Sclerotinia sclerotiorum / southern blight infestation?

Asked June 30, 2016, 11:52 AM EDT

I am concerned my home garden has a soil infestation of Sclerotinia sclerotiorum/southern blight or a similar fungus. Can this be tested for confirmation; can I work with someone on treatment plan? The UMN site recommends "Replant infested areas with nonsusceptible plants". What plants are nonsusceptible? By late August, My peony stems look similar (worse) to the attached picture (from Missouribotanicalgarden.org site) - though I haven't noticed the little "seeds" - and the stems whiten from the ground up and the leaves look like they have powdery mildew. Every year, the plant(s) come back and look great, but they don't bloom, and look awful by end of the season. My question may be shared on "Ask an Expert" if my name and email aren't shown.

Hennepin County Minnesota

5 Responses

I checked in with our plant pathologist. She doubts you have southern blight, but suspects powdery mildew. How about sending me some photos of your own plant? That would help considerably.

Hi.

Currently the plants look pretty good, except most of the buds in the peony plants in the attached pictures didn't bloom this year. 2 buds bloomed, or partially bloomed, and the rest all died as buds.

Except for the lack of blooms earlier this , this is how the plants usually look this time of year. It is in the next month or two when they usually start looking bad.

Pic 325 shows the peony bushes with the 2 "blooms" and dead buds (all the poppies have been removed from the bed since photo was taken); 329 shows an individual stem and some markings; 330 shows the base of the plant - in the lower left, you can see a white spot, which will eventually extend up the stem and be on other stems.

Thanks.

Thanks for the additional information and photos. Overall your plants look really healthy.

The red spots shown in your second picture are stem spots. They are common on peonies and are caused by different fungi. The recommendation in our Extension publication Diseases of Peony indicate that cutting and removing these infected stems and / or leaves at the end of the growing season will help to curb this disease. Leaf and stem spots can also affect buds causing them to be "blasted" (killed). This may explain why you had limited flowering.

The white growth you noted might be the very beginning of some white mold (Sclerotinia sclerotiorum) growth or more likely the beginnings of powdery mildew (very common). In either case, it is almost impossible to get rid of these fungal diseases. Sanitation and proper plant spacing / care are the best approaches. The above publication has good information on management strategies as well.

If you continue to be concerned and want a more in-depth analysis of your plants, you can send a plant sample to the U of M Plant Disease Clinic. Instructions for ho to submit a sample can be found on their website: pdc.umn.edu





Thanks for the information. In the information found in the link you sent, under the white mold section, it suggests to "Replant infested areas with nonsusceptible plants." What are some nonsusceptible plants?

Thanks again.

As far as I know, there is not a list of non-susceptible plants - it is more a process of avoid planting those plants we know to be susceptible. In White Mold in the Flower Garden by Michelle Grabowski, annuals noted to be susceptible are listed. The publication from the University of Guelph, White Mold of Vegetables and Ornamentals, contains a very good list of susceptible varieties including vegetables. Cultural practices such as avoiding overhead watering, mulching plants, spacing plants well to improve air circulation and sunlight, and selecting plant varieties that have an upward branching instead of prostrate or vining also will reduce the occurrence of white mold and powdery mildew. Sanitation (cleaning up and removing infected plant parts) will also help reduce both of these.