Thresholds for Treatment

Pest monitoring provides information on pest activity and population size. To decide if control is required, pest density and potential crop loss must be weighed against the treatment cost. If the cost of treatment is more than the potential crop loss, do not treat. Activity of natural enemies must also be considered when determining whether to treat. Some pests like aphids or spider mites can be kept below economic injury levels by a healthy population of predators. 

Most threshold levels, where known, are provided for the pests in each crop chapter of this book, but some examples include the following:

• Asparagus beetle: treat when 10% of crowns are infested with beetle adults.
• Corn earworm: implement treatment (if plants are in silking stage) if two to five moths have been captured in Heliothis traps over 3 consecutive nights.
• Onion thrips: treat when there is an average of at least seven thrips per plant.
• Squash bug: treat when the average number of egg masses is more than one per plant.
• Striped cucumber beetle: treat melons when an average of four to five adults are found per 50 plants.