1.2-DIHYDRO-PYRIDAZINE-3.6-DIONE (Maleic Hydrazide, MH) 



This chemical is formulated as a water-soluble sodium or diethanol- 

 amine salt for use as a herbicide. It has shown promise for control of 

 several annual and perennial grasses when applied in combination with 

 tillage and cultural treatments. It is being used also as a grass inhibitor 

 to reduce mowing on areas such as roadsides. The chemical, however, 

 has performed erratically both as a herbicide and as a grass inhibitor. 

 Additional research is needed to determine the place of this compound in 

 the field of weed control. 



MH has low oral toxicity (LD^q = 5,800 mg./kg.) for rats. 



PHENYL MERCURIC ACETATE (PMA) 



This herbicide is available in a number of formulations. It is sometimes 

 impregnated on various carriers such as vermiculite, but PMA is also 

 available as a liquid concentrate that must be diluted with water and applied 

 as a spray. Most of the formulations presently available contain 10 per- 

 cent PMA by weight or approximately 1 pound of active ingredient per gal- 

 lon of concentrate. PMA is an effective herbicide for selective control of 

 crabgrass in lawns. 



The compound is highly toxic to humans and warm-blooded animals and 

 must be handled with care. Its oral toxicity for rats: LD50 = 27 mg./kg. 

 It is not used presently for weed control in cultivated crops. 



POTASSIUM CYANATE (KOCN) 



This herbicide is a white, water-soluble powder, effective in controlling 

 seedling weeds. It is used as a selective spray for weed control in onions, 

 and to control crabgrass and chickweed in lawns. For best results against 

 crabgrass, it should be applied when the crabgrass is small. The herbi- 

 cide will often discolor lawn grasses at rates required to kill crabgrass, 

 but the discoloration usually will disappear in 7 to 10 days. 



KOCN has relatively low oral toxicity (LD^q = 780 mg./kg.) for rats. 



CALCIUM CYANAMIDE 



Calcium cyanamide is a water-soluble solid. It usually is formulated as a 

 granulated solid or pulverized powder. The byproducts of calcium cyanamide 

 decomposition in acid soils possess both phytotoxic and fertilizing prop- 

 erties. For this reason it is often used as a combination herbicide and crop 

 fertilizer. 



This chemical has long been used in tobacco plant beds as an herbicide 

 for weed control and as a fertilizer. In recent years, it has been used with 

 erratic performance for pre-emergence weed control in corn and in several 

 horticultural crops. The herbicide is also being used as a temporary 

 pre-planting soil sterilant for turf seedbeds. The chemical should be ap- 

 plied and worked into the soil surface at least 3 weeks before seeding 

 lawns and other turf. 



In some areas, calcium cyanamide is being used in turf renovation pro- 

 grams. 



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