Follow guidelines for Cercospora leaf spot resistance management in sugarbeets
Cercospora leaf spot resistance to strobilurin fungicides was identified in Michigan in 2011 and will require closer spray intervals and tank-mixing crop protection fungicides.
Cercospora leaf spot, if not controlled in sugarbeets, can cause yield losses of 5 tons per acre and reduce sugar content by two percentage points. In the last couple of years, growers have reported more difficulty in season-long control of leaf spot. Research by Michigan Sugar Company and test results from Michigan State University and North Dakota State University have confirmed the onset of strobilurin resistance in Michigan. New management guidelines for control of leaf spot have been developed and will need to be implemented by sugarbeet growers. This will ensure good leaf spot control and help preserve efficacy of existing fungicides.
The two major changes to leaf spot management are tightening up spray intervals and always tank-mixing with fungicides of different modes of action. Generally, a systemic fungicide will be mixed with a contact-type fungicide. It is recommended when tank-mixing to always use the full rate of each material. Re-application intervals are based on Disease Severity Values (DSV) and are different depending on variety and disease severity for your area. This information can be found on the BEETcast website at Michiganbeets.com. A REACh fact sheet called Cercospora Leaf Spot Resistance Management in Sugarbeets can also be found there by clicking "REACh" under the "Resources" tab.
Currently, about two-thirds of our sugarbeet varieties are moderately or highly susceptible to Cercospora leaf spot. These varieties should be planted only if growers are willing to adhere to an aggressive crop protection program. For these varieties, in a high disease area the recommendation would be starting at a DSV of 50 and re-apply every 35 DSVs throughout the season. Based on historical DSVs, it is expected that growers would apply crop protection fungicides between four and five times in the season.
Growers who feel that the strobilurin fungicides are not working well for them should discontinue use and look at alternative chemistries for their tank-mix programs. It is recommended that Headline and Gem (strobilurin) or Topsin be used only one time in a leaf spot fungicide program in the Great Lakes growing area. Never apply these products alone.
Always remember when managing Cercospora leaf spot in sugarbeets to not delay your first application of fungicide. Re-application intervals found on BEETcast should be strictly followed based on the susceptibility of your variety and your growing area. When spraying, use a minimum of 80 PSI and 20 gallons of water per acre. In heavy canopies, higher pressure and gallons would be beneficial. Make sure you rotate and never spray the same mode of action fungicides back-to-back.
The 2012 growing season is about three weeks ahead of schedule and most of the sugarbeet acreage will be canopied close to June 20. With the early canopy and extended length of the growing season, growers will need to be potentially prepared for first crop protection application by late June. With the extended season, we will need to be extra vigilant in controlling Cercospora leaf spot. Allowing a little bit of leaf spot to develop can result in a big problem by the end of the season. Disease-free foliage is highly correlated with increased tonnage, sugar content and beet payment. For more grower specific information on leaf spot management, contact your local agriculturist or REACh research team.