8 The Colorado Experiment Station. 
rise to what is known as holdover blight. It is the germs which ex¬ 
ist in this holdover blight which serve to reinfect the orchard the 
following spring. In most instances, however, the germs die out of 
their own accord during the winter and leave the whole tree or por¬ 
tions of it free from the infection of the previous season. Although 
the disease is usually at its best in the early spring, the writer has 
in mind an orchard in Central iOhio, numbering some four hundred 
trees, in which the blight assumed its most severe form about three 
weeks previous to picking the fruit. Up to the middle of August 
there were but three or four badly infected trees, and within three 
v/eeks from that time, every tree in the orchard was suffering from 
a severe attack. The fruit had to be picked two weeks before time 
in order to prevent all from being ruined by the blight. 
Pear blight is variously known as pear blight, apple blight, fire 
bPght, twig blight, blossom blight, and body blight, the name de- 
]'ending upon the species and portion of the tree affected. If the 
blight attacks the larger branches and trunk where there has been 
some bruise or mechanical injury, the symptoms are much the same 
as what is known as sun burn or sun scald. This form of the malady 
is known as rough bark or body blight. 
It is only within comparatively recent \ears that we have 
known that the cause of apricot and plum blight is the same as that 
of pear blight. Prof. Paddock,* in describing the disease as it oc¬ 
curs on the apricot, says : 
“At this time many of the fruits were attacked, the diseased areas 
varying in size from a spot an eighth of an inch in diameter to irregular 
a.reas that involved three-fourths of the fruit. The skin over these places 
soon became nearly black in color and shrunken as the tissues were con¬ 
sumed till the outline of the pit was disclosed. These discolored areas were 
always definitely outlined and bordered with a zone of watery appearing 
tissue usually about an eighth of an inch in width. The latter was green 
in color and as hard as the sound flesh. 
“The smaller spots where the disease had evidently just started, in¬ 
variably surrounded a lenticle, thus indicating that the disease gained en¬ 
trance to the fruit through these openings. 
“The injury to the twigs may be described best by saying, that they 
resembled closely, blighting pear or apple twigs. So far as noticed only 
tender twigs of the current season’s growth were attacked. These were 
shrivelled and discolored from a few to several inches in length, and small 
drops of sticky fluid were occasionally found on their surface and upon the 
shrivelling leaf-stems. The discolored outer bark blended gradually into 
normal appearing tissue, but the inner bark was discolored for some dis¬ 
tance below any external evidence of disease.” 
HiSTctRY.— The disease is by no means recent, for it dates l)ack 
to the time of William Denning, who first reported the trouble from 
the Highlands of the Hudson in 1770. He described it fairly well 
and ascribed the cause to a borer'in the trunk of the tree. 
The oldest book on American Fruit Culture, published in 1817 
’•■'Lull. 84, Colo. Expt. Sta. 
