This is called drop in lettuce; older leaves wilt and lie flat on the ground
while the center is reduced to a slimy wet mass. In celery it is called
pink rot; in beans, carrots, crucifers, and cucurbits the disease is known
as cottony rot. In all cases the sclerotia drop to the ground and in spring
produce rather large apothecia, up to an inch across, which eject spores
in a veritable cloud. There is no conidial stage.
Control. Commercial growers often have to flood the soil or to treat
it with calcium cyanamid to kill sclerotia. In home gardens peonies and
other plants whose stalks or flower heads are invaded should be cut and
burned immediately, making sure that the slerotia do not fall out through
breaks in the stem before the specimen is safely in a paper bag.
STRAWBERRY RED STELE ROOT DISEASE (Phytophthora fragariae).
relatively new and most destructive strawberry disease destroys
fine feeding roots first, then invades the stele which turns dark red. New
leaves are small, blue in color; leaves from the previous season dry up;
little or no fruit is produced; many plants die.
Control. Resistant varieties provide the most feasible control. Use Aberdeen, Pathfinder, Sparkle, Temple, or Fairland. Dithane as a ground
treatment has helped.
There are a number of common turf diseases that are
rather difficult to classify. They are as near rots as anything else.
BROWN PATCH (Pellicularia filamentosa).
Roughly circular, wilted brown
areas appear in lawns, from a few inches to 3 feet across, rarely to
20 feet. The leaves are first water-soaked, then light brown, dry. Infection comes from very small, dark-brown sclerotia on the soil surface,
in warm, humid weather. Watering late in the day encourages the disease
and so does an excess of nitrogen in the soil. Mercury compounds-
calomel and bichloride of mercury (Calo-clor), phenyl mercury acetate
(PMAS)-apparently give best control.
DOLLAR SPOT (Sclerotinia homeocarpa).
The lawn spots are small, about
2 inches across, first brown, then straw-colored, but they may grow
together to make larger patches. You can usually see a fine cobwebb
mycelial growth in early morning when dew is on the grass.
Cadmium fungicides are preferred for dollar spot and also for copper
spot which causes coppery orange patches, i to 3 inches across, more often
on velvet bent grass in acid soil.
SNOW MOLD (Typhula spp.)
This is a scald that takes place as snow is
melting, resulting in conspicuous white circles in lawns, 1 to 3
feet across, due to another sclerotial fungus that lives over in the soil.
Mercury compounds as for brown patch are recommended, but in my
experience grass returns to normal color later in the season without