Squash, cucumbers and melon belong to the cucurbit family. They produce separate male and female flowers on the same plant. Bees are necessary to pollinate the female flowers. Don't use pesticides during the day when bees are about. A fungicide spray may also be necessary during periods of wet weather.
Nematodes are microscopic roundworms that live in the soil and attack plant roots.
The chemicals that were used in the soil to control nematodes are no longer available, but there are several other choices. Many vegetable varieties have a build-in resistance to some of the nematodes. Also adding organic matter such as compost or manures to the soil helps to keep down nematode populations. Another method of nematode control is soil solarization. Some are evergreen, others lose their leaves in the fall.