What is the best way to treat japanese black pine for root rot , my tree is showing lots of yellow needles , the roots are breaking apart easily ?
If it’s repotting season, repotting is the best course of action. I try to remove all of the affected soil, usually dark areas that can smell bad. When I find dead roots, I cut back to healthy growth, even if it means cutting back to the base of the trunk. Leaving dead roots will let the rot continue. I leave the healthy roots alone.
After repotting, the tree can be dipped in a mixture of zerotol or a similar contact fungicide that’s safe for the roots. About a month later I might use a systemic fungicide, though in general, proper repotting and using soils that don’t retain too much water will usually take care of root rot.
If there’s lots of rain, I’ll keep trees in a sheltered spot so they can dry out between waterings. As much as possible, I want affected trees to get sunlight and warmth to stimulate healthy growth.
A couple things that may help in the future. One is using a good free draining mix like pumice, akadama and scoria. Another is adding a handful of horticultural charcoal in the mix and lastly keeping your tree in full sun and making sure you are watering the correct amount and frequency.
One additional strategy is to adapt the granule size and type of your soil mix to compensate for your climate and or watering tendancies. Pines like dry feet, so if the free draining mix holds some moisture but does not trap water then it will be more effective for pines. Pines like to dry out between watering. One way to accomplish this is a larger particle size of pumice for a drainage level on the bottom, medium size particles for the root ball and only smaller size particles on the top 1/2 inch. The smaller grain size distributes the moisture evenly and the water drains faster as it progresses through the pot. Check to make sure your pots and containers have adequate drain holes and that they have not become restricted by roots or other debris. One should remove and replace the top smaller grain layer whenever it becomes restricted or begins to break down. I replace the top 1/2 inch layer annually. Soil components that work well are pumice, lava, decomposed granite, akadama and coarse sand. Particle size for the top 3/16" middle 1/4" bottom drainage 3/8 to 1/2 inch.
What would you recommend if it’s outside of repotting season?
If the confirmed situation is Root Rot then the condition needs to be corrected. Repot, remove all dead and decaying roots. Keep only brown healthy roots. Remove all compacted soil that is not draining freely. Ensure a good mix of particle size as suggested above,( i like to use some used soil with Mycrohyzae in the mix) secure the remaining rootball carefully in the pot. keep the plant from too much heat, sun wind or frost while in recovery. Mist the foliage regularily and allow plenty of time for the tree to recover before attempting any other work. I wait until the condition improves and i see lots of new growth on the tree. Do not fertilize right away give the tree time to recover.
Repotting out of season is often referred to as an emergency repot and the key is to take appropriate steps to aid the recovery. Leaving the tree in a decaying condition will not improve its health.
Thank you Frank. Emergency repot it is. It makes a lot of sense. I appreciate your explanation.
Interesting article on root rot in hydroponics. I have not tried this, but interesting subject.
Interesting. A number of folks use XeroTol, another H2O2-based product, as a fungicide.