Vietnam War: Forest Fire as a Military Weapon - Paperless Archives

SECRET
6. Effectiveness of foliar spray is reduced if applied during a dry period when the vegetation is under moisture
stress. Effectiveness of a soil-applied herbicide is optimum if applied during a period when it is moved into the
soil by moderate rainfall at a time when plants are actively growing.
7. Many species of trees and shrubs. particularly in tropical regions, are resistent to all commonly used herbicides
Such species have been little affected by defoliation or desiccation sprays at the various locations we have
observed, In mixed evergreen forests and shrub types, however, the resistant species make up a small proportion
of the total vegetative cover and can be ignored in planning desiccation treatments.
8. In general, higher dosages of systemic herbicides were required in humid tropical areas for effective desiccation
of groundstory vegetation than in drier areas.
Timing of Desiccation Treatments
Desiccation treatment aims at producing the maximum possible amount of dry ground fuel by the time of burning.
Where possible. the time requirements for effective desiccation should be considered before deciding when to burn. However,
military considerations and restrictions on choice of weather suitable for burning may leave little latitude in planning
"the sequence of desiccation and burning operations.
Use of herbicide desiccants must be geared to the yearly patterns of both precipitation and temperature. Consequently,
timing of operations will not be exactly the same in any two climates. The following list of requirements for effective
herbicide desiccant application will supplement the recommendations listed in Appendix B for each of the climates.
Planning of desiccation operations can be based on the readily available records of average monthly precipitation and temperature-the
same records used for classifying each climate. Remember, the weather of any year at a location may differ
considerably from the averAge. Consequently, any additional information that can be obtained concerning typical variations
for each month at the location will be of benefit in selecting the best month for each treatment. Also, the actual dates ot
herbicide application should be adjusted slightly from the planned dates if current weather makes such changes advisable.
Following are the requirements to be met, as far as possible, in planning herbicide desiccant treatments (references to
months for treatment apply to the Northern Hemisphere):
I
Aerial spraying of systemic herbicides, including both defoliating and desiccating treatments, should be done
when woody plants are in their most active growth stage-near the time when new leaves become fully formed.
Growth processes for all species are restricted by deficient soil moisture and by low temperatures, acting singly
or in combination.
Air temperature: Monthly daily mean should be above 600 F., but spraying can be done when average
} daily mean is between 500 and 600 if the spray date must be advanced to allow an adequate drying period before
burning.
Under climates having most months, or all months, with average daily means above 600 F., the best spray
months are from spring (March) through the summer, provided precipitation requirements are met.
S
i
SECRET