Agriculture Reference
In-Depth Information
Fig 18.14 Section through strawberry crowns infected
with
Phytophthora cactorum.
Importance
Crown rots may occur wherever strawberries are grown.
Losses can occur at any time but significant losses occur as
the weather warms up in spring. Incidence in crops varies
from a few infected plants to severe outbreaks involving
almost total loss of plantings. Ratooning of strawberry
crops has become largely impractical owing to losses from
crown rots.
Management
•
Fig 18.13 A wilting strawberry plant caused by crown rot.
Plant disease-free runners.
Fumigate soil before planting.
•
nicotianae
,
P. cactorum
,
Colletotrichum
spp.,
Sclerotium
rolfsii
and
Macrophomina phaseolina
.
Plan block layout to avoid waterlogging and raise beds
as high as possible.
•
Symptoms
Infected plants wilt, collapse and die. Symptoms usually
appear first on the outer leaves. Crown tissues become
discoloured and small to large necrotic areas are seen when
affected crowns are cut lengthwise. Roots become black
and rotted if the disease is severe.
Symptoms of crown rot differ from those of Fusarium wilt
in which leaf wilt is slower and only the water-conducting
tissues are discoloured.
The cause of crown rot is almost impossible to diagnose
on symptoms alone, and laboratory isolations are necessary
to identify the fungi involved.
Source of infection and spread
The pathogens inhabit the soil and invade the plant
through roots and crowns. Crown rot is favoured by warm,
wet weather, although symptoms often appear when plants
are suffering from a lack of water.
Fig 18.15 Sections through strawberry crowns comparing a plant
with crown rot (right) with a healthy one (left).
