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<br />001723 <br /> <br />Tests indicate that tamarisk may be controlled by mowing followed <br />immediately with a spray application of 8 pounds of silvex ester per <br />acre in diesel oil. When this procedure has been followed, stands <br />were reduced as much as 83 percent. <br /> <br />Experiments have been conducted to determine the most effective time to <br />apply herbicides. Maximum results are obtained when the plant is in <br />its most active growth stage; for tamarisk, this is in the latter part <br />of Mayor early June. Tests at Los Lunas indicate that 2 pounds of <br />silvex low volatile ester applied in May with a repeat application in <br />August may be three times more effective than one application of 4 <br />pounds of silvex per acre. <br /> <br />Carbohydrate reserves have been studied for 5 years in our Denver <br />laboratory. These tests confirm that there are definite cycles in <br />carbohydrates stores in the plant. From the carbohydrate analysis <br />run, it has been determined that the low period for carbohydrate level <br />is in late spring or early summer (May-June). Generally, we feel that <br />the best results from herbicidal application have been obtained during <br />the period when carbohydrate level was lowest. Recent laboratory <br />research tests indicate that high quantities of salt present in tama- <br />risk foliage may have a definite effect on the efficiency of herbicide <br />applications. Application of herbicides immediately after a rain <br />appears to be more effective than similar applications before the rain. <br /> <br />The phreatophyte control program along the Rio Grande has been accom- <br />plished by using several different mechanical measures and herbicides. <br />To date, the most effective equipment for complete eradication of <br />tamarisk is the root plow (photograph 3). This type of equipment has <br />been used on approximately 6,500 acres at costs varying from $7 to <br />$9.50 per acre depending on the stability of the land upon which the <br />equipment is operating. The disadvantage of using this equipment for <br />control is that it is harmful to grasses which we would like to encour- <br />age. <br /> <br />Another method which has been effective for maintenance of regrowth is <br />the rotary brush cutter (photograph 4). This machine does very little <br />to reduce the number of plants infesting the area; but, because of its <br />ease of operation, effectiveness in removing top growth of seedling <br />plants, and cost of operation, this equipment has been used extensively. <br />Over the past 3 years, approximately 12,000 acres have been mowed at <br />an average cost of from $2 to $3 per acre (photograph 5). Contract <br />cost for accomplishing this type work in Nevada averaged $4 per acre. <br />No evaluations have been made to determine the amount of water saved <br />through control of plants by this method. <br /> <br />Other types of ground-operated equipment which have been used are the <br />disk and brush chopper. The uses for this equipment are limited. On <br />occasions, we have attempted to use a chain pulled between two large <br />tractors. This works on large growth and can be used for initial <br /> <br />29 <br />