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 water per acre applied any time after planting but before emergence. 

 Pre-emergence treatment will not control 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 cultivation. In most States 

 the ester formulations are preferred for pre-emergence treatment, and 

 some States specifically suggest that the amine salt formulations not be 

 used for pre-emergence weed control in corn. 



Comments and precautions .- -Treatment generally is not advised on 

 sandy soils when excess rainfall is likely to occur. Use lower rate of 

 application on loam soils and higher rate on clay soils. 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. Deep planting of corn provides additional 

 safety. 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. 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 cer- 

 tain vegetables. 



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

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

 broadleaved annual weeds: Ester or amine salt of 2,4-D at 1/4 to 1/2 pound 

 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 inbred lines in the Corn Belt, use the amine salt of DNBP at 3 to 4 

 pounds per acre between the emergence of corn and the 4-leaf stage of 

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



Comments and precautions. - -In the western Great Plains and Inter- 

 mountain region, 2,4-D at 1/2 to 1 pound per acre usually is suggested 

 for control of most weeds in corn. 



If corn is more than 12 inches tall drop nozzles may be advantageous 

 to direct the spray to the top of the weeds and to partially reduce the 

 injury hazard of spraying in large corn. 



Some injury to corn from 2,4-D applications made at any time from 

 emergence to tasseling may occur if the treatment is applied during 

 conditions favoring rapid growth. Avoid applications when temperatures 

 are high and corn is growing at a maximum rate. Use the esters of 2,4-D 



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