Fall is for fungal fruit

Summer is done. The last apples are coming off my orchard trees now and persimmons are ripening fast. Some fruit remains to be picked but most is off. As garden productivity subsides we turn our tasks to winter. In Southern California it means planting the winter vegetable garden, in Northern Mn snow has already flown so gardens are shut down now. For fungi that may be pathogens in our gardens, it is a time for reproduction. Fall is the time for fruiting and for gardeners a time to reckon with next year’s disease cycles.

Most fungi are saprophytic, that is they live on dead or decayed organic matter. Fungi are largely responsible for recycling forest nutrients from litterfall (leaves, branches and whole trees) back to soil minerals. Without fungal decay, mulch would never break down and organic matter would pile up. If you use fresh wood chips (often advocated in this group) you may notice that after some time they are full of fungal mycelium or cordons (rhizomorphs). This is normal and healthy—a good sign that your mulch is decomposing and improving the underlying layers of soil.

Furngi survive as fruting bodies in cankered branches, dead wood and leaves

Some plant pathogen fruiting bodies are edible. The mushrooms formed by Armillaria are often collected and considered delectable by many. Most edible fungi are saprophytes or mycorrhizal fungi. Truffles and other edible mushrooms like Chanterelles are plant symbionts often benefiting oaks and other northern temperate trees. Some wood decay fungi are also considered a delicacy such as the Oyster mushrooms (Pleurotis spp.) or the sulfur mushroom (Laetiporus gilbersonii). I don’t recommend harvesting wild mushrooms for food unless you are able to accurately identify what you collect, even then, second opinions of mycologists are a good idea. Also, not everyone reacts the same to fungi when they consume non-commercial mushrooms, so moderation is best or just get your fungus from commercial sources.

The sulfur conk (Laetiporus gilbersonii) is an edible wood decay mushroom

Not all fungi are beneficial. Some have evolved life histories that allow them to gain energy not from organic matter or dead plant materials but from living plants. These are parasites. Fungi have been evolving their lifestyles for about 400 million years and in that time have developed several strategies involving plant hosts to live and reproduce. Sixty five million years ago, after the Cretaceous-Paleogene extinction event that famously destroyed dinosaurs, fungi bloomed on earth and increased in importance. As land plants diversified, so did fungi developing many forms and parternships, many of them becoming essential to plants such as mycorrhizae. A few fungi specialized as plant pathogens.

Fungi use their reproductive structures to survive and ready themselves to attack susceptible plants. The most common fungal fruiting body the mushroom may not seem like a survival structure. But mushrooms can produce millions if not over a billion spores. Massive spore production ensures that some of those spores will find a place for the organism to survive. Also some mushrooms found on trees (sometimes called conks or bracket mushrooms) are perennial, and live for years—each year they add a new spore bearing surface over the last one. Many of the pathogenic tree fungi that produce conks fruit in the fall or winter.

Mushrooms help fungi survive by producing millions of spores. Don’t attempt to eat this kind though as it is an Amanita and is poisonous! Never eat wild or collected mushrooms without proper identification and study.

Many fungi form their fruiting bodies as small melanized structures that contain their spores. These are often formed in dead host tissue, such as dead twigs or branches. The spores are protected until they are splashed by water onto tender or susceptible plant tissues such as shoots. In soil, fungi can form hyphae that are very concentrated and melanized in to long lasting structures called scleortia. They lay dormant in soil for years until a susceptible root grows into them. Crop rotation often helps to limit disease but some fungi can last decades between crops and remain viable by producing thick walled spores called chlamydospores or sclerotia. The wilt fungi (Fusarium and Verticillium) survive in this way.

Another key strategy that fungi use is a kind of timing called phenotypic synchronicity. Fungi often have their spores ready to be dispersed exactly when new growth or susceptible plants are available for infection. The timing also often aligns with weather conditions that favor spore dispersal or arrival at the intended plant growth stage or phenotype.

Fungi evolved with land plants to take advantage of the environmental conditions and phenology of their hosts. We can interrupt the process with a bit of diligence as gardeners. As fall continues and winter approaches, it is a good time to remove dead twigs and branches from perennials that are prone to disease, clean up fallen or dead flowers from plants like Camellia that are attacked by petal blight because the flower mummies contain sclerotia that start the disease in the Winter. Unfortunately removing conks from trees does nothing to stem the progress of wood decay fungi in the tree they formed on, or their further spread, because so many spores are formed that the few mushrooms we remove will not stop those diseases. Some evidence suggests that increasing soil organic matter will over time reduce soil-borne pathogens, but once a pathogen has affected a perennial, there is often little to be done about it as in the case of Verticillium wilt of shade trees. No matter how fungi survive, its always a good idea to apply fresh tree trimming chips around perennials in the garden….

Smashing Pumpkin Myths: Bleaching to extend shelf (and porch) life

Peeps & Creeps - Home | Facebook

Scrolling through social media in September and October and you may see those basic signs of the season: scarves, pumpkin spice lattes, sweaters, and Halloween ideas galore.  One of those Halloween ideas is to extend the life of your pumpkins, carved or otherwise, by giving them a treatment with household bleach.  Keep scrolling and you might see another post decrying the use of bleach as inhumane and poisoning for wildlife.  So which is it?  Is bleach safe to use as a sanitizer on your jack-o’-lantern or are you poisoning the neighborhood squirrels?  Let’s use our gourd to explore the science.

The bleach acts as a sanitizer, neutralizing fungi and bacteria on the surfaces of the pumpkin that will cause decomposition and rot.  Even un-carved pumpkins will eventually succumb to degradation under the right conditions.  But if bleach kills fungi and bacteria, will it kill wildlife? The answer is – not if it is used correctly.  Bleach, and sodium hypochlorite (the active chemical in bleach) are toxic if consumed directly in concentrated amounts, however, dilute solutions break down quickly in the environment.  Products containing sodium hypochlorite, including plain household bleach, are actually approved and labeled for use as a sanitizer by produce farmers to reduce both human pathogens and decomposition microorganisms and extend the shelf life of produce that finds its way to the grocery store, farmers market, and any other avenue from the farmer to the consumer.  These wash water sanitizers are used more for reducing cross contamination of from pathogens introduced to the water from dirty produce, but it can reduce the microorganism load on produce items. If used correctly to sanitize the surface of the pumpkins, bleach DOES NOT pose an increased risk to wildlife (or human) health.

What is the proper way to use bleach in sanitizing that pumpkin so that it doesn’t face an early demise?

  1) Make sure the pumpkin is clean by washing with plain water or a mild detergent to remove any soil or debris.  Sanitizers like bleach are quickly neutralized (used up) on dirty surfaces (this is a good lesson for home cleaning, too – you cannot sanitize a dirty surface). 

2) Prepare a DILUTE solution of plain household bleach (unscented, and not “splashless”). The recommended concentration is 200ppm sodium hypochlorite, which you can achieve with 1 Tablespoon of bleach per gallon of water.

3) Apply the solution to the pumpkin using a spray bottle.  Alternatively, you can prepare enough solution to dunk the pumpkin(s) and immerse them in the solution.  If you are sanitizing a carved pumpkin, I would opt for the spray method – dunking may result in infiltration of the solution in to the exposed flesh. It will still break down since it is a dilute solution, but it will slow down the process since it protects the bleach atoms from air and sun exposure.

4) Allow the pumpkin to air dry.  Sanitation is not immediate (keep that in mind for sanitizing surfaces in the home, as well) and wiping can cause cross contamination

If I can do this with a pumpkin, should I be doing this with my other produce?

The short answer is NO.  It is not recommended that home grown or purchased produce be washed with any sort of detergent or chemical in the water.  Fresh cold water and friction should be sufficient for removing soil and pathogens on the surface.  Proper protocols, equipment, and training are needed to make sure sanitation is done properly. Knowing which produce items can and cannot be washed with a sanitizer is important. However, if you are harvesting produce like pumpkins or winter squash for long-term storage you may want to consider sanitation using the above methods.

I don’t want to use bleach, can I use something like vinegar?

There are many sanitizers approved for use by produce growers for sanitation, so bleach is not the only option.  For home consumers there aren’t so many options.  Vinegar is often mentioned as a wash for produce.  I found no direct mention in produce handling guides of using vinegar on pumpkin, but most produce wash solutions use vinegar at a much higher concentration because it is much less effective at sanitation.  I found rates ranging from 1/3 c vinegar to 1 c water to 100% undiluted household vinegar for use as a produce wash.


Sanitizers Labeled for Use on Produce (Produce Safety Alliance)

Produce Wash Water Sanitizers (UMN)

Guidelines for the use of chlorine bleach as a sanitizer in food processing operations (OSU)

When littering is a good thing

Dried leaves shred easily (photo from needpix.com)

I’ll be the first to admit it: I am a neat freak. I work best on desks with little clutter and feel calm and relaxed in spaces that are well-organized. But outdoors, it’s a different story. Dynamism is in charge and it’s refreshing and exhilarating to be surrounded in nature’s chaos. So this time of year can bother me when I see gardeners putting their neatness imprint on their gardens – especially onto their soils.

It may look neat, but it’s not really soil (photo from freeimageslive.com)

If you Google the word “soil” and look at the images that pop up, nearly all of them look the same. Nice, dark brown, granular stuff, often lovingly cradled in a pair of hands, that really looks more like coffee grounds than soil. In fact, the only realistic picture in the first page of images comes from the Soil Science Society of America. THAT’S actual soil.

One of these things is not like the others….
This one.

So gardeners must discard the “tidiness ethic” that seeps out of the house and into the soil. Soils are living ecosystems, and living ecosystems are messy. A living soil will have some sort of organic topdressing (mulch) resulting from dead plant and animal material that accumulates naturally. In temperate parts of the world, this happens every autumn, when leaf fall blankets the soil with a protective and nutrient-rich, organic litter. And what do we do? Why, we rake it or blow it and bag it and toss it. Then we turn around and buy some artificial mix of organic material and spread it on top – because it looks nice and tidy.

Keep the leaves out of the landfill!

Let’s stop this nonsensical cycle. Stop buying plastic bags for leaf disposal. Stop buying organic matter for mulch. Instead, use what nature provides to protect and replenish your soils. This doesn’t mean you have to leave messy piles of leaves that blow around rather than staying put. Instead, shred them! They look nicer, they stay in place better, and they break down faster. The easiest way to do this is to either run a lawnmower over them, or to put them into a large plastic garbage can and plunge a string trimmer into them. (Bonus – if you use a battery-operated mower or string trimmer you reduce your fossil fuel use.)

Likewise, if you have twigs, prunings, and other woody material, save these too. A chipper is a useful, though expensive, purchase. But those woody chips are the best mulch you can use over your landscape and garden beds. Most plants rely on mycorrhizal fungi, and these fungi require a source of decaying wood to function optimally. The chips can go right on top of your leaves to keep them in place and add a slow feed of nutrients.

Lovingly cradled fresh wood chips

So this fall, see how much of your garden’s refuse can stay on site. Compost soft materials; shred dead leaves; chip woody material. You’ll reduce your contribution to the landfill, and improve the health of your soils and plants alike.