tomato leaves yellowing badly

my tomato plants are yellowing badly - not just the old underbelly leaves but all over. Looks like there might be tiny black winged critters on the leaves. looking for an organic solution. help!?

Again this season, after planting in April and 2 great months of growth and fruiting on the cucumbers and squash, powdery mildew has attacked! I watched it spread for a few days (cutting the most infected part out) and then finally pulled them all out. I am just perplexed as to why...I water every other day in the early morning, the plants seemed healthy and we had tons of squash. P.S. I ran out and bought 2 new zucchini squash and more cucumbers, and I'm hoping it isn't laying in wait. Any suggestions?