Sugar Beet Webworm 



Since that time it has spread over the entire sugar beet growing areas of 

 the country. 



The worst outbreaks of webworms which have occurred in the ter- 

 ritories in which The Great Western Sugar Company is operating took 

 place in 1918 and 1919. During the season of 1918, the June and August 

 broods both caused great damage. Some fields were injured by both 

 broods. 



An accurate statement of the acres damaged in 1918 and the degree 

 of damage was reported by the fieldmen of The Great Western Sugar 

 Company. These reports show that 31,000 acres were injured. The 

 first brood injured 5,500 acres and the second 25,500 acres. Over 7,000 

 acres were damaged to the extent of two tons per acre, over 7,000 acres 

 to the extent of one ton per acre and nearly 15,000 acres to the extent of 

 J ton per acre. The total loss to the growers and the industry was not 

 less than 26,450 tons of beets. These at $10.00 per ton, the price in 1918, 

 represents a money loss of $264,500. Over 16,000 acres were sprayed 

 with Paris green at the average rate of 4 pounds per acre, and much loss 

 thus prevented. This required 84,000 pounds of Paris green, much of 

 which was furnished the growers at a reduced cost per pound by The Great 

 Western Sugar Company. 



This loss could have been very much more reduced if all growers had 

 realized in time that there was danger and had had themselves properly 

 prepared. Too late spraying was responsible for much of the loss. 



As this bulletin goes to press the campaign against the first brood 

 of 1919 is drawing to a close. This brood, which is the largest known in 

 the history of sugar beet growing in the United States, covered practically 

 all beet growing areas in Colorado, Nebraska, Montana and Wyoming. 



In order to assist the growers in combating it The Great Western 

 Sugar Company purchased several hundred traction sprayers and dis- 

 tributed about 700,000 pounds of Paris green in its territories. Had it 

 not been for this assistance the loss to the growers would have far exceeded 

 that caused by both broods of 1918. 



NATURE OF INJURY 



Webworms injure sugar beets by destroying the leaves. This re- 

 tards the growth, thus reducing the yield and sugar content. All other 

 things being equal, the loss is quite proportional to the loss in leaves. 

 The greater the amount of leaf surface destroyed, the greater the loss. 

 On the other hand, the losses depend somewhat upon the time of season 

 when the damage is done, also upon the weather condition immediately 

 after it is done. 



Small beets may be killed outright if the leaf surface is so small that 

 the worms attack the crowns. Larger beets may have their leaves 

 entirely eaten off but recover by putting out new leaves. (See Fig. 9, 

 Page 69, and Fig. 10, Page 70.) 



The first indications that a crop may be injured by the sugar beet 

 webworm is the appearance of the moths (Fig. 11, Plate V, Page 19) in 

 the field. These moths are active and easily disturbed during the day. 

 When present they will be noticed flying ahead of the cultivator or of 

 one walking through the field. Their flights are short and jerky and they 

 usually alight on the under side of a leaf or on the ground. Catch one 



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