Annual Variation in Effect of 2,4-D and 2,4,5-T on Ponderosa Pine
Author: Gratkowski, H. J.
Source: Forest Science, Volume 24, Number 2, 1 June 1978 , pp. 281-287(7)
Publisher: Society of American Foresters
Abstract:Early spring foliage sprays of low volatile esters of 2,4-D and 2,4,5-T are not safe for releasing ponderosa pines in the Cascade Range. Pines became susceptible to the two phenoxy herbicides in mid-February when the trees appeared completely dormant; susceptibility coincided with first flowers on greenleaf manzanita. Annual variation in susceptibility of ponderosa pine to foliage sprays of 2,4-D and 2,4,5-T provide timing for aerial sprays to release pines in southwest Oregon. Trees are susceptible to damage months before beginning height growth in spring and are most susceptible during active growth in May and June. Susceptibility to herbicides decreases rapidly after new buds form in late June; full resistance is attained in late summer. Ponderosa pine remains resistant until late winter. In Pacific Northwest forests, late summer is the best season for aerial application of 2,4,5-T or 2,4-D to release ponderosa pines with minimum damage to the trees. Greenleaf manzanita was highly susceptible to 2,4-D from late November through May the following year. Ponderosa pine can be released from greenleaf manzanita by aerial application of phenoxy herbicides during late autumn and early winter. Forest Sci. 24:281-287.
Document Type: Journal Article
Affiliations: Research Forester at Pacific Northwest Forest and Range Experiment Station, USDA Forest Service, Forestry Sciences Laboratory, Corvallis, Oregon
Publication date: June 1, 1978
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