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Thresholds for Treatment & Treatment Options


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 gainst the cost of treatment. 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.

Heliothis trapsHeliothis traps are used to trap corn earworm. Traps are constructed from a mesh fabric in a funnel shape. The lure is hung from an elastic strap at the bottom with a binder clip. Moths collect in the top "bag" and can be counted and removed

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

  • asparagus beetle: treat when 10% of crowns are infested with beetle adults
  • corn earworm: treatment (if plants are in silking stage) should be implemented if 2 to 5 moths have been captured in Heliothis traps over 3 consecutive nights
  • onion thrips: treat when there is an average of at least 7 thrips per plant
  • squash bug: treat when the average number of egg masses is more than 1 per plant
  • striped cucumber beetle: treat melons when an average of 4 to 5 adults are found per 50 plants

Treatment Options

Cultural Control

Options include tilling debris, crop rotation, cover cropping, application of proper irrigation and nutrition, improving soil health, using resistant varieties, and other similar methods. Often, practicing proper cultural controls throughout the year is enough to keep most pests in check

Mechanical Control

Options usually involve methods to exclude pests such as applying row covers, discing weeds, and good sanitation practices (keeping tools clean, prompt removal of unhealthy plants, etc.).

Biological Control

For greenhouse or high tunnel crops, biological control using release of organisms works very well for controlling many insects and diseases. Because some insects used for biocontrol tend to disperse after release, they are not suitable for use on crops grown in the field. A better alternative is to enact measures that conserve and promote naturally occurring beneficial organisms through border or edge habitat plantings, applying compost to soil, and reducing pesticide use.

Using genetic resistance is an effective and low cost strategy to minimize insect and disease outbreaks. Resistant varieties tolerate insect and disease injury better and result in more vigorous plants.

Chemical Control

If it is determined that a pesticide is needed for treatment, be aware that for insects (and many diseases), treatments should be applied only during the time period when the most susceptible life stage is active. For example, leafhopper on potato is most easily treated before the young (nymphs) develop wings. Once they can fly, they can avoid the insecticide application, and they are already producing new offspring to infest the crop. In addition, if symptoms of feeding are found but no causal insect can be identified, a chemical spray is not recommended.

Pesticides are grouped by mode of action (how they kill the target organism), which is usually designated by a group number. Pesticides with similar active ingredients will have the same number. Rotating among pesticides in different group numbers will reduce the likelihood of pest resistance.

For each pest group (insects, diseases, weeds), there are many pesticide options from which to choose. Products that are “broad-spectrum” kill a range of organisms, including beneficial ones, whereas other options target certain species and are less toxic. The EPA’s Conventional Reduced Risk Pesticide Program registers certain pesticides as “reduced risk.” These are pesticides that pose less risk to human health and the environment than existing conventional alternatives. (Biological and antimicrobial pesticides are all reduced risk, but are handled through separate registration processes.)

Products given the Reduced Risk designation have:

  • low impact on human health Ȉ lower toxicity to non-target organisms (birds, fish, plants)
  • low potential for groundwater contamination
  • low use rates
  • low pest resistance potential
  • compatibility with Integrated Pest Management (IPM) practices