That Yellow-Orange Dust Is Not Mustard
We recently purchased a few larger mature plumeria for landscaping a customer’s yard. We did not grow these from cuttings in our air pots. They arrived with yellow orange pustules on many of their leaves. We have found the best course of action with rust is to cut every leaf that has rust present. We followed that plan with these plumeria and cut every leaf off that had rust. Then we bagged the leaves so they never hit the ground, and started those plumeria on GrowSafe. After about 4-6 weeks they will regrow their leaves and be ready to deliver to our customer.
That was a rescue. It is not how the rest of the grove is run. The photos below are from this rescue job on the larger plumeria trees.
What we do on the trees we grow
Almost all of our plumeria grow in air pruning pots, outside, in Denham Springs weather. Leaves stay wet here longer than they would in a dry climate. Rust likes that.
What we have found works really well for us is GrowSafe by Agronagen, used as a weekly preventative on the trees we raise to sell and our personal collection. We spray so rust has a harder time getting started. We are not waiting until a rack is yellow/orange and then reaching for the bottle.
Hundreds of plants live here. We cannot flip every leaf every day. The weekly spray is how we cover that gap, and it has kept rust from settling in on the stock we grow ourselves. If you have two or three plumeria on a patio or back yard, you can do the part we cannot. Look under several leaves on each plant every day or two. You will see a new rust spot while it is still a small job.
If you want to be help stop rust before it can get started, we recommend spraying the entire trees, especially the undersides of the leaves with GrowSafe. That is where the fungus sits. Spray morning or evening, once the leaf is dry, not while rain is still on it. Follow the label instructions.
What you are seeing on the leaf
Plumeria rust is a fungus, Coleosporium plumeriae. It stays on the foliage. It does not rot the stem, and it does not mark the flower the way black tip can.
Early on, the dust is on the bottom of the leaf. The top may only show pale yellow flecks, sitting over those spots. That is the moment worth catching. Let it go and the pustules come through to the top and damage the leaves. The leaf yellows. Rub it and your fingers come up orange.
A yellow lower leaf in September is often just the season. Rub the underside. Orange dust means rust. A clean yellow leaf, with no powder, can stay on the plant.
If you find it on yours
Spores need a wet leaf. From late spring through fall we give them plenty of those. The rust spores move on the air, on rain splash, and on whatever cut the last tree. This rust is known as a plumeria fungus. The plant at risk is the next plumeria in the row, not the roses beside it.
Cut the infected leaves leaving about an inch of the stem. Do not yank them and let them drop. A leaf on the soil sits there until the next shower splashes it back up. Cut leaves into an open bag, tie it shut, and put it in the trash. Leaves already on the ground go with them. Never compost leaves with rust.
White beads at the cut ends of the stem are sap. Ordinary plumeria latex. Leave it.
More than one tree means more than one cutter. We buy the 300-piece boxes of retractable utility knives on Amazon. A fresh blade for each plant is simpler than wiping one down while your hands are already coated. The used blades go out with the bag of leaves.
That orange on your fingers is the spore load from the leaf you just cut. Wash before you touch a clean tree.
On the trees that came in infected, GrowSafe started after the leaves were off, on what foliage was left and on the new growth as it pushed. Taking the bad leaves off is still the first job. The spray does not stand in for that.
A few things we keep coming back to when someone writes us about rust:
Look under the leaf. The top of the leaf can be green and beautiful and the bottom already spotted with rust.
A handful of leaves in a bag is an easy afternoon. A tree that has leaves covered with rust can turn into a long afternoon and quickly spread to other plumeria.
One tree, one blade. One pair of pruners is fine if you finish the plant, bag the debris, and wash the tool before moving to the next plumeria.
Give the pots some room. Trees with heavy foliage can remain damp long after a storm. It’s okay to thin the leaves to help with air flow.
Water the soil when you can not the leaves. The rain here in the south will wet the leaves no matter what we do. The hose does not have to.
Rust seldom kills the tree. It thins the canopy and, if the leaves stay on the ground, it spreads quickly. On one or two plants, a daily look will tell you more than any spray schedule. In our grove with hundreds of plumeria, the weekly GrowSafe pass is what we count on.
If a leaf has you unsure, send a photo of the underside. We are happy to look.
Thank you for growing with us.