This is a question I get all the time. “Every year in the middle of the summer, I get hit with aphids which attack my squash and string beans. What can I use to control them”?
Aphids can not only wipe out some of your vegetable plants, but they are very bad about spreading disease to other plants in your garden. Here are a few suggestions. First, keep on the lookout. They can spread and multiply quickly, but they tend to travel in thick groupings so they are not too hard to spot if you are looking. The first line of defense should be a stiff spray of water. Believe it or not, this is very effective. They are blasted off and become a tasty meal for other beneficial insects or birds that might be nearby. Just be careful that the water stream is not so strong that is damages your plants.
Next, be sure to have lots of lady beetles and lacewings around. They are both crazy about aphids. As long as there is a food source around, like aphids, the beneficial bugs will have no reason to leave. You can even order these insects in catalogues and online if you don’t have any in your garden. Try The Beneficial Insect Company.
If it is practical for you to do so, you can also use a barrier, such as a floating row cover during part or all of the growth cycle. However, this would not be practical for string beans or squash.
Then, if your problem is not going away, you may need to resort to organic sprays. My first choice would be insecticidal soaps. Note that these will also kill beneficial insects. Use sparingly. These soaps have varying degrees of toxic properties to plants. Apply either in the cool of the evening or early in the morning for the least plant damage. You can buy or make your own. Just add from one teaspoon to several tablespoons of liquid soap, such as Ivory to each gallon of water. Start with the lesser concentration first and see if you need to strengthen it. Avoid using detergents. Keep it as simple and pure as possible. But, if you want to boost the effectiveness, add a tablespoon or two of cooking oil as well.
Finally, here is a recipe for an effective, organic all-purpose insecticide:
1 bulb of garlic
1 small onion
1 tablespoon cayenne (red) pepper
2 tablespoons liquid soap
1 quart water
Finely chop onion and garlic; mix with tap water; add cayenne pepper; let sit for one hour, then add soap. Mix well. When foam subsides, strain into spray bottle. Keep refrigerated. Good for 1-2 weeks.