Protection Methods

- During cultivation

No product is approved for this use in France

The greenhouse climate should be strictly controlled in order to avoid excessive moisture and high temperature. For that, structures should be well ventilated. Nitrogen fertilisation should not be too low because it makes the seedlings more susceptible.

Although not always effective against infections by basidiospores of Thanatephorus cucumeris, recommended sanitation measures in the section of Protection methods to be adopted in nursery should be applied (figure 1). Note that Thanatephorus cucumeris, like many other micro-organisms, survives quite easily in the crevices of polystyrene seedling trays.

Wherever possible, try to harvest the lower leaves quickly to improve the ventilation of the canopy and thus  prevent the development of Thanatephorus cucumeris.


- Next crop

In the nursery, it is necessary to use healthy potting media. The soil should be disinfected in traditional nurseries. Plants produced in mini-clods should not be placed on the soil, especially if it has not been disinfected; they must be separated by a plastic film. Application of registered fungicides to the soil before sowing or planting may reduce the damage caused by this soil surface fungus.

Solar disinfection of the nursery soil (solarisation) can be used in some countries; spectacular results have been recorded especially in some Mediterranean countries. It involves covering the well-prepared and moistened soil with a polyethylene film of 25 to 40 µm, and holding it in place at least a month during a very sunny period of the year. This is a cost-efficient method, which helps eradicate the fungus colonising the surface area of the soil.

In the field, one should avoid too high planting densities which generate a humid microclimate, especially at the base of plants. They favour many airborne fungi. Heavy and wet soils should be drained. Fertilisation should be balanced, and not be too low in nitrogen.

Lesser varietal susceptibilities to airborne contaminations were observed on some cultivars; however, this was not enough to eliminate the disease.

U.S. situation

In the greenhouse good ventilation and air circulation along with removing plant debris at the end of each clipping are important to reduce the disease risk. Trays where seedlings infected by Rhizoctonia were grown should be sanitated by fumigation with Methyl Bromide or steam. Diseased seedlings should not be transplanted in a field.

In the field removing the lower leaves and ensuring adequate nitrogen are recommended management tactics. Quadris (Azoxystrobin) is registered for control of target spot in the field in the rate of 6 to 12 fl oz/acre. Quadris is a “locally systemic” product (i.e. it can move only a short distance from the point where a drop lands on a leaf). Therefore, use of drop nozzles and high volume of water (ranging from 20 to 100 gal/acre depending on the size of the plants) are highly recommended when applying Quadris in the field to ensure uniform coverage of the foliage.

(Mina Mila - North Carolina State University)