184 
WISCONSIN HORTICULTURE 
July, 1917 
Fight Fire Blight of Apple. 
Circular No. 70, Extension Serv- 
ice, Coll, of Agr. 
By R. E. Vaughan. 
Fire blight is one of the most 
destructive apple diseases found 
in Wisconsin orchards. It often 
kills the trees entirely or injures 
them so severely that they require 
years to recover from the attack. 
Outbreaks of fire blight are rela- 
Healthy Blossoms 
tively more severe when the 
weather is warm and rainy or 
cloudy at blossoming time, or dur- 
ing the period when the young 
wood grows rapidly. Pear trees, 
quince bushes, wild crabs, and 
some ornaments belonging to the 
apple family are also affected by 
fire blight. The disease is known 
under different names, as fire 
blight, pear blight, blossom blight, 
canker blight, and canker and 
collar blight, according to the 
tree or part attacked. 
CAUSE OF FIRE BLIGHT 
Fire blight is caused by bac- 
teria which get into the young 
growing tissues through the nec- 
taries (the part of the flowed con- 
taining nectar) in the blossoms or 
through wounds made in young 
twigs by insects, or into larger 
branches through wounds made 
by pruning tools. Once in the 
growing part of the wood where 
there is plenty of moisture, the 
bacteria increase rapidly in num- 
ber and kill all the parts they in- 
vade leaving them shriveled and 
dark colored. When the young 
wood and bark are soft, as in 
spring and early summer, the 
bacteria work rapidly down the 
twigs or shoots into the larger 
limbs or trunks where cankers 
are formed. These cankers are 
known as “hold-over cankers’’ 
because it is at their edges, where 
the tissue does not dry out, that 
the bacteria are kept alive over 
winter. When the sap starts in 
the spring, the few bacteria which 
are alive multiply rapidly and 
form little pockets in the cank- 
ers next to the live bark. In 
rainy weather they come to the 
surface through the bark lenti- 
cels, or cracks, and are ready to 
spread the disease. 
SYMPTOMS OF FIRE BLIGHT 
Fire blight has some very strik- 
ing symptoms : 
Brown blossoms accompanied 
by a withering and blackening of 
the young fruit and fruit spurs. 
2. Sweetish, sticky, milk-white 
or brownish ooze which in rainy 
weather comes from the freshly 
blighted parts and cankers. It 
attracts insects which distribute 
the disease germs. 
3. Black or dark brown leaves 
which are withered after the dis- 
ease has passed through them but 
which for some time cling to the 
trees. Affected trees have the ap- 
pearance of having been swept by 
fire, hence the name “fire blight.” 
4. Shriveled and blackened 
bark on the blighted twigs and 
suckers. 
5. Cankers on the larger limbs 
or trunks. These cankers are 
usually slightly sunken and black- 
ened and have their bark rough 
and cracked along the edge be- 
A Blighted Apple Twig 
tween the diseased and healthy 
wood. 
6. General yellowing and 
dwarfing of the leaves in the 
growing season, and premature 
dropping from one or more of the 
larger limbs. This is frequently 
due to blight attack at the base of 
the trunk, a form of the disease 
which is known as “collar 
blight.” The bark over the col- 
lar blight has a watersoaked ap- 
pearance in mid-summer. Simi- 
lar yellowing of the leaves may 
