Updated: May 8, 2019
Ahh friends, no doubt you have seen the sad, spotty browning of these beauties all over East TN. It's likely caused by one of two fungal pathogens (or both simultaneously). The Seiridium canker is typified by elongated, sunken cankers on stems with crusty edges and/or oozing sap. See pic below. The second pathogen is a Botryosphaeria which causes girdling cankers at the base of the dead shoot. These can also produce a dark, cracked appearance on the tissue lining the canker (sunken dark spot or crack-like elongation) don't ooze however.
What to do?!?
The best solution is to replace the trees and have the cut material burned. It's starting to kit other cultivars e.g. Cryptomeria. If you want to keep them as long as possible, the remedy is to change the soil environment for the tree(s). There are no known fungicides to cure the canker(s) but caring for the soil and disciplined, sterile pruning can keep your trees in the landscape for years to come. It all depends on how hard they have been hit and how quickly the soil can be changed.
Better Nature provides a biofertilizer to help keep the roots healthy, increase soil aeration and aggregation (a missing quality in most clay soils), and increase the trees' immune response.
I also offer tree surgery which is a bit like it sounds - it's cutting out all the cankers and dead stems because that is where the fruiting and infecting fungi are living. It is absolutely necessary to do these selective, sterile cuts IF you want the trees to survive another decade. It is also quite expensive! The tree surgery is intensive work and thus not an inexpensive option. If you have a specimen tree and you want to maximize its life - tree surgery combined with the biofertilizer will do just that. There are options to get a new green-fence started while the Leylands are dying, rather than tree surgery.
In Summary, remediation includes:
1. pruning out the dead stems and sterilizing the pruning equipment between each cut to avoid additional spreading - unscented lysol is a great sterilizer,
2. removing old mulch, ensuring proper mulching (1 inch away from the trunk) extending out to the canopy's drip line,
3. mulch rich in cedar and pine straw to reduce spore survival,
4. never watering or allowing irrigation to contact the canopy (spore spread is highest via water), and
5. thinning the canopy to allow light and air penetration,
6. planting your trees at least 10' apart or thinning mature 'green-fence' to increase aeration and sun penetration,
7. watering the trees during long, hot, dry spells.
We can't cure it but we can keep the trees!
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This is the world we live in now - one with more disease and higher density of problematic insects. But remember - for every blog post about a problem there are 100s of wonderous, beautiful phenomena occurring out in nature. Many of them involving beneficial insects and mutualistic microbes.