Brown and black leaf margins

[auhurta]

Hello everyone,

I have been reading you for a while now. Never had the guts to write but I think it´s about time because I have done a lot to combat the unknown. I hope you have some encouraging answers.

There are several issues I would like to discuss with you but for now there is one that is killing me.

For a year maybe, I have been fighting something I thought was some kind of fungus on an orchid that has never bloomed (I think it's a Cymbidium). The leaves began to brown up from the margins. This thing tends to spread toward the center of the plant. I used a fungicide sold in my country called Derosal, active ingredient carbendazim, it is a benzimidazole.

It kind of improved the condition but not entirely. Then I bought what I think is either a Maxillaria or Rodriguezia. It got it too.

Then another cymbidium which I keep in my room (apart from these other two) started to show the same. I thought I could keep it under control since none of these have died.

Oh also, in both cyms and in the maxillaria I have noticed some spots which lack green colouring.

I bought a Zygopetalum redvale fireburst. It got it. this last one has presented these simptoms much faster. I really fear for this one.

Some additional treatments I have tried are:
Physan 4ml per liter.
Leaf trimming each time I see the brown/black rim followed by cinnamon covering of the wounds.

3 days ago I tried the listerine sprinkling along with physan drenching and cinnamon altogether. Today the Zyg is already showing brown rims where I cut before.

I´ve got 12 more orchids, none of them with this thing I don´t want it anymore and I realize I don´t really know what it is. HOPE IT'S NOT A VIRUS!!!!!!!!

Here are some pictures. I attached them in the order I mentioned them in the message.

Thank you and don't hate me for letting this go so far

[auhurta]

Please post something , anything...

I´ll go shopping tomorrow for some supplies I need. Besides, your opinion is a lot to me on this.

Thank you!!!

[RosieC]

Hi Aura,

I really wish I could help, but it's not something I know about.

Hopefully my post will bump you back up a bit.

[camille1585]

A lot of times when trimming leaves, there will be a dried brown rim below as the cut heals. That is probably the case of some of them.(like pic 3 for example) Just watch them,and see if it continues to progress. When you cut off brown parts on the leaves, are you cutting just the bad stuff, or also healthy leaf as well? Normally you want to cut well into the healthy tissue, to make sure you got everything. You also should disinfect the cutting utensil between each leaf or plant, as a precaution.

If the leaves are browning from the tips it could be fertilizer burn if you're fertilizing too much. Also, what's your humidity like? If it's really low sometimes leaves will dry up a bit, and if it's really high you might have fungus problems. Increasing air circulation with a fan might help in that case.

[Ray]

Like Camille, I would look first at the fertilizer use, then humidity, but also consider that watering - if you let the pots get too dry for too long, the same thing can happen.

The spotting is probably fungal in nature.

[auhurta]

Thank you all for posting.

Camille, I cut about 1cm into healthy tissue always. The bown sometimes stops at some point, maybe 5mm, but sometimes progresses further and that`s when I decide to cut again. I wonder if I should cut the whole leaf just to make sure. I also disinfect my utensils with straight bleach; sometimes I do so with a saturated solution of detergent.

Ray
I use a 16-16-12 fertilizer which also has Sulphur, Boron, Cobalt, Copper, Iron, Manganese, Molybdenum and Zinc. To have a gross idea of the concentration it´s 160 g of N per liter of fertilizer. The concentration I use is 3ml/L once every week or every two weeks. Is it right? How ca i find more info on fertilization?

I have my hygrometer in my room where I keep the one in pic. 5. It says it's 55%. But the other 3 are in a different room and I don´t know how it's there. I'll move my hygrometer there to be sure.
It might be a lot drier there.

In case it's a fungus, what would you recomend?

Thanks again,

Aura

[camille1585]

I may be wrong, but if you are using 3ml/L of 16-16-12 that works out to a whooping 486ppm N! I used Ray's super duper PPM calculator at the bottom of this page: Firstray's fertcalc
I'm also using 3ml/L of fertilizer, but mine is 5-6-7 so that's roughly 150ppm N. You say that you water with fert once every week-2 weeks, but how many times do you water per week? You might not be flushing out the pot enough between ferts, hence the black tips. Ray will probably know better. If you want more info on fertilizing, check out the stuff on Ray's site, it's good! First Rays' Free Info

[auhurta]

Ok so I'll do some reading and correct those values. Meanwhile, do you suggest any fungicide? or should I just wait?

Hahahahah sorry to insist, it's just that I don't want any evil fungus to take over.

Also, today I found little bitty insects on the plate below the pot (I never leave them with "post drenching" water) of one of them. Will dimethoate do?

[camille1585]

Sorry I can't help you with fungicides. I don't know what you have available, and here in EU non-professionals are getting limited in terms of fungicides. The EU is pulling more and more products every year. I usually use stuff like mancozebe or myclobutanil, but I don't know what I would use for your plants since I'm no too sure what it is.

[auhurta]

Should I post a link of this thread at the Pests and Disesases forum? I'll do that for now. Thank you