II. Plant Emergence to Three Leaf Stage

A. Striped and Spotted Cucumber Beetles

• Sampling: The greatest amount of feeding injury and disease transmission occurs from planting until runner formation Sampling should begin as soon as transplants are set in the field or at plant emergence. Sample fields twice a week, especially along field margins next to overwintering areas. During hot, windy days, look for beetles hiding in cracks in the soil surface and under the plastic mulch. Examine 5 plants in 5-10 locations throughout a field and count the number of beetles per plant.

• Thresholds: Even if soil insecticides are used, fields should be checked to be sure that control is adequate, especially during cool, wet conditions. Treatments should be applied before adult beetles feed extensively on cotyledons and first true leaves. Sprays should be applied at plant emergence and repeated weekly if beetles continue to invade fields.

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III. Three Leaf Stage to Harvest Maturity

A. Melon Aphid

• Sampling: Scouting should begin as soon as plants form runners. Look for wilting and curled leaves that will be found in small-scattered spots throughout the field. Examine 5 runners in 5-10 locations throughout a field and record the percentage of runners with 5 or more aphids per leaf. The level of natural controls (e.g. lady beetles, lacewings, and parasitized aphids) should also be considered when making a treatment decision.

• Threshold: A foliar treatment should be applied if beneficial insect populations are low and you find 20% or more of the runners infested with 5 or more aphids per leaf.
  

B. Spider Mites

• Sampling: Since infestations generally begin along field margins next to grassy areas, near rye windbreaks, and in the sandiest areas of fields, be sure to carefully sample these areas early in the season. Look for the early signs of white stippling on the crown leaves. Mites can be identified by shaking leaves onto a sheet of white paper and watching for moving specks or by using a hand lens to count the number of mites per leaf. Examine 5 crown leaves in 5-10 locations throughout a field for the presence of mites and feeding damage.

• Thresholds: A treatment should be applied when 10-15% of the crown
  leaves are infested with mites. In addition, do not mow adjacent grassy areas or windbreaks that harbor mites and force mites to disperse into the field.

C. Thrips

• Sampling and Decision-Making: Thrips are generally found on the undersides of leaves producing silver flecking near the large leaf veins. Examine 5 crown leaves in 5-10 locations for the presence of thorps and rate the feeding injury as light, moderate or heavy. Although no thresholds are available, controls may be needed if the thrips population is heavy, leaf feeding is present and plants are not actively growing.

D. Potato Leafhopper

• Sampling and Decision-Making: Examine runners in 5-10 locations for the presence of leafhopper nymphs. A sweep net can also be used to sample for adults. Controls will be needed if hopper burn is detected on leaf edges and injury is expected to retard fruit maturity and yield.

E. Striped and Spotted Cucumber Beetles

• Sampling: After runners form, transmission of disease is less likely and stem damage is rarely economic. However, if beetle populations are high infestation levels should be rated as light, moderate, or heavy.

• Thresholds: Treatment should be applied if adults are feeding on small fruit resulting in reduced quality. In cantaloupes, high beetle populations before and after bloom should be controlled to avoid larval damage to the surface of the rind where the fruit meets the soil surface.