Biology Reference
In-Depth Information
Stem rot and wilt of snapdragon starts with
water-soaked lesions on the stem; these turn yel-
low, brown, enlarge to girdle the stem; plant
wilts. Sterilize soil before planting.
Phytophthora capsici One of the species caus-
ing buckeye rot of tomato. See under
mold, except in moist air, but a slightly rancid,
penetrating odor. Lemons and oranges may be
affected on the tree, on branches near the ground,
and there is much loss in storage. The fungus
lives in the soil; spores are splashed up in rainy
weather and are spread in the washing tank.
Lemons are most susceptible to gummosis, then
lime, pumelo, grapefruit, sweet orange and
finally sour and trifoliate oranges. The latter two
are used as fairly resistant understocks.
Control
Plant susceptible trees high, with lat-
eral roots barely covered; expose the root
crownofinfectedtreeswithabasin6inches
deep and 4 feet across. Once a year cover
crown and lower trunk with bordeaux paste.
To control fruit rot, spray ground and lower
branches, up to 3 feet, with bordeaux mixture
just before rains begin. If fumigation is to be
practiced, substitute a copper-zinc-lime spray
for the bordeaux.
Phytophthora colocasiae
Root Rot
of ginseng.
Phytophthora cryptogea
Collar Rot
of rhodo-
dendron, China aster, marigold, gloxinia and zin-
nia; root, crown, and stem rot on watercress,
juniper, African daisy, chicory, beet, globe this-
tle, lettuce, parsley, peach, sage, spruce, and ice
plant; stem rot on sunflower, pink rot of potato.
Stems and roots appear water-soaked, then black
from a soft rot. Sterilize soil.
Phytophthora cryptogea var. richardiae
Root
Rot
of calla. The feeder roots rot from tips back to
rhizomes, leaving the epidermis a hollow tuber.
New roots sent out from the rhizome rot in turn.
Leaves turn yellow and drop, starting with outer
leaves; plants do not flower, or the tips of blos-
soms turn brown. Rot in the rhizome is dry and
spongy, not wet and slimy. Clean old rhizomes
thoroughly; cut out rotted spots. Grow in steril-
ized pots rather than benches.
Phytophthora drechsleri
Root Rot
on fir, basil,
blackberry, columbine, juniper, sage, linden,
pine, and spruce. Sometimes associated with
tomato buckeye rot, basal decay of sugar beets,
tuber rot of potato, root rot of safflower.
Phytophthora erythroseptica
Pink Watery Rot
of potato,
Rot
of calla lily and golden calla,
Crown and Root Rot
of wild rice. The rot starts
at stem end of potatoes; affected tissues exude
Blights
▶
for pepper rot and blight.
Phytophthora cinnamomi
Avocado Root Rot
,
Pine Little Leaf
,
Collar Rot
of hardwoods and
conifers, seedling root rot, on more than 100
hosts, including firs, cedars, cypress, juniper,
Japanese umbrella tree, larch, pine, spruce,
arborvitae, heaths, heather, azalea, Heuchera,
cranberry, highbrush blueberry, rhododendron,
camellia, birch, western swordfern, manzanita,
walnut, oak, locust, yew, venus-flytrap and
gold-dust plant. In conifers root rot is dry with
resin flow; needles gradually lose color. Infected
tissue of hardwoods turns reddish brown except
in black walnut, where it is black; seedlings die.
The disease is aggravated in pine by poor aeration
and low fertility.
Root rot is the most serious avocado disease in
California, present also in Florida and Texas. It
occurs on soils with poor drainage, excess mois-
ture being necessary. As the roots rot, leaves
become light-colored and wilt even if soil is
moist; trees decline over a period of years. The
fungus can be spread with seed if fruit is allowed
to lie on the ground. Treat suspected seed with hot
water, 120
to 125
F for 30 min; use nursery
stock grown in fumigated soil; prevent movement
of soil water from infested areas; plant on well-
drained soil; water trees individually to avoid
excess moisture.
Phytophthora citricola
Root Rot
of pine, hem-
lock and Fraser fir seedlings in Christmas tree
plantings; also fruit rot of avocado.
Phytophthora citrophthora
Root and Crown
Rot
of Penstemon.
Phytophthora citrophthora
Brown Rot
,
Gum-
mosis
,
Foot Rot
of citrus. Masses of amber gum
break out from the trunk near crown; the bark is
killed above and below ground; foliage turns
yellow; trees may die. The disease is prevalent
where excess water stands around the tree after
irrigation or where there is poor drainage. Brown
rot of fruit is a decay with no visible surface
