It's tough to keep an Alocasia too wet since they often grow on the edges of streams or in shallow water. Is the humidity high around the plant? Spider mites can usually be avoided by increasing the humidity instead of using a chemical.

Do you have a species or common name for the plant? I'm not certain what the "black stem" form might be. Are you talking about the petioles that support the leaves? Is it really black or purple? The stem is the main axis of the plant and isn't the leaf support. Any other info or a photo could be useful to help you find a good answer.

Here is a link that might be useful: Is it a stem or a petiole?

I have had the same problem this year with one of my Alocasia Argentea. As the leafs unfold there are several holes in them. The holes are forming while still inside the plant itself not after it emerges. Some holes are small like a hole punch size and others are as large as a quarter. But most are hole punch size. The strange thing is that not all the leafs do this. Just several back to back than I get one that is untouched than several back to back again.

The only ID I got with this was 'Black stem' but it does look more purple as you can see in the third picture.

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Now my aurora has a hole also.

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I have an idea what it might be but I'm going to ask LariAnn to take a look. She knows more about this genus than anyone I know.

This plant is Alocasia macrorrhizos "blackstem", referring to the dark petioles and main veins on the leaves. Sometimes I see that kind of damage on my plants, but it is not pest damage. It is a response to an environmental stress, such as too little fert or too much, temps too cool or too warm for a period, or other environmental irregularity occurring while the leaves are still hidden within the sheathing petiole and developing. These plants are very sensitive to cooler temps, as mine grow best only when temps are in the 80s day and 70s night.

You mentioned using Ortho systemic and, depending upon when you sprayed as well as the rate used, that might have been a factor in causing the problem. In the heat of summer, spraying of any kind should be done only very early in the morning, just prior to sunup, or near sundown in the evening. Plants vary in their sensitivity to chemical pesticides also.

Hope this helps!

LariAnn
Aroidia Research

Here is a link that might be useful: Blackstem Mac

Thanks erf & Lariann, I'm thinking maybe a combo of too much fertilizer and ortho together. It sure wouldn't be from too little fertilizer. I will give it a break from fert. for two or three months, maybe even until spring and see how that goes.