Good Fungi vs Bad Fungi, Molds, Mildews, and Blights

A reader from Texas posed some very good questions relative to my recent post on the importance of building the soil and, in particular, the essential role fungi play in the process. (Read: To Convert an Orchard to a Food Forest, Start with the Soil)

Specifically – How do you differentiate between the good guys and the bad guys?

She asks, “Don’t we always seem to be spraying trees against fungus?” “What about all the mildew, fire blight, early blight, and other diseases that can take down tomatoes, squashes, and cucumbers seemingly overnight?”

Where do you start?

How do you help one without helping the other?  Or the converse, destroy one without harming the other?

Can you introduce good fungi? And can good fungi fight off the bad ones?

My response started to get a bit lengthy, and I decided it would be better as its own blogpost. Maybe some of the other readers out there can shed some light on this as well.

Rust on Quince Leaves
I am definitely going to try to be more on top of spraying this plant this year with nutritious compost teas, and maybe even something with baking soda. I have a lot of mulch around the base, but maybe it hasn’t had time to break down and feed the soil yet?? I believe this was the Quince. Hope it makes it!

Because I couldn’t agree more on how confusing some of this is! I, too, have seen my cukes keel over and turn to mush, my hollyhocks look like they’d been dusted with dirty flour, and my tomatoes look like they’d been hammered with a heavy frost when there was no frost in sight. Not to mention the rust that made my garlic look like a teenager with a bad case of acne. Agggh!

Keep in mind, this reader is from Texas, where “Even the grass gets fungus!” (her words!) – and although I’ve never been there, I hear Texas gets every scourge known to man! Still, we here in the soggy Pacific Northwest also live with the humidity that clothes us like a wet blanket. We might not get the heat that people wade through in the South – in fact, we might not get much heat all summer! – but we do have a close relationship with the moss and mold that grows in every nook and cranny and even between our toes!

She is right – not all fungi are alike. There are those in the soil that help the plants get the nutrients they need, and then there are those mildews and assorted blights that just seem determined to take a plant DOWN – and sometimes it is hard to know who’s who.

The best advice I can give is to treat the whole system, not just the symptom…

…and the best way I know to do that is by building the soil with lots of compost and mulch (that turns to compost). Adding assorted individual nutrients can lead to things getting out of whack. The underground world is so incredibly complex, we cannot hope to “fix” it by adding something out of a bottle or a box. Layer on a well-balanced compost, though, and the microbial communities will work magic. Even while you sleep.

That said, I have trouble following my own advice. I never have enough compost or other mulch. I test the soil, see what’s lacking on the NPK/pH scale, and do my best to adjust accordingly. I am guilty of going overboard with supplements. It’s an inexact science, after all, is it not? We count on the zillions of creatures, most of them invisible to our naked eyes (really? Naked?? Such a strange expression!) – to make corrections for us.

But, naked or not, here is what we’re up against: mildew and fungal diseases often form under damp conditions that later warm up and dry out (like spring into summer, right?). The spores are lurking there, waiting for the right conditions. They are carried by wind, rain, and insects – so we can’t very well stop them. As with a lot of unwanted guests, though, we can make them not want to stay; and we can improve the strength of the plant so it fights off disease like a ninja, even under stress.

From the Colorado State University Extension publication on Powdery Mildews:

“Powdery mildews are severe in warm, dry climates. This is because the fungus does not need the presence of water on the leaf surface for infection to occur. However, the relative humidity of the air does need to be high for spore germination. Therefore, the disease is common in crowded plantings where air circulation is poor and in damp, shaded areas. Incidence of infection increases as relative humidity rises to 90 percent, but it does not occur when leaf surfaces are wet (e.g., in a rain shower). Young, succulent growth usually is more susceptible than older plant tissues.”

This publication states that the mycelium (fungal threads) of the powdery mildew only grow on the surface of the plant; they don’t break through and invade the plant itself. In other places, though, I have read quite the opposite: that mildews are, indeed, systemic, and that if you see the “powder,” what you are actually seeing are fungal blooms of spores, meaning the fruiting body of the mildew that is IN the plant.

Of course, if you try to obliterate them with a spray of toxic fungicides, you will most likely also knock out beneficial microbes and insects as well – and we need all of them that we can get on our side! Instead, Michael Phillips advocates routinely spraying trees with nourishing teas made from compost, fish fertilizer, horsetail, comfrey, nettles, and other mineral- and silica-rich liquids that strengthen the cell walls in the leaves and provide extra nutrition.  That way, the plants are better able to resist invasion. He also uses Neem oil sprays, timed to target certain life stages of damaging insect larvae and spore outbreaks. Applied sprays in the canopy serve a double purpose: they help the entire plant when absorbed by leaves, and they also feed the underground mycorrhizal communities when they drip to the ground.

I used to scoff at the idea that I would damage the “delicate soil structure and all the microbes.” I figured they replenish themselves pretty easily. However, I have learned to revere these unseen organisms that do so much for us.

Again, the beneficial fungal activities going on at the root level are the real key to providing balanced nutrition that strengthens the whole immune system of the tree (or other plant). The best way to help the good fungi, microbes, worms, and other creatures that make nutrients easier to access is, as mentioned, to pile on the mulch and compost. If you build it, they will come. It works. Phillips writes in great detail about holistic approaches to improving soil, microbe health, and providing a balanced nutrition for your orchard and other fruits (which I would think could be applied elsewhere in the garden as well), and I highly recommend his book (“The Holistic Orchard”).

However, I suppose it’s like any of us. Even the most health-minded occasionally get run down and become more susceptible to getting a bug. Sometimes you just need something to knock it out. (As in, please just give me something to end my misery….) With that in mind, here are a few tips I have collected from experience, friends, assorted readings, & from around the web – (disclaimer: I haven’t tried all of them – so I am not advising them as a solution in your particular situation!). Some are prevention-oriented; others quick “fixes” when disaster strikes.

Preventative Measures:

Rotted garlic were put in the burn pile
Sad day for this garlic! Into the burn pile it went.
  • Select varieties that are resistant to powdery mildew, leaf spot, or whatever else is a problem in your area.
  • Plant things at wider spacings to increase airflow as much as possible.
  • Prune a little more radically, for the same reason – and also to let in more sunlight.
  • Simply remove the offender, as murderous as that may seem (which doubles as a means of increasing the distance between plants).
  • Water with compost teas.
  • When you water in the vegetable garden, water the ground; don’t spray the plant. (That said, although I avoid spraying beans, cukes, tomatoes, and the like, I often spray other plants, including garlic, with diluted fish fertilizer and compost teas, which they seem to readily absorb. You can actually see them perk up after spraying. But sprays need to be timed so they don’t burn plants in the afternoon sun – or conversely, make them cold and damp overnight, conditions conducive to more molds.)
  • Be careful with heavy nitrogen fertilizers, especially in late summer, which can promote lush growth that is more susceptible to mildew.
  • Similarly, be careful Not to mulch with compost that is too high in nitrogen around plants that can’t handle it (like I did one year with my garlic crop; I lost close to 75% to molds! I applied the mulch in the fall and left it there until harvest time. Bad idea.)
  • Mulch with plants high in silica and minerals, such as comfrey, oat straw, rice hulls, nettles, and seaweeds.

Mechanical Measures:

  • Cut off infected leaves and burn – or compost if your pile is hot enough.
  • Pull the entire plant.

Teas and Spray Cures:

This guy needs some help. Too late for prevention.
This guy needs some help. Too late for prevention, although I will keep adding to the mulch around the tree. But no way am I going to pull it! Not unless I absolutely have to!
  • Very Strong Chamomile Tea. Chamomile has antibacterial and fungicidal properties. Simmer a couple cups of chamomile in a half gallon of water, let it steep, strain (use used herb as mulch). Water seedlings from the bottom up to prevent damping off, or use as a foliar spray on older plants.
  • Baking Soda & Soap: Mix 2 tsp baking soda and ½ tsp Dr. Bronner’s, Murphy’s oil soap, or other natural soap in 2 qts of water. Great on roses. (Be sure to use soap, not detergent. Beware! Lots of so-called dish soaps are actually detergents!)
  • Baking Soda, Oil, Soap, & Vinegar: 1 ½ t baking soda, 1 T canola or other light oil, ½ t liquid soap,  ½ cup white vinegar, 1 gallon water. Good on hollyhocks or any other rust-prone plant. I should have done this on my garlic, but the rust didn’t seem too bad, and then suddenly it was everywhere! So don’t wait for it to be a problem! I am going to remember to try this on my Cornelian Cherries this year. Keep it in a handy spray bottle, shake it up, apply weekly to leaves.
  • Garlic: Powerhouse of nutrients, anti-fungal, anti-bacterial, anti-viral. Make a strong concoction by putting 2 cloves (I usually use more) of garlic in the blender and blending. Wait a minute to give chemical reactions in the garlic a chance to optimize the garlic’s properties; add 1 qt of water and blend for a few minutes or so. Let it steep for a bit and strain into a jar. Add a few drops of soap (if you add this to the blender, it will make too many suds – seems obviously obvious, but it’s been known to happen! Ahm!) Use 1 part garlic water with 10 parts plain water as a spray. Watch out for beneficial insects when you do this. Garlic leaves and scapes are also good for this concoction.
  • Aspirin: Dissolve 2 uncoated (325 mg) aspirin in 1 qt water & spray against black spot, powdery mildew, and rust. Have not tried this, but some people swear by it. I wonder whether a feverfew tea would also work?
  • Neem Oil spray: 1 Tbsp Neem oil, 1tsp dishwashing liquid, 1 tsp diatomaceous earth. Shake it up good in a half gallon of water. The clay dries out and smothers things – or they cut themselves crawling around in it. Can use without the diatomaceous earth, too. Watch out for beneficial insects either way. I have been leery of using Neem oil ever since I heard it was banned in Canada. I am always mindful of not using it in places where my bees might be. I have used it on my trees before they budded out or after apple harvest, for example.
  • Other Anti-fungal Herb Sprays: Cedar (Thuja) and bee balm, for example, are known to have anti-fungal properties. A tea made from chopped up quantities of these types of plants and then sprayed on the infected plant or on the ground as a preventative measure might be helpful. This is a tip offered to me by someone on the permaculture forum at the Regenerative Learning Institute.


It strikes me that the key in a whole lot of this is achieving a “balance” and in looking at the whole system, not just the problem.

Would like some feedback here – what kinds of things have you tried to combat fungal-type disease, mildew, rot, black spot, rust, or???

Thanks for your tips!


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