The relationship between shoot growth and area of trunk cross-section was curvilinear for apple, peach, pear, plum, and hybrid Carolina poplar trees grown in rhizotron compartments in Fox sandy loam under natural conditions. The coefficient of determination (R2) values ranged from 0.86 to 0.99, indicating trunk diameter, transformed to area of cross-section, may be substituted for shoot growth in estimating tree vigor.
Rooted cuttings of Anthemis nobilis, Arctostaphylos uva-ursi; Veronica officinalis and Houttuynia cordata were grown in the greenhouse and in nutrient solutions differing only in pH. The levels of pH were adjusted to 3 to 9 for A. nobilis and A. uva-ursi, to pH 4 to 9 for V. officinalis and to pH 4 to 6 for H. cordata. A. nobilis grew well at pH 4 to 7 but best growth was near pH 5. Arctostaphylos uva-ursi made best growth at pH 4 but not significantly better than at pH 5 to 7. V. officinalis grew well over a wide pH range (4 to 7 inclusive) and plants died gradually at pH 9. For the H. cordata trial a limited number of plants was available and at the imposed pH levels (4, 5 and 6) all plants grew uniformly and well.
Root growth of pine (Pinus mugo var. mughus (Scop.) Zen.) was studied at a rhizotron (underground root observation laboratory) on an in situ basis. Greater root elongation occurred in peat than in mineral soil and when there were sustained periods of temperature extremes, root growth increased or decreased 2 to 5 days following increases or decreases in soil temperature.
Roots of poplar (Populus alba var. pyramidalis Bunge), grown in glass-sided boxes under controlled growth conditions, suberized more quickly when exposed to natural and artificial light than when kept in the dark.
Handgun treatments of abamectin and oil applied between mid-June and late August caused distinct epidermal rings where drops of spray liquid dried on the surface of pear fruit (Pyrus communis L.). The severity of epidermal injury was related to the concentration of oil in the abamectin spray mixture (abamectin applied without oil caused no fruit damage). Of six pear cultivars tested, `Anjou' was most susceptible to injury, followed by `Cornice' and `Bartlett'. `Sensation Red Bartlett', `Bosc', and `Seckel' showed little or no phytotoxicity symptoms from abamectin and oil treatments with oil concentrations from 0.125% to 2.0% (v/v). On sensitive cultivars, the concentration of oil should not exceed 0.25% (v/v) when combined with abamectin to reduce the risk of epidermal injury. Oil at 0.25% provides for adequate leaf penetration of abamectin and results in commercially acceptable spider mite (Tetranychus urticae Koch) control. Chemical names used: avermectin B1 (abamectin).
In situ root growth of young plum trees (myrobalan rootstock on which ‘Shiro’ plum was budded) was studied for one season at the University of Guelph rhizotron. Root growth of this combination, at the field-transplant stage, began before leaf growth and extended past leaf fall. Relatively large roots of myrobalan stock made some winter growth in length, below frost penetration. The rate of growth during July to mid-September was twice that of the balance of the season, corresponding closely to shoot and trunk increments. Root diameter and elongation rate are positively correlated. Irregular and patchy suberization was the rule with the young plum roots.