No. 6. r-EPARTMENT OF AGRICULTURE. 447 



tension of the blight on a tree after infection are dependent upon 

 a number of ditterent conditions. The factors controlling an out- 

 break of pear-blight may be summed up as follows: 



First. The presence of the germ and the amount of holdover 

 blight available for reinfection. 



Second. The amount of bloom on thetrees. It is difficult for 

 young orchards to catch the pear blight until they blossom. 



Third. The number of insect visitors available. This is largely, 

 however, constant if the next is favorable. 



Fourth. The weather during blossoming time. If the weather 

 is favorable for insect activity and nectar sjecretion, the blight germs 

 are generally carried about. On the other hand rainy weather or 

 cold, dry, sunny weather discourage the spread of blossom blight. 



Fifth. The variety and species of the tree. Each different 

 horticultural variety and each species of pomaceous fruit has a 

 different relative resistance to the disease. 



Sixth, The age of the tree. Young trees are more susceptible 

 than older ones. The most susceptible age comes at the time the 

 trees are first in bearing, say the first four or five years they are 

 in bearing. 



Seventh. The vigor of growth. This is influenced by fertility 

 of the soil, soil moisture conditions, favorable weather, artificial 

 manuring, fertilizing and cultivation. In general, those conditions 

 most favorable to vigor of growth of the tree are most favorable 

 to the blight, and conversely those influences which dwarf or check 

 the growth of the tree tend to hinder the progress of the blight. 



Most of the blight dries out in the trees during the summer. 

 On the other hand, occasionally at the bases of the blighted twigs or 

 more commonly on the thick fleshy bark on the large limbs and on 

 the bodies of the trees, the blight keeps slowly progressing until the 

 close of the season. The germs die out in the dead bark, but keep 

 alive on this advancing margin and the cool, moist weather of win- 

 ter, though it checks their growth, tends to keep them alive until 

 spring. This type of blight we call ''holdover blight" and is the 

 source of the new infections each season when the trees spring into 

 growth. 



Collar Blight. — I wish to call particular attention to collar blight 

 at the bases of apple trees of this State. I saw some very remark- 

 able axamples of this in the orchard of Mr. D. Maurice Wertz, at 

 Quincy, Pennsylvania. Pear blight is able to attack the thick bark 

 of vigorous young apple trees at the soil line and produce a sort 

 of collar girdle. The terms enter also through water sprouts, or 

 by means of the punctures of insects, or through growth cracks 

 directly into the fleshy bark. Once in the fleshy bark, the germs 

 spread out on to the roots and up the trunk of the tree. Frequently 

 a large irregular area occupied by the blight germs entirely girdles 

 the tree at the soil line, thus absolutely killing it. Trees so affected 

 usually take a year or two to die and sometimes the bliglrt has all 

 dried up before the tree actually dies. The seeding stocks are often 

 more susceptible to the blight than the grafted top of the tree. At 

 any rate some lots of French stocks are probably much more so than 



