Beginner

Scientific Name
Acalymma vittata

Identification

• 6- 7 mm (1/4 in.) long with 3 black stripes
  
• The less common, spotted cucumber beetle is slightly larger
  
• Feeding damage can seriously harm seedlings
  
• The main threat to cucurbit yield is the transmission of bacterial wilt

Often Confused With
Western Corn Rootworm - Western Corn Rootworm will occasionally feed on cucurbits, although it greatly prefers corn. The stripes on the Western Corn Rootworm do not extend all of the way down the wing pad and it has black legs. The Striped Cucumber Beetle has stripes that extend the length of its wing pad and it has yellow legs with black “knees.”

Period of Activity
The first generation of adults emerges in mid-June to early July, precisely as many direct-seeded cucurbits emerge. They may be present in the field throughout the summer. However, early populations are generally the most damaging. Late-season feeding on the fruit may reduce marketable yields.

Scouting Notes
Carefully inspect 10 groups of 10 plants across the field. Count the number of beetles feeding on the plants and divide by 100 to determine the number of beetles per plant. Be sure to monitor field borders and other potential overwintering sites. 

Beetles will often take shelter in leaf axils and in cracks in the soil when the plants are small.  Once blossoms are present, beetles are usually found inside older (spent) flowers.

Thresholds
Treat when beetles exceed 0.5–1 per plant. Use the lower threshold on bacterial wilt–susceptible varieties. A follow-up spray may be necessary, as beetle emergence is often staggered.

Advanced

Scientific Name
Acalymma vittata

The cucumber beetle is a major pest of all cucurbits.  Beetles attack all parts of both young and mature plants.  Young plants are most susceptible to yield losses due to direct feeding on the cotyledons and developing leaves.  High populations of beetles can completely skeletonise the plant.

The cucumber beetle is the primary vector of bacterial wilt disease.  Once a plant is infected, there is no control for bacterial wilt.  Effective control of the beetle population is the only method to prevent crop losses due to bacterial wilt infections.

Identification
Striped Cucumber Beetles are the most common species found in Ontario cucurbit fields.  They are approximately 6- 7 mm (1/4- 2/7 in.) long, with 3 black stripes on yellow wing pads.  The stripes of the cucumber beetle extend the entire length of the wing pad.  The lower portions of the legs are black, giving the beetles the appearance of wearing knee-socks.

The Spotted Cucumber Beetle, also known as the Southern Corn Rootworm, is slightly larger than the striped cucumber beetle. It has yellow wing pads with black spots.

Mid-season cucumber beetle populations may congregate on the flowers, feeding on both the petals and the pollen.  Severe feeding at this stage will cause blossom abortion and yield loss.  After fruit set, the 1st generation adults will occasionally become problematic as beetles feed on the fruit, rendering it unmarketable.

Often Confused With
Western Corn Rootworm - Western Corn Rootworm will occasionally feed on cucurbits, although it greatly prefers corn. The stripes on the Western Corn Rootworm do not extend all of the way down the wing pad and it has black legs. The Striped Cucumber Beetle has stripes that extend the length of its wing pad and it has yellow legs with black “knees.”

Biology
Cucumber Beetles over-winter as adults in grassy fencerows and sheltered areas. They begin to emerge as the soil temperatures reach 10°C (50°F).  Emerging beetles feed on weeds, grasses and early-planted cucurbits until they breed, lay eggs and die.

There is one generation of cucumber beetles per year, however; beetle development is often very staggered.  As a result there may be several “flushes” of beetle activity throughout the season.

The percentage of cucumber beetles harbouring bacterial wilt tends to increase dramatically over the course of the summer. The best way to stop the occurrence and spread of this disease is to control early season adult beetles.

Period of Activity
The first generation of adults emerges in mid-June to early July, precisely as many direct-seeded cucurbits emerge. They may be present in the field throughout the summer. However, early populations are generally the most damaging. Late-season feeding on the fruit may reduce marketable yields. 

Scouting Notes
Carefully inspect 10 groups of 10 plants across the field.  Count the number of beetles feeding on the plants and divide by 100 to determine the number of beetles per plant. Be sure to monitor field borders and other potential over-wintering sites.  Beetles will often enter the crop from adjacent fields used to grow cucurbits in the previous year. 

Beetles will often take shelter in leaf axils and in cracks in the soil when the plants are small. Once blossoms are present, beetles are usually found inside older (spent) flowers.

Thresholds
Spray when beetle populations exceed 0.5 to 1 beetle per plant.  Use the lower threshold on bacterial wilt sensitive varieties.

Management Notes

• Cucumber Beetle populations tend to peak a week after the first beetles appear in the field.
  
• Continue scouting after an insecticide application.
  
• Delayed and staggered emergence of the beetles often results in the need for follow up treatments.
  
• Management of the first generation will often prevent a population rebound later in the season.
  
• Cucumber beetles tend to congregate within certain areas of a field, making them excellent candidates for spot spraying or border sprays.  Cucurbits vary greatly in their susceptibility to bacterial wilt disease. They also vary in their attractiveness to beetle feeding. 
  
• Cucurbit varieties, such as Turk’s Turban, known to be particularly attractive to the beetles may be useful as a trap crop.

SUSCEPTIBILITY TO BACTERIAL WILT:

• Cucumbers > Melons > Pumpkins > Zucchini

ATTRACTIVENESS TO BEETLES:

• Zucchini > Pumpkins > Melons > Cucumbers