252 INSECTS AFFECTING VEGETATION 



fasten the canvas closely and securely to the sides. Beds canvased 

 in this way escaped injury in 1907. 



Spray infested beds with arsenate of lead at the rate of 1 pound 

 of arsenate of lead, paste form (one-half this amount of the powder), 

 to from 12 to 16 gallons of water. Mix thoroughly and apply to 

 the bed until every leaf is thoroughly dampened. Arsenate of lead 

 adheres well to the foliage, and unless a very heavy rain falls the 

 application need not be repeated until the plants have grown con- 

 siderably. At setting time dip the tops of the plants in arsenate 

 of lead made according to the above formula, and if flea-beetles con- 

 tinue to be injurious in the field spray the plants with the above in- 

 secticide, using a knapsack spray pump. With this pump one man 

 can spray 5 to 6 acres of young tobacco in a day. 



Cutworms. Cutworms as a class are very injurious to tobacco. 

 Their injury consists in cutting off the top of the young plant at 

 or near the surface of the ground. Thirteen species have been known 

 to be injurious to tobacco. 



If possible, plow sod land in the fall, keep it free of vegetation 

 for some weeks before tobacco is set, and thus starve the cutworms. 

 If the field is infested with cutworms at setting time, use one of the 

 following trap baits: Spray green clover with Paris green and drop 

 handfuls of it about the field at intervals of a few feet; or, make a 

 poisoned bran mash by mixing 1 pound of Paris green with 50 to 

 60 pounds of bran, sweeten with molasses, and drop about the field 

 four or five days before setting time. If plants have been set, drop 

 two or three small handfuls about each hill. 



The Tobacco Hornworms. These are the most serious pests of 

 tobacco in the United States. They are found in all tobacco fields. 

 The observations recorded here were made upon the southern spe- 

 cies, but since the life histories and seasonal histories of the two 

 species are so nearly alike, remedies that are recommended for the 

 southern species will apply equally well to the northern. It requires 

 forty-five to forty-eight days for the complete life cycle of the south- 

 ern tobacco worm. 



Eggs deposited June 1, June 15, July 1, or July 15 will hatch, 

 the larvae or worms will mature upon tobacco, will enter the ground, 

 where they remain about three weeks in the pupal stage, and will 

 emerge as moths of the second generation about July 15, August 1, 

 August 15, and September 1, respectively. LarvaB that enter the 

 ground after August 10 to pupate are very likely to hibernate. 

 Therefore, only moths that are abroad before July 15 will produce a 

 second generation. 



The tobacco moth hibernates as a pupa in an oval cell, at an 

 average depth of about 4 inches for second bottom soils of the Cum- 

 berland River. Numerous experiments at Olarksville, Tenn., 1907 

 to 1910, demonstrate that usually not more than 25 per cent of the 

 hibernating stage pass the winter successfully. This stage is, there- 

 fore, a critical period in the seasonal history of the insect. Hence 

 any artificial disturbance of natural conditions should produce an in- 

 creased mortality. The most simple means of disturbance is by 



