Optimizing fungicide timing for the control of Rhizoctonia crown
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Alerts. Check the label of any pesticide referenced to ensure your use is
included.
Recent
weather conditions may have been suitable for the development of
Rhizoctonia crown and root rot and possibly damping-off. Quadris can be
applied early in the sugar beet growing season for control of
Rhizoctonia damping-off and Rhizoctonia crown and root rot caused by Rhizoctonia solani anastomoses
groups (AG) 4 and 2-2, respectively. Work at MSU/MSC has evaluated
fungicide application timings based on crop growth stage and soil
temperature thresholds in inoculated small-scale trials and in
commercial fields with a history of Rhizoctonia crown and root rot. Soil
temperature thresholds 50°F, 59°F and 68°F were selected for fungicide
application timings and used to test whether soil temperature could be
used to better time applications of azoxystrobin. In both small and
large plot trials, timing applications after attainment of specific soil
temperature thresholds did not improve efficacy of Quadris in
controlling damping-off or Rhizoctonia crown and root rot, compared to
application timings based on either planting date, seedling development,
or leaf stage in a susceptible (E-17) and a resistant variety (RH-5).
Application rate and split application timings of azoxystrobin had no
significant effect on severity of crown and root rot. Other
environmental factors such as soil moisture may interact with soil
temperature to influence disease development. The variety RH-5 had
higher sugar yield attributes than the susceptible variety (E-17) in
seasons conducive and non-conducive to crown and root rot development.
The rate of 0.4 or 0.6 fl.oz./1000 row feet were equally effective but
the best timing over the three years of trials was at leaf stage 4 to 6
and 6 to 8.
Quadris is only labeled for banded applications for Rhizoctonia crown and root rot control (up to leaf stage 6 to 8) and at a lower
broadcast rate for foliar diseases such as leaf spot. The broadcast
rate (max 15.5 fl.oz./A) is equivalent to about 20 percent of the
in-furrow application rates and an equivalent rate for control of crown
and root rot as a broadcast application would be about 40-60 fl.oz./A.
There are no known data for crown and root control using 15.5 fl.oz./A
of Quadris and it is likely that control of crown and root rot would be
compromised as such a low rate. Mixing Quadris and Roundup is not an
illegal tank mix, but there is no information available on the efficacy
of such a mixture, given maximum permitted rates, for crown and root rot
control. In addition, no phytotoxic studies have been completed using
this combination, and the risk of crop damage to the beets has never
been assessed.
