Almond (Prunus amygdalus Batsch cv. Nonpareil), apricot (Prunus armeniaca L. cv. Royal Blenheim), and peach [Prunus persica (L.) Batsch cv. Halford] grafted nursery stock seedlings were exposed once per week for 4 hours to a maximum O3 concentration of 0.25 μl·liter-1 in field exposure chambers. Exposures were repeated for a total of 4 months in 1986 (year 1) and 1987 (year 2). Trunk caliper, number of shoots, and net growth (total seasonal weight increase) were measured at the end of each year. Almonds appeared to be the most sensitive to O3. Almond seedlings exhibited extensive foliar injury from O3, while apricot and peach seedlings were relatively insensitive. Total net growth of O3-exposed almond was reduced during both years relative to the controls and an impact on caliper was evident after year 2. Apricot seedlings exposed to O3 developed a thinner trunk but more shoots than the controls in both years. Peach tree seedlings exposed to O3 had fewer shoots than the controls at the conclusion of year 2 but thicker trunks after both years. No significant difference in variance or shape of distribution of net growth within the treatment populations between O3-exposed seedlings and controls was detected for any of the three fruit crops. The impact of O3 on young, nonbearing perennial fruit crops may be most evident in specific growth characteristics, such as net growth or trunk caliper.
Patrick M. McCool and Robert C. Musselman
C.M. Roberts, G.W. Eaton, and F.M. Seywerd
Paclobutrazol treatments of 0, 0.125, 0.250, and 0.500 mg/plant improved the form of Tibouchina urvilleana (DC.) standards and eliminated the need for pruning during the display season. Paclobutrazol did not improve the form of Fuchsia × hybrida Hort. ex Vllm. Paclobutrazol inhibited trunk caliper development in both species. Paclobutrazol at 0.125 mg/plant slightly increased Tibouchina flower size. Chlormequat at 0, 1000, or 2000 mg/plant did not hasten flowering of Tibouchina. Chemical names used: ß-[(4-chlorophenyl) methyl]-α- (1,1-dimethylethyl) -1H-1,2,4-triazole-1-ethanol (paclobutrazol); α-chloro-N,N,N-trimethylethanammonium chloride (chlormequat).
Edward F. Gilman
Roots of four-year-old, field-grown southern magnolia (Magnolia grandiflora L.) were pruned in 1987 once during dormancy, following the first shoot growth flush or after the second growth flush, prior to transplanting in January 1988. By the end of the 1987 growing season, root pruning at all stages of growth reduced leaf number, tree height, trunk caliper, and total-tree leaf area and weight compared with unpruned controls. Total root weight was less for trees pruned during dormancy or following the first growth flush. Root pruning increased the proportion of fine roots (0 to 5mm-diameter class) to coarse roots (>5 to 10-mm diameter class). Shoot:root ratios were not affected by root pruning. During the first year after transplanting, root pruned trees grew at a slightly faster rate than unpruned trees but growth rates were similar for root pruned and unpruned trees the second and third year after transplanting. Trees required, at most, 1 year per inch of trunk caliper to become established in the landscape.
David W. Burger, Pavel Svihra, and Richard Harris
Treeshelters were used for the nursery production of Cedrus deodara Loud. (deodar cedar), Quercus ilex L. (holly oak), and Magnolia grandiflora L. (southern magnolia) trees growing in 19-liter containers. Air temperature, relative humidity, and CO, concentration were higher inside the treeshelters than outside. Trees grown inside treeshelters were 74% to 174% taller than trees grown without shelters. Trunk caliper of Magnolia and Quercus was not affected, however, for Cedrus trees caliper was larger for trees grown without a shelter. Upon removal of the shelter, Cedrus trees were incapable of supporting their own weight. Lateral branch development was inhibited and leaf senescence was greater with Magnolia trees grown in a shelter. Quercus trees grown in shelters were ready to be transplanted into the landscape. Water use was similar for trees grown with or without shelters. Trees grown in shelters had lower root fresh weights.
Chris Starbuck, Daniel K. Struve, and Hannah Mathers
Two experiments were conducted to determine if 5.1-cm-caliper (2 inches) `Summit' green ash (Fraxinus pensylvanica), and 7.6-cm-caliper (3 inches) northern red oak (Quercus rubra) could be successfully summer transplanted after being heeled in pea gravel or wood chips prior to planting in the landscape. Spring harvested trees of each species were either balled and burlapped (B&B) or barerooted before heeling in pea gravel or wood chips. Compared to B&B `Summit' green ash, bareroot stock had similar survival and shoot extension for three growing seasons after summer transplanting. Bareroot and B&B northern red oak trees had similar survival and central leader elongation for 3 years after summer transplanting. In the third year after transplanting, northern red oak bareroot trees heeled in pea had smaller trunk caliper than B&B trees heeled in wood chips. These two taxa can be summer transplanted B&B or bareroot if dormant stock is spring-dug and maintained in a heeling-in bed before transplanting. This method of reducing transplant shock by providing benign conditions for root regeneration can also be used to extended the planting season for field-grown nursery stock; the method is called the Missouri gravel bed system.
Dennis J. Werner and Dana F. Moxley
The relationship between malate dehydrogenase (MDH) genotype and plant vigor in peach [Prunus persica (L.) Batsch] was examined in two F2 populations (selfed `Belle of Georgia' and `Cresthaven') segregating at the Mdhl locus. Total numbers of progeny examined were 1610 and 998 in the `Belle of Georgia' and `Cresthaven' populations, respectively. In both populations, plant vigor (as defined by total height and trunk caliper after 1 year of growth) was significantly less in homozygous F/F (Mdh1-1/Mdh1-1) individuals. Homozygous S/S (Mdh1-2/Mdh1-2) individuals showed the greatest vigor, and were significantly different in vigor from homozygous F/F (Mdh1-1/Mdh1-1) individuals in both populations and from heterozygous F/S (Mdh1-1/Mdh1-2) individuals in the `Belle of Georgia' population. A significant deviation from the expected 1 F/F:2 F/S:1 S/S ratio was observed in the `Belle of Georgia' population, suggesting moderate lethality of homozygous F/F genotypes.
Don C. Elfving and Dwayne B. Visser
A new bioregulator, cyclanilide (CYC, Bayer Environmental Science, Research Triangle Park, NC 27709), was compared with a proprietary formulation of 6-benzyladenine and gibberellins A4 and A7 [Promalin (PR), Valent BioSciences, Walnut Creek, Calif.] for branching effects on sweet cherry trees. CYC stimulated the formation of lateral shoots on current-season's shoot growth under both orchard and nursery conditions. In the nursery CYC was as effective or better for feathering compared to PR in all cherry cultivars tested. There were no synergistic effects of CYC/PR tank mixes on feather development. Crotch angles of induced feathers were not different from the angles of feathers that formed spontaneously. The growth of CYC-induced feathers was sufficient to produce acceptable quality feathered trees. Trunk caliper of nursery trees was either not affected or reduced to a very minimal degree. CYC is effective for lateral branch induction in sweet cherry, especially in the nursery. Chemical names used: 1-(2,4-dichlorophenylaminocarbonyl)-cyclopropane carboxylic acid (cyclanilide); N-(phenylmethyl)-1H-purine-6-amine + gibberellins A4 and A7 (Promalin); polyoxyethylenepolypropoxypropanol, dihydroxypropane, 2-butoxyethanol (Regulaid).
R.E. Byers, D.H. Carbaugh, and L.D. Combs
`Fuji'/MM.111, `Pink Lady'/M.7A, and `Summerfield'/M.7A apple trees were planted in several types of individual root restrictive bags in the field in 1995. Bags were made of Knit and Woven fabrics, Galvanize hardware cloth (6.4 cm) with various holes sizes and of different bag volumes. The bags confined the development of large roots to within the bag. Roots that penetrated the bag resulted in root branching and large root inhibition. As the roots enlarged, roots penetrating the bags were restricted in diameter by the fabric hole size. Roots enlarged to some degree on both sides of the fabric holes but were not killed by girdling within the first few years. Root restriction bags decreased trunk caliper, shoot growth, pruning weights, number of cuts per tree, increased flowering, fruit numbers, and weight per tree. Fruit firmness, soluble solids and color was increased and starch was lower than the nonbagged controls. In cage and tank trials pine and/or meadow voles easily penetrated all of the fabric and polypropylene bags within 24 h, except for the galvanized hardware cloth (6.4 cm). Susceptibility of each material to vole damage was tested by placement of an apple inside a small bag of each. Root restriction bags seemed to be a viable alternative to dwarfing rootstocks for control of tree size, early flowering, and early fruiting.
Edward F. Gilman and Michael E. Kane
Roots of field-grown southern magnolia (Magnolia grandiflora L.) were pruned once during dormancy, following the first shoot growth flush or after the second growth flush or twice at the following times: during dormancy and following first growth flush, during dormancy and following second growth flush, following first and second growth flush before transplanting in the winter. By the end of the growing season, root pruning at all stages of growth reduced leaf number, tree height, trunk caliper, and total tree leaf area and weight compared with unpruned controls. Total root weight was less for trees pruned during dormancy or following the first growth flush. Root pruning increased the proportion of fine roots (0- to 5-mm-diameter class) to coarse roots (> 5- to 10-mm-diameter class). Shoot: root dry weight ratios at transplanting were not affected by root pruning. Root-pruned trees grew at a faster rate following transplanting than unpruned trees. Despite these initial differences. trees in all treatments were the same size 1 year after transplanting.
Greg Litus and James Klett
In May 2004, at the request of local nursery owners, young Acer ×freemanii 'Autumn Blaze' (Autumn Blaze maple) trees previously grown in a number 20 (#20) container pot-in-pot (PIP) system were planted at the Colorado State University Horticultural Farm alongside similarly sized trees field grown, balled and burlapped (B&B). These trees were planted using methods recommended by the International Society of Arboriculture with half receiving 30% by volume soil amendment consisting of Organix compost mixed with the native soils. In addition, five trees grown for one year using the #20 PIP container system were maintained a second year in the same containers and compared to five trees transferred to #45 containers. After one season, the PIP-grown trees showed significantly more shoot growth and increased trunk caliper than the B&B trees. The application of amendments had no effect on the growth for either the B&B or PIP trees. Trees maintained in PIP containers for a second year had similar growth regardless of the container size.