AFM 91-19 / TM 5-629 / NAVFAC MO-314
24 May 1989
Use nozzles that apply a coarse spray. Get advise from agricultural engineers and weed-control
Use low pressures -- no more than 30 lb/in2
for boom sprayers, 100 pounds for spray guns.
Avoid spraying on windy days and do not spray with ground equipment or from airplanes when the
wind velocity is sufficient to cause drift to sensitive areas. Usually, stop spraying when wind speed
reaches 5 mi/h. Never spray above 10 mi/h. 2,4-D and similar herbicides should never be applied
when wind of any velocity is blowing across the spray area toward nearby valuable sensitive plants.
Do not spray when an air-temperature inversion exists. An inversion is characterized by little or no
wind and by air temperatures that are lower near the ground than at higher levels. A continuous
smoke-generating device on aircraft can be used to indicate the direction and velocity of air
movement. Layering of the smoke may indicate a temperature inversion. When spraying large
acreages, use the burning tire or other smoke generator to indicate the presence of inversions.
Spray when a light wind is blowing away from susceptible crops and toward the area being sprayed.
Where special drift hazards exist, either do not spray or use specialized spray equipment. One of the
special drift control agents or formulations in properly designed and adjusted equipment can help
reduce drift. Obtain professional advice before using these products.
Figure 2-2. Suggestions for Minimizing Drift Hazards.
preemergence treatments, the herbicide may
(2) Water temperature has a strong influ-
ence on the effectiveness of aquatic herbicides.
wash off of treated areas or may leach below
Poor herbicidal activity can be anticipated at
surface soil where weed seeds germinate; and
temperatures of 60F (16C) or lower. Herbi-
weed control may be reduced or crop damage
cides such as acrolein and xylene perform poorly
at high water temperatures due to rapid losses
2-8. Counteracting Misapplications and Spills.
d. Effects of Rainfall. Rainfall affects effi-
If herbicides are overapplied, applied on the
cacy of herbicides in other ways than by affect-
wrong plants, or spilled; or if residues persist;
ing the plant's rate of growth.
they usually can be detoxified with activated
carbon such as Gro Safe or Aqua Nuchar A.
(1) Rainfall immediately after postemer-
Fast action is needed. Even 2,4-D injury can be
gence foliar applications of herbicides may wash
prevented or reduced if the accident is treated
spray off of leaves of plants and reduce the
immediately, before plant uptake. One hundred
effectiveness of water-soluble formulations such
to 200 lb. of activated carbon are required to
as salts of 2,4-D; glyphosate, dinitro, and ami-
completely absorb 1 lb or active herbicide.
trole compounds; and some other foliar herbi-
Normal field rates are 100 to 400 lb of carbon
cides. Effectiveness usually is not reduced if a
per acre to detoxify residues. Apply either dry
moderate rain occurs 4 to 6 hours after poste-
carbon alone, dry carbon mixed with soil, or
mergence application. Check the weather fore-
carbon as a slurry at 1 to 2 lb/gal water. To
cast before applying herbicides,
detoxify residues in soil, thorough incorporation
(2) The effectiveness of preemergence herbi-
of the activated carbon into the soil is needed.
cide treatments may be increased by moderate
rain occurring shortly after application. In low
Section C -- Storing Herbicides
rainfall areas, sprinkler irrigation is often used
with good results when the water is applied
immediately after preemergence herbicide appli-
2-9. Flash Points. Chemicals with low flash
cation. However, if heavy rains occur soon after
points (40F or less) are dangerous in storage.