My Euphorbia lactea 'White Ghost' has spots

[WayneByerly]

My Euphorbia lactea 'White Ghost' resides outside in the greenhouse, where temperatures, even with the assistance of an exhaust fan, rise as high as 100 degrees Fahrenheit. A few minutes ago, I was in the greenhouse doing a small amount of watering when I noticed that it had some spots of discoloration on it. My first thought was sunburn, but I have sprayed everything in the greenhouse with a multi-purpose insecticide/anti-fungal (sulfur-based), and wondered if that MIGHT be contributory.

This is the worst spot ...

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This is what makes me think sunburn

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There are a few small places that look like this

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And this place, at the top, I think MIGHT be normal exposed-to-the-bright-sun coloration, but decided to include it here anyway, in case it helps.

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Can I get some opinions about what this might be, and what I might do to effect a cure if that is what is needed?