Rhizoctonia management: Are all fungicides the same?

When managing sugarbeet Rhizoctonia, expect only seedling disease control from seed treatments, use proven practices and be cautious of generic fungicides.

Rhizoctonia has been one of the biggest production problems for sugarbeet producers in Michigan. Rhizoctonia can cause losses at the seedling stage by damping-off or later in the season as crown and root rot. This pathogen can significantly decrease tonnage and sugar along with triggering serious losses of quality in storage.

In sugarbeet trials conducted by Michigan Sugar Company and Michigan State University Extension Sugarbeet Advancement, it has been found that Rhizoctonia can be effectively controlled with a two application program of azoxystrobin (Quadris) along with the use of resistant varieties. The best disease control with fungicides has been by combining an in-furrow T-band application with a well-timed foliar application just before the time when the infection takes place.

If an operation is not set-up for an in-furrow T-band application with Quadris, data has shown in the last four years the most successful single foliar application has been at the six to eight leaf stage. Applications applied at an earlier stage were not as effective and had reduced efficacy. Sugarbeet growers that have applied Quadris as an in-furrow T-band should be protected at least up to the six to eight leaf stage.        

Seed treatments have been gaining momentum over the past few years. It is very important to understand when using seed treatments for Rhizoctonia control that the products are not a stand­alone. These products provide help against seedling disease, but do not provide long-term control for crown and root rot. In high pressure areas, Michigan Sugar Company and Sugarbeet Advancement agree that seed treatments may help, but the most effective control will be from Quadris applied in-furrow in combination with a six to eight leaf foliar application. For low pressure areas, growers may be able to get away with a seed treatment and a single Quadris application either in-furrow or foliar.

There are some very important principals to keep in mind when considering the management of Rhizoctonia in sugarbeets with seed treatments.

  • Varietal tolerance to Rhizoctonia is not typically expressed until about the six to eight leaf stage.
  • The effectiveness of seed treatments is about four to six weeks from planting.
  • Michigan Sugar Company and Sugarbeet Advancement data shows in most cases a fungicide application is beneficial even when growers use a seed treatment.
  • When compared to seed treatments, in-furrow Quadris applications provide both seedling and long-term control of Rhizoctonia and are very cost effective when applied in a 3- to 4-inch band at half the rate.

In 2014, Quadris went off patent, allowing several companies the opportunity to compete with the Quadris market. So the big question is, “How do the other azoxystrobins compare to Quadris?” Neither Michigan Sugar Company nor Sugarbeet Advancement tested any of the other azoxystrobins for Rhizoctonia control as of March 2015. However, in 2015, research will be conducted to see how the efficacy of the other fungicides compares to Quadris. The efficacy trials for azoxystrobins for Rhizoctonia management will include AFrame (Syngenta), Equation SC (Cheminova), Azoxy 2SC (Willowwood), Satori (Loveland) and Trevo (Innvictus).

When comparing generic products to original products, keep several things in mind. These products may be manufactured in foreign countries which may have less quality control. Generics may not have the same amount of active ingredients, may require a higher use rate and may increase foaming that result in increased preparation time, operator and environmental exposure and cleaning time.

Surfactants and other inert ingredients may also be different which may alter performance. Particle size can be different or inconsistent, causing mixing and spraying problems. Compatibility with other products such as insecticides can also be an issue. Also, generic products may not offer a good level of customer support if an issue occurs.

Just remember, research has shown that a reduction in tonnage of 2 to 10 tons and a 0.6 percent loss in sugar, along with a decrease in clear juice purity, can occur when heavy infection transpires in a field. Be sure to weigh out all the options before using a product that has not been tested by Michigan Sugar Company or Michigan State University Extension.

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