Seeking help with fusarium treatment

[chickazilla]

Hello experienced and wise orchid growers! I am sending out an SOS for help with treating one of my orchids with fusarium - the Myrmecatavola Frances Fox, which I absolutely love. In the process of repotting, I checked it for fusarium b/c she was showing signs of weakness, poor root growth and black marks on new roots, etc... She is indeed infected. I read an article which advises that you keep cutting into the rhizome until you don't see the purple ring, before repotting, but I fear I would be down to only two pseudobulbs.

I'm so conflicted about keeping the four pseudobulbs or do as advised and keep cutting until I land on a healthy rhizome patch! My plan is to do foliar treatments with thiomyl. I would appreciate any words of wisdom. Thank you.

[Roberta]

Don't cut!!!!! I doubt very much that your orchid has fusarium. This seems to be a "diagnosis" bandied about on YouTube. I would suggest rinsing off the roots (probably some rot due to being too wet) and pot it up in fresh, well drained orchid bark. It will grow new roots. It is important that the plant be held in place firmly - so even less-than-stellar roots serve a purpose - and they can help keep the plant hydrated as well until it grows some new ones. The well-drained part is vital - water until it runs out of the pot, then let it drain before putting it on a saucer or other hard surface. It doesn't likely have a dread disease, just needs some TLC.

[chickazilla]

Thanks for your response but the article I referenced was posted on the St. Augustine Orchid Society's website - Orchid Diseases. Youtube hysteria aside, there are purple rings on both sides of the cut rhizome and I'm just looking for some sober advice about how to proceed. Thank you for your input!

[estación seca]

I agree with Roberta. I don't think your plant is sick. Plants infected with fungus of the rhizome tend to die quickly. I would repot and take good care of it.

Myrmecs tend not to grow much until it's very warm and sunny. I don't think your weather is warm enough to expect much yet.

[Roberta]

The only situation where I would advise drastic surgery is when you see a significant part of a pseudobulb turning brown or black... when that sort of rot gets into a rhizome, it can take a plant quickly unless cut down to clean tissue. But when that happens, it's not subtle. In your case, the rootless back bulbs are firm and green, the leaves look good - so the plant needs them for reserves. The front bulbs have nice roots, and I think that it will grow just fine once repotted.

---------- Post added at 06:34 PM ---------- Previous post was at 06:31 PM ----------

Diseases (and pests) are somewhat regional, depending on climate and other environmental factors. So apply advice from an area with a very different climate with caution.

[chickazilla]

I'm absolutely willing to follow your advice... but can you address the purple rings I found? Is this just a myth spreading around the orchid world?

[estación seca]

Pretend you never heard about purple rings, and they don't exist. Los Angeles has relatively low humidity. You are never, or almost never, going to have any fungus problems.

[Roberta]

I zoomed in on the photos, and don't see anything that is unusual. The dark spots and bands are pretty normal on older but still viable roots, and the darkening on the cut rhizome also looks clean. I just don't see anything that I haven't seen dozens or even hundreds of times, on plants that don't need anything more drastic than repotting. (I HAVE seen the black rot that can run through a rhizome and kill a plant, alas... happily, it's not there on your plant)

[chickazilla]

It's hard to see the purple color due to my kitchen light but on my honor they are purple rings. I stopped cutting and repotted the plant. Crossing fingers that it survives and thrives! One thing, according to the weather channel does say we got up to 90 percent humidity during the summer last year. Just sayin' . Thank you ladies for chiming in. I am cautiously optimistic! Have a great weekend.

[Roberta]

[QUOTE=chickazilla;871283 One thing, according to the weather channel does say we got up to 90 percent humidity during the summer last year. Just sayin' . [/QUOTE]

It can get damp overnight and early morning, 85-90% RH. But at mid-day I think the worst we got last summer was around 60-70% RH (My little "weather station" gives both outdoor temp and humidity) And I'm about 4 miles from the coast. It got unpleasantly muggy by California standards, but summer in south Florida is a whole different level of miserable.