- 2 - 
Factors affecting sev erit y: Susceptibility of host is the most 
important factor. Wart is said to be confined to areas 
with growing seasons of 140 days or less. Soils with tem- 
peratures of 60° to 64° F. are said to favor development of 
wart and with temperatures of 70° to 72° F. to inhibit de- 
velopment. Periodic flooding of soils followed by drainage 
and aeration favors development of wart. (2, 10, 11, 16) 
Method s o f spread: Any agency that v/ill distribute soil, tubers 
or other plant parts containing or bearing spores, including 
drainage water, farm implements, men, animals, diseased 
tubers, tubers with adhering spores, manure from animals 
fed diseased tubers, garbage, etc. Local spread seems to 
be especially prevalent in areas of dense population with 
small holdings. Long distance spread is most likely to 
occur with potato tubers in the form of adhering spores or 
inconspicuous lesions. (6, 8, 10, 22) 
L osses inc ur red : In Finland as a whole the average loss due to 
wart, on infected land, was 7.4%. In Austria and in England 
planting of a susceptible variety in contaminated soil has 
been known to result in practically a total loss of crop. 
(1> 10, 18) 
Comparative losses: Strict state quarantine measures and the use of 
immune varieties has prevented determination of possible 
crop losses in this country. Where a prompt change to re- 
sistant varieties is made, little direct loss results, though 
the substitute variety may yield less and be of less de- 
sirable quality. 
Con tro l methods: Quarantines and use of immune or highly resistant 
varieties are the usual control measures. The use of fungi- 
cides is not profitable in general. Continuous growing of 
cultivated non-susceptible crops makes possible planting of 
potatoes once in eight years without serious losses. 
Where the infected area is small, eradication by slow 
starvation or by treatment of the soil with chemicals may be 
profitable. (2, 10, 12) 
Quarantine action: Section 7 of the plant quarantine act of August 
20, 1912, provides that the quarantine provisions of this 
section, as applying to potato wart, shall become and be 
effective upon passage of the act. Under this provision the 
Potato Wart Quarantine No. 3 was signed September 20, 1912 
(issued September 28, 1912), effective immediately. More 
recently the entry of potatoes has been governed by the 
potato regulations which were originally issued December 22, 
1913, and since revised or amended several times. These 
regulations are based on potato wart primarily. 
