One of the most prolific and delicious summer crops is squash--yellow crookneck squash, yellow summer squash, pattypan squash (sometimes called scallop squash), and the ever-present zucchini. They are all justly famous for producing huge quantities of fruit--yes, they are fruit, even though we treat them as vegetables--and they are easy to grow. If you plan to grow summer squash organically, you will have to work to protect the plants from pests and disease. The most important of these are cucumber beetles, squash bugs, bacterial wilt and downy mildew.
Preparation, Prevention and Treatment
Summer squash like full sun and rich soil. Do a soil test to find out what your garden needs--your county cooperative extension office, listed in the local phone book, will help you find a testing laboratory. Amend the soil as recommended by the soil report.
Start summer squash from seed--just follow the instructions on the seed packet and sow right in the garden. The advantage of starting from seed is that seed catalogs offer a wide choice of varieties. Many nurseries and garden centers sell transplants (young plants) of only the most popular varieties.
Avoid problems with many insects and the diseases they carry by searching for varieties that offer some resistance. Heirloom varieties have little or no resistance, but many hybrids have been bred to at least tolerate diseases without succumbing.
Install floating row covers to protect summer squash plants from cucumber beetles. Put row covers in place as soon as the transplants go into the ground or the first seedlings appear. There are two kinds of yellow-and-black cucumber beetle, striped and spotted. In addition to feeding damage, they are responsible for spreading bacterial wilt, which causes the whole plant to collapse and die.
Clean up leaf trash at the end of the growing season to reduce damage from squash bugs. Adult squash bugs shelter in leaf debris over the winter and may re-infest your new crop in the spring. Young squash bugs, called nymphs, feed on leaves. As the squash bug feeds by sucking the plant's juices, it injects a substance that causes wilting. Vines and leaves turn black and brittle, and all or most of the plant will die.
Row covers will ward off these pest as well. Destroy egg masses on the underside of leaves by squishing them (wear gloves if you're squeamish), or by brushing them into a container of soapy water that you flush down the toilet.
Spray neem oil--an organic insecticide and fungicide--on any downy mildew as soon as it is detected. An alternative is to neem oil is to thoroughly wet affected plants with a spray made of 1 heaping tablespoon of baking soda in a gallon of water, mixed with a ½ tsp. of dishwashing liquid soap or insecticidal soap.
The first symptoms of downy mildew are pale green areas on the upper leaf surfaces, which change to yellow angular spots. A fine white downy growth then appears on the lower leaf surface.