16 WORK ON THE WHITE PINE BLISTER RIST IN MINNESOTA 



two to six \cars. or ])Ossibly longer, hciicc. its occurrence in any state is 

 no reflection upon the work of inspection officials or plant pathologists. 

 The bodies producing teliospores looking like tiny threads less than 

 one-cjuarter inch long-, grow in clusters on the underside of the leaf and 

 are easily visible with a lense. A tree attacked by these spores after a 

 time exhibits a swelling of the bark at the diseased portion, generally 

 losing- its natural green color. \*ery early in the spring, and frec|uently 

 at other seasons a clear liquid exudes in drops from this discolored 

 bark. This liquid contains microscopic spores known as "pycnospores," 

 the function of which is not readily understood. The appearance of 

 these drops generally precede the appearance of the lilisters. 



After the peridermium spores are discharged from the blisters on 

 the pines, said blisters remain as open cavities and the bark in the vicin- 

 itv dies, exhibiting later a cracked and discolored appearance and show- 

 ing evidence of a cancerous growth. The region about the blister may 

 in fact exhibit "canker" of some sort during the period of spore dis- 

 charge or before. This was clearly evident in the case of our first find- 

 ing in Nursery B. If the tree is not killed immediately by the attack, 

 and a large tree may not be, it may give ofif spores every year there- 

 after to infect currants and gooseberries in the vicinity. It is not 

 known that spores live over winter on currant and gooseberry; so 

 far most of the evidence would indicate the contrary. It has been 

 generally supposed that if all currants and gooseberries within a 

 radius of 1,500 feet from an infested pine or pines were destroyed, 

 the danger of the infection spreading would be elin-iinated. but this 

 year's observations indicate that this is possibly an unsafe assertion. 



The life history of this parasitic fungus has been given very 

 brieflv, Init we believe sufficient data have been presented to make it 

 clear what a difficult problem is before us, if we wish to eradicate it in 

 Minnesota, and how impossible the solution of this problem is unless 

 neighboring states ofifer efficient co-operation for their own protection, 

 as well as for the protection of this state. 



WORK DURING THE SUMMER AND AUTUMN OF 1916. 



Immediiiteh upon the discovery of the rust in the two nurseries 

 abo\e referred to. the State Entomologist, by the authority invested in 

 his office, imposed a ciuarantine forbidding the sale and shipment of 

 anv five-leaf pines, currants and gooseberries from either of the above 

 nurseries until the rust had been eradicated therefrom. Acting upon 

 the adxice of the Division of Plant Pathology of the Experiment Sta- 

 tion and the luitomologist, owners of these nurseries voluntarily de- 

 stroxed all pines known by them or suspected by them to be infected. 



