2 A MANUAL OF WEEDS 



of the first class, Burdock and Wild Carrot of the second, and Field 

 Sorrel and Canada Thistle of the third. Some plants that round 

 their life-cycle in a year are known as "winter annuals" ; the seeds 

 that have matured during the summer germinating in the fall, mak- 

 ing a certain growth before the closing in of winter, and completing 

 their development in the next summer. To this class belong the 

 hated Penny Cress, or Frenchweed, the Corn Cockle, and the Field 

 Gromwell or Wheat-thief. Obviously, the best time to compass 

 their destruction is in the spring, before they can develop fruiting 

 stems. Spring plowing or harrowing is of course in order, but it is 

 with such plants as these that the newer method of killing with a 

 chemical spray, or herbicide, is most successful, particularly when 

 they appear in grain fields. The grains are resistant to injury from 

 the spray, for, being " center growers," they make a swift recovery 

 from the slight harm received on outside sheath-leaves, while the 

 tender, outspread foliage of the weed seedlings is often totally 

 destroyed. 



For biennials, also, the one sure means of destruction is prevention 

 of seeding. Where plowing out is impracticable, frequent cutting 

 must be practiced, in the first season spudding out or cutting off 

 the rosettes, or crown leaves, and in the second season mowing 

 off the flowering stems before the formation of seed. 



Perennial weeds are by far the hardest to fight, sometimes requir- 

 ing the cultivation of special hoed crops in order to insure their 

 complete eradication. The plowing and harrowing given to ordi- 

 nary field crops often only stimulate the growth of these pernicious 

 plants by breaking or cutting the long-lived underground stems and 

 inducing them to send up new shoots. It should be remembered 

 that their food reserves are in fleshy or woody roots, underground 

 stems, bulbs, or tubers, and that the growth above ground never 

 seems to exhaust these hidden stores of nourishment. However, 

 there is a time when they are most vulnerable. to attack, and it is 

 just at that stage of growth when flowering stems are nearing full 

 size, but before the formation of seed. They should then be plowed 

 down, or, if too tall for that, first mowed and then plowed under. 

 Any and every plant, even the sturdiest tree, must die if kept de- 

 prived of leaves during the growing season ; for it is in these green 

 laboratories that the food gathered from soil and air is so changed 



