Biology Reference
In-Depth Information
water under pressure. When tubers are cut, flesh
turns pink or red, then black. The fungus can exist
in soil 4 years.
Phytophthora fragariae
Strawberry Red Stele
Disease
,
Brown Core Rot
, a very serious straw-
berry disease, first noticed in Illinois in 1930, now
widespread in northern strawberry sections and in
California. A strain of this pathogen causes root
rot of loganberry. The fungus attacks roots only,
destroying fine feeding roots first, then invading
the central cylinder, stele, which turns dark red.
New spring leaves on badly affected plants are
small, bluish, have short petioles; large leaves
from the previous season dry up; little or no
fruit is produced; plants die in the first dry period
or are stunted.
The fungus is most active in cold, wet soil, in
rainy periods in late fall, winter, and early spring
except when ground is frozen. Zoospores pro-
duced on roots are spread by water; resting spores
formed in the red stele carry the pathogen in
a dormant state through the heat of summer.
There are at least three physiological races, and
once the fungus infests a field it is worthless for
strawberries for 10 years.
Control
Buy clean, certified plants. Aberdeen
and Stelemaster varieties are resistant; Temple,
Sparkle, Fairland, Redcrop, and Pathfinder,
fairly so.
Phytophthora lateralis
Cypress Root Rot
on
Lawson cypress (
Chamaecyparis lawsoniana
)
often called Port Orford cedar, and Hinoki
cypress (
C. obtusa
), killing thousands of trees in
Oregon nurseries and landscape plantings. It is
found on juniper and azalea in North Carolina. It
is also reported on mountain-laurel and
Photinia
in NC and on cypress from Washington and
apparently native to the Northwest. The fungus
enters through the roots and spreads to lower part
of main trunk killing the tissues. Blue cypress
changes to purple, green, finally tan and dies.
The color changes take several months in cool,
damp weather, only 2 or 3 weeks in hot, dry
weather. There is no practical chemical control,
and Lawson cypress seems to be incompatible
with resistant rootstocks. Grow disease-free
propagating stock in new soil. Avoid large plant-
ings of Lawson cypress such as windbreaks or
hedges. Remove and destroy infected plants, get-
ting the entire root system.
Phytophthora megasperma
Root Rot
, occa-
sional on cabbage, cauliflower, brussel sprouts,
carrot, artichoke, stock, citrus, soybean and wall-
flower. Diseased plants wilt suddenly; leaves turn
red to purple; underground stems and roots rot.
The disease is more prevalent in winter plantings
in California and in low, poorly drained areas.
Level ground properly before planting to avoid
waterlogged spots. Root and crown rot on peach.
Phytophthora
megasperma
f.
sp.
glycinea
Root and Stem Rot
on soybean.
Phytophthora nicotianae var.
nicotianae
Crown Rot
,
Root Rot
, and
Stem
Canker
on flannel bush.
Phytophthora nicotianae var. parasitica Syn.
Phytophthora parasitica
(
P. terrestris
).
Brown
Rot
of citrus, in Florida;
Buckeye Rot
of tomato,
also on lily roselle, sempervivum, potato (tuber
rot), zebra plant (stem rot), sage (root rot), and
Christmas cactus (root rot). The disease appears
on the lowest tomato fruits, where water stands
after rains. The lesions have concentric narrow
dark brown bands alternating with wide light
brown bands. The decay is rapid and the internal
tissue semi-watery, though the exterior is firm.
Control by staking tomatoes; avoid poorly
drained soil or plant on ridges. This species is
often present with
P. citrophthora
in cases of
citrus foot or collar rot.
Phytophthora nicotianae var.
parasitica
Crown Rot
on petunia and poinsettia
(stem rot).
Phytophthora palmivora
Palm Bud Rot
,
Leaf
Drop
,
Wilt
of coconut,
Washingtonia
, and queen
palm, root and crown rot of mango; also root rot
on English ivy. The fungus is an omnivorous
tropical species, presumably the one causing
stem rot of dieffenbachia and peperomia. It has
been prevented in nurseries by using cuttings
from healthy plants in pasteurized soil.
Phytophthora parasitica var. nicotianae (Syn.
P. nicotianae
var.
parasitica
).
Root Rot
on pine.
Phytophthora porri
Head Rot
on cabbage.
Phytophthora sojae (Syn.
P. megasperma
f. sp.
glycinea
).
Root and Stem Rot
of soybean,
a relatively new disease reported from Illinois,
