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Plant diseases, pests & problems: answering community FAQs

How do you prevent plant viruses from spreading? Can you cure powdery/downy mildew? What IS dog vomit slime mold? Get the answers to these questions and more in this episode of Digging in with gardenstead.

On the pod, our fave plant and soil expert Aaron Deacon of BIOS Nutrients sits down with Katie to tackle gardenstead community FAQs about the pests, viruses and other problems that plague our gardeners’ plants.

Basically, it’s twelve minutes of plant first aid. For more detail on what Katie and Aaron chat about, skip to the show notes after the video.

Show notes:

Aaron is one of our favourite podcast guests for a reason – he gives us so much of his time, and always takes on such a broad range of questions with perfect equanimity and ease. Below, we break down what he and Katie cover in the episode.

How do you prevent plant viruses from spreading?

The answer to this one couldn’t be simpler: clean your tools! Wipe, soak or thoroughly spray your secateurs, scissors or snips with isopropyl alcohol or hydrogen peroxide between uses and from plant to plant. Your future self will thank you, trust us.

Can you cure powdery/downy mildew?

Yes! Aaron’s favourite method is to use lactic acid bacteria. It works so well, in fact, that it’s what he made the BIOS probiotic from — he created the probiotic specifically to treat powdery mildew on plants.

A hydrogen peroxide solution can also be effective to treat and prevent powdery mildew. You can wipe affected leaves, or spray larger areas with the mixture.

Aaron also suggests using diatomaceous earth to eliminate powdery mildew, as it’s a natural fungicide. Yucca extract is another option that has shown effectiveness. Vinegar can also be an effective fungicide for powdery mildew, as it contains acetic acid, which will destroy the fungal spores responsible for the mildew.

To quote Aaron, powdery mildew is “super easy to get rid of”, but beware. Once you spy powdery mildew on your plants, act quickly, because the dreaded white stuff spreads quickly, and the more it spreads, the bigger your job becomes to get it under control. You’ve been warned.

What are the signs a plant has been over fertilized?

One of the surest signs of an over-fertilized plant is leaf tip burn — if you see the tips of leaves dying back or curling, and you suspect you’ve overfed your plant, your suspicions may be confirmed. Other signs of over-fertilizing include a visible crust of fertilizer on the surface of your plant’s soil, slow or no growth of the plant and yellowing lower leaves.

How can you help an over-fertilized plant? Aaron’s advice is to flush the fertilizer out — run “a ton of water” through your plant’s growing medium. Then, allow your plant to take in plain water to hopefully rinse it out of the plant’s tissues as well.

Lastly, if you have a plant that’s suffering from over-fertilization, avoid heat. In hot weather, or as a plant becomes overheated, it will try to take up more water to deal with the heat it’s experiencing. As it tries to take up more water, it will take up fertilizer from its soil along with the water, which will exacerbate the existing problem.

What causes dog vomit slime mold?

The rather aptly named “dog vomit slime mold” (scientific name: Fuligo septica) is a variety of slime mold (described by most as a nuisance mold, rather than a disease per se). Its spores are commonly found in soil.

Similar to fungal spores, it will activate when the conditions are right (much like stinkhorn fungus). There’s no cause for concern if dog vomit slime mold is present in your plant’s soil. If it starts to climb up the stem of your plant, however, you need to take action. Simply wipe it off of your plant.

PSA from Aaron related to this question: mushrooms growing in your soil are a very good thing! Leave them be. It’s “completely healthy and fine”. Pro tip from an expert.

What does it mean when plants aren’t fruiting or they’re producing small fruit?

As Aaron says, “usually this is a nutrient issue”. It’s likely your plant isn’t taking up phosphorus, the nutrient associated with flowering and fruiting.

Plants need phosphorus to develop fruit properly and there are a number of reasons why your plant(s) aren’t taking up this vital nutrient. One of which is a tricky one – plants have a very difficult time absorbing phosphorus.

When a plant is having difficulty absorbing phosphorus, it could be due to an absence or scarcity of mycorrhizal fungi. Soils need mycorrhizal fungi to help gather phosphorus. These highly beneficial fungi act as a kind of miner for the nutrient, by first seeking it out, then transporting through the soil to be used by your plants’ roots.

Aaron’s final thought on phosphorus is that there could be a nutrient conflict in the soil itself that’s limiting access. He references the Mulder’s chart, which is about push-pull relationships among nutrients and how those relationships can inhibit the availability of micro- and macronutrients in soil.

All this being said, when plants aren’t fruiting or they’re producing small fruit, this could also be a watering issue. Plus, when soil becomes too dry, there’s no opportunity for plants to take up nutrients through their roots, either.

Why do flowers fall off vegetable plants without producing fruit?

Typically, this is a temperature issue. During an extended period of heat in their growing season, plants can become stressed, causing a change in their flowers. This can prevent pollination, and often what happens is the plant will drop (abort) their flowers.

Aaron acknowledges that this kind of plant behaviour could be the result of a nutrient deficiency (see question and answer above), but more often than not, the culprit here is heat.

What are some of the signs of deficiencies in plants?

There are quite a few different signs of nutrient deficiencies in plants, and to make things interesting, quite often they’ll mimic other concerns. For example, calcium deficiency and windburn look the same.

As a result, it can be difficult to say for sure when a plant is suffering a deficiency, but some of the signs are: yellowing leaves, crispy edges or browning on the tops or bottoms of leaves (depending on what the deficiency is).

The bottom line on this one is: soil testing is the best way to know. If your plant(s) appear to be suffering and you suspect a nutrient deficiency, test your soil and become empowered with the information you need to address the problem.

Can you fix blossom end rot with antacids?

Yes! (Surprisingly.) Blossom end rot is caused by a calcium deficiency. Calcium uptake may be inhibited by a lack of watering, and there could also be lack of calcium in soil due to overwatering (dilution of nutrients). In either scenario, adding antacids — which contain calcium — to soil will supply the required calcium back into the mix.

But beware (and listen to Aaron’s answer, it’s illuminating) — if you add too much calcium, you could create a cascade of problems, as calcium can inhibit the uptake of other necessary nutrients. As Aaron says, “it’s a fine balance”.

Best advice here: take care of your soil at the end of every growing season by adding compost and organic matter, so that your soil’s nutrient profile is naturally balanced to be a good growing environment. Soil will take what it needs from the “food” it’s provided.

What can we do to keep deer out of our gardens?

We confess, we were surprised by this answer, but a little research has proved Aaron right (per usual). It turns out that one solution to this large pest problem is to install a (wait for it) fishing line fence!

Apparently, when deer brush up against such a seemingly insubstantial fence as a fishing line fence, they become confused or frightened and avoid it (and in the process, avoid your garden, too).

Some people (Aaron included) recommend hanging small, brightly coloured tags of tape or string so you can see the fence, but others nix that, contending the effectiveness of this kind of barrier hinges on not giving the deer a clue where the fence is.

We have mixed feelings about the idea of a fishing line fence, and would love to hear feedback from people who have used this method. Is it effective? Is it safe?

Do you have a plant problem that we haven’t covered on our podcast? Share it with us in the comments for this episode on YouTube, and we’ll add to our List of Things to Ask Aaron! (And, yes, there really is such a list.)

yellow petaled flower by elias sorey unsplash

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