680 IOWA DEPARTMENT OP AGRICULTURE 



tains bad weed seeds and is low in vitality. Certain weed seeds are 

 prohibited in the Iowa seed law, like Canada thistle, quack grass, mus- 

 tard, dodder, etc. Are we not paying the penalty for the weediness of 

 our fields? Some of the weed seeds keep their vitality for a long period 

 of time. Thus some of the seeds of velvet weed retain their vitality for 

 more than half a century. The seed of shoofly likewise retains its 

 vitality for a long time. 



Weeds may be classified as annual, biennial, perennial and winter 

 annual. 



First, annual weeds, represented by foxtail. Their seeds germinate in 

 the spring, flower, produce seeds and then die. Their roots are fibrous, 

 and are usually easily killed by exposure to the sun in ordinary methods 

 of cultivation. In some few cases, as in crabgrass, roots are produced 

 from the joints where such weeds lie on the ground. 



Second, biennial weeds. Their seeds germinate one season and pro- 

 duce a mat of leaves, pass through the winter, and the next season send 

 up a stem which bears flowers and seeds, and then dies. Such weeds 

 should be cut off several inches below the surface of the ground. This 

 should be done the flrst season, or before the plant has produced seed. 

 Never cut them off at the surface of the ground. If so treated they act 

 like perennials. Weeds of this class are represented by burdock and 

 parsnip. 



Third, perennials. This class of weeds is represented by Canada 

 thistle, quack grass, dock, and sheep sorrel. They continue to grow 

 year after year. 



Fourth, winter annuals. The seeds germinate in the fall, pass 

 through the winter, flower and seed early next season. Wild barley or 

 squirrel tail, horse weeds are types of winter annuals. 



The following rules may be laid down for the extermination of weeds: 



GENERAL RULES TO BE OBSERVED. 



1. Prevent the Formation of Seeds. This applies to all kinds of weeds. 

 Many seeds of weeds like foxtail, and other weeds of the grass family, 

 do not retain their vitality very long. Some, however, like shoofly, 

 velvet-leaf or butter print, retain their vitality for a long period of 

 years. It is essential that no seeds be allowed to form because a con- 

 tinuous crop of weeds will appear when the soil is brought under 

 cultivation. 



2. Always Buy the Best Seed. See that such weed seeds as dodder, 

 buckhorn, dock, Canada thistle, chicory, carrot, and other weeds are 

 not sown with clover and other seeds. 



3. Rotation of Crops Is Important. First, because the conservation of 

 the soil, second, to destroy insects. Many of the insects cannot be de- 

 stroyed in any other way. Third, to destroy fungus diseases (smut of 

 oats and corn are caused by parasitic fungi.) These root parasites of the 

 fungus type cannot be prevented in any other way. Many of these occur 

 on the roots of cultivated plants. Many weeds are found in special 

 crops. In this rotation clover should occur, because a thickly grown 



