Chojubai Notes: Part 3—Why is my Chojubai weak?
Few plants come without a puzzling issue or two. For ‘Chojubai’ Dwarf Flowering Quince, the most serious issues are in the roots. Chojubai are strong plants that will normally extend 6” (to 18″) per growth surge. If this is not seen, then be on the alert.
A weak tree will not make typical extensions in the spring and might have a yellowish color. Some weak Chojubai are simply in soil that is too fine, are overwatered or underwatered, or are in pots that are too shallow, and those are easy to correct.
Otherwise the root zone of a Chojubai is susceptible to several problems that can weaken your tree. The first is a nematode, the second is a bacteria, and the third is a root gall, and they’re all separate but interrelated parts of the disease known as crown gall. It’s not frequent, but if you have a Chojubai, be on the alert for general weakness. I’ve been looking into this problem for a while, and my apprentice Bobby has been very helpful in discovering some of the links too, so I’d like to offer here what we’re doing now to tackle these root issues.
- In a quick summary, root lesion nematodes cause wounds in the Chojubai’s fine roots that provides an entry for a truly rascally bacteria, Agrobacterium tumefaciens, which causes crown gall. A wound from a root-pruning tool can also provide entry. The bacteria lives inside the root, and transfers part of its DNA to the DNA of plant cells, which, with cell division, cause the callus-like galls we see on the roots of affected plants. So the bacteria is very sneaky fella, and not too easy to get rid of!
If you see galls (Warty and friends) on the roots of Chojubai, try these treatments:
- Shift the tree into a bigger pot. If the weakened Chojubai is in fine soil, a small pot, compacted soil, or a shallow pot, definitely transfer it to a deeper, larger container or box with coarse pumice (1/3” + size) or similar on the bottom and sides surrounding the original soil mass. Let it grow freely, without overwatering it (algae and liverwort are the clues), while controlling the other issues.
- Control the root lesion nematode. There are nemacides specific for the control of nematodes, and these may be used. With a suggestion from a friend and a couple of tests I found that soaking the root ball in Zerotol at 1.25 oz / gal will kill the nematodes. This can be done while the tree is still in the pot.
- Control the bacteria. The problem with the bacteria is that it’s inside the root itself. Copper is effective for this bacteria, (the Japanese bonsai professionals use Streptomycin, but it’s puzzling to figure the proper concentration for plants since they are made for internal use with animals). I’ve been using Phyton 35, which is a systemic copper bactericide/fungicide. Be sure to read the label carefully—Phyton 35 requires a change in the water we mix it in to a pH of 5.5-6.5.
- Control the gall. Cut the gall away with pruners when repotting. It may take several repottings to get all the gall removed.
What seems to be important is to take care of this three-ring circus systematically. First knock out the nematode. Then go after the bacteria. And finally cut away the gall. Even if you’ve killed your nematode and the bacteria, you may still have the gall as the DNA from the bacteria will keep replicating with cell division. But if you’ve killed the nematode and are controlling the bacteria, a weakened Chojubai often shows a very rapid jump back into strong growth. I’ve seen new, large, strong leaves and even shoots on a totally stalled Chojubai in under two months with these treatments.
The nematode is often the primary culprit, which appear to think that Chojubai roots are like crack cocaine, chocolate, nirvana, or all three. They can knock down the root system of a quince quite rapidly, and then you see a weakened tree with a gimpy root system that does not have the typical vigor of Chojubai. Many other Rose family plants are particularly tasty to nematodes.
A few of the nematodes you can see without a loupe (I’ve seen some about ½” long, and look like glassy worms), others are nearly microscopic. If you find the gall you can assume you’ve got the bacteria. Prevention is best, such as being careful about sterilization of cuts, and controlling the nematode.
Hopefully you’ll never see galls on your tree, but if you do, try these remedies to bring your tree back to health!
A few older posts about ‘Chojubai’ Dwarf Flowering Quince: