I think the problem could be you're in zone 8b and growing zucchini in a bucket. The plant is most likely stressed from all the heat to the rootzone from the sun hitting the outside of the bucket. Don't get me wrong squash and zucchini like heat but not so much on the roots. Next year plant some in a raised bed or in a garden plot and they will do much better. Stressed & diseased plants are what pests are mainly interested in. it's all natures way of getting rid of the bad to make room for the good. So expect more bug damage if the problem is not fixed. I also noticed a bag in the bucket do you have a way for the water to freely drain from the bucket? The plant could be saying it's drowning and needs air to it's roots. I'm with Elaine on the yellow ball it's probably just a fertilizer prill. Good luck and keep us updated.