Ask your compost source what their source was. If they get it from a place that grows mushrooms, it may have been mushroom compost, which is SPENT/USED UP compost, and it has virtually no nutrients in it at all. There is nothing wrong with incorporating compost into your sandy soil, it can only help it. Your plants need the minerals in that soil, as well as the nutrients in the compost (if it has any). But why use compost when you're pouring on the chemical fertilizers? The chems mostly kill the micro-organisms in the soil/compost that break down the nutrients to feed the plants, so what's the point? And most of those fertilizers salts only contain Nitrogen, Phosphorus and Potassium. There are a bunch of other nutrients needed, but the chemical companies are only wired in to NPK. You're asking what could be lacking, but you don't want to get a soil test... HUH? I'm sure you waste your time and money on a lot of stuff, so include a soil test. $10 or so can get you a lot of useful info. If you've got a serious deficiency (or excess), you can keep doing what you're doing, year after year, and still get the same results. Einstein said that is the definition of insanity. Many people avoid getting soil tests because they seem scary. What do you do once you get the results? Most results have suggestions right with the numbers. If you still don't understand, CALL THEM and ask. These people sit in a lab all day and are probably THRILLED to talk to a live person asking questions. You're probably making their day. For Lexington, SC, here's the info on your local Cooperative Extension Service. If they give you choices, ask for the Master Gardener, then ask him/her who does soil tests in your area. Ask how to collect a sample properly (it makes a difference). The Master Gardener also knows about plants, and is sitting there waiting for you to ask something so they can show you how they're not wasting your tax dollars. But get the soil test. You're going to feel pretty silly if it's a quick, cheap, easy fix, aren't you? Well, JOIN THE CLUB! LEXINGTON COOPERATIVE EXTENSION SERVICE 605 West Main St., Ste. 109 Lexington, S.C. 29072 Phone: 803-359-8515 Office Hours: Monday - Friday, 8:30 a.m.-5:00 p.m. Sue (been there, done that) Here is a link that might be useful: Required soil nutrients

Mildew at beginning is white. Far too little info for diagnosis. Dan

"Daily watering" is almost always over-watering. Add rain and it definitely becomes too much water. But in this case i suspect lack of any nutrients is the main issue. They need to be fed. All plants need to be fed something and in containers it needs to be fed regularly.. I would normally recommend one of the many organic liquid fertilizers available but in order to recover from the excess water, a granular one would work better this time. There are probably 35-40 different organic granular fertilizers available so it all depends on what you can find locally. Any of the big box stores like Walmart, Home depot, Lowe's etc sell them, so do most nurseries. Follow the label directions for amount and frequency of application. Dave.

Link below is to several discussions of the same question that the search pulls up and will answer your question. Looks like you have both powdery and downey mildew problems and both are discussed in the link. Dave Here is a link that might be useful: Squash leaves turn yellow discussions