I have noticed that several of my cucumbers are drying up and turning white before they mature. Is this some type of fungus or insect? I have treated these plant once with Bt and once with spinosad for cucumber bettles. What can I treat this with?
The most likely cause of your cucumber fruit problem is a lack of pollination. If there are not bees working the flowers to transfer pollen from the male blooms to the female blooms the fruit won't set and develop normally but will abort instead. The problem can be due to a lack of bees or due to inclimate weather conditions which prevent the honeybees from getting out and doing their work.
If you are using insecticides on the plants or on nearby flowering plants that kill bees this can contribute to the problem. Nearby neighbors spraying their flowers can also be causing a decline in the bee population around your neighborhood. B.t. is not toxic to bees. Spinosad is highly toxic to bees if sprayed on them or if they encounter recently sprayed foliage or flowers. However, once it has dried completely the danger of toxicity has been shown to be negligible in research trials. It may also be that your plants are located where the bees have just not yet discovered them. In the absence of bees you can use a very small artist's type paintbrush to gently brush the male blooms and then the female blooms to transfer pollen manually and do the work of the bees!