After some investigation, I finally understand that what I've been buying in the grocery store for years - what is labelled "yam" is actually "sweet-potato-yam" (Ipomoea batatas), with reddish skin and orange flesh. This is my third year at attempting to find a way to grow these things in White Rock, BC and this is my closest yet. Things were looking good up until a few weeks ago and then I notice some brown spotting on the tips and edges of the leaves on one plant; now it has spread to all three plants in the same pot. I can not figure out the problem. I was growing lettuce at the same time in this pot, which grew beautiful heads and then started to rot. I also have Alyssum growing in the pot with them. When I pulled the last of the lettuce, I dug down to see if maybe the roots were rotting but the soil was actually bone dry about 3-4 inches down. That made me think that maybe the sweet potatoes were not getting enough water, so I increased the water and added a little rock phosphorus on the soil surface but still no change; they just keep getting yellower and now look like they are starting to wilt a little in this heat. I dug down just a few days ago to search for any insects - nothing. I have potatoes growing in a pot right next to them (which looks healthy) and another pot next to the potatoes with pickling cucumbers (which are being sucked dry by thrips), but I can see no thrips or other insects on the leaves of the sweet potato plants. Does anyone recognize what I'm missing?
It looks like a little bit of natural sunburn to me, nothing at all to worry about! Last time I grew camotes/yams/sweet potatoes I saw that after days that had been brutally sunny after nighttime rains, so water-drops were focussing the light and burning the leaves a little. I still got a great harvest, though!
SOLVED: Sweet Potato - Brown Leaf Tips -- Leafhopper Burn First off, I need to correct my original posting. I was misidentifying the insects on the potatoes and cucumbers as thrips. It turns out that they were actually leafhoppers (2-3 mm in length) as seen in the new images. I now know that the problem with the sweet potatoes is leafhopper burn. The difficulty was that they were very difficult to find at first; I looked probably 10 times at the plant before I started to actually see one or two on a few leaves. They are very destructive in the sense that they wreck the foliage of the plant, causing the leaves to brown on the edges and turn yellow. I have not been able to explain the curious tiny puncture-like marks on the leaves themselves, so I must assume they are caused by the same insect. I only noticed these leafhoppers after taking a flash-light at night to see if it was a night feeder. My guess is that the leafhoppers were moving down off the leaves by day and back up at night. On a cloudy day I finally noticed them on the leaves.
