overwatering could do it. Brown crispy edges for houseplants are usually overwatering , underwatering or overfertilizing.

Post this one on annuals. There is an explanation but it's escaping me at the moment.

It does look like nutrient deficiencies, which have the twin benefits of being slow and correctable. The interveinal yellowing, where the veins stay green, is more likely magnesium than iron... but the real way to tell is where it's happening. Magnesium starts at the bottom, iron starts at the top. The pictures make me guess it's the former; you could mix up a tablespoon or so of epsom salts in a spray bottle and spritz down the plants, and see whether the leaves color up again. The yellow leaves probably are nitrogen, and a light foliar feed is very unlikely to give them too much nitrogen. Spray them down with fish emulsion and see if they green up. If they do, start giving them light doses of nitrogen regularly. Clay soil can be very rich in just about everything... except nitrogen; your amendments weren't with anything that would boost that N level for any length of time, particularly if the chicken manure was old. Best of luck -- the plants should be fine once you can give them what they need. --Alison

Very possible that the little black fellows are aphids. If so, they suck plant sap and will weaken the plant. Rub them off, or use direct hits of insecticidal soap, diluted according to label directions. In both cases, repeat as needed. I'm not able to see enough detail to suggest what the white might be.