No. 6. DEPARTMENT OE AGRICULTURE. 183 



NURSERY INSPECTION IN PENNSYLVANIA. 



The law of this State iHMniires thai all uiirsei-ies fi-oin which trees 

 or shrubs are to be sold shall be inspected annually, by an expert, in 

 order to protect obnoxious insects and diseases, if present, and to 

 prevent their spread throughout the State and to other states and 

 countries by the shipment of the young trees upon which they might 

 otherwise be disseminated. When trees^ are found infected with 

 such diseases as Crown Gall and Peach Yellows they must be de- 

 stroyed, and when infested with such a serious pest as the San Jos^ 

 Scale they must be either destroyed or fumigated with hydrocyanic 

 acid gas before any shipment will be permitted from the nursery in 

 which the infested trees were found. This fumigation must be done, 

 in a fumigating house that has been inspected and approved by the 

 authorized representative of this Department, and the law further 

 prescribes the exact amount of the potassium cyanide (1 ounce per 

 100 cubic feet of space) that must be used in generating the gas, as 

 well as the length of time (at least fortj' minutes) that the infested 

 trees must be subjected to the poisonous fumes in order to destroy 

 the pests. 



Other states have similar laws and methods, and no trees of spe- 

 cies likely to be infested with San Jos^ Scale can be shipped into this 

 State from another without the certificate of inspection from the 

 latter; neither can any trees grown in this State be shipped to an- 

 other without our certificate of inspection. This is a fairly effective 

 means of checking the dissemination of the most destructive pest 

 that has ever attacked the horticultural interests of America, yet it 

 is not wholly satisfactory in its practical results. Theoretically, 

 fumigation is the very best and perhaps the only certain method of 

 treating the San Jos6 Scale, but in practice the destruction is not 

 always effected on account of some of the following conditions or 

 their combinations: (1) A leaky or improperly constructed fumigat- 

 ing house. (2) The use of a cheap grade of cyanide of potassium, 

 which may contain so little of the poison as to fail to generate gas 

 strong enough to complete the desired work of destruction within 

 the allotted time of exposure. (3) Fumigation for too short time or 

 in gas too weak. (4) Fumigating the trees while they are wet, as 

 the gas does not act as effectively on the scale when a film of water 

 covers the bark as it does when the tree is dry. (5) Over-packing 

 the fumigating house, to the extent that the gas does not permeate 

 all the spaces and reach all infested twigs. For these reasons any 

 purchaser of trees is justified in rejecting any bunch of trees which 

 he may receive and upon which he may find the San Jos6 Scale, even 

 though they may have been fumigated. To do this he should have 



