gallons of sjjray material per acre. 



After three years of weed control 

 experiments in corn fields, our ad- 

 vice is not to throw the cultivator 

 away, although it has been found 

 that a 2,4-D application can be effec- 

 tively substituted for one or more 

 cultivations. 



A pre-emergence spray at one to 

 one and one-half pounds of 2,4-D 

 acid per acre applied just about the 

 the time the corn is coming up (6-8 

 days after planting) is effective in 

 controlling most weeds, and may 

 eliminate one or more cultivations 

 at the beginning of the season. Spray- 

 ing at lighter rates, one-half pound 

 of 2,4-D acid per acre, will not ma- 

 terially damage the corn while grow- 

 ing. Such an application is useful in 

 controlling susceptible weeds in 

 drilled corn, even after the corn is 

 ]2 to 18 inches high. 



In our experiments, we have been 

 dealing with corn fields that carried 

 a varied weed population, some of 

 which were not particularly suscepti- 

 ble to injury by 2,4-D. For this rea- 

 son, plots which were not cultivated 

 but sprayed exclusively with 2,4-D 

 had as thick a weed growth and the 

 corn was almost as poor as on those 

 plots where no spraying or cultiva- 

 tion had been done. The weed popu- 

 lation, however, was entirely differ- 

 ent. Quick growing tall weeds like 

 mustard and pigweed were in the 

 ascendancy on the unsprayed, un- 

 cultivated plots, while red rooted pig- 

 weed {Amaranthus retro flxus) and 

 smart weed (particularly Polygonum 

 Pennsylvanicum) were just as abun- 

 dant on the sprayed uncultivated 

 plots. 



There are many factors that in- 

 fluence the effectiveness of 2,4-D. 



.<_*»*«."*► »«*. .A.«**i»**.iai« 



Figure 6. This quackgrass plot was treated with sodium TCA, 50 lbs. per acre, on Septem- 

 ber 7, 1950, during cool weather. Precipitation was heavy during the preceding month. 



40 



