48 BULLETIN 995, U. S. DEPARTMENT OF AGRICULTURE. 



fungus does not generally attack any part of the beet plant except 

 the leaf blade and the petiole, while the Phoma may attack leaf 

 and root. If these fungi are present in large numbers they may 

 do considerable damage to the beet crop. If the attacks are severe 

 early in the season the growth of the beets is retarded, and conse- 

 quently the yield is reduced. If the attacks do not occur until 

 late in the season, after the beets have practically reached their 

 normal growth the disease will reduce the sugar without appre- 

 ciably affecting the tonnage. If these fungi attack the beets in 

 midsummer both the yield and the quality will be generalty reduced. 

 These diseases may best be controlled by deep fall plowing and by 

 crop rotation. Crop rotation is especially recommended where it 

 can be practiced, but in cases where it is necessary to follow beets 

 with beets after these diseases have appeared, the ground should 

 be plowed in the fall to a good depth, not less than 12 to 14 inches. 

 In fact, all plant-pathological problems, from a practical stand- 

 point, are closely connected with the cultural phases of crop pro- 

 duction. Production can not be successfully studied without a 

 knowledge of the diseases affecting that particular crop, nor can the 

 disease of a crop be intelligently considered with reference to con- 

 trol measures except in conjunction with the cultural practices and 

 with a knowledge of the conditions under which that crop is grown. 



INSECTS. 



The principal insects affecting sugar beets have been treated in 

 various publications of the Bureau of Entomology. A list of these 

 publications is given at the end of this bulletin. Among the im- 

 portant forms which affect the leaves are web worms and the beet 

 army worm. In some localities blister beetles, leaf beetles, and local 

 pests do considerable damage, mainly by destroying the foliage. 

 They also have a retarding effect on the growth of the beet, but the 

 principal injury is due to the destruction of the foliage and the con- 

 sequent expenditure of energy and food required by the plant to 

 produce a new set of leaves. Usually these insects start in small 

 areas on one side or a corner of a field and spread rapidly. Of some 

 species there are several generations in a season, and if weather con- 

 ditions favor their development much damage is frequentty done. 

 In the case of insects working early in the season the tonnage of the 

 beets may be greatly reduced, and if the insects continue until late in 

 the season the sugar content also will be lowered considerably. 

 Sugar-beet insects as a general rule are more or less local and are 

 seldom very destructive for more than one or two years in succession. 



All biting or chewing forms of insects are susceptible to poisons 

 and may be controlled by the use of arsenate of lead, Paris green, or 

 other arsenicals. 



