Quantcast Figure 2-l. Factors Influencing Herbicide Application Rates

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AFM 91-19 / TM 5-629 / NAVFAC MO-314
24 May 1989
ment is made, the desired period of residual
2-6. Application Rates:
a. Application rates of herbicides are often
toxicity, the amount and distribution of rainfall,
given in minimum and maximum amounts, de-
soil texture and composition, and other environ-
mental conditions. Figure 2-1 shows situations
pending on the situation. This range is necessary
to accommodate differences in the response of
when light and heavy application rates are
plant species, the stage of growth when treat-
Variable Factor
Heavier rates
Lighter rates
Herbaceous plants
Susceptible species
Tolerant species
Annuals and biennials
in flower
Established perennials-
Perennials in bud
flower to maturity
Woody plants
Susceptible species
Tolerant species
Foliage applications
Foliage applications
when plants are in
before and after full
full leaf
Actively growing
Several years
Residual toxicity of herbicide
Short period
Humid regions
Arid regions
Cool climate
Warm climate
Low in organic-matter
High in organic-matter
High in clay content
Low in clay content
Well drained
Poorly drained
Bare soil
Heavy trash
Root-absorbed chemical
Figure 2-l. Factors Influencing Herbicide Application Rates.
herbicide applications to foliage by reducing
b. In some cases, rates are given in units of
evaporative losses of spray and aiding the foliar
the chemical per 100 or 1,000 square feet, per
absorption of herbicides. Low humidity reduces
square rod, or per acre. It is not necessary,
the effectiveness of herbicide sprays by increas-
however, to measure the area to be sprayed each
ing the rate of evaporation. The disadvantages
time an application is made. Calibrate the
of low humidity can be partly overcome by
sprayer to deliver the proper amount of chemical
using oil and oil-water emulsions instead of
per unit area (see chapter 9).
water as spray diluents.
c. Effects of Temperature. Temperature af-
2-7. Effects of Weather:
fects the rate of chemical reactions in plants
a. Effects of Wind:
and animals and also evaporation rates of
(1) Wind causes improper distribution of
herbicides and greatly increases tile hazard of
(1) Moderate temperatures, ranging from 70
damage from drift to sensitive plants in nearby
to 85F (21 to 29C), are favorable for spray
fields, gardens, or ornamental plantings (figure
applications of most herbicides. The carbamates,
dinitro compounds, and high-volatile esters of
(2) Vapors of some herbicides, such as 2,4-D
phenoxy compounds volatilize rapidly at temper-
or other phenoxy herbicides, kill plants. When
atures above 80F (27C). At temperatures
vapors from the herbicide are likely to injure
above 90F (36C), even the low-volatile esters
adjacent crops or other plants, an amine salt, or
of 2,4-D and other phenoxy compounds become
a low-volatile ester formulation should be used.
significantly volatile. In general, do not apply
b. Effects of Humidity. High or moderate
herbicidal sprays when the temperature is above
humidity increases the effectiveness of most


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