Cucumber beetles are one fourth inch long with a black head.

Types:

Striped cucumber beetle has yellow wing covers with three black stripes running the length of its body.

Spotted cucumber beetle has a yellow-green body with twelve black spots on its back.

The cucumber beetles Diabrotica balteata carry bacterial diseases such as cucumber wilt. It also feeds on the blooms of a variety of ornamental flowers.

It is especially important on many fall-grown crops. In addition to leaf damage, it can cause serious below-ground damage as a worm.

The banded cucumber beetle has become a major pest on sweet potatoes. The larval stage causes greatest damage to sweet potatoes, although the adult may cause considerable damage above the ground to cucurbits.

Cucumber beetles are present throughout the United States and cause serious damage to cucurbit crops. Overwintering adult insects cause feeding damage on young plants, larvae in the soil feed on plant roots and second-generation adults cause feeding damage on plant leaves, blossoms and fruits. Adult insects transmit bacterial wilt and squash mosaic virus. Organic and biorational integrated pest management measures include delayed planting, trap crops, floating row covers, parasitic organisms and botanical pesticides. Field scouting or yellow sticky traps can monitor insect populations.

The sap of a healthy plant is watery and will not exhibit stringing and bacterial oozing (Snover, 1999).

Bacterial wilt is most severe on cantaloupe and cucumber, less damaging on squash and pumpkin and rarely affects established watermelon plants. Wilt-resistant varieties are available for some cucurbits, but still lacking for others. For example, County Fair 83 and Saladin are resistant varieties of cucumber, but resistant varieties of muskmelon are not developed.

Squash mosaic virus

The western striped cucumber beetle and the spotted cucumber beetle are alternate vectors for another disease: squash mosaic virus. Aphid insects are the primary vector. While the virus is seed-borne, the incidence of this disease is enhanced through cucumber beetle feeding and transmission. Squashes and melons are particularly susceptible to this disease because of a greater occurrence of infected seeds in these species.

The symptoms of squash mosaic virus vary according to host species and cultivar, but include mosaic patterns, leaf mottling, ring spots, blisters and fruit deformation (Provvidenti and Haudenshield, 1996). Besides the use of certified virus-free seeds, control measures are aimed at minimizing the presence of cucumber beetles (Provvidenti and Haudenshield, 1996 and Davis et al., 1999).

Organic control measures

Growers can use homemade yellow sticky traps or purchase commercial yellow sticky cards for detection of cucumber beetles. Homemade and commercial insect attractants can enhance the trapping effect. Cucumber beetles and most insects are attracted to the color yellow.

To make a simple sticky trap, coat an 8-ounce yellow plastic cup with insect glue, like commercially available Stickum Special or Tangle-Trap. Invert the cup and secure it on a 2-foot wooden stake (Levine and Metcalf, 1988). Eugenol, a naturally occurring insect attractant found in clove oil (82 to 87 percent eugenol), allspice oil (65 to 75 percent eugenol) and bay oil (40 to 45 percent eugenol), lures diabroticine beetles (Peet, 2001 and The Scientific Community on Cosmetic and Non-food Products, 2000). Cinnamaldehyde, found in cassia oil and cinnamon bark oil, functions as an insect attractant and natural cucumber beetle bait (Environmental Protection Agency, 2007). Attach a cotton swab soaked in these aromatic oils to increase the sticky trap’s trapping effect.

Integrated pest management suppliers sell rectangular yellow sticky cards imprinted with grid patterns for detection of diabroticine beetles. These include the Pherocon AM trap card from Trece, Inc., the Intercept AM trap card from Advanced Pheromone Technologies, Inc., the ISCA yellow sticky card from ISCA Technologies, Inc. and the Olson yellow sticky card from Olson Products, Inc. These products are listed under the Products section of Resources at the end of this publication.

Cultural practices are land and crop management practices that affect the reproduction of pests or the time and level of exposure crops have to pests. Cultural practices that can protect against cucumber beetles include:

Crop rotation within a field, a well-known pest management tool for disease control, is ineffective to control cucumber beetles since the beetles migrate from areas surrounding the fields. Since these insects survive on a number of wild hosts, the removal of alternative hosts from the farm would be difficult and ineffective because of immigration. A two-year study in Massachusetts compared the effectiveness of synthetic and biorational insecticides on the control of striped cucumber beetles and the occurrence of bacterial wilt in direct-seeded and transplanted pumpkin using the susceptible Merlin variety. Results of the trial indicate the need for long-distance crop rotation for insecticides to be most effective. Rotation to an adjacent field close to the pervious year’s cucurbits did not reduce beetle numbers (Andenmatten et al., 2002).

Delayed planting is an effective pest management strategy in some regions and cropping systems. Growers can avoid the first generation of cucumber beetles by keeping fields cucurbit-free until the establishment of summer cucurbits like cucumbers, pumpkins and squash intended for fall harvest. Delayed planting is an especially useful cultural strategy in cucurbits because this technique also bypasses first-generation squash bugs. However, this method is not relevant for plantings of early-market spring cucurbits like cucumbers, squash and melons or in regions with short growing seasons.

Floating row covers physically exclude both cucumber beetles and squash bugs during the seedling stage of plant growth. Providing a bug- and beetle-free period allows the plants to thrive and develop a mass of leaf and vine growth by the time row covers are removed at bloom. At this stage of vegetative growth, plants can withstand moderate pest attacks. In regions with established cucumber beetle populations, row covers can make the difference between a harvestable crop and crop failure. Row covers are removed at the onset of flowering to allow for bee pollination and to release vine growth. Applying botanical and biorational pesticides provides season-long protection, depending on location and pest pressure, after row covers are removed.

Weed control is a special consideration when using floating row covers over cucurbit seedlings in bare, moist soil. Row covers create a favorable environment for the germination and growth of weeds. Periodic removal of row covers for mechanical cultivation to stir the soil and disrupt weed seedlings is not very practical. Row covers are normally used for the first 30 to 40 days of vine growth until the onset of flowering. This corresponds to the critical weed-free period for cucurbit plant growth, when weeds should be controlled and excluded as much as possible. In organic production, row covers are commonly used in combination with weed-suppressive mulches like plastic mulch, geotextile weed barriers, straw, hay and paper.

Mulching can deter cucumber beetles from laying eggs in the ground near plant stems. Mulches can also function as a barrier to larval migration and feeding on fruits (Cranshaw, 1998 and Olkowski, 2000). Tunneling larvae need moist soil to damage ripening fruit. Limiting irrigation at this time can minimize damage (Cranshaw, 1998). Mulches are known to harbor squash bugs, however, and mulches do not deter beetles from feeding on leaves, flowers and fruits of cucurbits.

Researchers at Virginia Tech showed a dramatic reduction in the occurrence of striped cucumber beetles in a Meteor cucumber crop and similar reductions in both striped and spotted cucumber beetles in a General Patton squash crop by comparing aluminum-coated and aluminum-striped plastic mulches to black plastic mulch (Caldwell and Clarke, 1998). On various sampling dates, yellow sticky traps located next to the aluminum-coated plastic mulches had two, four and six times less cucumber beetles than stick traps located next to black plastic mulch. Researches, after correlating the number of beetles found on sticky traps to the integrated pest management threshold, concluded that reflective mulches reduced cucumber beetle populations to below treatment levels.

The Virginia Tech research article contains a brief economic comparison between costs of production and prices received for organic squash versus conventional squash gown on reflective mulches. Researchers emphasized the ability of reflective mulches to reduce bacterial wilt and virus transmission by cucumber beetles and aphids.

Cultivation and residue removal can help reduce overwintering populations of cucumber beetles. Cornell University research suggests deep tillage and clean cultivation following harvest (Petzoldt, 2008). However, an organic farming sequence that shreds crop residues, incorporates fall-applied compost or manure and establishes a winter cover crop will facilitate decomposition of above- and below-ground residues.

Insect vacuuming is a form of pneumatic insect control that dislodges insects from plants through high-velocity air turbulence and suction. Large, mechanized bug vacs gained notoriety in the 1980s for control of the lygus bug in California strawberry fields. Hand-held and backpack vacuuming equipment is available through integrated pest management suppliers. Market farms use the equipment to collect beneficial insects and control pest insects in combination with perimeter trap cropping.

The D-Vac, a commercially available vacuum, evolved from insect sampling research by the biological control pioneer Everett Dietrick (Dietrick et al., 1995). Insect vacuuming combined with perimeter trap crops is an appealing non-chemical control strategy. Researchers have employed this dual technique in attempts to control flea beetles in brassica fields (Smith, 2000). This dual technique has also been suggested for mass trapping of cucumber beetles followed by vacuuming as a pest reduction strategy and as an alternative to insecticide applications (Olkowski, 2000). The next section explains how pheromones attract cucumber beetles to perimeter trap crops where beetles congregate in great numbers. The efficacy of this dual technique for control of cucumber beetles is not verified in field trials and is mentioned here as an experimental approach that organic market farmers may wish to explore.

Trap crops, trap baits and sticky traps, if positioned correctly, can intercept beetles through the use of smell, color and pheromonal attraction.

Trap crops release chemicals known as kairomones, which are highly attractive to insects. Kairomones produced by cucurbits include cucurbitacin, the characteristic bitter substance in cucurbitacae that stimulates compulsive feeding behavior in diabroticine beetles, and a mixture of floral volatiles that lure adult beetles from some distance.

Cucurbit trap crops are designed to lure and concentrate cucumber beetles where control measures using insecticides or vacuuming can be focused, reducing the need for field-scale insecticide applications.

Pioneering research in the 1970s and 1980s by Robert L. Metcalf (Ferguson et al., 1979) in Illinois, as well as more recent research in Texas, Oklahoma, Maine, Connecticut and Virginia, shows that certain species and varieties of cucurbits can serve as trap crops next to larger fields of cucurbits (Stroup, 1998, Suzkiw, 1997, Radin and Drummond, 1994, Boucher and Durgy, 2004 and Caldwell and Stockton, 1998). Diabroticine beetles preferentially congregate, feed and mate on these kairomone-effusive trap crops. Table 1 ranks the feeding preference of cucumber beetle on different varieties of cucurbits.

Researchers elsewhere used Lemondrop summer squash, Peto 391 summer squash, NK530 squash, Blue Hubbard squash and Turk's Turban squash. However, experience shows that cucurbit varieties highly susceptible to bacterial wilt, such as Turk's Turban, should be avoided as a trap crop (UMass Extension, 2002).

Early research in Maine examined the percentage of land devoted to the trap crop. When researchers grew NK530 squash as a trap crop on 15 percent and 50 percent of the cucumber crop acreage, the trap crop attracted 90 percent of the cucumber beetles (Radin and Drummond, 1994). The researchers concluded that strategically placed strips of squash plants could be more advantageous.

In Oklahoma, Lemondrop and Blue Hubbard squash planted as trap crops and occupying just 1 percent of the total crop area highly attracted cucumber beetles in cantaloupe, squash and watermelon crops (Pair, 1997). The Oklahoma researchers also showed that small squash plants in the four- to six-leaf stage are vastly more effective as trap crops than large squash plants in the more-than-six- to 12-leaf stage, which corroborates findings that cucurbitacin occurs in higher concentrations in young leaves. Recent integrated pest management field trials suggest that perimeter trap cropping, where border rows encompass all four sides of the field, is a pragmatic and an effective approach (Boucher and Durgy, 2004 and Boucher and Durgy, 2005).

To deter entry into the field by cucumber beetles and minimize the spread of bacterial wilt:

• Plant trap crops on the perimeter of the field as border strips.
  
• Plant multiple rows if beetle pressure is extreme.
  
• Plant trap crops a week or two earlier than the primary cucurbit acreage since insects migrate to the earliest emerging cucurbit plants in the field.
  
• In organic production, apply botanical and biorational insecticides to the trap crop before the beetles migrate into the cucurbit patch. In integrated pest management production, several synthetic insecticides can be applied to the trap crop for beetle control. Vacuuming is a novel approach to controlling beetles that congregate on the trap crop.
  
• Use yellow sticky ribbons in combination with trap crops to enhance the attractant effect and perform mass trapping.
  
• Remove and destroy diseased plants from border strips and the main field.

Bats are voracious eaters of insects and more farmers are erecting bat houses to enhance biological control of crop pests. John O. Whitaker, Jr., a vertebrate ecologist at Indiana State University, used data partly derived from studies on the evening bat (Nycticeius humeralis) to estimate that a typical Midwestern colony of 150 big brown bats (Eptesicus fuscus) might consume 38,000 cucumber beetles, 16,000 June bugs, 19,000 stink bugs and 50,000 leafhoppers in one season (Whitaker, 1993).

In a detailed follow-up study where he dissected fecal pellets of big brown bats from Indiana and Illinois, Whitaker calculated that a colony of 150 bats might consume 600,000 cucumber beetles, 194,000 scarabaeids, 158,000 leafhoppers and 335,000 stinkbugs in one season. Assuming that half of the cucumber beetles were female, and using a value of 110 eggs per female, this means the potential destruction of 33 million diabrotica larvae (Whitaker, 1995).

An April-June 2006 article in California Agriculture evaluated the best way to attract bats to farms through the placement, shape, size and color of bat houses (Long et al., 2006). For more information about creating on-farm bat habitat and the use of insectary plantings to attract beneficial insects, see the ATTRA publication Farmscaping to Enhance Biological Control.

Entomopathogenic fungi, commonly grouped among biopesticides, produce infective spores that attach to the larval host and then germinate and penetrate. The fungi multiply inside the host, acquiring nutrient resources and producing conidial spores. This causes the infected larvae to reduce their feeding and die, releasing fungal spores into the soil environment and further distributes the entomopathogen. The two fungal organisms most widely used as biopesticides, Beauveria bassiana and Metarhizium anisopliae, have been evaluated for suppression of diabroticine larvae with varying levels of biocontrol. Mycotrol-O is a commercially available, Organic Materials Review Institute-approved biopesticide containing Beauveria bassiana and cucumber beetle is listed as a target pest on the label. See the section on botanical insecticides below with notes from Reggie Destree for foliar mixtures containing Mycotrol-O.

Entomopathogenic nematodes, commonly known as parasitic nematodes, actively find and penetrate soil-dwelling larvae of insect pests. The nematodes release toxins and transmit bacteria that is lethal to the larval host. Both species of commercially available parasitic nematodes, Steinernema spp. and Heterorhabditis spp., are effective in biological control of diabroticine beetle larvae.

Researchers in Pennsylvania obtained a 50-percent reduction in striped cucumber beetle larvae using Steinernema riobravis in organic and conventionally managed plots of cucumbers under field conditions (Ellers-Kirk et al., 2000). The decrease in cucumber beetle larval populations resulted in superior root growth under both soil management systems.

The researchers suggested delivery of parasitic nematodes through drip irrigation in combination with plastic mulch, since earlier studies showed that plasticulture provides an environment conducive to nematode survival while increasing effective control of cucumber beetle larvae.

Organic Control: Dust with rotenone.

Prevention:Crop rotation and heavy mulching can help.