Lincoln, Nebraska
December 10, 2004
Source:
University of Nebraska
Lincoln, Crop Watch News Service
Since the initial discovery of
soybean rust in early November, it has been identified in
several other southern states. Soybean rust was confirmed on
November 9 from soybean leaf samples collected near Baton Rouge,
Louisiana. Soon after, plant pathologists throughout the
southern soybean producing regions began looking for rust
symptoms on green soybeans and alternate hosts, such as kudzu.
Subsequently, numerous samples have been collected and rust has
been confirmed.
On November
12, rust was confirmed at two locations in Louisiana, Pointe
Coupee Parish and near Baton Rouge. A few days later the disease
was confirmed in Iberia and St. John Parishes, Louisiana, and
from a site in Adams County, Mississippi and near Quincy,
Florida. On November 19 positive confirmations were announced at
two locations in Georgia — Seminole and Jeff Davis counties --
and in Mobile County Alabama. On November 22, rust was confirmed
in Crittenden County, Arkansas. On November 30 rust was
confirmed in Pemiscot and New Madrid counties, Missouri and
Allendale and Pickens counties in South Carolina. On December1,
soybean rust was confirmed near Memphis, Tennessee.
It appears
that soybean rust was widely distributed by hurricane Ivan in
September 2004. While this disease is not expected to overwinter
north of the 30o north latitude (north of Baton
Rouge), it is predicted that summer weather patterns will move
spores north from overwintering, sites much as wheat rust
spreads northward in the late spring and summer.
EPA gives
Section 18 approval to fungicides
Several
products have received EPA approval for soybean rust under a
Section 18 emergency use exemption. Those products are:
myclobutanil (Laredo), propiconazole (Tilt, Propimax, and
Bumber), and tebuconazole (Folicure). Additional products still
pending Section 18 approval include tetraconazole (Domark) and a
mixed product of propiconazole and trifloxistrobin (Stratego).
In addition to these, other products may be submitted for
Section 18 approval. Federal tolerances for pyraclostrobin
(Headline and Pristine) have been established for soybean and as
of December 3, Headline had received full label for use on
soybean. Products which have soybean rust on the label and are
registered in Nebraska include chlorothalonil (Bravo and Echo)
and stobilurins (azoxystrobin – Quadris and pyraclostrobin -
Headline).
In general,
chlorothalonil and strobilurin products have not been shown to
be effective in South America after rust is well established in
the field. In some studies, increased residual activity has been
observed with strobilurins in a tank mix application with a
triazole. Therefore, when soybean rust arrives in Nebraska, I
would recommend using Section 18 products in the triazole
chemical group unless you are making a preventative application
prior to arrival of rust. Based on South American trials, the
triazole group appears to be very effective. It includes
myclobutanil, propi-conazole, tebuconazole, and tetraconazole.
Surely, over the winter, more products will apply for and
receive a Section 18 emergency use exemption.
The
bottom line
We are ready
for soybean rust. It will have an impact on U.S. soybean
production, but its annual impact in Nebraska will vary
depending on the weather. Nebraska is on the fringe of favorable
climate for disease development.
Many
University of Nebraska Cooperative Extension programs, including
the January Crop Protection Clinics, will feature soybean rust
information and updates.
Loren J.
Giesler
Extension Plant Pathologist |
