90 



BULLETIN 1105, U. S. DEPARTMENT OF AGRICULTUEE. 



(e) Lightly infected yellow pines 

 will be left when uninfected trees are 

 not available for seed and protection. 

 On areas adequately stocked with re- 

 production, all infected trees will be 

 cut. Lightly infected blackjacks and 

 intermediate trees on ax'eas on which 

 reproduction is not established, will 

 not be cut when otherwise thrifty and 

 sound except where thinnings to obtain 

 increased growth are desirable or 

 where reproduction, as noted above, 

 is established. Such thinnings may be 

 slightly heavier than in uninfected 

 stands, but it is not felt that in lightly 

 infected blackjack stands where repro- 

 duction is not established, vigorously 

 growing and thrifty trees should be 

 radically sacrificed. 



8. Defects due to other fungus dis- 

 eases. — All trees containing other fun- 

 gus diseases will be marked for cut- 

 ting where sound, healthy trees are 

 available as seed trees and for pro- 

 tection. Where satisfactory trees can 

 not be left, the extent to which the 



ures would have to be repeated at 

 intervals of something like 10 years. 

 Here again we are confronted by the 

 physical impossibility of carrying out 

 the work with the men and funds 

 available. Nor is it certain that the 

 effects of mistletoe are sufficiently 

 serious to warrant the expense of 

 complete control. More information 

 is needed in regard to rate of spread, 

 and the time required for the parasite 

 to injure a tree. 



The present instructions in regard 

 to the removal of mistletoe-infected 

 trees cover the subject satisfactorily, 

 except that there seems to be a need 

 for more specific definition of the dif- 

 ferent degrees of infection. Lack of 

 a clear understanding on the part of 

 field men of what is meant by heavy, 

 medium, and light infection may lead 

 to serious misinterpretation of in- 

 structions. The following standards 

 are proposed : 



Heavy infection. — ^Trees which show 

 clear evidence of injury by mistletoe, 

 as indicated by distorted, dead, or 

 dying branches in more than one-half 

 of the crown. The condition of the 

 crown, rather than the visible amount 

 of mistletoe, will ordinarily be the 

 criterion, although the presence of 

 large quantities of mistletoe in other- 

 wise apparently normal crowns will 

 class the tree as heavily infected. 



Medium infection.— Injury by mistle- 

 toe in the form of distorted branches, 

 but few dead or dying branches in the 

 lower one-half or less of the crown. 

 Mistletoe is usually present in ap- 

 preciable quantities. 



Light infection. — Mistletoe present 

 in small quantities limited to the lower 

 one-fourth or less of the crown. No 

 dead or distorted branches. The pres- 

 ence of a single sprig of mistletoe is 

 sufficient to class the tree as lightly 

 infected. 



It is presumed that the appearance 

 of any disease which might seriously 

 endanger the stand would call for the 

 removal of all specimens affected. As 

 far as is known, no such diseases 

 occur in the Southwest. 



