Blackheart in Fruit Trees: What It Is and What You Can Do
Over the past few weeks on Talkback Radio, I’ve had several callers describing apricot trees that were just... not thriving. Poor fruiting, sparse foliage, and increasing amounts of dead wood creeping through the canopy. Often, by the time someone notices, it’s too late. One of the biggest culprits in these cases? A silent destroyer known as Blackheart—a common name for Verticillium wilt, a soil-borne fungal disease that targets stone fruit trees and is particularly harsh on apricots.
A Difficult Diagnosis
Verticillium wilt is frustrating because it doesn’t always show clear signs straight away. Trees may look a little underwhelming—less fruit, fewer leaves, a bit of dieback here and there. It’s easy to blame poor nutrition or a rough season. But it’s what’s happening inside the tree that gives Blackheart its name: a dark rot in the heartwood, usually only noticed when pruning or removing branches in winter. By then, the tree is already well into decline.
What Causes It?
This fungus thrives in cool, wet soils, especially in clay-based ground that holds water. The last few years of unseasonably cool and damp springs and summers across parts of Tasmania have been ideal conditions for it to flourish. It enters the tree through the roots and works its way up the vascular system, restricting the tree’s ability to transport water and nutrients.
Unfortunately, there’s no chemical cure once it takes hold.
So, What Can You Do?
While it’s not great news for the infected tree, there are steps you can take to protect the rest of your garden—and to start fresh with a healthier planting strategy.
Remove the Tree (Roots and All)
You’ll need to dig out the tree, including as much of the root system as possible. It’s hard work, especially in heavy soils, but any infected roots left behind can continue to spread the fungus.
Don’t Compost the Timber
It’s tempting to mulch the removed tree, but don’t. The pathogen can survive in chipped wood or infected compost. Burn it safely, turn it into biochar, send it to your local green waste facility, or use it for firewood—just don’t let it cycle back into your soil.
Avoid Replanting Stone Fruit in the Same Spot
This one’s critical: don’t plant another apricot, peach, nectarine or plum in the same location. The fungus can remain in the soil for years. One caller told me they replaced their infected apricots with two Nashi pears (‘20th Century’ and ‘Kosui’), which pollinate each other and are much less susceptible to Verticillium wilt. Great choice!
Improve Soil Drainage
Fungus loves soggy soil. Replace compacted or clay-heavy soil with a freer-draining mix of compost, coarse sand, and spent mushroom substrate if you can get it. This will not only improve drainage but help support healthy microbial life in your soil.
Solarise the Soil
If you’re not replanting immediately, cover the affected area with clear plastic sheeting for a couple of months in the warmer weather to heat the soil and reduce pathogen levels. It’s not a guaranteed fix, but it can help suppress fungal activity.
Help from the Good Fungi – Tricho-Shield™, Root-Guard™ & Mycorrhizae
At Harmony, we’re strong believers in rebuilding soil health after a loss like Blackheart—and the best way to do that naturally is by reintroducing beneficial microbes.
One of our go-to products are Life Force® Tricho-Shield™ which contain strains of Trichoderma fungi—powerful natural allies that help rebalance the soil microbiome and protect future plantings.
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Tricho-Shield™ is a probiotic mix that can be applied to seeds, seedlings, transplants or even established trees. It promotes strong root development and helps tip the balance in favour of beneficial microbes. You simply mix 1 tsp into a 9-litre watering can and apply monthly to the soil or foliage.
This product wotks beautifully alongside Life Force® Platform™, which includes mycorrhizal fungi that form a symbiotic relationship with plant roots, increasing nutrient uptake and overall resilience. These fungi literally grow with your plants, creating a vast underground network that helps them access water and minerals far beyond their original reach.
Losing a fruit tree is gutting—especially one you’ve nurtured for years. But gardening is full of lessons, and this is one of them. If you've lost a tree to Blackheart, know you're not alone. Many gardeners, even seasoned ones, have faced this quietly devastating issue.
And like every good gardener knows: when one tree goes, there’s always a chance to plant another—wiser, and maybe even better-suited to the conditions.
"Somewhat" Happy Gardening !