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IPM - Thresholds for Treatment & Treatment Options

Heliothis traps
Heliothis 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.

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.

Insect NettingDwarf grain sorghum planted around the perimeters of tomatoes serve as a trap crop to control stink bug populations.

Row coversRow covers draped over leafy green production at a northern Utah commercial vegetable farm.

Insect netting bowMetal hoops supporting insect netting

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.

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

Trap cropping

Trap cropping involves growing plants alongside a target crop that are more appealing to certain pests, thereby protecting the crop. It is an important cultural control method within Integrated Pest Managment
(IPM) that is not widely used in Utah. But when successfully implemented, trap cropping provides a sustainable, longterm management option.

There are several types of trap cropping which are characterized by the type of plant, where the plants are grown within the farm, and when they are planted.

        • Conventional Trap Cropping – A traditional and proven-effective plant is planted around or within the cash crops that is more attractive to a target pest as either a food source or for reproduction.
        • Dead-End Trap Cropping – Plants that are attrac-tive to a target pest, but on which, offspring will not survive. Dead-end trap crops serve as a “sink” and prevent movement of the target pest to a cash crop later in the season. Dead-end trap crops are planted in field borders or edges where they inter-cept insect pests.
        • Genetically-Engineered Trap Cropping – Plants may be genetically engineered to act as a trap crop. Prevention of insect-vectored diseases is one example, where the trap crop is capable of har-boring a certain virus but its insect vector cannot acquire it from that plant. In this example, the trap crop helps reduce the insect-vectored pathogen as opposed to the insect itself.
        • Perimeter Trap Cropping – Trap crops that are planted around the border of the main crop.
        • Sequential Trap Cropping – Traps crops that are planted either later or earlier than the main cropto increase the attractiveness to insect pests dur-ing certain times of the season.
        • Multiple Trap Cropping – Planting several trap crop species to manage several pests or control-ling a target pest by combining plants whose growth stages enhance attractiveness season-long
        • Push-Pull Trap Cropping – A combination system where a trap crop is planted around the perimeter of a crop to attract the target insect pest (pull) and a different plant is inter-cropped to repel (push) the insect away from the cash crop.
        • Biological Control-Assisted Trap Cropping – Trap crops that are planted within and around the crop that enhance populations of natural enemies that then help suppress multiple pests.
        • Semiochemical-Assisted Trap Cropping – The use of either manually hanging insect semiochemicals (such as pheromone lures) on a perimeter plant-ing, or using genetically modified plants that emit semiochemical lures to attract the target pest.

Examples of Trap Cropping Options in Utah Vegetable Production

Cash Crop Insect Pest
Trap Crop
Broccoli Potato Leafhopper Various Mustardss
Cabbage Cutworms Chinese Cabbage, RadishC,S
Cabbage Diamondback Moth Various Mustardss
Cauliflower Colorado Potato Beetle Chinese Cabbage, Marigolds, SunflowersM
Cruciferous crops Flea Beetles Various Mustardss
Cruciferous crops Cabbage Maggot Chinese Cabbage, TurnipsC
Cucurbit crops Cucumber Beetles Specific Varieties of Cucurbit CropsC,S
Sweet Potato Wireworms Corn,WheatC,S,SA
Curubit crops Squash Bugs Hubbard SquashesM,S
Lettuce Aster Leafhopper LettuceS
Lettuce Thrips Various WildflowersC,P
Sweet Corn Stink Bugs Various MustardsC,P
Tomato Colorado Potato Beetle PotatoS
Tomato Whiteflies SquashC
S=Sequential.Early,and/or Late Planting
SA=Semiochemical Assisted

C=Conventional                             P=Perimeter                                                                SA=Semiochemical Assisted     
M=Multiple                                      S=Sequential.Early,and/or Late Planting

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.).

Row Covers

A variety of cover options are available. Lightweight materials (approximately 0.5 oz./yd2) are effective as an insect barrier starting in late spring. The material may be non-woven, spun-bond fabric with 90% - 95% light transmittance. Other fabrics that are heavier in weight (1.5 - 2 oz./yd2) are used to extend the growing season by protecting the crop from early or late frosts. These thicker materials allow for 50% - 70% light transmittance. A few common brands of the spun bond fabrics include Agribon and Reemay. Ventilated plastic covers are also available for heat retention. Woven materials include thicker fabric or plastic mesh. For example, the Proteknet brand of mesh is available in 6 grades ranging in sizes from 0.85mm2 too 0.85mm x 1.4mm. Ensure the pest being controlled will not be able to pass through the selected mesh grade. Row covers can be purchased online through garden supply and seed companies, or may be available at some select garden centers. When selecting the support structure for row covers, consider whether it will be used for a single season or multiple uses. Options include 3/4” PVC that can be bent, metal hoops, or small wire hoops.

When constructing your row covers, first decide which crops are going to be covered. Then, identify the purpose of the cover. For example, if the purpose is insect exclusion, be aware that timing is important Understand when the pests can be most destructive to the crops and plan to leave the covers up for that duration of time. The timing and crop size should also be considered for the height of the row cover. The structure can be built over existing beds and rows with plastic mulch and drip line. First install the PVC, metal, or wire hoops, then lay the cover over the frame and secure with binder clips. A tight seal to the ground is important, but avoid using stakes or anything that could tear the material. Use shoveled soil, or place bricks, rocks, or other heavy objects on the fabric.  Regularly monitor the structure to ensure the covers are secure and free of any tears or other damage.

Examples of Trap Cropping Options in Utah Vegetable Production

0.0335"2 0.05" x 0.7" 0.19" x 0.12"
Aphids X      
Flea Beetles X      
Lacewings X X X  
Ladybugs X X X  
Leafhopper X X    
Lygus Bug X X X  
Moths X X X X
Root Maggot Flies X X X  
Stink Bugs X X X X
Spider Mites C=X      
Squash Bugs X X X X
Thrips X      
Whitefly X      

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.

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