Page 16

ally attacked and therefore the planting of white pine in mixtures
with other pines or hardwoods seems to be the logical means of avoid-
ing losses under forest conditions.
White Pine Blister Rust
Crowartium ribicold
  The most serious disease of white pines is blister rust, which was
brought into the United States from Europe on white pine planting
stock. It was discovered in Wisconsin in 1915, when it was introduced
on seedlings grown in Germany, purchased through an Illinois nursery,
and since then it has been found in 22 counties in the state.
  The rust is spread by wind-blown spores from infected trees to the
leaves of currant and gooseberry bushes. From these bushes a dif-
ferent spore is blown to healthy white pine trees.
  Blister rust is a deadly tree disease that attacks the white pines
only. It can be controlled by removing the currant or gooseberry
bushes from the area to be planted, and for a surrounding distance of
900 feet. The cultivated European black currant is extremely sus-
ceptible to this rust.
  Before the trees are planted, a systematic check for wild bushes on
the area is advised so that none will be missed. This check can best be
made by a two to five man crew which can begin at a fence, working
abreast, and follow parallel strips from this fence. The outside man
on each strip should mark the edge of the strip with suitable markers,
such as bits of paper which can be attached to limbs on trees or
shrubs. On the next strip this paper can be removed by the inside man
of the crew and used again on the following strip.
  Currant and gooseberry bushes are most easily pulled in early
spring immediately after the frost is out of the ground. - An ordinary
grabhoe can be used effectively-in removing the large bushes, but ex-
treme care should be taken so that the larger crown roots that may
sprout are not left in the ground.
Other Insect Enemies
  There are occasional outbreaks of the Scotch pine scale, the spruce
bud-worm, the pine bark louse, and the larch sawfly, but they are by
no means as destructive as to discourage the planting work.
16