Orchid Culture - 2021 Questions & Answers
by Sue Bottom, from the St. Augustine Orchid Society Newsletter.
Email us with any orchid question, if we can't answer it we'll find someone who can! Send photographs too!
Droopy Phal Leaves
Q. This is a Phal. Yaphon Green Batman that seems okay except for the drooping. I use reverse osmosis water with Epsom salts when watering. Any suggestions?
A. Perhaps you should knock it out of the pot and take a look at the roots. I'd guess there is a root problem. Norman's Orchids packs the sphagnum very very tight on their phals, so even when the top may feel dryish, the bottom of the pot is still wet, so it is very easy to overwater them. Knock it out of the pot and check the roots, that will guide your course of action.
Q. I am having a problem with the flowers of some of my dendrobiums.
The buds are damaged. They either fall off or if they develop
into flowers the petals are small, deformed and damaged.
I don't really know if it is a fungal disease or caused by pests.
A. Just looking at the flowers, you couldn't rule out bacterial blighting, but my guess would be thrips based on the damage you are seeing on the buds. Thrips are very difficult to control. They crawl into the buds and chew on them long before the flower is ready to open. If this is a persistent problem, you can spray the buds and flowers once or twice a week with Orthene to prevent the damage, or drench the plants every 6 weeks or so with Orthene. There's more information here.
Catasetum Bulb Rotting
Q. I got my first 2 Catasetums last year and am noticing something strange on both. There are dark brown, slightly sunken and a bit sticky, spots on a couple of older pseudobulbs.
This only developed after I stopped watering them for their winter rest so I’m not inclined to think it is rot. The newest bulbs are still quite plump and I have a new growth just starting on one. Should I be concerned about these spots?
A. Yes, it is rot. Feel the bulb, it probably feels pretty soft compared to the one next to it. This is not an aggresive rot like black rot in cattleyas. It is slow moving and you can just cut away the older bulbs when you repot, which you should consider doing now as the new green growth is emerging.
Green Blotches on Phal Leaf
Q. Are the green blotches on the phal leaf something I should be concerned with, they are more pronounced on the keiki than the mother plant. The plants were moved into the greenhouse when cool weather arrived.
A. My best guess would be some cold water damage, either from overnight condensation dripping on the leaves or cold water from the tap. Check the temperature of the water coming out of the hose and see how close to 70F it is, the water should be within 5 to 10 degrees of the air temperature. The keiki leaves are likely more tender than the Mom's leaves, and more sensitive to cold water damage that can cause mesophyll cell collapse.
Pool Algaecide Strengths
Q. I have a question regarding pool algaecide versus Physan. Is the product in the photo appropriate and what rate per gal should I use?
A. Physan, which contains 20% quaternary ammonium compounds, recommends 1 tsp/gal as a spray. Your product appears to contain 30%, so you would use 2/3 strength, or 2/3 tsp/gal.
Leaf Damage on Phalaenopsis
Q. This phal was with all my others on the north face of a wooden fence. Any ideas what caused this damage?
A. My guess would be the new tender leaves were damaged somehow while they were forming and the scars simply enlarged as the leaves got larger. Perhaps it was mechanical damage, or perhaps water in the crown. The other leaves look great. (Feb-21)
Cattleya Flowers Blotchy
Q. One of my Cattleya flowers looks splotchy. It looks questionable to me, could this be because of a virus or disease?
A. That sure looks like color break on that orchid, which would suggest Odontoglossum Ringspot Virus or ORSV. It's a shame, cause it's a beautiful flower otherwise. Kiss it goodbye.
Mottled Cattleya Leaves
Q. I was reading about fungal problems and noticed that many of my cattleyas have leaves that are becoming mottled. I have attached pictures for examples of what I am seeing. I am concerned that most of my cattleya plants are diseased.
A. Leaf mottling is typically caused by one of three things:
1 - Scale, turn the leaf over to make sure you don't have the dreaded boisduval scale on your cattleya.
2 - Fungal Infection, turn the leaf over and see if you see tiny dots or blotches of dots, the spores.
3 - Magnesium deficiency, which is what I suspect you have and what I had for many years.
Our water is very magnesium deficient and most fertilizers do not contain magnesium. Magnesium is an essential component of chlorophyll, that's what turns the leaves green. During extremes of heat and cold, the chlorophyll can degrade and give you that mottled appearance. I add magnesium sulfate, Epsom salts, to my fertilizer solution. Some people apply it in the spring and fall, others apply it monthly. I give mine Epsom salts every time I fertilize, which is every time I water. If you use 1/4 tsp/gal fertilizer, add 1/4 tsp/gal Epsom salts at the same time. The only caveat is you can't mix Epsom salts with a CalMag fertilizer, but with a CalMag fertilizer you shouldn't have to add supplemental magnesium.
Tiny Castings from Cork Mount
Q. I have a giant Dinema polybulbon mounted on cork. It was outside all summer, but now that it’s in the greenhouse, I realize that the cork is inhabited by something that is creating copious tiny castings. I’ve got a new piece of cork, and I guess I can re-mount the plant, but I’m worried that the critters will move into the new cork with the plant, and also move into my other mounts.
I found info about steaming and baking the cork, but I can’t do that with the plants on it!
A. That looks like frass from dry wood termites. You might try soaking the mount for an hour in a strong solution of imidacloprid, say double strength. That's not the strength they use to treat foundations, etc. for termites, but it's probably as strong as you'd want to try with your orchids. I don't think the termites will go after your plants, but of course you don't really want a colony of termites anywhere close to your house.