Recurring Fungus on Plants

(Question)

Hi, for the past 3 or 4 seasons a black fungus has attacked my peonies and more recently my lilac bushes. I’m thinking it is an airborne problem b/c even container plants on my deck seemed to “catch” this disease. I don’t know if my soil is contaminated and I would like to have an expert check it out and treat it and the plants appropriately. Cutting back the peonies to the ground one summer didn’t keep the problem away the following year which is why i think it is the soil. So far my hydrangeas have survived though. Soil is loose on top, sandy deep down. I don’t overwater and tend to water under the leaves of the plants as opposed to spraying everything. My lilac blooms were fine but this really destroyed the health of the leaves and look of the bush. I didn’t think to take photos of it last year so I can’t submit a photo. However, I even think my hellebores in the front yard has been affected. It too has gorgeous blooms this year but the leaves are withering and brown. So I have included a photo of that plant, which is again located in the front not the back yard where the problem originated. My neighbour has 4 composters and I wonder if that is the source of this fungus? Please help me stop this blight from destroying everything!

(Answer)

Thanks for getting in touch with us. It’s clear that there may be some issues with regard to plant diseases in your garden–peonies and lilacs.

However, it’s doubtful that the Hellebores in the attached picture are suffering from any fungal disease. The browning leaves are actually last year’s growth that have been ‘scorched’ by harsh winter conditions. Hellebore orientalis [Lenten Rose] is one of the first plants to flower in the early spring (February or March). New leaves will gradually emerge from the plant after the blooms; one can easily cut back and remove the old leaves to make way for the new leaves.

The problem with the peonies, and perhaps some other plants around the peony, could be a botrytis blight. It is a fungus (Botrytis cinerea) that can appear on all parts of the plant especially in the early spring when the weather is cool and rainy; the spores infect the young shoots and will easily spread during wet periods to other plants in close proximity. Where is your peony sited? Is it in full sun? Does it have good air circulation around it? Favourable conditions for growing peonies include full sun, good air circulation, and good drainage (which you do have). How much space is there among plants? Although it may be difficult to stop this disease during the season it appears, there are steps one can take to manage and prevent it.

Sanitation is key–inspect your plants as soon as possible for evidence of this disease–when the weather conditions are dry, remove any parts of the plant that show disease; carefully dispose of any infected plant material including any mulch around the plant. Do not put into the compost bin, green bin or with garden waste. In the fall, cut back the peony (or other plant) stalks at or below ground level; remove plant debris and discard into the garbage. Once the area is cleared of infected plant material and the area is dry, “add well-composted organic material as a light mulch in the early fall to help add nutrients and improve the soil”–“this compost can be worked into the top inch or two of soil.” Adding well-composted material (leaves, etc.) to your garden beds on an annual basis will help to continually improve your soil; and of course, the soil will feed your plants.

Making sure that your plants are sited according to their needs (sun, moisture), that there is good air circulation around them [give your plants adequate space], and that you use good sanitation practices will definitely help to prevent any further disease problems in your garden.

If you have any further concerns, please let us know. There is a lot of information on our Toronto Master Gardener website.

For more information and references:

https://www.extension.umn.edu/garden/yard-garden/flowers/diseases-of-peony/

https://www.missouribotanicalgarden.org/Portals/0/Gardening/Gardening%20Help/Visual%20Guides/Peony%20Problems.pdf

https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/fungal-spots/botrytis-blight-of-peony.aspx