Many things aside from urea based fertilizers sprayed on leaves can lead to yellowing of foliage - as could the three possibilities mentioned in the first response. It's such a HUGE leap to suggest it might be one of the perchlorate toxins. (The sky is falling.) While we have to allow there is a minute possibility, it's thousands of times more likely it's not perchlorate. First, contaminated fertilizer is not considered to be a major source of perchlorate. Chilean fertilizer, the only known source of perchlorate in fertilizer, currently makes up only 1/10 of 1 percent (.001) of the U.S. fertilizer market. In addition, the company that distributes Chilean saltpeter has made processing modifications which has greatly decreased the concentration of perchlorate in the final product sold. After many studies, there is now a consensus among researchers from the EPA, the fertilizer industry, and other federal and state laboratories that fertilizers currently being used are negligible contributors to perchlorate toxicity. Al

Just looks like salt burn from a build-up of salts from your fertilizer combined with a heavy slow draining potting mix. I am not a container guy; but some here will give you better advice. BTW your tree looks fine... don't stress... few leaves are perfect.

I don't know if this is the case with your trees, but I've had that happen to a couple of my Meyer lemons when I've been lax about fertilizing. They tend to need fertilizing at about twice the frequency as my other citrus. Maybe your Eureka also needs a bit more food than the other citrus. Also, I've not found the yellow leaves to really green up again, at least not much. Usually what happens when they get to that point is they tend to drop the yellow leaves over time and replace them with new leaves. If I've been good about fertilizing, the new ones will be nice and green. So I think if you keep up the better care, the next flush of leaves should be much greener. This post was edited by BarbJP on Thu, Jun 19, 14 at 13:42

When I made the mix I added about 1 tbsp of Lime per gallon. I will do a soil PH test tomorrow. I use tap water, will check its PH as well. I took a closer look and found some small long light-colored bugs that move pretty fast. Maybe thrips? I think I found a few mites as well. Will try to take a picture tomorrow. So would a simple soap/neem oil spray take care of these bugs?