White
mold is the most destructive disease of sunflower. Symptoms include wilting, middle stalk rot,
and head rot. The wilt symptom is most
common because the fungus survives in the soil and first attacks the
roots. A dark canker forms at the base
of the plant and eventually girdles the stem.
In advanced stages, the pith decays and the stalk becomes
shredded. Also, hard black resting
structures of the fungus, known as sclerotia, form at
or near the stem base. They can be found
in the pith or outside on the stem, and are an excellent identification aid for
the fungus. Middle stalk rot and head
rot usually begin as gray, water-soaked lesions on the upper stem and fleshy
part of the head. In the stalk, a dense
snowy white fungal growth and some sclerotia will
often be produced. On the head, the
entire seed layer falls away leaving only a bleached, shredded skeleton
interspersed with large sclerotia.
Favored by cool weather, and high rainfall or irrigation.
Manage
the disease by planting in non-infested fields, extended crop rotations with
non-host crops (wheat, corn, sorghum), weed control,
avoiding high nitrogen rates, reducing plant populations, and timely
application of fungicides.
Categories: Sunflowers, White mold
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