I have 2 pickling cucumber plants (I can't remember the name of the variety), and one is fine, but the other was doing fine until recently, but now the lower leaves are yellow and the recently produced cuke is yellow, though it is large enough that it should be ripe. I have had some aphids on the nearby tomatoes, but couldn't find any on the cucumber plants. I sprayed with insecticidal soap and put kelp fertilizer around the soil, so I hope that will help. What do you think it could be?