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<br />especially true when floodways or river channels are treated. <br />cides having long persistence are especially hazardous in this <br /> <br />Herbi- <br />respect. <br /> <br />Finally, river valleys funnel cold air downhill much the same as water. <br />Late spring frosts that may not affect surrounding upland vegetation <br />may selectively defoliate plants intended for spraying. This results <br />in a stand of phreatophytes being in various stages of physiological <br />development at time of treatment. Consequently, varying results can <br />be expected. In addition, research has shown that peak growth periods <br />and associated low level of carbohydrate storage of adjacent saltcedar <br />plants may vary as much as 4 weeks (10). <br /> <br />It may be impossible, then, to expect any given stand of phreatophytes <br />to be in the l1maximum susceptible condition" for an application of <br />herbicides, thus making retreatmenta necessity. <br /> <br />Research in Control of Saltcedar <br /> <br />Basal.J!..e.1::~ <br /> <br />Wyoming studies (15) have shown that basal spray applications of a 1:1 <br />mixture of the esters of 2,4-dichlorophenoxyacetic acid and 2,4,s-trichlo- <br />rophenoxyacetic acid at 2- and 8-percent concentrations provided very <br />effective control when the chemical was applied in mid-summer. Research <br />in New Mexico (7) showed basal and stump applications of ester and <br />oil-soluble amine formulations of 2,4,s-trichlorophenosypropionic acid <br />(silvex) to be effective for control of saltcedar. Trees with trunks <br />2 inches or larger in diameter were harder to kill than smaller trees <br />and retreatment was often needed. Spraying the lower 2 feet was no more <br />effective than spraying the lower foot. Cutting the larger trees and <br />spraying the stump increased effectiveness. <br /> <br />Granular and Soil-Spray Herbicides <br /> <br />Applications of 3-phenyl-l,l-dimethylurea (fenuron) pellets at 10, IS, <br />and 20 lb/A active ingredient in April gave 97-100 percent control of <br />saltcedar in Wyoming (15). Final results, however, were not apparent <br />for 28 months. <br /> <br />Results of April applications of six granular herbicides for control <br />of saltcedar in New Mexico (8) indicated that 2-methoxy-3,6-dichloro- <br />benzoic acid (dicamba) killed a high percentage of plants. A similar <br />study conducted the following year using nine herbicides again showed <br />that dicamba was very promising. Rates of 5 and 20 lb/A active ingredi- <br />ent were used. Even at the lower rate, better than 50 percent control <br />was obtained. Another herbicide, 4-amino-3,5,6-trichloropicolinic acid <br />(picloram) waS moderately effective at the higher rate. <br /> <br />Applications of soil-spray herbicides for control of saltcedar over <br />a 2-year-period showed that only one herbicide, 3-(3,4-dichlorophenyl)-I, <br />_l-dimethylurea (diuron) plus dodecyl ether of polyethylene glycol <br /> <br />20 <br />