III. WEED CONTROL IN FIELD CROPS 



CORN 



(1) Pre -emergence .- -For control of annual grasses and broadleaved weeds, 

 such as crabgrass, foxtail, ragweed, pigweed, lambsquarters, and others: 

 An ester or amine salt of 2,4-D at 1 to 2 pounds in 5 to 20 gallons of w^ater 

 per acre, or atrazine or simazine at 2 to 4 pounds in 20 to 40 gallons of 

 water per acre, or on corn to be harvested for grain only, a mixture of 3-1/2 

 pounds of CDAA plus 8-1/2 pounds of trichlorobenzyl chloride [TCBC] in 

 5 to 20 gallons of water per acre. These may be applied any tinne after plant- 

 ing corn but before its emergence. Pre-enaergence treatment will not control 

 certain perennial grasses, such as Johnsongrass and quackgrass, or other 

 perennial weeds such as Canada thistle or field bindweed, but treatment may 

 temporarily inhibit their growth and make them easier to control by cultiva- 

 tion or post-emergence herbicide treatments. 



In most States the ester formulations of 2,4-D are preferred for pre- 

 emergence treatment, and sonne States specifically suggest that the amine 

 salt formulations not be used for pre-emergence weed control in corn, es- 

 pecially on sandy soils. 



Comments and precautions .- -Deep planting of corn provides additional 

 safety for pre-emergence treatnnents w^ith all herbicides. Lack of soil 

 moisture may reduce effectiveness of treatment, but under such conditions 

 weed populations usually are not serious. Pre-emergence treatments are 

 especially valuable when excessive rainfall prevents cultivation for extended ' 

 periods after corn emerges. Pre-emergence treatments applied to dry soil 

 with subsequent extended drought may fail to control weeds. Use lower 

 rates of all herbicides on loam or lighter soils and higher rates on clay 

 soils. Treatment with 2,4-D is generally not advised on sandy soils when 

 excessive rainfall is likely to occur. On muck soils and on heavy clay soils 

 high in organic matter, 2 to 4 pounds of 2,4-D per acre may be required to 

 control weeds. Although the amine salts may be used on heavy soils, the 

 esters of 2,4-D are not as likely to leach through the soil as amine salts 

 and are less likely to cause injury, if heavy rains follow application. Only 

 the low-volatile esters or amine salts of 2,4-D should be used for pre- 

 emergence weed control in fields adjacent to susceptible crops such as 

 cotton, tobacco, grapes, and certain vegetables. 



(2) Post -emergence . --For control of pigweed, ragweed, lambsquarters, 

 field bindweed, annual morning-glory, cocklebur, smartweed, and other broad- 

 leaved annual weeds: Esters or amine salts of 2,4-D at 1/4 to 1/2 po\ind in 

 5 to 20 gallons of water per acre applied when weeds are small and corn is 

 4 to 18 inches tall. Treatment does not control annual or perennial grasses, 

 but may temporarily inhibit growth of such perennial broadleaved weeds as 

 Canada thistle, milkweed, and horsenettle. 



For control of weeds in the Corn Belt, use the annine salt of DNBP at 1 to 2 

 pounds per acre between the emergence of corn and the 2-leaf stage of groNvth. 

 2,4-D usually is not recommended for inbred lines of corn. 



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