Timely Tip: Before the kids, cats and dogs have a chance to get out and romp in newly fallen snow, walk the landscape and look for signs of foot traffic. Four-legged foot traffic that is. Rabbits, voles and deer that are grocery shopping in your yard today will be dining on spring bulbs, newly emerging perennials and tender young seedlings in a matter of weeks, so now is the time to ask them to leave. Live trap the rabbits, mouse trap the voles and fence out the deer.
If asked to pick the toughest plant in my garden, I’d name the hosta. When I moved from my old house I discovered three live hostas, still in their containers, hiding beside the compost bin. As the saying goes, out of sight out of mind.
I figured those tough little plants had spent at least two years hidden away in those pots, yet they were none the worse for wear. So I packed them up, trucked them out to the country and planted them in front of my new home. I’m pleased to say they are growing like crazy.
This summer I received a couple of emails from readers asking why their hosta suddenly up and died. The only pests that ever attack my cast iron characters are deer and slugs, but the damage is only cosmetic. Voles have been known to munch on hosta roots, but their presence is easy to detect. The roots of the plants are missing.
At the time, my best guess as to the cause of the readers’ sudden hosta demise was crown rot, caused from over-watering and poor drainage. But according to an article in the January/February edition of the Michigan Nursery and Landscape Association publication, The Michigan Landscape magazine, there may be much scarier explanation – Sclerotium rolfsii var. delphinii or Hosta Petiole Rot.
According to Mark L. Gleason of the Department of Plant Pathology at Iowa State, author of the article on Host Petiole Rot, this relatively new fungal disease, has begun to rear its ugly head here in Michigan,
If you are a hostaholic, you should know that this nasty stuff, once established in the landscape, has the ability to wipe out your entire collection, so I recommend you become familiar with it and be on the lookout for it.
Infected hosta develop soft brown areas at the base of the petioles or leaf stalks, followed by withering and the collapse of the leaves. Within a short period of time the plant dies.
To date there is no fungicide available to kill the disease so the best defense is to keep it out of your garden. Whether you receive new plants from friends or buy them from a garden center or nursery carefully inspect every hosta crown for signs of the disease.
Because Hosta Petiole Rot is a sleeper disease that remains dormant in the upper Midwest most of the year, infested hostas with otherwise healthy looking crowns may be sold in May through July. However, upon close inspection, Gleason says infected plants will display sclerotai – tiny B-B like spheres, which may be white, tan or brick red in color and closely resemble mustard seeds. He describes them as little spaceships that encapsulate and protect the dormant fungus until the weather conditions are right for it to thrive.
However, don’t mistake slow release fertilizer capsules, such as Osmocote, as signs of the disease, says Mark Gleason. These plastic coated fertilizer spheres often found in container plantings are three times as large as the fungal spheres and lack their colorations.
When the disease is active, only is warm wet weather when day time temperatures reach into the 80’s and 90’s and night time temps climb into the 70’s along with evening rains or irrigation, the leaf stalks begin to turn brown and mushy.
If you have a plant that you suspect may be infected with Petiole Rot Fungus, send a sample into the plant-testing laboratory at MSU for proper id. In the mean time, quarantine the area and avoid tracking surrounding soil to other areas of the garden. If the diagnosis is positive, Mark Gleason recommends carefully removing the infected plant and destroying it. Gleason also suggest removing the surface soil and mulch surrounding the plant and either burying it 6 to 12-inches deep in an area that will remain untouched for at least a year or disposing of it in the trash. Under no circumstances, add it to the compost pile. Fungus buried in the ground will become food for the beneficial microbes that live in the soil.
After working with the infected soil, be sure to wash all tools, shoes, gloves and clothing clean of any soil to prevent tracking the fungus to other areas of the garden and spreading the disease. Tools should be disinfected with alcohol or bleach.
Unfortunately, hostas aren’t the only plants this fungus attacks. According to Mark Gleason, HPR can travel from hostas to other nearby plants. Iris, delphiniums, astilbe, ajuga and aconitum are among the list of 20 other plants that have succumbed to Hosta Petiole Rot.
Unlike other kinds of fungus, HPR does not produce spores so it is not carried about by the wind. When the conditions are right, it travels along the surface of the soil in search of fresh petioles. Water droplets crashing into the earth during rainstorms and irrigation also disturb the soil, facilitating fungal movement.
Mulching with several inches of mulch, taking care to leave a six-inch ring of exposed soil at the base of the plants has proven to help contain the spread of the disease. However, the HPR fungus does not appear to spread in pine needle mulch says Gleason.
Skilled gardeners are good detectives, they’re always looking for trouble.
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Several readers e-mailed me regarding safety concerns of the vermiculite used in Mel’s Magic Mix, the soil-less potting mix used in raised bed gardens featured in the “All New Square Foot Gardening” book.
Nancy's Garden
