332 ANNUAL REPORTS OF DKPAUT.MKNT OF AOKICULTURE. 



The labor shortage has also broufrht the problem of dosajres into 

 prominence. The (|uostion now to be solved is not to find the mini- 

 mum dosa<2:e that will satisfactorily kill the worms present upon the 

 plants, but to find a dosa<re that will be eifective upon the worms for 

 the lon«rest possible period Avithout injury to the plants. Experi- 

 ments durinjj: the year show that under some conditions twice the 

 usual amount of arsenate of lead was economical when compared 

 with the usual practice of one lif^hter dosa^^e plus even a moderate 

 amount of hand Avormin^r. In one particular experiment the savinjr 

 •of labor amounted to $5 per acre, and the conditions in this par- 

 ticular Held occurred quite <renerally over the entire so-called Black 

 Patch in Kentucky and Tennessee. 



Careful tests of calcium arsenate in comparison with arsenate of 

 lead Avere made, and the results indicate that the use of calcium 

 arsenate is not to be recommended for tobacco. Even <^rades con- 

 tain in<i; a very low percentage of water-soluble arsenic oxide injured 

 jjlants more seriousl}' than did the arsenate of lead. 



An important new line of investigation has been started, the result 

 of which can not be determined until the sununer of 1922. This work 

 included nearly 1,000 acres of tobacco in Kentucky and Tennessee 

 upon which an effort will be made greatly to reduce the hibernating 

 generation of hornworms by killing them with in.secticides upon the 

 suckers, Avhich often grow to great luxuriance after the tobacco crop 

 is housed. The region selected is one in which the growers are the 

 most Avide-awake and in which they control the horuAvorm A'ery 

 Avell. indeed, during the groAving season. If there is anything to be 

 gained by a fall control of the horuAvorm, the region selected offers 

 the best opportunity for the determination of the A^alue of such con- 

 trol. This suggestion Avas made by the chief of the bureau for 

 tobacco insects in general more than 20 A'ears ago, but has never been 

 tested on a large scale. 



The mosiac-disease work Avas stopped almost completely during the 

 -winter because of the resignation of the investigator Aviio had it in 

 charge. This Avork has been reassigned to S. E. Crumb, Avho already 

 has determined one means b}' Avhich the disease overwinters and has 

 started a comprehensiA^e series of experiments upon the epidemiology 

 of the disease. 



The Avork on tol)acco insects at Quincy, Fla., has been divided 

 principally betAveen tAvo primary insect pests — the tobacco thrips and 

 the tobacco flea-beetle. It has been shown that undoubtedly the best 

 time for attacking both of these pests is during their emergence from 

 hibernation, when the plants are small, and sprays and dust mixtures 

 can be more easily and more thoroughly applied. 



Through cooperation of one of the manufacturers of spraying 

 machinery, a special power sprayer was secured which is sufficiently 

 narroAv to go between two rows of tobacco. However, owing to cer- 

 tain faults in construction and owing to the late date at which this 

 machine was receiA^ed, it w^as impossible to use it between the roAvs 

 this year, but before tobacco Avas tied up to the top of the sheds the 

 mule machine Avas mounted upon a farm wagon and five rows of 

 tobacco were sprayed at a time. The results indicate that this 

 method of control "is sound, and that undoubtedly this type of ma- 

 chine, Avhen the faults in construction are remedied, will be Aery 

 A'aluable to the growers. 



