Some kind of mechanical damage - just trim the tip of the leaf. The best - Fiskars pinking shears Deckle - the brown handle ones. Make a new rounded tip look as natural as possible. http://www.amazon.com/Fiskars-Deckle-Paper-Scissor-12-92187897/dp/B000BDH9KU For Streptocarpus - any kind of mishap - the tips of the leaves suffer - not enough water, too much water. They are kind of expendable in nature - in a dry season Streps sacrifice the tips of the leaves to decrease the water consumption. IMHO - the damage is cosmetic and not the cause to worry.

The plastic is a weed mat. I wasn't watering regularly - but after I first planted it, it got watered daily for 20 minutes by my lawn sprinkler. I thought maybe that was too much water, so I turned off that zone. How often/much should I water it? Do these leaves look like they are being underwatered, or perhaps overwatered?

I use a product called Infuse. It was the old Monterey Fungi Fighter (MFF). You spray it every 21 days, no more than 4 times a year. I do not spray if the peaches are going to be ripe in the next 30 days. When the peaches are harvested I quit spraying. If after 21 days and no rain is forecast, I will wait until the day before ( or after if an unexpected rain comes). The first year or 2 you may get by without any spraying. In dryer climates you can get by with less spraying. I use to live in a drier climate and brown rot would get some of the fruit but not all. Plum cucurlio is another pest that can hurt a crop. It lays its eggs and larvae eats the peach. Scab and scale can also pose a problem. I do use a dormant oil spray and all copper in winter. I live in a very humid area and it can be difficult to grow stone fruit.

Those are definitely new branches, I might pick off the small lemons to let it direct the energy to recovery, especially with the mites. Be careful with the dawn dish soap as it can damage the leaves. If they're that bad, I would probably be inclined to do a full plant soak if the tree is small enough the next time it needs to be watered. Just enclose the pot in a mesh to keep in the soil and submerge the whole thing, pot, leaves, and all for at least 45 minutes to an hour. Then pull it up and let it drain. I don't do that often, or recommend it as a first pass, but as a last resort it does work well. I had a brush cherry that got infested with the red spidermite that lives outside in my area and it was the only thing that killed them all. I have not had any come back since doing so. Adding a single drop of dawn to a bathtub full of water can help kill any that might make it to the edge of the tub, but I wouldn't recommend more than that.