Cercospora Leaf Spot Management in 2016

Cercospora Leaf Spot Management in 2016
Mark Bloomquist – Director of Research
Cercospora Leaf Spot reached damaging levels in many fields throughout the SMBSC growing area in
2015. Cercospora spores overwinter in the soil, and thus with the high levels of disease seen in 2015 it is
very likely that the 2016 season will also have above average Cercospora leaf spot pressure. In the
previous edition of the Agricultural Beet, the reasons for the 2015 Cercospora outbreak were discussed.
This edition of the Agricultural Beet will concentrate on management options to help control Cercospora
and the reasons behind the changes to the 2016 SMBSC Cercospora Spray Program.
Variety Tolerance
Varieties possess different levels of CLS
resistance. The placement of varieties in
your field can have a significant effect on
CLS management. In Figure 1 are the
varieties available for planting in 2016 and
their CLS rating. Higher numbers mean less
resistance (red) and lower numbers are
more resistant (green). Try not to plant
susceptible varieties (in red) on common
lines to beet fields that had high levels of
CLS in 2015. Plant more resistant varieties
(in green) in these areas to help reduce the
disease potential in these zones.
Figure 1
Application Techniques
The fungicides used to control Cercospora leaf spot are mostly protectants. This means the fungicide
only protects the foliage that the fungicide contacts from new infections; the fungicide does not move
systemically throughout the plant to protect the whole plant. Because these products are protectants,
thorough coverage of all the foliage is very important. For ground applications it is recommended to use
20 gallons of water per acre and a spray pressure of 100 psi. Proper spray nozzles are also important to
attain small droplets. Small droplets are important for maximizing spray coverage. Small droplets also
increase drift potential from applications, which needs to be considered when deciding on application
scheduling. Improper spray nozzles or cheating on water volume and spray pressure will decrease the
effectiveness of the fungicides.
2016 SMBSC Cercospora Leafspot Spray Program
For 2016, SMBSC is changing the recommended CLS spray program from the program we have been
recommending for the past several years. In Figure 2 is the 2016 SMBSC CLS spray program. The
remainder of this edition of the Agricultural Beet will discuss the 2016 recommendation and the reasons
for the change.
Figure 2
1.
2.
3.
4.
5.
The recommendation for the first application is a tank-mix of a Tin fungicide + a Benzimidazole
(Topsin or generic) fungicide. The Tin + Benzimidazole application was moved up in the rotation
to provide a tank-mix of two effective fungicides at the beginning of the season. This also
further separates the Tin fungicides used later in the program.
The second application is recommended to be a Strobilurin fungicide (Gem, Headline, or
Priaxor). These fungicides were moved ahead in the rotation due to concerns regarding the
trend of increasing resistance levels of Cercospora to this family of fungicides. By using these
products second in the rotation, it may be possible to lessen the selection pressure against
these products by CLS. The later in the season these products are used, the more CLS that is
present. Once CLS develops resistance to these products, their usefulness as a CLS fungicide will
be lost, and this resistance will not disappear over time. For these reasons, the Strobilurin
fungicides are recommended in the second application in 2016.
The third application for 2016 is a Triazole fungicide. The triazole fungicides are currently the
best preforming fungicide family against CLS in our growing area, and thus this product was
moved later in the rotation when CLS pressure is highest. There are several triazole fungicides
labeled for CLS including: EminentVP, Inspire, Minerva, and Proline. While all of these products
are in the Triazole family, it is believed that some differences exist in how the fungicides act on
the fungus. By rotating the use of these fungicides, it may help in resistance management. For
these reasons, in 2016 we are recommending you apply a different Triazole fungicide to your
crop than you used in the 2015 season.
The fourth application for 2016 will be a Tin fungicide. The Tin fungicides have a seven day preharvest interval which allows more flexibility during the pre-pile season.
In the event a 5th spray is necessary in 2016, we are recommending to apply another Triazole
fungicide (See Figure 3). For the fifth spray, you should use a different Triazole fungicide than
was used for the 3rd application. This is again a measure to reduce the potential for resistance
development. The pre-harvest intervals for the Triazole fungicides vary from 7 – 21 days. Be
sure to know the pre-harvest interval for the Triazole product you are considering applying.
Figure 3
Cercospora will likely be a significant issue again in 2016. Having a good management program in place
prior to the season beginning will aid in successfully controlling this disease in 2016. For specific
questions on the SMBSC spray program or on Cercospora Leafspot, contact your Agriculturist.