I left my Aglaonema firecracker with my neighbor for about a month while I was away. When I came back, I found that one of the leaves had completely turned yellow and a brown spot (slightly translucent) was on it. One of the tips of the top leaf also went brown and translucent, and a tiny stem with two leaves completely died. My neighbor had no experience taking care of plants, so I did write out a watering schedule, but it was on the conservative side. However, I had to extend my time away, and so there were no schedule for her to follow for the last two weeks. She also thought it was a good idea to periodically “sun” the plant and had them in full afternoon sunlight in her yard. I’ve never had a problem with my Aglaonema before leaving them with her, and I’m trying to figure out if the leaf issues are from over watering or from under watering and sunburn. I tried looking it up, but I can’t find a good answer. I’ve attached the pictures, and the rest of the plant looks healthy. I really really appreciate any help!
Your Aglaonema is completely stressed out from the recent, frequent changes in it's environment and light levels.
The possible short-term overwatering could have contributed to the plant's stress but is not likely to be the main cause of the problems. Overwatering is more of a long-term problem. However, I was a little concerned when you mentioned a 'watering schedule'. Watering plants should only be done as needed, not on a schedule. Also the 'watering schedule' you left for your neighbor would have been completely useless since the plant was in a different environment (especially different humidity and light), which would have changed it's watering needs. In general, the top 1-2 inches of soil should be allowed to get dry to the touch between watering.
Aglaonema is a low light plant native to the floor of tropical forests. In their native environment, they receive dappled sunlight through the forest canopy, so the direct sunlight didn't do your plant any favors.
Your plant still looks very healthy. Just give it proper care and some time and it should recover completely from it's adventure at your neighbor's house.