Control. Because the bacteria are swarming down inside the tissue some
distance beyond the part visibly blighted, always prune out infected
branches several inches below the dead part. Disinfect pruning shears
between cuts with formalin or 70% alcohol. Spraying fruit trees at blossom time with a very weak bordeaux mixture has been helpful. Dithane
Z-78 may be somewhat less effective but is less apt to russet copper-
sensitive varieties. Recent experiments indicate that an antibiotic-thiolutin-can be useful.
HAWTHORN LEAF BLIGHT (Fabraea maculata).
Infection of English hawthorn takes place in a wet spring, but the blighting is not apparent
until August when the leaves, dotted with dark reddish angular spots,
drop prematurely. By September defoliation is complete. The fungus winters in old leaves on the ground. The same or a closely related fungus
blights pears and quinces.
Control. Three copper sprays, the first applied when the leaves are just
starting out, followed by two more about a week apart, usually control
this blight. Bordeaux mixture (4-4-100) or a fixed copper can be used.
Other chemicals take care of the blight but are too injurious.
LONDON PLANE BLIGHT (Endoconidiophora flmbriatd),
canker stain of
plane. A killing epidemic started in the Philadelphia area about
1935 and has since destroyed thousands of plane trees, mostly London,
sometimes American, over a rather wide area. Eventually we learned the
fungus was spread in pruning and even in the tree paint from brushes
dipped into it after painting a diseased tree. Trees show sparse foliage,
smaller leaves, and long sunken regions on trunks and larger branches.
The wood is discolored blue black or reddish brown in wedge-shaped
sectors. Cankers widen annually, girdling and killing the tree in 3 to 5
Control. Once infection starts, the tree is doomed, but we can prevent
infection by pruning only when absolutely necessary and then in winter,
December 1 to February 15, when the trees are almost immune. Pruning
cuts should not be painted unless a gilsonite varnish, containing 0.2%
phenylmercury nitrate, is used.
SOUTHERN BLIGHT. See Crown Rot under Rots.
TOMATO BLIGHT (Phytophthora injestans).
Different strains of the same
fungus cause late blights of potato and tomato. Potato blight produced the great Irish famine of 1845 and still can cause an almost total
loss of the potato crop unless farmers apply control measures. In wet
weather large, dark-green water-soaked spots appear on leaves, which
turn brown and wither, with a white fungus growth on underside. Plants
are often killed early in the season, and tubers rot in storage.
The disease comes late on tomatoes, starting with the same dark leaf
spots, then the leaves hanging lifeless and fruit rotting on the ground.