Plant Diseases
Wheat Diseases in Arkansas
Septoria Leaf Blotch
Septoria leaf blotch is caused by two fungi, Septoria tritici (left) and
Septoria nodorum (right), and probably can be found in every wheat field in
Arkansas. Lesions caused by S. tritici are irregular in shape with more or less
parallel sides. Lesions caused by S. nodorum are more oval. Both types begin as
watersoaked spots, then become dry, yellow and finally brown. S. tritici
generally produces numerous black fruiting bodies in the lesion that are readily
visible. S. nodorum produces reddish brown fruiting bodies that are difficult to
see without a magnifying glass. Positive identification of the species may
require use of a microscope to identify the spores that are produced inside the
fruiting bodies.
When the leaves are wet, asexual spores ooze out of the fruiting bodies and
are splashed by rain to other leaves and neighboring plants. The pathogens also
may produce airborne sexual spores that are spread over long distances. Disease
symptoms first develop early in the spring on the lowest leaves and progress up
the plant during the season as environmental conditions permit. Disease is
favored by frequent rain and temperatures between 70 and 75 F.
Most adapted varieties are susceptible to both Septoria species. A few
varieties are moderately resistant to one or the other of the pathogens.
Septoria inoculum may come from infested crop debris, volunteer wheat, some
grassy weeds, and in the case of S. nodorum, from the seed. Cultural practices
such as crop rotation and tillage to destroy volunteer wheat and bury crop
debris can reduce the amount of initial inoculum. Chemical seed treatment for S.
nodorum generally has not been used.
Tilt or Bayleton plus mancozeb fungicides can be applied to control Septoria
leaf blotch and have been cost-effective in many situations.
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