What is Contans and how can it be used in western Oregon to control white mold?

Contans™ is a biological fungicide registered for post-harvest use on snap beans and other crops and approved for use in organic production systems. Coniothyrium minitans (C. minitans) is the fungal biocontrol agent in the product Contans™ (Coniothyrium minitans strain CON/M/91-08, active ingredient of biocontrol product Contans® WG, SipCamAdvan LLC, Roswell, GA).

Coniothyrium minitans (C. minitans) is a mycoparasite of Sclerotinia sclerotiorum (S. sclerotiorum, causal agent of white mold). It has been isolated from white mold sclerotia (the large black survival structures of white mold) in many regions of the world and was recently developed as a commercial product for suppression of white mold. C. minitans is primarily considered a parasite of S. sclerotiorum but also has some ability to parasitize S. minor, the pathogen that causes lettuce drop (Matheron and Porchas, 2006). C. minitans also can infect S. sclerotiorum mycelia (hyphal strands of the fungus) when colonizing leaf or bean tissue. C. minitans parasitizes sclerotia optimally over a temperature range of 50 - 68°F , with little activity occurring at > 80° or < 41°F (Turner & Tribe, 1976). 

Cm spores infect sclerotia that they directly contact, resulting in dead, C. minitans spore-filled sclerotia (Fig. 1). These dead sclerotia remain intact under field conditions for one or more years, effectively increasing the longevity of the Contans application, as the Cm spores are protected within the sclerotia and ooze out over time.

Fig. 1. A white mold sclerotium that has been colonized and killed by C. minitans. Each bump on the surface of the sclerotium is a dried droplet of Coniothyrium minitans spores. Below each spore droplet is a sac-like pycnidium, which is the resting structure of the biocontrol fungus C. minitans. Photo credit: Mikio Miyazoe


Fig. 2. A white mold sclerotium plated on an agar plate. Each shiny droplet is filled with C. minitans spores that have oozed out of a pycnidium (the resting structure of C. minitans) located just under the surface of the white mold sclerotium. Photo credit: Mikio Miyazoe.

Pre- or At-Plant Soil Applications
The standard application recommendation has been to apply Contans to the soil surface a month or two before planting, or at planting, and then incorporate it lightly or irrigate it into soil.  This approach has been the most commonly researched and demonstrated because most pesticide applications to annual crops are applied during the crop growth cycle, and when Contans is compared to other fungicides in spray trials it is impractical to apply it at times very different from the other fungicides applied. Under research conditions this approach has shown some efficacy in reducing sclerotial viability and/or disease severity in a variety of crops.

Cm spores must contact sclerotia and kill the pathogen before the sclerotia produce apothecia (the mushroom-like structures that emerge from the sclerotia and release spores that infect bean flowers, Fig. 3). However, if Contans is applied in the spring at or soon before planting, high rate applications (3 to 4 lbs per acre) are recommended, This is because sclerotia are buried in the soil (and therefore it is difficult for the spores to achieve contact with sclerotia), and there is a short window between Contans application (at or soon before planting) and apothecia production (at bloom). These high application rates are typically cost-prohibitive.


Fig. 3. Orange apothecia of white mold at the soil surface. Buried underneath these apothecia are one or more sclerotia. Apothecia are the structures that release the spores that initiate foliar and pod disease development by colonizing decomposing bean flowers.

Soil Applications Targeted to Overwintering Sclerotia
Lower rate (1-2 lbs per acre) fall Contans applications to diseased crop residues have been shown to be effective in killing sclerotia under western Oregon environmental conditions. To reduce rates and costs, post-harvest applications of Cm can be applied only to the diseased areas of a field. A potential disadvantage of this strategy in some regions of the country is that growers may need to irrigate the treated residue to provide a microclimate suitable for sclerotial colonization.  Mild, wet winter conditions in western Oregon provide a long, relatively warm and wet window for Cm colonization of sclerotia without the need for irrigation. Furthermore, Cm-colonized sclerotia produce pycnidia (resting structures of Cm, oozing thousands of Cm spores: Fig. 2).  The Cm spores ooze out of the pycnidia in droplets (Fig. 2).  Sclerotia left on the soil surface ooze spores and the spores splash and disperse under rainy conditions, falling onto and infecting new sclerotia as they disperse. Spore splashing and disperal occurs through most of the winter (when temperatures are above 41°F, generating a series of Cm infection cycles, or a “biological control epidemic”. Contans can be applied to the soil surface and crop residues through overhead irrigation lines.

Other Possible Application Strategies
Cm will colonize plants, diseased residues, and sclerotia at any time during the year except when temperatures are above 80°F or below or 41°F, or under very dry conditions.  A potential strategy to suppress white mold sclerotial populations on a farm scale and throughout the rotation cycle is to apply Contans in any manner that is permitted by the label and does not require additional application costs, for example by watering in transplants, adding to transplant water tanks, or applying through irrigation lines to crop residues.



Matheron, M. and M. Porchas, 2006.  Comparison of products to manage Sclerotinia Drop of lettuce in 2006. UA Campus Repository. http://hdl.handle.net/10150/215027

Turner, G.J., and H.T. Tribe, 1976. On Coniothyrium minitans and its parasitism of Sclerotinia species. Transactions of the British Mycological Society, 66:97–104.


This development of this article was supported by grants from USDA NIFA programs Western SARE and Western Region IPM.