WEST LAFAYETTE, Ind. — An abundance of rain that for weeks
delayed many Indiana farmers from planting corn has teamed with humidity to
create conditions prime for foliar diseases in the young crops, a Purdue
Extension plant pathologist said.
Three diseases, which could lead to reduced yields at
harvest time, have begun showing in some fields, Kiersten Wise said:
* Gray leaf spot, caused by a fungus, is appearing in the lower canopy of
susceptible hybrids across the state;
* Northern corn leaf blight, also caused by a fungus, has been detected in
the lower canopy of fields in northern Indiana; and
* The bacterial disease Goss’s wilt has been confirmed in plants grown for
popcorn and in hybrid corn in northeast Indiana.
“Many fields across Indiana are currently at a younger
growth stage than normal due to delayed planting and, therefore, may be at
greater risk for yield loss due to disease development,” the plant pathologist
There are fungicides to treat foliar diseases such as gray
leaf spot and northern corn leaf blight, Wise said. In Indiana, they are most
effective in preventing loss of yield when applied during the growth stage of
tasseling to early silking, or VT-R1.
Wise said scouting fields just before tassel emergence — V14
— can help determine the level of disease and if a fungicide is warranted.
Because Goss’s wilt is a bacterial disease, fungicides will
not be effective against it. Although several products are promoted for
in-season management of the disease, Wise said, research in Indiana indicates
they do not consistently reduce the disease once a plant shows symptoms of
Farmers suspecting that Goss’s wilt is in their fields
should have a sample analyzed by a diagnostic lab, the plant pathologist
“Fields with confirmed Goss’s wilt should be planted to a
hybrid that is more resistant to Goss’s wilt in subsequent years,” she said.
“Tillage and crop rotation will also help reduce the amount of residue that can
harbor bacteria for the next corn crop.”
Wise cautioned that severity of plant diseases can be
unpredictable in Indiana even when conditions favor them.
“Before deciding on in-season management of any foliar
disease, consider threshold guidelines, cropping practices, planting date,
predicted weather conditions and economic factors,” she said, “and manage
expectations for what type of yield response an in-season fungicide or
bactericide application will provide.”