Bean
Cucumber Beetle
Diabrotica spp.
Insect
In a Nutshell
- Feeding damage on roots and stems.
- Weakens the stalk and lead to lodging.
- Yellow-green colored beetles with either black stripes or spots on their back.
Can also be found in
Bean
Symptoms
Adults feed mainly on foliage and flowers, interfering with pollination and grain/pod/fruit development. Larvae feed on root hairs, roots and stems, reducing the ability of the plant to absorb water and nutrients from the soil. Root tips may be chewed back to the base of the plant or appear brown and bored with tunnels. Symptoms show as drought or nutrient deficiencies. At later stages of plant growth, the damage to the root can weaken the stalk and lead to harvesting difficulties due to plant lodging. Damage by larvae also favors opportunistic pathogens. Moreover, some species of Diabrotica are vectors for the maize chlorotic mottle virus and the bacteria that cause bacterial wilt. This can lead to more yield losses.
Recommendations
Organic Control
Several species of nematodes, predators (mites, insects) and parasitoids flies and wasps can be used to control the population. For example, the tachinid fly Celatoria diabroticae can be introduced when the population of the cucumber beetle is not that large. The fungi Beauveria bassiana and Metarhizium anisopliae also naturally attack some species of Diabrotica.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments if available. Damaging populations of cucumber beetles are usually treated with insecticides. Insecticides of the group of acetamiprid or fendropathrin should only be applied if the beetle occurs in high numbers, but take into account environmental issues. Soil treatments with pyrethroids are another option.
What caused it?
Diabrotica species are a group of insect pests that attack several crops of agricultural importance including common beans and maize. Cucumber beetles are usually yellow-green colored and are divided in two groups depending on their aspects. The first group have three black stripes down the back, while the second one is characterized by twelve black spots on the back. The adults overwinter in surrounding areas and become active in mid-spring, when temperatures begin to rise. Females deposit eggs in clusters in soil cracks near their host plants. The larvae feed in and on the roots first, later also on the shoot while adults feed on foliage, pollen and flowers. The development from egg to adult takes about a month, depending on environmental conditions. As temperatures increase, development time decreases. Cucumber beetles like moist areas with good water supply and dislike heat.
Preventive Measures
- Delayed planting can avoid worst damage.
- Avoid planting your crop next to alternative host plants like melons, pumpkins or beans.
- Use mulch to cover soils and break the life cycle of the beetle.
- Use kaolin clay as a protective film to ward off the beetles.
- Use traps to monitor and mass-catch the insect.
- Remove residues after harvest and destroy them.
- Plan a crop rotation with non-susceptible plants.
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