Biology Reference
In-Depth Information
Fig. 1
Bean Anthracnose.
Pod and seeds with dark,
sunken areas; section
through bean seed showing
spores formed in an
acervulus marked with
prominent black setae
infected later in the season have irregular brown
areas along the veins. Conidia ooze out from
acervuli on underside of veins in flesh-colored
masses, in rainy weather, and are splashed to
other leaves. Twigs and branches have sunken
cankers with more acervuli. Native sycamores
may be nearly defoliated, with smaller twigs
killed. Larger branches die with several succes-
sive wet springs. The trees usually put out
a second crop of leaves after defoliation, but
this is a devitalizing process. Dead twigs and
branches give a witches' broom effect to the
trees.
On white oaks anthracnose appears as brown
areas adjacent to midribs and lateral veins.
Control
Although raking up and burning all
fallen leaves has been stressed for years, the
overwintering of the fungus on twigs makes this
measure rather ineffective. The spray schedule
has called for three applications of bordeaux mix-
ture; a dormant spray, one when the buds swell,
and another 7 days later. Trees should be fertil-
ized to stimulate vigorous growth.
Fig. 2
Oak Anthracnose
Colletotrichum
rose-colored pustules. In wet seasons, defoliation
in early summer may be followed by wilting and
death of branches. Cut out and burn such
branches.
Apiognomonia veneta (formerly
Gnomonia
platani
)(
G. veneta
).
Sycamore Anthracnose
,
Twig Blight
, general on American and Oriental
planes (London plane is rather resistant) and on
California and Arizona sycamores. The fungus
winters as mycelium in fallen leaves, producing
perithecia that discharge ascospores when young
foliage is breaking out. Mycelium also winters in
twig cankers. Young sycamore leaves turn brown
and die, looking as if hit by late frost. Leaves
Deuteromycetes, Coleomycetes
Spores are formed in acervuli, erumpent,
cushionlike masses of hyphae bearing conidio-
phores and one-celled, hyaline, oblong to fusoid
conidia. Acervuli have stiff marginal bristles
(setae), which are sometimes hard to see. Conidia
(slime-spores), held together by a gelantinous
coating, appear pinkish in mass. They are not
wind-borne but can be disseminated by wind-
splashed rain. On landing on a suitable host, the
conidium sends out a short germ tube, which,
