Evaluate effectiveness of sugarbeet Cercospora spray program at harvest
Cercospora leaf spot should be controlled season long. Significant leaf spot at the end of the season can reduce both tonnage and sugar content.
In the Great Lakes growing region, Cercospora leaf spot is the most significant foliar disease. Left uncontrolled, losses can impact yield by six tons per acre and reduce sucrose content by three percentage points. This loss can exceed $700 per acre at current crop prices. Fortunately, most growers do a good job of controlling leaf spot by utilizing BEETcast for timing of fungicides along with tank-mixing different modes of action. However, it is not uncommon to see fields where a significant amount of leaf spot is present at harvest time. All growers should evaluate Cercospora leaf spot levels at harvest to determine the effectiveness of the 2012 program.
Effective leaf spot control programs should have three main considerations:
- To keep disease levels below economic thresholds.
- To minimize Cercospora inoculum levels that may affect future sugarbeet crops.
- To minimize disease resistance to applied fungicides.
Fields at harvest that have no leaf spot or a light sprinkling indicate a very effective control program. Fields that have greater than 20 spots per leaf can increase inoculum loads, potential fungicide resistance and should raise concerns. A balanced approach to these objectives is needed.
Many years of research conducted by Michigan Sugar Company research agronomist Jim Stewart indicate that at harvest leaves with spots averaging 50 can begin to reduce sucrose content by 0.05 points and yield by 0.3 tons per acre. Heavier infestations where spots begin to merge together and brown tips begin to flag can reduce sucrose content by 0.5 points and 1.5 tons per acre. This damage is easily seen from the road. Research also indicates leaf spot at non-economic levels in late August can balloon into a significant economic loss resulting from a drop of 0.6 points of sugar and 1.8 tons per acre by late October. Sugarbeets scheduled for permanent pile should have fungicides applied through mid-September.
Sugarbeets growers that have significant Cercospora leaf spot levels at harvest should re-evaluate and modify their crop protection program. Michigan State University Extension suggests these areas be questioned:
- Fungicide application applied before first spot
- Spray intervals tight enough
- Fungicides always applied with a tank mix partner
- Full rates applied
- Fungicide classes always rotated
- Applied a mid-September fungicide
- Spray pressure and water volume correct
- Resistance to strobilurin fungicides
Failure to control Cercospora in your field can and will affect those around you.