I also have a problem with yellow leaves at the bottom that turn brown. That's from all the rain......................
but just incase it is little bugs.............wait for the sun to pass over and mix up 1 teasp of liquid hand soap and 1 qt water and spray...............you can repeat this and it is safe to use on other plants liek roccoli & cauliflower..........they are getting tiny black beetles. If tht happens wash them out when you cut them on a slant with 1/2 cup salt in very cold water.....wash again............3rd time in just cold water then steam.