Several products containing recommended active ingredients may be available for application with boomless ground equipment or aircraft. Before you buy, be sure that proposed uses comply with label restrictions. This is especially true for chemicals used specifically for growing tree crops.
In most cases, it is preferable to spray 2,4-D or triclopyr with aircraft late in the dormant season to avoid injuring Douglas-fir, hemlock, or true firs. Glyphosate and/or imazapyr are effective and selective in later summer, after conifer buds have hardened. Pines are very sensitive to 2,4-D or triclopyr between March and early July. In most situations, helicopter and broadcast ground applications with coarse sprays (VMD 1,000 microns or less) drift less and are as effective as finer sprays. Boomless nozzles cannot project fine drops to the edges of their swaths. They are best suited for soil-residual products and those with good systemic activity if applied in large drops, for example, hexazinone, glyphosate, and imazapyr.
Recommendations for Broadcast Spraying
For Control of Listed Species
This table lists herbicide rates for site preparation and conifer release. In most instances release rates are for Douglas-fir before bud break in spring or after bud set in the fall. Users should check tolerance of other conifer species in the table "Effectiveness of Major Forestry-registered Herbicides" earlier in this chapter and the product label.