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<br />001724 <br /> <br />RESEARCH IN CHEMICAL CONTROL OF VARIOUS PHREATOPHYTES <br /> <br />by <br /> <br />Eugene E. Hughes <br />Agricultural Research Service, Los Lunas, New Hexico <br /> <br />As has been previously stated in this symposium, phreatophytes consume <br />large quantities of water, choke river channels and irrigation systems. <br />Mechanical control of phreatophytes, especially on irrigation ditch- <br />banks, has been in uSe for many years. Chemical control studies have <br />been conducted for more than 18 years and were primarily directed <br />toward species growing on or in irrigation systems. In 1957 (14), it <br />was estimated that losses of $11,937,418 were prevented at a cost of <br />$6,521,167 for treating ditchbank weeds alone. A considerable portion <br />of these costs and savings were attributable to phreatophytes. <br /> <br />Earlier, you heard of the extensive areas of phreatophytes and <br />tial savings in water which might result from their control. <br />purpose of this discussion is to review the research underway <br />chemical control measures in use directed toward reducing the <br />from phreatophytes. <br /> <br />pot en- <br />The <br />and <br />losses <br /> <br />Problems in Chemical Control of Phreatophytes <br /> <br />One of the major problems in the chemical control of phreatophytes is <br />due to their growth habits and location. Because of their water-loving <br />characteristics, they are found in irrigated valleys and other areas <br />with high water tables. Thus, it is difficult to treat the plants with <br />many herbicides without damaging susceptible crops--especially, when thE <br />treatments are made during the growing season. Recent advances in <br />dormant-applied herbicides show promise of overcoming this problem (6). <br />Although more expensive than foliage-applied treatments, they are much <br />safer and appear to be effective. <br /> <br />Another problem in phreatophyte control is the killing of undesirable <br />species only. Many times, species are so intermixed that treatment of <br />individual trees sometimes becomes necessary. Where plants tend to <br />grow in small patches, aerial application of herbicides using drift- <br />reducing carriers, such as the invert emulsions, may Serve the purpose. <br />Poorer results f~om herbicides applied in invert emulsions, compared <br />to oil:water emulsions, to saltcedar (Tamarix spp.) for control (8) <br />indicate that spraying mixed stands of phreatophytes may result in <br />control of broad~leaved species and fail to control species with <br />extremely small leaves such as saltcedar. This may be due to the <br />large droplet size of the invert emulsions. In addition, a herbicide <br />applied for control of one species may have little effect on others. <br /> <br />Whenever large areas of land are treated with herbicides, contamination <br />of water resulting from surface runoff is always a hazard. This is <br /> <br />19 <br />