Section 10

Properties of Herbicides Registered for Forestry Use
&
Behavior of Herbicides in Forests

Properties of Herbicides Registered for Forestry Use

The tables and figures included in the appendix to this unit summarize the properties of herbicides registered for use in forestry. When employing these chemicals, it is essential that the specifications for use on the label be followed exactly.



*General range of useful rates of application and seasons of application. Consult label or Weed Control Handbook for complete label range of rates and conditions; susceptibility of species.
Weed Group Product Name Common Name Rate, #/AC Active Season
Grasses, annual Aatrex Atrazine 2-4 March
Grasses, annual & perennial Velpar L Hexazinone 1-2 March-April
Grasses, annual & perennial Oust Sulfometuron 1/8-3/16 March-April
Grasses, annual & perennial Kerb Pronamide 1-2 Nov-Jan
Broadleaf herbs, alder, madrone, and manzanitas Many 2,4-D 1-4 March-July
Deciduous shrubs and hardwoods Garlon 4 or Garlon 3A Triclopyr ester or Triclopyr amine 1-2 March-April(release)(June site prep)
Deciduous shrubs and hardwoods Accord Glyphosate (Good for herbs too, but best early summer) 3/4-2 June-Sept (site prep) Aug-Sept(release)
Deciduous shrubs and hardwoods Arsenal Imazapyr 1/16-1/4 w/ glyphosate
Deciduous shrubs and hardwoods Escort Metsulfuron 1/32-1/16 May-June
Deciduous shrubs and hardwoods Weedone DP Dichlorprop 1-4 March-June
Deciduous shrubs and hardwoods Tordon Picloram 1/2-1 summer site prep
Ferns, Bracken Asulox Asulam 1 1/2-2 summer
Ferns, Sword & Bracken Oust Sulfometuron 3-4 spring

Behavior of Herbicides in Forests

Obviously, the intent of spraying herbicides as a site preparation technique is to have the material absorbed by the target species. However, not all the chemical applied reaches the target, but falls instead upon the forest floor or leaves the target area through drift or volatilization (the aim of the competent regeneration forester, of course, is to reduce the last losses to a minimum).

The chemical which remains in the target area may be absorbed and metabolized by plants, degraded by solar radiation, or decomposed by micro-organisms. Virtually none of the applied herbicide will be leached to streamwater.

TABLE XXIII Spray Droplet Size and its Effect on Spray Drift.
Droplet Diameter (microns) Type of Droplet No. Droplets/Sq. In. from 1 gal. spray/A Distance Droplet Travels in Falling 10 w/ 3 mph wind
5 Fog 9,000,000 3 miles
20 Very fine sprays 143,190 1,109 feet
50 Fine Sprays 9,224 178 feet
100 Mist; fine aircraft spray 347 48 feet
240 Medium aircraft spray 78
400 Coarse aircraft spray 18 8.5 feet
1/25" Moderate rain (very coarse spray) 1.1 4.7 feet

Forest mammals may ingest herbicides by feeding on treated foliage, but these chemicals are not retained because, in general, they have low fat solubility. Similarly, herbicides, unlike some insecticides, have little direct effect on bird populations because herbicides do not accumulate through the food chain.

Fungi may use herbicide residues as substrate, and certainly the application of such chemicals affects the decomposing organisms through a dramatic, short term change in the quantities of litter deposited on the treated area.

[Next: Selectivity of Herbicides] [Section 10: Table of Contents]