SITE INFORMATION AND CORRESPONDENCE_FILE 2

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r,..r NUN", and 2, 4, 5-T herbicides are now on the market. These formulations reduce, but do not entirely eliminate, the dangers of volatilization and drift of herbicidal vapors to the trees. Volatility is not a major hazard when the amine salt and emulsifiable acid formulations of 2,4-D are used; however, 2,4-D at heavy rates (2 pounds per acre and up) can cause soil sterility resulting in the uptake of injurious quantities of the herbicide by the roots of trees. Normally, use of 2,4-D near avocado trees should be limited to spot treatment of small areas using the amine salt or emulsifiable acid formulations, taking maximum precaution to prevent spray drift. Another approach to orchard weed control, which has proven successful in citrus culture, is selective sterilization of the soil with CMU (3-(p-chlorophenyl)-1; 1- dimethylurea). Application of this material to the soil at the rate of 2 pounds per acre provides seasonal prevention of weed growth by killing the weed seedlings as they germinate. Established perennials and mature annuals are not controlled by CMU. Citrus is not injured by treatments at this rate, and tests are now in progress to determine whether or not CMU can be safely used under avocados. Preliminary results indicate that avocados are, less tolerant than citrus. At the present stage of experimentation, it appears probable that CMU, or one of the chemicals related to CMU, will prove to be usable in avocado orchards, as in citrus, but with a lower margin of safety for errors in application. CMU is not recommended for use in avocado orchards at the present time. Dalapon (dichloropropionic acid) is a new herbicide that has proven to be particularly useful in controlling perennial grasses. Perennial grasses can be controlled by wetting the foliage with solutions of Dalapon containing 10 to 20 pounds of the formulation per 100 gallons of water. Two or more applications may be required. Although Dalapon is systemic, in that it is absorbed by the foliage and translocated into the rootsand rhizomes of grasses, it also has a sterilizing effect on the soil and is taken up by the roots of trees causing injury. The amount required to kill perennial grasses is injurious to avocados when applied in the root zone of the trees and, therefore, should not be used in orchards. Dalapon has been used to good advantage for spot treatment in eliminating bermudagrass around headstands and along irrigation ditches outside the root zone of the trees. Amino triazole, also a systemic herbicide, appears to be less toxic to trees. It is a promising material for control of general vegetation, including perennial grasses and is now being tested for use under avocados and other tree crops. The use of these and other newer chemicals, while not proven safe for use in avocado orchards, should not be overlooked by the grower for the control of weeds in irrigation canals and along the edges of his property. Programs for the elimination of seed sources should proceed abreast of control programs within orchards. Weed control should extend into roadside ditches, along fences, boundary lines, rights-of-way, and all other areas near the orchard where weeds mature and go to seed. Such a program is a matter of community cooperation, and, as such, is one from which the community as a whole —farmer, home owner and industrial land user— benefit. Weeds are equally the problem of all land users, and thus their control deserves the concerted effort of everyone.