About 4 days ago I started noticing that some of the flower spikes on my D. amethystoglossum have stopped maturing and are drying up - blasing (?). [I don't know if that term refers to the spike also or just the bud....]
It's a young plant that I picked up in Aug '18 and it's the first time I've grown this type of orchid. It's growing conditions have been consistent with dendrobiums requiring a winter rest period and I was elated when it started growing flower spikes around mid December . It's been doing fine until a few days ago - I started noticing (with dread) that the buds on certain spikes looked lighter in color. And today there's no doubt that 2 of the spikes are dry/dead. I will be devastated if I lose all of them ….. and not knowing why. I didn't know this could happen. I've never lost spikes before. Does anyone know what could be the cause?

Dead spike

Dead spike

Healthy spikes

What light orientation do you have your plant in? Dens like a lot of bright light when it is in spike.

There are a few possible causes.
1. Uneven water. As the buds develop, the plant puts out a full effort to develope those buds. If they don't get proper water, they can abort them.
2. Too warm temperatures could cause them to abort.
3. Too low humidity is possible but that would be my last thought.
4. Insects, either thrips, aphids, false spider mites would be the top three culprits.
5. Too strong light leading to the buds overheating and aborting.

When I looked at your images magnified just now, I am almost positive that you have a fairly serious mite infestation, either false spider mites or true spider mites.
Soapy water should help. Fill a quart spray bottle with water and add 1/4 tsp. Of dish soap. Spray entire plant, topside and underside.

I've checked out those spots too @BigBill, and they aren't mites. The spots have been there since I bought it. The pics are a bit deceiving. The tiny black spots are embedded in the leaf tissue. I don't know what the cause is...maybe they picked up something when they were grown in the nursery??
I put the plant in a separate grow space the end of Oct so I could keep it cooler than my other orchids. Humidity, water and light is good. But I just recently brought the nighttime temp up to the mid 60's (from the mid 50's). I'm sure that's what caused the smaller spikes to abort. So I've corrected that! Thank you for the check list. You've confirmed what I was suspecting. I'm just hoping that the remaining 4 spikes pull through.

I would take the position of being cautious nonetheless. Mites, especially the false spider mites are so tiny that the naked eye can easily miss them.
But the rapid deteriorization of the buds points to an insect as the cause. Typically a mite lives about three weeks. You may not even notice them at first.
That spotted damage is so typical, trust me. Look carefully at the undersides of the leaf. Look down the length of the leaf and roll it slowly along the long axis. If mites are there the leaf takes on a "silvery cast" or sheen. I would not even attempt it without my lighted, trusty 10X magnifier. Let me know what you see.
Thrips and aphids are famous for bud kill. I assume you could see the aphids but thrips are like dark slash marks and if you hold the plant or leaves over white paper and gently tap the leaves, the little buggers should drop to the paper.
A thrip is about as fat as a human hair and fully grown is about a millimeter and a quarter long!
Good luck!!

Yep, @BigBill, I've got red spider mites!!!! When I looked at the leaves through a jeweler's loop I saw some that were moving. I can't thank you enough for detecting this problem and telling me about it. Now I need to know how to proceed. Is there a solution that I can make from things I have at home or do I need to buy a solution?
These pics are pretty bad...I held the loop against my cell phone lens to try getting a close-up for you to see.
I used a dampened cotton pad to wipe the back side of the leaves. BTW about the silvery color - I thought the plant was just deficient in magnesium! You saved this plant Bill [if I can manage to get rid of the bugs!]

@BigBill oops. I just reread your comment above. I'll mix up a spray now. Does the soap/water solution take care of them entirely or is it just an intermediate step? Do I need to spray them daily...?

Susan, try a solution of 409 cleaning spray mixed with alcohol. That should take care of your problem.

Thank you @sugarcane. What ratio should I mix this? Do you think one application take care of the mites?

Your very welcome! I am happy that you were able to see them!

I use Neem Oil as a one a month preventative for everything disgusting. I have a gallon and a half pump sprayer that I fill with water, the three or four drops of dish soap then a tbs of Neem. It is effective again bacteria and fungal issues. It is systemic. But by using it faithfully for some three and a half to four years now, oh wait, maybe 5, my bugs are next to nothing!

@BigBill!

I would try Lindsey's cure. Mites are tough, so you might have to repeat two or three times, about a week apart to make sure you get any newly hatched ones. Spray thoroughly, rinse after an hour, and repeat as needed.

Susan , Bill's advice is excellent ! Since I've switched to neem...' next to no bugs' is what I generally see. For an emergency we use the 409 / alcohol spray in windex sized bottles at the University greenhouse.We mix it in a gallon jug. 2 16 oz. bottle of 70% alcohol and 1/3 cup of 409 and fill with water. I also make sure to spray the potting mix as well.
1 application of anything rarely takes care of the entire problem..I always follow up 7-10 days for 3 applications.

I've found that Neem doesn't work for spider mites. I suppose it may work as a preventative after they're gone. Add to that, I've read here that Neem oil extract comes in different strengths.

Thanks Lindsey! You are the best!

I have not found Neem in different concentrations interesting
I think that if you do not mix it correctly, it does not work as well or if you don't spray completely, it is not as effective.
If you ask Lindsey, she didn't believe in Neem Oil a while back either but she does now! If you spray it correctly it is like BigBills personal okie dokie sure fire 100% guarantee!!

I have encountered people who use it right out of the bottle! Now that ain't going to work.

I agree with the Neem -oil! I have been using it this Winter and I do see a major improvement! I see a lot less bugs, this indoor season I finally feel that I am on top of the bug invasion. It is actually under control!

Oh wonderful Ursula. That is just great to hear. Another Neem disciple!!


That makes 2!

If you compare brands, you will see in the ingredients list that the % of neem oil extract differ. I was a licensed pesticide applicator for many years. I know how to read labels and follow directions. The brand I used on my last standing tomato plant did not get rid of the spider mites. So far, keeping a fan on my orchids 24/7 has kept the pests at bay pretty well, and I haven't had any fungal issues in the shack. The heavy rains have caused some rot outside though.

Thank you all for your advice. I appreciate it so much. Since I don't have neem oil at here at the moment I'm going to mix up the 409/alcohol concoction and spray the plant today. Maybe find neem oil and keep it on hand though. I'm not sure what neem oil is or where to find it so I'll figure that out. Anyway since I only have a problem with the one plant - and it's isolated from the rest - I'll have to do some math to make a smaller batch! I'm assuming that the roots will be OK after spraying the potting medium? I watched a video about this that said to "avoid spraying the roots and change out the potting medium".
How do you feel about Natria or Miracle Grow insecticidal soaps? I've successfully used both of those before for scale that one of my bird of paradise occasionally gets. It sounds like anything that you use has to be used over and over again.