ask-ruth-pictureRuth,

We are experiencing an infestation of stinkhorns this year. Over the last month, we’ve had 120-150 of them this fall (including the unopened pods) complete with the flies and the stinkhorn beetles to spread their spores. They came into our garden either from some leaves or some irises that were given to us. They mostly are concentrated in the iris bed, but we’ve had 20 or so in another area in the leaf mulch.

I don’t use any chemicals but would consider doing so in the iris bed if they continue so heavily. Their stench is nauseating.

Is there any safe control for these vile fungi?

Brotherhug

Dear Brotherhug,

As an avid and knowledgeable gardener, you must be very frustrated that these mushrooms are making your garden unbearably “stinky” and unpleasant. I have never had this problem or even seen a stinkhorn mushroom myself, so I did a little research to see what I could find out. Stinkhorns are reputed to emit a smell like rotten meat, decaying flesh, or feces. I told Brotherhug that I didn’t realize they smelled that bad, and he replied…“they actually smell worse than THAT bad!” Flies are attracted to those sorts of awful smells. When the flies land on the slimy, smelly substance secreted by stinkhorns, the substance sticks to the fly and is then relocated when the fly lands on something else. That is how the stinkhorn spores are spread around.

stinkhorn1Stinkhorn volva (immature fruiting body) resemble hard-boiled eggs and these “eggs” are the first visible sign that a stinkhorn is  about to sprout. Oftentimes sprouting takes only several hours. The mushroom (mature fruiting body) emerges from the egg and is soon covered with a slimy dripping mass that smells repugnant to most people. If you pull up the egg and prevent it from sprouting, you will prevent the spread of spores.

But remember that the stinkhorn mushrooms are just the visible fruiting body of a much larger fungal mass (mycelium) that is growing beneath the surface. When fungal spores find the right habitat, they send out long filaments called hyphae. Groups of hyphae can sometimes be spotted in soil or under bark. They look like a mass of fine white or dark threads; this growth is called mycelium. Destroying the fruiting body (the mushroom) will not destroy the source of the stinkhorns…any more than picking an apple will kill the apple tree. In fact, fungi can remain dormant for long periods, producing fruiting structures only when the conditions are just right ~ like during periods of heavy rainfall. Please note that the presence of mycelium in your garden is not necessarily a bad thing, since many fungi, such as mycorrhizae, are beneficial.

Many of the stinkhorns have novel names ~ dead man’s fingers, lizard’s claw, starfish stinkhorn…and numbers of them are phallus-shaped with somewhat explicit names. Stinkhorns fall into two main groups, Phallaceae (single-stemmed) and Clathraceae (usually multi-stemmed). Brotherhug suspects he has Mutinus caninus and the Octopus Stinkhorn, Clathrus archeri. The Squid Stinkhorn, Pseudocolus fusiformis, is more commonly found in the Eastern USA. Phallus ravenelii is another stinkhorn common from Quebec to Florida, and west into the Midwestern states. Check out this YouTube of a stinkhorn in action, and note the flies (they spread the stinkhorn spores): http://youtu.be/VG7JTuJN6qQ

Some stinkhorns are eaten instrinkhorn2 Europe, and certain varieties of netted Phallus stinkhorns are sold in Asian markets and considered to be an aphrodisiac. Into the 20th Century, stinkhorns were used medicinally by some folks for rheumatism, gout, and other ailments. However, do NOT eat any mushroom unless you are 100% sure of its identity and whether it is edible. Many mycologists will not eat any mushroom found in the field just to ere on the safe side.

Brotherhug and I discussed the possibility of using an organic copper fungicide on his stinkhorns; however nothing in the research supported this approach. Mulch was implicated as the main carrier of the stinkhorn spores, and Brotherhug does use a lot of fresh wood chips, and leaves as mulch (in the pathways initially, and later moved into planting areas). Generally, mulch contributes to positive outcomes in the garden and landscape ~ such as weed suppression, moisture retention, production of beneficial microorganisms including mycorrhizal fungi, and eventually mulch helps to build humus in the soil. The trick is to keep the bacteria/fungus ratio in balance in your mulched areas.

Here are a few practices that can help prevent stinkhorns:

  • Do not add fresh mulch on top of the stinkhorn-contaminated mulch because that will not solve the problem, and the stinkhorn cycle will be repeated next time conditions are optimal.
  • You can till the stinkhorn-contaminated mulch into the soil, soak down the soil, and then re-mulch the area with new mulch.
  • Wet all new mulch thoroughly at the time of application (within the first day) in the landscape. Dry mulch allows fungi (think nuisance fungi) to out-compete bacteria. When rain eventually arrives later in the season, the fungal mass is well developed and ready to fruit. Ideally, maintain the water content of mulch at least at 40% of the total weight, without making the area swampy.
  • Deeper mulches of 4” to 6”, especially if composed of fresh woody materials, begin to decompose in the heat of summer. The decomposition process dries out the mulch, which can then be colonized by fungi to such a degree that it can actually repel water, leaving your plants high and dry. The ideal mulch depth is 1 ½” to 2”. It is interesting to note that, according to reforestation studies, mycorrhizal development is encouraged by a shallow mulch, and discouraged by a deep mulch (mycorrhiza is a beneficial fungi that forms a positive relationship with plant roots, so you want to encourage it).
  • The type of mulch you use can also make a difference. To discourage stinkhorn habitats, use bark chips (nuggets) from older pines or cypress since they resist decay. Avoid using hardwood bark mulches, and most species of ground wood (hardwood and softwood) mulches, or other small-particled mulch. They are inclined to rot faster ~ so they more readily contribute to problems in the landscape.
  • Finely ground mulches will steal the nitrogen they require for their decomposition process from your plants, and leave your plants nitrogen-deficient. If you do use finely ground mulches or hardwoods, consider composting the mulch prior to adding it to your beds. Try adding a strong supplemental nitrogen source such as blood meal (12-0-0) to the mulch, and then compost it (at 130-160 degrees) for about six weeks. This will lower the carbon/nitrogen ratio and result in a product that is supplying nutrients to your plants rather than starving them.
  • Composting will also kill any pathogens imported on diseased plant material, and can correct pH issues in the mulch, as very acidic mulch (below 5.2) promotes fungal growth and inhibits the growth of bacteria (you want a balance of both fungi and bacteria).
  • Pay attention to the moisture content in your mulch. Maintain moisture in the mulch ~ whether in pathways or in planting beds ~ throughout the season to prevent fungal take-overs.

See the Stinkhorn Hall of Fame   http://www.mushroomexpert.com/stinkhorn_fame.html

Conclusion:

Brotherhug, it sounds like you already have a lot of mulch-type material on your property that you probably don’t want to waste. I would either till the current mulch into the soil and then wet that area thoroughly, OR remove the contaminated mulch and compost it in windrows for 6 or more weeks (with additions of nitrogen and attention to moisture content…sounds like a lot of work doesn’t it?). I suspect that the stinkhorn spores may be developing in the mulch when it is still in the pathways and that they remain viable once spread on your garden beds. Since you like to use thick mulches in your pathways, I suggest that any new mulch that you add is composted first, or composted right in the pathway. This could be accomplished by layering the leaves/wood chips with manure, grass clippings, or by adding bloodmeal (or other nitrogen source) to the leaves/wood chips as you mulch your pathways. I think the dry summer enhanced conditions that favored your stinkhorn population. At the very least, I would pay attention to the moisture content in any mulched beds or pathways, since dry mulch will encourage undesirable fungal dominance.

I know you are completely disgusted with the hundreds of stinkhorns in your yard, and find the odor beyond revolting (I don’t blame you!). But many of the experts I encountered doing this research found stinkhorns fascinating. My friend Stacia, a naturalist, reacted this way…“Are you kidding me? These are fantastic fungi! Why would you want to banish such an evolutionarily cool fungi…one that can mechanically mimic the smell of decomposing flesh? Why wouldn’t you want to take every kid you know out there to check them out?”

All I can say is…I am really glad they are not in my yard.

Brotherhug, I truly hope this has been helpful and that your stinkhorn problem is better next year.

All my best,

Ruth

I consulted a number of sources in writing this article, but this one on mulch was particularly helpful. If you would like more in-depth information about mulch, here is the link:

http://ohioline.osu.edu/hyg-fact/3000/3304.html

Ask Ruth © 2013 Ruth Gonzalez & Organic Growers School

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Ruth Gonzalez

Ruth Gonzalez

Ruth Gonzalez is a former market farmer, current gardener, and local food advocate. She has written numerous local food and gardening articles, blogs about local food, and writes the “Ask Ruth” Gardening Column for Organic Growers School. In her job at Reems Creek Nursery, Ruth offers advice on all sorts of gardening questions, and benefits daily from the shared wisdom of local gardeners. She has a special affection for clouds and finds delight in the natural world at every turn. Read more from Ruth at her blog: http://tailgatemarketfanclub.wordpress.com/