As soon as cucumber-family crops become available, cucumber beetles find them and begin to feed. This is your cue to bring out the artillery; row covers and kaolin clay should be your first line of defense.
This article is part of our Organic Pest Control Series, which includes articles on attracting beneficial insects, controlling specific garden pests, and using organic pesticides.
The most common of cucumber pests are black and yellow cucumber beetles, including striped cucumber beetles, spotted cucumber beetles, and similar species. In addition to chewing on leaves, flowers and fruit of cucumber, melon and squash, cucumber beetles transmit a disease called bacterial wilt, which causes plants to wilt and die, and may spread several viruses.
Organic controls for cucumber beetles include handpicking, excluding them with row cover barriers, or using kaolin clay to disguise plants. You also can make cucumber beetle traps and use companion planting to deter these cucumber pests. Cucumber beetles are found throughout North America, and more than one species may be found in the same garden.
These two types of cucumber beetles are frequent pests of cucumber family crops:
Striped cucumber beetles (Acalymma vittatum) are less than a quarter inch long, with three black stripes down their wing covers. The slightly larger Western striped cucumber beetle (A. trivittatum) is more common west of the Mississippi River. The little beetles fly away when disturbed, and are common visitors to all members of the cucumber family, including cucumbers, melons, gourd and squash.
The spotted cucumber beetle (Diabrotica undecimpunctata) is about one-third inch long, and is bright greenish-yellow with 12 black spots on its wing covers. The slightly smaller Western spotted cucumber beetle (Diabrotica undecimpunctata undecimpunctata) is found in the far West, from Oregon to Arizona. Spotted cucumber beetles emerge later in spring than striped cucumber beetles.
When seedlings are young, cucumber beetles tend to feed on the stems and leaf undersides, rasping away at tender tissues. Mated adults lay eggs at the base of cucumber-family plants, and the larvae weaken plants by feeding on their roots. Later in spring, when plants begin to flower, numerous beetles may be found eating flowers and tender young fruits.
These cucumber beetles often spread bacterial wilt, which causes infected plants to die, one branch at a time. After a plant is infected, nothing can be done to stop the progress of the disease, which clogs up the plants’ vascular systems to the point where they cannot function.
Cucumber beetles overwinter in woods and low vegetation. When temperatures reach the mid-50s in spring, spotted cucumber beetles emerge and begin feeding on the pollen, petals and fruit of roses and various perennial flowers. As soon as cucumber-family crops become available, the beetles find them and begin to feed. Spotted cucumber beetles often appear later, especially in northern areas. Cucumber beetles are strong fliers, and also travel northward on strong southerly winds.
Mated females lay eggs near the base of host plants. Striped cucumber beetles may lay 1,500 eggs in their two-month lifespan; spotted cucumber beetles lay 200 to 300 eggs per female. The cucumber beetle life cycle takes four to six weeks, and goes faster in warm weather. The tiny white larvae begin eating plant roots as soon as they hatch, though vigorous plants continue to grow despite this feeding. The larvae change into pupae after feeding for about two weeks. It is not unusual for new waves of adult cucumber beetles to appear every three weeks or so through the first half of summer.
Numerous natural predators attack cucumber beetles at various life stages, but they seldom provide adequate control. General predators include birds, frogs and various wasps and flies, including the small tachinid fly. Below ground, nematodes and fungi claim victims among cucumber beetle larvae.
Overall insect balancing is important managing these cucumber pests. An abundance of several repellent plants (radish, nasturtium and tansy) should be grown nearby, or you can use the cut foliage from radish, tansy or carrot as a pest-repellent mulch. At the same time, companion plantings of buckwheat, catnip or borage grown within a few yards will attract beneficial insects to the area.
The top-rated control among MOTHER EARTH NEWS readers is the use of floating row covers, which are installed over plants the day they are set out. In addition, several field trials on organic farms have shown that delaying spring planting by two weeks helps to avoid natural spikes in cucumber beetle populations. Row covers must be removed to admit pollinators when the plants reach the flowering stage, and again a delay of seven to 10 days can enhance season-long cucumber beetle control without reducing yields. A little extra time under row covers works out well with cucumber-family crops, which tend to set their best fruits from their second sets of flowers.
In the absence of row covers, young plants can be defended surprisingly well by spraying them with kaolin clay, and by placing a flat piece of aluminum foil beneath seedlings, with a slit made to accommodate the main stem. Cucumber beetles do not like to feed in this highly reflective environment.
Cucumber beetles are easily trapped in yellow sticky traps, which can be purchased or made from small pieces of wood painted bright yellow/orange (the color of squash blossoms), covered with Tangle-Trap and mounted on stakes just above foliage level. In a home garden, one of the most effective uses of sticky traps is in late spring, before you plant your crop. To create an irresistible trap, grow several seedlings of ‘Blue Hubbard’ squash or ‘Big Max’ pumpkin — two of many varieties known to attract cucumber beetles — in quart containers. When daytime temperatures rise above 60 degrees Fahrenheit, sink the containers in the ground around the outside of your garden, and install a yellow sticky trap just above the foliage of each trap plant. Handpick cucumber beetles found on the plants. After three weeks, pull and compost the trap crop, shaking any beetles present into a bucket of soapy water. This procedure will set back the first generation of cucumber beetles.
Handpicking cucumber beetles is often futile during midday, when they quickly fly to cover. You will be more successful in the morning or evening. In the morning, place a piece of cardboard (or open pizza box) beneath plants to catch beetles that drop to the ground. Coat the fingertips of a yellow rubber glove with petroleum jelly to make it easier to collect beetles clustered in flowers. When handpicking in the evening, it may help to wear a yellow shirt. Instead of flying away, beetles will fly to your sleeve where they are easily knocked into a pail of soapy water.
If you have chickens, you can use your tamest hens to do a supervised flash-forage in plants infested with cucumber beetles. About an hour before the chickens normally go inside to roost, lead a few chickens to the problem area, enclosing them in a portable pen if necessary to protect nearby plantings. Remove the chickens after 30 minutes of feeding.
Managing these cucumber pests requires constant attention, but it is time well spent. Several dangerous systemic pesticides are routinely used in conventionally grown cucumbers and melons, so implementing organic controls for cucumber beetles is worth the time and effort.
Experiment with companion plants and repellent mulches to keep cucumber beetles manageable in late summer, after row covers are removed.
When it’s time to pull up infested plants, gently move them onto a tarp and drag it to your compost pile or chicken yard on a cool morning to keep the beetles from flying away. You also can use chickens to rid soil of cucumber beetle larvae by parking a portable pen over the bed after the plants are harvested.
Cucumbers that lack the bitter gene are naturally non-preferred by cucumber beetles, so you can prevent problems by growing resistant varieties such as ‘Little Leaf’ picking cucumber and most “burpless” slicing cucumbers. Unfortunately, comparable levels of resistance are not available in melons or winter squash.