:hemical warfare on weeds 



n's method of weeding carrots has been estimated to save six 

 dollars annually. This article is the first of a series of four reports 

 lotion's second highest cause of annual crop loss. 



Pre-emergence Spraying Successful 



Many chemicals that kill crops 

 on contact may be useful for killing 

 weeds in pre-emergence applica- 

 tions. This involves spraying the 

 soil before the crop comes up. Weeds 

 near the surface are killed by the 

 chemical residue; crops are thus 

 weed-free for five to six weeks. 



Sweet corn may also be weeded 

 with 2,4-D in pre-emergence ap- 

 plications. By this method, the 

 growth of almost all annual grassy 

 and broad-leafed weeds except 

 smartweed is prevented for five to 

 six weeks. Several other chemicals, 

 such as the di-nitros and sodium 

 pentachlorophenate, may also be 

 applied in this manner. The di- 

 nitros are particularly useful for 

 weeding fields of beans. 



Moisture Conditions Important 



Proper moisture conditions are 

 necessary in the soil for these 



weedkillers to work efficiently in 

 pre-emergence apphcations. Under 

 very dry conditions, they may not 

 kill any weeds. Moreover, in very 

 fight soils, heavy rains soon after 

 treatment may leach the chemical 

 and kill the germinating seedlings. 



Two More New Chemicals 



Many unsuccessful experiments 

 were tried in weeding small seeded 

 crops, such as spinach, beets, and 

 lettuce, with fittle hope. Now, 

 however, a chemical called chloro- 

 IPG has been found apparently 

 fairly dependable in kiUing most 

 weeds without harming the crop. 



Chemicals are even eliminating 

 the need for hand-weeding onions. 

 Potassium cyanate, another new 

 chemical, is selective in kiUing all 

 small annual weeds in this crop. 

 The strength of this chemical must 

 be adjusted to the weather condi- 

 tions prevailing before and at the 

 time of treatment, (cont. on page 15) 



One week before fhis photo- 

 graph was taken the carrot 

 ptot at the left was sprayed 

 with Stod ard Solvent. 



Photo by Robert L. Coffin. 



