Biology Reference
In-Depth Information
In lemons the disease is a soft, dark internal rot of
old or weak fruit in storage. Firm dark brown
spots are formed on the rind. Grapefruit some-
times has a dark internal storage rot, not readily
discernible externally.
Control
Chemical treatment after picking is not
very satisfactory. Produce sound fruit in the
orchard; avoid holding too long on the tree;
avoid holding weak or old fruit too long in stor-
age; store at low temperatures.
Alternaria mali
Fruit Rot
, widespread storage
rot of apple, sometimes quince. Also a weak par-
asite enlarging injured spots on foliage. Try cap-
tan at 6-to 14-day intervals.
Alternaria radicina (Syn.
Stemphylium
radicinum
).
Black Rot
of carrots, a soft storage
rot of roots held over winter. Rot may start at the
crown or from some wound on the side of the
root. Initial infection may be in field or in storage
house; a black mycelial weft with large, brown
muriform spores develops over the rotted tissue.
There is no control except to choose firm, healthy
roots for storage and to store at low temperatures.
Alternaria solani
Collar Rot
of tomato, also
fruit rot and early blight, general on tomato with
the collar rot stage most frequent in the South.
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arranged in a single row and encysting at the
mouth; saprophytic or parasitic, living in the
soil and causing root rots or damping-off.
Aphanomyces
cladogamus Causing
rootlet
necrosis of
tomato, pepper,
spinach,
and
a severe root rot of pansy.
Aphaomyces cochlioides A seedling disease of
sugar and table beets, part of the complex called
black root; causing tip rot, a wilting of tops. Crop
rotation and proper fertilization are helpful.
Aphanomyces euteiches
Pea Root Rot
, also on
bean, sweet pea and perennial pea. The fungus is
also a weak parasite in roots of many nonle-
gumes. First described in 1925, the fungus prob-
ably existed earlier in various root disease
complexes and was responsible for giving up
land formerly devoted to canning peas. Consid-
ered the most important of the pea root rots, found
in every district, it is particularly destructive in
eastern and central states.
The fungus is parasitic on subterranean parts,
causing root and stem rot in peas of all ages,
symptoms and crop yield varying with the time
of infection. If the root system is invaded when
only three or four nodes are formed, the plant may
wilt and die suddenly; later invasion results in
dwarfing and drying out of foliage from the
ground upward. When seedlings are pulled out
of the ground, the roots do not break off but come
out as a fibrous string or vascular cylinder freed
from cortex. The fungus invades only the cortex
or roots and base of stem, causing softening and
rapid decay of tissue. Large numbers of thick-
walled oospores are formed in the cortex; these
may remain viable in the soil more than one
season.
It is a novel root pathogen on alfalfa in
Canada.
Control
A well-drained soil with low moisture
content decreases rot. When soil moisture is at
45 % of saturation, there is no disease; at 75 %
there may be more than 70 % infection. Nitroge-
nous fertilizers are helpful.
Aphanomyces raphani
Radish Black Root
and
Damping-Off
, wide-spread; more important on
long-rooted icicle varieties. Also on Abyssinian
mustard, cabbage, Chinese cabbage, Chinese
kale, honesty, mustard green, rape, rocuet salad,
Blights
.
Alternaria zinniae
Stem Rot
on
Ageratum
.
Alternaria sp.
Flower Rot
of Vanda orchids,
causing infection in transit along with
Botrytis
.
Alternaria sp. On Schefflera in Florida.
Alternaria sp.
Calyx-End Rot
on apple.
Amphobotrys
Cankers and Diebacks
.
Amphobotrys ricini
Stem Rot
and
Wilt
of
poinsettia.
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Aphanomyces
Phycomycetes, Saprolegniales
Thallus composed of cylindrical branching
hyphae without definite constrictions; sporan-
gium cylindrical,
threadlike,
swarm spores
