Wednesday, February 6, 2008

Greenhouse - Root Diseases of Pansies

Pansies can develop root diseases if media moisture conditions are not monitored in the greenhouse. Problems are more common when grown on the floor, especially if there is any potential contact with soil. The following is an article on root rots in pansies.

Diseases of Pansies- Monitor for Pythium and Black root rot:

February weather is often cloudy. This can promote diseases in pansy seedlings. Pythium and Black root rot (fungus Thielaviopsis) are the major root rots found in cool, wet soils. Pansy crops are often grown at cooler temperatures at this time of year. Experienced growers know to keep plants slightly on the dry side. In addition to root rots, pansy seedlings sometimes develop leaf spots from fungi that were on the seed. Check leaf spots that show up early, these could require fungicide treatments. Use HAF fans to circulate the air and prevent the moist microclimate around the plants that is conducive to foliar diseases. Better air circulation also improves evaporation from wet soil, helping to prevent Pythium root rots. Symptoms to monitor for: The first symptoms that suggest root rot in a pansy seedling flat is usually seen as uneven stand, some seedlings just don’t grow, some are stunted, yellow and fade away. Larger seedlings with root rot may start toshow yellowing, wilt and fade away. Pansy roots are transparent and don’t show the typical symptoms of tan water-soaked cortex and sloughing off of cortex tissues, seen in many other crops with Pythium root rot. Pansy does not show blackening of fine roots from black root rot very clearly either, although black root rot is common on pansy, and very destructive. When you notice poor stand and suspect a root rot, submit a sample to the diagnostic lab right away. Fungicides to prevent/control Pythium include: Subdue Maxx, Alude, Aliette, and Truban and one of the fungicides (etridiazole) in the mixture Banrot. Fungicides that help with Black root rot include: Terraguard, Thiophanate-methyl (Cleary’s 3336, Banrot and others). In general, if the seedlings have black root rot, I advise they be discarded. Even the best fungicides don’t provide good control once symptoms are seen. In addition the diseased plants/soil mix can serve as a source of contamination in the greenhouse. Remember, fungus gnats can spread the black root rot spores.

Extracted from the January 31, 2005 edition of the TPM/IPM Weekly Greenhouse IPM Report from the University of Maryland Cooperative Extension.

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