than nondeacclimated pistils. Differences in hardiness among ethephon and pruning treatments were observed, but there was no relationship between pistil moisture and hardiness.

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Ethephon (100 mg·liter-1) was applied to mature peach trees [Prunus persica (L.) Batsch. cv Jerseydawn] on 1, 2, 3 or 4 dates beginning 15 Sept. 1990 at approximately 2 week intervals for a total of 12 treatments. Ethylene evolution from flower buds and flower bud phenology were monitored through bloom the following spring. Total flower bud density, live flower bud density, percentage live pistils, yield and number of fruit per tree were also measured. The response to multiple ethephon applications was greatly influenced by the timing of specific treatment combinations rather than by the total amount of ethephon applied over the course of the experiment. Ethylene evolution was elevated for about 2 weeks following application(s), however, no clear relationships between bud phenology or survival and ethylene evolution was observed. Several of the multiple ethephon applications significantly delayed bloom to the 75% pink stage, however, none of the treatments significantly influenced development to 75% balloon or fully open stages. Several of the multiple applications caused significant pistil mortality.

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Fall-applied ethephon (100 ppm) delayed bloom by 6 days the following spring in peach [Prunis persica (L.) Batsch]. Whitewashing entire trees in January added 1 to 2 additional days of bloom delay to that provided by ethephon. Whitewashing delayed pistil elongation in quiescent buds from control trees, but did not significantly delay pistil elongation in buds from trees treated with ethephon. Pistils from ethephon-treated trees were significantly smaller than those from control trees from just before bud swell through bloom. Flower bud survival after freezes during bloom was enhanced for whitewashed compared to control buds as measured by fruit set. Chemical name used: 2-chloroethylphosphonic acid (ethephon).

Free access

Abstract

The potential for annual cropping of strawberries in hill culture on black plastic mulch was investigated using 2 experimental plantings in southeastern North Carolina from 1982-1984. In 1982-1983, a plant density trial was conducted with freshly dug plants set in mid-October at a plant spacing of 33 cm between the double rows and spacings of 15, 20, 25, and 30 cm between plants in the row. Except with ‘Titan’, the highest strawberry yields in the spring of 1983 were obtained at the 15 cm in-row spacing. Fruit size of all cultivars was somewhat reduced at closer spacings. In a 1983-1984 trial, summer planting of dormant plants was compared to that of freshly dug plants set in mid-October. In December of 1983, record cold temperatures (− 14°C) severely damaged leaves, crown tissues, and blossom primordia of dormant plants, whereas freshly dug plants had less freeze injury and higher fruit yields the following spring.

Open Access

Six-year-old peach trees [Prunus persica (L.) Batsch] were sprayed with ethephon (100 mg·liter–1) in Oct. 1989, whitewashed in Jan. 1990, and sprayed with dormant oil on one or two dates in Mar. 1990 to study possible interactive effects on flower bud hardiness, pistil growth, time of bloom, and yield. Flower buds from ethephon-treated trees supercooled to a lower temperature [mean low temperature exotherm (MLTE) of –18.5C] than buds from nontreated trees (MLTE of –17.7C) in February; there was no main effect of whitewashing or any interaction with ethephon. No treatment effects on hardiness were detected in March. Ethephon-treated pistils were smaller than nontreated pistils, and pistils from buds on whitewashed trees were smaller than those on nonwhitewashed trees. No main effects or interactions of dormant oil on pistil size were detected. Ethephon and whitewashing delayed bud development during bloom, but prebloom oil application(s) had no effect. Buds from ethephon-treated and whitewashed trees were more tolerant of freezes during bloom than buds from oil-sprayed trees, and yield was enhanced by ethephon and whitewashing. Prebloom oil sprays reduced yield compared with controls. Chemical name used: 2-chloroethylphosphonic acid (ethephon).

Free access