Vietnam War: Forest Fire as a Military Weapon - Paperless Archives
Vietnam War: Forest Fire as a Military Weapon - Paperless Archives
Vietnam War: Forest Fire as a Military Weapon - Paperless Archives
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SECRET<br />
Applied to woody vegetation, the contact sprays affect both the leaves and small twigs. These plant parts-with high surfae.volume<br />
ratios can be killed because a large proportion of the tissue is exposed to contact with the chemical.<br />
Larger branches, stems, and buds commonly arc protected with resinous or waxy coverings, or by corky bark.<br />
Typical drying of leaves and twigs after application of contact desiccants is shown in Figure 37. Most leaves die within<br />
2-4 weeks, but additional leaves and twigs continue to die and dry f.•r <strong>as</strong> long <strong>as</strong> two months. A few succulent stems may<br />
die. But most stem tissue remains alive, capable of producing new foliage when weather becomes favorable.<br />
Under humid tropical climate, <strong>as</strong> with guava in Puerto Rico, the regrowth starts on most stenis soon after the original<br />
leaves have dried. After a few months the plants show little or no effect from the desiccant spray. In a tropical climate<br />
with a long dry se<strong>as</strong>on the plants recover during the next wet se<strong>as</strong>on after the leaves have been desiccated. Under climates<br />
with cool or cold winters, the leaves remain dry and brown until replaced by new foliage during the following spring or suminer.<br />
Most of the desiccated leaves drop quickly from the plants under tropical climates and under humid climates with<br />
cool or cold winters. Leaves remain attached for months on evergreen vegetation under climates with a long dry se<strong>as</strong>on.<br />
Contact desiccants are effective in making b'irnable fuel out of the leaves and a small proportion of the twigs. But<br />
since understory vegetation is usually small-stemmed, this represents only about 35-40 percent effective desiccation of the<br />
potential small fuel (Figure 38). Although contact desiccants are relatively ineffective in incre<strong>as</strong>ing the amount of available<br />
fuel. they do reduce the dampening effect of green leaves and open shrub crowns to speed drying of litter. This, along with<br />
adding dry leaf fuel, is all that is needed in certain situations, and will promote good burning if adequate litter and dead<br />
stems already are present. But contact desiccants are not adequate <strong>as</strong> the only treatment for use in climates where total<br />
available fuel weight is less than 0.3 pounds per square foot (see Appendix B). The contacts are recommended <strong>as</strong> a supplement<br />
to systemics in situations where a quick kill of green leaves is essential. One common situation is where new green<br />
foliage h<strong>as</strong> regrown short;y before the planned date of burning.<br />
Several different cherricals will serve equally well <strong>as</strong> contact desiccants.<br />
Paraquat - II'-dimethyl-4,4'-bipyridinium salt<br />
Diquat - 6,7-dihydrodipyrido( 1,2-a: 2', i'-c) pyrazidiinium salt<br />
Cacodylic acid - hydroxy dimethylarsine oxide<br />
Dinitro - 2' s butyl-4,6-dinitrophenol<br />
Paraquat and cacodyllc acid were used in most trials and produced consistent results. The best dosage for each<br />
chemical w<strong>as</strong> not apparent from out trials: in some c<strong>as</strong>es the lowest applied dosage w<strong>as</strong> <strong>as</strong> effective <strong>as</strong> the highest. We<br />
recommend any one of the following contact desiccants: paraquat at 4 pounds acid equivalent per acre, cacodylic acid at<br />
12 pounds, diquat at 12 pounds, or dinitro at 12 pounds. The dinitro should be mixed with diesel oil, and the others with<br />
water, to make 5 gallons per acre total volume of spray mix.<br />
If weather will be sunny and warm (daily mean temperature above approximately 60 0 F.) the contact desiccant should<br />
be applied 3-4 weeks ahead of the planned date of burning. If cloudy, cool weather is expected, the contact desiccant can<br />
be applied two months in advance of burning. Longer periods of drying are not advisable because additional regrowth of<br />
green vegetation may occur before burning.<br />
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