Dahlia Smut

Have you ever heard of Dahlia Smut?

Have you ever heard of DAHLIA SMUT? Symptom is circular bruises on the leaves that blacken and brown and then die. They look like hail damage, except that they start on the lower leaves. A lot of people experienced it in 1997 due to the early season cold rains. Sometimes it is called Ringspot, but that is incorrect as Ringspot is a viral infection that does not cause the spot center to actually die (necrosis).

The disease spreads upwards via spores from the soil and may completely involve the whole plant including the blooms. The main cause is the frequent and tempting habit of tilling or digging last year's stems & leaves into the soil.
Don't do it!

Other related issues that can increase the rate & degree of infection are:

Poor air circulation, especially if closely planted
Soft, over fertilized foliage.
Water drops standing on the leaves from overhead watering or an over wet season, especially during the cool times and usually only hits in the Fall.
On the positive side - A mulch is very useful to deny splash transmission from the soil.
but the best cure is a clean, kept clean growing area.

The best use of old stalks and leaves is to stack them 2 or 3 feet high and cover with soil for the winter. Next season plant Zucchini or winter squash or pole beans into these hills. After a year this well processed soil can be safely used as compost. I like to treat all my rough vegetative matter this way. It takes an extra year, but I get excellent vegetables, I can plant a bit earlier due to the bottom heat from the composting action, and when I screen the result, the larger chunks can just go back for another year. This screened soil & peat & vermiculite is the best potting soil there is. Add a bit of OSMOCOTE time release fertilizer (and maybe some Lime) and your potted plants are good for a year. I still recommend something like Sunshine Mix for germination, but after that the above mix is excellent for growing healthy seedlings of all types.

DAHLIA SMUT - 1997 Pacific Northwest Plant Disease Handbook

Cause: Entyloma calendulae f. dahlia. A soilborne fungus. It overwinters in plant debris in soil. IT IS NOT TRANSMITTED IN SEED OR TUBERS. High humidity and wetness favor disease development.

Symptoms: Yellowish, circular to irregular spots appear onleaves, which later become brown and dry. Severe infections may result in reduced vigor or poor tuber development. Young cuttings or seedlings may die if infected early in the year.

Cultural Control:

1. Remove and destroy plant debris.

2. Space plants for good air circulation and drying conditions.

3. Maintain proper fertility and soil pH.

4. Plant immune cultivars.

Chemical Control:

No chemicals are specifically labeled, but broad-spectrum products such as copper or mancozeb used for gray mold control will help control smut. I have found that the fungicide Daconil 2787, a Rose spay, works well in control of the disease.

Reference:

Mordue, J.E.M. 1984 Entyloma calendulae f. dahliae. CMI Description of Pathogenic Fungi and Bacteria, No. 802, Surrey England. Commonwealth Mycological Institute.

2/27/98

email to nospam_hydahlia@shaw.ca just delete the nospam part!

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