Stop rhizoctonia in sugarbeet crops
For sugarbeet growers, rhizoctonia is a common foe of their sugarbeet crops. rhizoctonia is a fungus that favors hot temperatures and often overwinters in the soil and on plant tissue before beginning a new season of infection in the spring. Different types of rhizoctonia called anastomosis groups cause a number of diseases like crown and root rot, damping off, and foliar blight. Rhizoctonia penetrates the beet through leaf petioles, the crown or the root, and can cause up to a 50% loss in yield.
Prevention of rhizoctonia is critical. Management practices begin in the fall with postharvest fieldwork and careful varietal selection. Oliver T. Neher, University of Idaho Extension plant pathologist, emphasizes the importance of taking time after harvest to minimize inoculum for following years.
“It is important to manage plant residues. Plan crop rotation to break up infection cycles and to reduce inoculum buildup. Minimize areas with standing water, hard pans or soil compaction, as they favor the development of rhizoctonia.”
• Management practices begin in fall with postharvest work and varietal selection.
• Plan crop rotation to break up infection cycles and to reduce inoculum buildup.
• Fungicide application at the four- to six-leaf stage is suggested for protection.
A proactive approach of planting tolerant varieties is especially important in fields with a chronic history of the disease. Corn and dry beans are alternate host crops for rhizoctonia, which means that different crops should be considered for rotation with sugarbeets. With all crop rotations, it is important to maintain a clean field as rhizoctonia has many alternate hosts in weed species, too.
“Growers should use all the tools available to maintain a healthy crop and prevent rhizoctonia. Plant a tolerant variety and apply a seed treatment. Make a fungicide application and watch irrigation amounts and schedule,” Neher says.
Because rhizoctonia is soilborne and has an effect on many crops, sugarbeets are at risk even before they are planted. Experts recommend planting tolerant seed varieties to help the crop stand up to the disease.
“Planting tolerant or highly tolerant varieties is the most important tool we have,” Neher says. “As part of an Integrated Pest Management program, the use of a tolerant variety is the first step that should be taken as they are effective in minimizing losses due to rhizoctonia later in the season.”
Because the rhizoctonia trait kicks in later in the season, it’s crucial to protect the crop from the moment the seed hits the soil.
As the crop emerges in spring, scouting becomes essential, Neher says. “If you see a lot of wilted plants in the field with dried up brown and black petioles around them, it is a really good indication that you have rhizoctonia.”
To positively identify rhizoctonia, Neher says, “Dig up those beets! It’s not a good idea to go with foliar indicators alone. Take a shovel and dig it up. Then take a knife and cut the beet in half to find the margin of healthy and diseased tissue of the beet.”
Research over the last 10 years from the Michigan State University Sugarbeet Advancement Program and Michigan Sugar Co. has shown that rhizoctonia can be effectively controlled with proper variety selection and optimum timing of an application of a fungicide.
Neher warned that rhizoctonia is not going away and growers need to embrace management practices to reduce the risk of infection. “Sadly, we are going to see an increase in this disease,” Neher notes. “Our crop rotation gets closer and closer with fewer non-host crops being planted on the same acres as sugarbeets. I tell my growers and crop consultants that they need to start keeping a log of fields with rhizoctonia, so that when they come back to plant in that field, they can make a sound decision by using a tolerant variety and seed treatment. As a preventive measure, we also recommend a fungicide application at the four- to six-leaf stage to protect against the threat of rhizoctonia.”
In other words, Neher says, “Be prepared for what is coming because we are not getting rid of rhizoctonia.”
This article published in the December, 2012 edition of MICHIGAN FARMER.