http://www.saferbrand.com/articles/leaves-foliage-problemsSo let me pick y'alls brain a bit.......
What would cause the leaves of the plant to start turing yellow?
An what type of fertilizer are you guys using on your garden?
6. NITROGEN DEFICIENCY
SYMPTOMS: Lower leaves look yellow and become soft and curl inward, then turn brown and crispy before falling off completely.
CAUSE: Nitrogen deficiency always affects the oldest (lowest) leaves first, because when new leaves aren't getting enough of the nutrient to sustain their growth, the plant redirects it from the existing leaves. As plants get close to harvest, it's normal for them to show signs of a nitrogen deficiency. At that stage, you want the plant to direct all of its energy into the fruit or flowers rather than growing new leaves. That's why "bloom" stage nutrient formulas are relatively low in nitrogen.
QUICK FIX: Give plants in their vegetative growth stage a high-nitrogen nutrient formula. Fertilizers made with fish tankage (decomposing processing waste) deliver a strong dose of nitrogen in a form that plants absorb and use quickly.
PREVENTION: A regular dose of an amino-acid supplement in your feeding program ensures that your plants always have access to all the nitrogen they need. Amino acids are building blocks of protein that help plants take up and use nitrogen.
Or it could be heat , compacted soil or potassium or phosphorous deficiency . Give them some fish emulsion