How to Manage Pests

UC Pest Management Guidelines

Western spotted cucumber beetle.


Cucumber Beetles

Scientific Names:
Western spotted cucumber beetle: Diabrotica undecimpunctata undecimpunctata
Western striped cucumber beetle: Acalymma trivittatum
Banded cucumber beetle: Diabrotica balteata

(Reviewed 12/09 , updated 6/12, pesticides updated 5/16 )

In this Guideline:


The western spotted and the western striped cucumber beetles occur throughout California and are major pests of cucurbits; the banded cucumber beetle occurs primarily in southern California. Cucumber beetles overwinter as adults and are active by the time the earliest melons are planted in spring. Adults lay eggs at the base of plants. As soon as they hatch, larvae begin to feed on plant roots. They complete their development in the soil. There are about three generations a year.

Cucumber beetles are about 0.36 inch (9 mm) long and either have a greenish yellow background with black spots or alternating black and yellow stripes. They fly readily and migrate into cultivated areas from alfalfa and other crops, and from uncultivated lands. Cucumber beetles like moisture and dislike heat; consequently, melon fields are especially attractive in hot weather during and after an irrigation.

Western striped cucumber beetle larvae feed exclusively on cucurbit roots, whereas western spotted cucumber beetle larvae feed on a wide variety of plants including grasses, corn, legumes, and cucurbits.


Cucumber beetles are serious pests of smooth-skinned cucurbits, especially melon varieties such as honeydew, crenshaw, and casaba. While the adults prefer tender, succulent portions of plants, including the flowers and leaves, which they may destroy with their feeding, it is the damage to the surface of the melon that reduces marketable yield. When temperatures are high, adults especially feed on the undersides of young melons, scarring them. After the skin hardens, melons are much less subject to attack. Scarring in the crown of the plant is also typical of adult damage. Feeding on stems of young plants, followed by sustained winds, may result in severe stand reductions making replanting necessary. In some situations, larvae may cause serious injury by feeding on roots, and young plants can be killed. Cucumber beetles also spread squash mosaic virus.


Damaging populations of cucumber beetles are usually treated with insecticides.

Biological Control

Cucumber beetles are attacked by a variety of natural enemies, the most important being a parasitic tachinid fly, Celatoria diabroticae. Natural enemies are rarely effective enough, however, to reduce populations below economically damaging levels.

Cultural Control

There are no effective cultural controls for these pests. Because spotted cucumber beetle larvae also feed on corn, avoiding planting cucurbits next to corn may help.

Monitoring and Treatment Decisions

Cucumber beetles are difficult to control. Pesticide sprays must be directed at adult beetles. Larvae of western spotted cucumber beetle develop outside of cucurbit fields and striped cucumber beetle larvae are located on roots where they cannot be controlled.

Start monitoring for cucumber beetles after transplanting or when seedlings emerge, through the fruiting stage. Pesticide applications for adults may be necessary if there is an average of one beetle per plant during the seedling-to-4-inch-tall stage. Infestations that develop late in the season are usually not as damaging as those that begin earlier because numbers tend to be lower. Apply insecticides before beehives are introduced into the field; typically, an application is often made the day before bees are put in the field.

Common name Amount per acre REI‡ PHI‡
(Example trade name)   (hours) (days)

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Not all registered pesticides are listed. Always read the label of the product being used.
  (Assail 30SG) 2.5–5.3 oz 12 0
  (Assail 70WP) 1.1–2.3 oz 12 0
  (Sevin 4F) 1 qt 12 3
  (Sevin XLR Plus) 1 qt 12 3
  COMMENTS: To avoid plant injury, do not apply when foliage is wet or when rain or excessive humidity is expected during the 2 days after application. May cause increased spider mite problems. The XLR Plus formulation is less hazardous to honey bees than other formulations if applied from late evening to early morning when bees are not foraging.
  (Danitol)* 10.67–16 fl oz 24 7
  (Asana XL) 5.8–9.6 oz 12 3
  COMMENTS: Use to control adults; repeat as necessary to maintain control. Do not exceed 0.25 lb a.i./acre per season. Highly toxic to honey bees.
  (Kryocide) 8–12 lb 12 See comments
  COMMENTS: Labeled for use on cucumber, squash, melons, and pumpkins. Can be applied as a spray or dust. Thorough coverage using ground equipment is necessary for adequate control. Do not apply immediately before harvest. Remove excess residues on edible portions by washing, brushing, or other effective means. Effectiveness of this material is lower than materials listed above. PHI is 7 days for summer squash and 14 days for winter squash, cucumber, melons, and pumpkins.
  . . . or . . .
  (Prokil Cryolite 96) 10–16 lb 12 See comments
  COMMENTS: Labeled for use on cantaloupe, squash, and watermelon. Applied as a spray. Thorough coverage using ground equipment is necessary for adequate control. Do not apply immediately before harvest. Remove excess residues on edible portions by washing, brushing, or other effective means. Effectiveness of this material is lower than materials listed above. PHI is 7 days for summer squash and 14 days for winter squash, cantaloupe, and watermelon.
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
1 Rotate chemicals with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode of action group numbers .( un = unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their website at



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445

Insects and Mites

E. T. Natwick, UC Cooperative Extension, Imperial County
J. J. Stapleton, UC IPM Program, Kearney Agricultultural Center, Parlier
C. S. Stoddard, UC Cooperative Extension, Merced & Madera counties

Acknowledgment for contributions to Insects and Mites:
R. L. Coviello, UC Cooperative Extension, Fresno County
C. B. Fouche, UC Cooperative Extension, San Joaquin County
L. D. Godfrey, Entomology, UC Davis
J. B. LeBoeuf, AgiData Sensing, Inc., Fresno
M. Murray, UC Cooperative Extension, Colusa and Glenn counties
C. G. Summers, Entomology, UC Davis and Kearney Agricultural Center, Parlier

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