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Organizing an Aerial Spray for Forest Pests:

Recommendations and Regulations

Forest Health Program, Wisconsin Department of Natural Resources (Revised September 2013)

In this document: Page Page

Introduction…………………….… 2 Appendices: Legal requirements……………… 2 Non-target species……………… 9 Determining spray areas……...… 4 Pest-specific information………. 15 Selecting a pesticide…….…….... 6 Typical project timeline…………. 7

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An aerial spray can be a cost-effective way to manage a forest pest that is at damaging levels over many acres. However, it usually requires more effort than simply calling a sprayer to take care of the problem. This guide describes the required steps and considerations for a safe, legal and effective aerial spray of tree-feeding pests such as gypsy moth, forest tent caterpillar, jack pine budworm and spruce budworm. First, correctly identify the pest you are thinking of treating. The timing and spray methods may differ for different pests. Images of common caterpillar pests can be found online via http://gypsymoth.wi.gov.

Key recommendation: If the area being considered for aerial spraying includes many property owners (i.e., a residential area), have a project coordinator - one individual or small group who is willing to see the project through to completion. The coordinator contacts potential applicators, oversees communications to neighbors and has the authority to decide whether the spraying should be postponed due to unfavorable weather conditions. You could also hire a consultant familiar with the pest and aerial spraying to coordinate a privately-organized spray treatment. This will be more expensive, but their expertise may be worth the cost.

Legal requirements for aerial sprays Wisconsin law requires that pesticide only be applied to property where it is intended to be used. Spraying property outside the intended application area, or significant amounts of spray drift outside of the intended application area, are violations of state Administrative Rule ATCP 29 - Pesticide Use and Control. Recommendation: Plan ahead to avoid or respond to objections. You may wish to obtain a signed consent-to-spray form from each landowner within and adjacent to the proposed spray area, to reduce the risk of objections being raised before or after the spray. If people within the proposed spray area object to having their property treated, steps must be taken to prevent overspray or drift onto their property, even if this means that some residents who want their property treated may not be able to be sprayed. This regulation has particular importance to neighborhoods or lake associations that contract for the entire area to be treated. The DNR Gypsy Moth Suppression Program has a similar requirement, and will exclude an area up to 250 feet from an objector’s property.

Aerial spraying for gypsy moth in Manitowoc County.

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If a landowner within the proposed treatment area raises an objection, a spray organizer may be able to reach a compromise resulting in the objector withdrawing their objection. Examples of compromises include:

Not charging that property owner for their share of the spray cost, Providing notification a day or two prior to spraying, or Covering food plants with a tarp.

If an objection remains, work with the applicator to determine the appropriate distance around that property that must be left untreated in order to avoid overspray or drift onto the objector’s property. With privately-organized aerial spraying, there is no deadline for objectors to raise their objection to being sprayed, and a legal complaint can even be brought after the spray has taken place. Licenses and permits Businesses that apply pesticides must be licensed by the Wisconsin Department of Agriculture, Trade and Consumer Protection. The pilots making the applications must also be certified in the aerial application category and have an individual applicator license. Applicators are expected to adhere to all regulations pertaining to aerial spraying included in Administrative Rule ATCP 29 - Pesticide Use and Control. Examples include record keeping, providing information to the customer, and having the required certification and licensing. Aerial applicators treating residential areas to control a forest pest do not need to post landscape application signs, and are not required to notify individuals on the ‘landscape registry.’ Contact the Wisconsin Department of Agriculture, Trade and Consumer Protection (608-224-4551) if you have specific questions about state pesticide regulations. If the proposed spraying is adjacent to or near a body of water (such as lake or river), the aerial applicator that you hire will likely need to be covered under a water pollution permit system known as the Wisconsin Pollutant Discharge Elimination System (WPDES) administered by the Wisconsin Department of Natural Resources. The sponsor of spraying (such as a lake association) would need to apply for permit coverage in cases where the aerial applicator lacks appropriate WPDES coverage. View more information on this permit. Endangered and Threatened Species laws may also restrict where aerial spraying can take place, in order to protect populations of these species. For details, see Appendix I on page 9.

Consider whether an aerial spray treatment is appropriate Aerial spraying is most appropriate for large areas that are square or rectangular in shape (lake or river boundaries are an exception). A spray area of at least 20 acres is a good starting point in situations where the treatment area is surrounded by infested forest that will not be sprayed. Parallel boundaries are encouraged, with the exception of lake and river edges. Treatment areas that are long and narrow, or

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oddly-shaped, should be avoided because of potential problems with re-infestation, spray droplet deposition and wind drift. Also, be aware that reports of poor spray coverage sometimes occur along the edge of a lake or river. If the problem area is only a few trees or a few acres, aerial spraying is probably not appropriate. Physical controls, a spray from the ground, or application of a systemic insecticide into the soil or the tree itself, are likely to be more practical treatment options. More information can be found at http://gypsymoth.wi.gov. An arborist or tree service may do these pesticide applications. Homeowner-applied products are also available. To find a certified arborist in your area, visit the Wisconsin Arborist Association website. Additional businesses offering pesticide treatments may be found in the phone book under ‘Tree Service.’ Determining the area to be sprayed If you have decided that an aerial spray is the appropriate treatment for your situation, you will need to determine the area to be treated. To avoid wasting money and effort, identify the area that is threatened and know whether the property owners are willing to pay for aerial spraying. Identify the area that is threatened

The area threatened by an outbreak of a forest pest is the combination of where the pest is present in high numbers and where its favorite trees are located. Complaints of nuisance caterpillars or defoliation in the current summer are two

Examples of well-designed spray blocks, showing square and rectangular shapes with no curved boundaries (water boundaries exempted).

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easy indicators of potential problems next summer. Surveys of egg masses can also be done to predict the population for next year. Some of these surveys, such as the one for gypsy moth, can be done by property owners. Instructions for doing

predictive egg mass surveys can be found in Appendix II on page 15. The favored trees for each pest are identified in the Appendix. Consider the distribution of favored hosts in the area you are considering spraying. You may be able to exclude some areas that would never be damaged because they have no favored trees. Conversely, you may want to extend your spray boundaries to cover areas dominated by favored trees that are likely to be heavily defoliated by a pest outbreak. Aerial photos can indicate areas covered in broad-leaved trees such as oaks, areas dominated by conifers and areas of open fields. County Planning and Zoning Departments often have free GIS websites that overlay property boundaries on top of aerial photos. Aerial photos and maps can also be obtained from internet sources such as Google Maps or Yahoo Maps. Consider buffers If populations are high around the treatment area, caterpillars from outside may invade the treated area and reduce the effectiveness of the treatment along the borders. To reduce the risk of this happening, consider spraying an additional buffer of 150 or more feet around the core area you want to protect. If this buffer will

This residential area in Oconto County was successfully protected from gypsy moth defoliation in 2010 (red lines added). The surrounding areas with a purple appearance were defoliated.

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extend onto the property of other landowners, make sure you have their permission (written suggested). Offering to pay for the buffer strip frequently helps. Know whether landowners will pay for the treatment While determining the area threatened, also keep in mind whether the landowners are likely to be willing to pay for its protection. In residential or recreational areas the trees are of higher value. Therefore, tolerance for defoliation and tree mortality is lower than in woodlots. In woodlots, the cost of spraying may exceed the value of the timber saved. Thus, a property owner whose land contains high value trees may be willing to pay for spraying, whereas a landowner with lower-value trees may not. Be cautioned that trees growing on very sandy soil, those already in poor health, or those weakened by drought stress may suffer very heavy mortality if defoliated, and thus protection would be needed to avoid catastrophic loss. Recommendation: Raising the funds through a lake association or other property owner group is usually the easiest way to pay for spraying. If collecting funds from individuals, collect more money than is theoretically needed from each property owner. This is to cover the cost of spraying roads, ditches, and property owners who agree to the spraying but then fail to send in their payment. Depending on the size and severity of the infestation, you may find varied willingness to pay. Sometimes everyone will pay. Sometimes a few property owners will not pay but will allow treatment of their property if someone else pays. Sometimes a few property owners won’t pay or allow treatment of their property.

If there is not enough interest and money to pay for the area initially proposed, perhaps you could proceed with a modified plan. For example, you may have initially considered a 100 acre area but there is not enough interest to spray the whole area. However, there is a 20 acre core of adjacent homeowners who are interested and willing to pay, and you could move forward with a spray of only that area.

Selecting a pesticide Aerial applicators frequently have several pesticides available for use. Consider the advantages and disadvantages of each when planning aerial spraying.

Bacterial insecticides Bacterial insecticides containing the bacterium, Bacillus thuringiensis Kurstaki, (Btk) reliably control caterpillars when properly applied, affect only small caterpillars, and have an active life of 7-10 days once sprayed. They are fairly environmentally benign and can be safely used near water. Impacts on human health, wildlife, fish and other insects are minimal. In Wisconsin, bacterial insecticides are the most frequently applied insecticides used for the treatment of defoliating forest pests.

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Chemical pesticides Chemical pesticides are much less specific than bacterial insecticides, and may kill any insects that contact them during their activity period. Some chemical pesticides will break down quickly, whereas others will remain active for months. Thus, environmental impacts are greater than with bacterial insecticides. Carbaryl, an insecticide sold under a variety of trade names (e.g., Sevin), is very toxic to bees. Carbaryl breaks down in about two weeks. The potential for adverse effects on human health is greater for chemical insecticides than for bacterial insecticides. The growth regulator “Dimilin” (a trade name for the insecticide diflubenzuron) kills leaf-eating insects by interfering with their molting process. These products can be extremely toxic to aquatic invertebrates and care must be taken to keep the pesticide out of water bodies. Dimilin remains active for months, and thus environmental impacts are greater than with bacterial insecticides. Typical project timeline

Summer before spraying

If you live in a residential or seasonal recreation area, talk to property owners while they and the caterpillars are present during the summer. They may also be unhappy with the caterpillars or defoliation and may be interested in spraying next year. Once the caterpillars have completed their development and turned into moths, people tend to be less interested in spraying.

Autumn before spraying

Determine the area to be treated next spring. Review the “Determining the area to be sprayed” section of this guide found on page 4.

If arranging spraying over multiple properties, obtain the permission (written recommended) of each landowner whose property is proposed for treatment. Most objections are for financial reasons, and many objectors will consent to having their property sprayed if the neighbors each chip in a few dollars and pay for it.

Winter before spraying

After you have decided which areas you want to spray, approach licensed aerial applicators. A list of licensed aerial application businesses that have expressed an interest in taking contracts for forest pest spraying can be found online at http://gypsymoth.wi.gov/. Recommendation: Examine the applicator’s license, certification, insurance and experience with forest pest spraying. After you have contacted applicators and received bids for the spraying, you will need to raise the money to pay for it. The cost per acre will be highly variable and depends on factors such as the size and shape of the treatment area, flight distance, pesticide to be used and whether the applicator is doing other spraying in the area.

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In recent years, costs have ranged from about $30-75 per acre, and per-acre costs are usually lower for larger treatment areas. In most cases, only one application of insecticide is done for tree pests. If the population is particularly high and there is interest in doing a second spray a few days later, consult your applicator. After sufficient funds have been raised and a contract has been signed, it’s time to wait until early spring.

Spring

By March, contact the applicator and determine how much advance notice is needed in order to spray your area at the appropriate time. Some applicators may only need a few days notice, while others may want more time.

As the spray day approaches, project organizers are encouraged to remind property owners that the area will be sprayed soon.

Many sprays, particularly bacterial insecticides, are most effective at specific stages of the insect’s development. Sprays must also be applied when leaves are large enough to intercept the spray droplets. Ask your applicator what insect and leaf development information they need to properly time the application of the chosen insecticide. See Appendix II on page 15 for information on how to monitor the development of the insect pest and its host.

Spray day

On days when spraying is planned, individuals within the treatment area may choose to stay indoors with the doors and windows closed during spraying, to avoid direct exposure. Significant health effects are highly unlikely, but to be on the safe side, those with severe asthma or food allergies may consider leaving the area during spraying. Consult your applicator for additional safety recommendations.

Spraying is usually done during the early morning, because humidity is higher and winds are calmer than later in the day. The project coordinator should be on hand to decide whether the spraying should occur or be postponed due to unfavorable weather conditions. Consult with your applicator about weather conditions that would warrant delaying the treatment. Typically, spraying should not occur if it is too windy or if significant rainfall is forecast before the product could dry on the leaves. A wind speed of 10 mph is a common cutoff for spraying, although a lower limit may be advisable if your spray area is small, thin or irregularly-shaped. Spray dates fluctuate from year to year because of variation in spring weather. In southern Wisconsin, spraying for most forest pests occurs in mid- to late May. In northern Wisconsin, spraying usually occurs in late May or the first half of June.

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Karner blue butterfly ‘High Potential Range’ as of 2013 is shown in light blue.

Appendix I: Protection of Non-Target Species Including Threatened and Endangered Species

Certain animal and plant species are protected by state or federal laws. We encourage you to request a review for your project (http://dnr.wi.gov/, keyword “ER Review”) to help determine how to avoid potential impacts to these species.

A. Karner blue butterfly

The Karner blue butterfly usually occupies open prairies, road rights-of-way, and other open or partially-cleared areas containing a plant called wild lupine. It is a federally endangered species that is protected by the Endangered Species Act. Wisconsin has the nation’s largest population of Karner blues, and has a statewide program in coordination with the US Fish and Wildlife Service to protect this species and its habitat. This program is called the Wisconsin Statewide Karner Blue Butterfly Habitat Conservation Plan (HCP). Can I spray for gypsy moth or other forest pests in areas where there might be Karner blue butterflies, a federally endangered species?

Karner blue butterflies are legally protected in parts of Wisconsin known as the “High Potential Range” shown in light blue on the map below. View more detailed maps. However, you may still be able to spray in this area if you meet certain criteria listed on page 10.

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Under the Karner HCP, private landowners that fall within the “Voluntary Category” (as identified in the HCP and listed below) are allowed to spray for gypsy moths or other forests pests even within the High Potential Range.

Voluntary Category (Non-regulated Landowners) Forest landowner with less than 1,000 acres Non-commercial forest landowner with greater than 1,000 acres of land where

the land is not primarily managed for the purpose of forestry (e.g., managed for recreation, as camps, or lake associations)

Agricultural landowner Private property owner planning an insecticide spray to control a forest pest Local government or landowner association organizing an aerial

spray of a forest pest

If you meet any of the above criteria, you can spray for gypsy moths or other forest pests within the Karner High Potential Range as long as you do not fall into one of the ‘Non-Voluntary Landowner Categories’ listed below.

Non-Voluntary Landowner Category (Regulated Landowners) The following groups are not automatically authorized to spray within the High Potential Range. Contact the DNR Endangered Resources program at (608) 264-6271 for additional assistance with organizing spraying.

Railroads Municipal, Cooperative or private utility or energy company Commercial Forests of > 1,000 acres (including county forests) Road or Highway departments Land developers HCP Partners

Outside of the High Potential Range, there are no legal restrictions for this species. However, landowners are encouraged to voluntarily protect Karner blue butterflies wherever they are known to exist. Karner blue habitat can also contain other rare species that should be considered for protection (see section C on page 12).

Will spraying for gypsy moth or other forest pests harm Karner blue butterflies?

It is possible, if not likely, but the impacts will be localized to the spray area. The HCP program recognizes that some Karner blue populations will be impacted by spraying to control gypsy moth or other forest pests. However, the HCP was designed to allow management activities to take place in certain areas while ensuring a healthy overall population in Wisconsin. Also, HCP partners work to protect the butterfly in several areas where recovery efforts are focused.

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What can you do if you want to conserve Karner blue butterflies but also want to spray for forest pests?

Use of several methods can minimize impacts on other rare species.

Planning the spray

Aerial sprays can be conducted in ways that minimize their effects on Karner blue habitat. Options can include avoiding forest openings when spraying, changing the direction of application to avoid drift into Karner blue habitat, avoiding spraying on windy days, and altering the treatment boundaries. When planning a spray, discuss the options with the DNR or your professional applicator. Karner blue can colonize suitable habitat once a pesticide has degraded. If you use a pesticide with a short persistence, such as those using Btk as its active ingredient, Karner blue can disperse to sprayed areas as early as that summer if there are abundant lupine and nectar plants and a nearby population of the butterfly.

Special insecticides

If you are spraying to control gypsy moth, the DNR Gypsy Moth Suppression Program has access to “Gypchek,” a gypsy moth-specific insecticide that is not commercially available to private spray projects. Karner blue larvae can feed on plants that have been sprayed with Gypchek because the virus in Gypchek only affects gypsy moth caterpillars. If you have Karner blues on your property and wish to avoid harming them, one option is to apply to the DNR Suppression Program (offered through participating counties) and express interest in using Gypchek. Gypchek may also be the best option if you have other rare species present (see section C on page 12). Temporary cover Small patches of lupine and flowering plants can be protected from insecticide sprays by covering them with a tarp during the spray application. Make sure you know when spraying will occur, as you don’t want to leave the tarp on the plants for days. Take the tarp off once the spraying is complete. Karner blue larvae can continue to feed, unaffected by the surrounding treated plants. This technique works best if the insecticide chosen is one with a short persistence, such as those using Bacillus thuringiensis kurstaki (Btk) as their active ingredient. If an insecticide with a long active life is used, any insects that move away from the protected patch may be killed when they feed on treated plants.

Small scale or individual treatments

Consider a systemic insecticide treatment if your property is not part of a larger aerial spray block and you only have a few trees to protect. Systemic insecticides are injected into the ground or into the tree, and move with the sap into the leaves. Karner blue larvae won’t be exposed to insecticides within tree leaves since they only feed on lupine plants.

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Non-toxic controls

For a small area or a few trees, there are non-toxic controls that can be used to manage moderate populations and to supplement insecticide treatments without harming Karner blue butterflies or other species. These techniques include removing egg masses, treating gypsy moth egg masses with horticultural oil, protecting trees with sticky barrier bands, using burlap collection bands, and spraying with an insecticidal soap. Visit the website, http://gypsymoth.wi.gov/, for more information.

What else can I do to help the Karner blue butterfly?

Your efforts to help conserve the Karner blue near lands where recovery of the butterfly is focused would be especially helpful. Those lands occur in areas termed “Significant Population Areas” and “Areas of Conservation Emphasis.” Maps of those areas are available on the website noted below. In addition, managing some areas for barrens habitat could benefit Karner blue as well as other rare species. For additional information including contact information for Karner blue butterfly experts, please visit the Wisconsin Karner blue butterfly website. B. Bald eagle nest avoidance

Bald eagles are protected by the Migratory Bird Treaty Act and the Bald and Golden Eagle Protection Act, even though they were removed from the Federal List of Endangered and Threatened Species in 2007. These laws prohibit adversely affecting bald eagles. The U.S. Fish and Wildlife Service has developed guidelines for determining if a permit is needed to conduct a given activity near a bald eagle nest. These guidelines are based on several decades of behavioral observations, science, and conservation measures for avoiding or minimizing adverse impacts to bald eagles. The guidelines require that aircraft avoid operating within 1,000 feet of active bald eagle nests during the breeding season (January through July – note that this covers forest pest spray periods). Projects that cannot implement this guidance may require a federal permit. The US Fish and Wildlife Service’s Step by Step Guidance offers more information. C. Avoiding injury to other threatened or endangered species

The Wisconsin Department of Natural Resources maintains a database of rare species that are protected by state laws (see http://dnr.wi.gov/, keyword “ET List”), similar to the federal list of Threatened and Endangered Species maintained by the US Fish and Wildlife Service. Certain rare species that have the potential to be harmed by aerial spraying of Btk are discussed in this section. Chemical

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insecticides are likely to impact many insect species, including rare ones. The proximity of spray blocks to State Natural Areas should also be considered due to their sensitive nature. To request a project review, please contact the Endangered Resources Review Program (http://dnr.wi.gov/, keyword “ER Review”). The ER Review will include recommendations to help projects comply with Wisconsin's laws. Your own personal observations from the site (and other sources of rare species information) are also important to protecting species that could be affected by forest pest spraying.

Threatened or endangered species that may be impacted by spraying These are legally protected species that could be affected by aerial spraying, and Wisconsin laws prevent the “take” (destruction) of any of these species. Rare moths and butterflies are directly susceptible to insecticide spraying, and rare insectivorous birds can be indirectly impacted by removing a large portion of their food source. It is possible that some pesticides may be prohibited from use where these species are known to occur:

Butterflies and moths: Northern Blue Butterfly, Swamp Metalmark, Frosted Elfin, Powesheik Skipperling, Silphium Borer Moth, Phlox Moth, Regal Fritillary, Karner Blue Butterfly (addressed separately on page 9)

Rare forest raptors: Osprey, Northern Goshawk, Red-shouldered Hawk

Colonial-nesting water birds: Great Egret, Snowy Egret

Insectivorous Birds: Cerulean Warbler, Hooded Warbler, Worm-eating Warbler, Kentucky Warbler, Acadian Flycatcher

Ospreys, hawks and birds that congregate in rookeries are sensitive to nest disturbance from low flying aircraft, and a minimum no-fly distance is required where nest sites are known. Although only the legally-protected species are listed above, there are additional uncommon species for which we encourage voluntary consideration (see the “Special Concern” species on the Natural Heritage Working List - http://dnr.wi.gov/, keyword “NHI”). The ‘Special Concern’ butterflies and moths are particularly vulnerable. Prairie white-fringed orchid (Platanthera leucophaea) is a federally endangered plant that requires certain moths for its pollination. Special care is warranted whenever spray blocks are being planned near its habitat.

Additional information on these and other species is available at: http://dnr.wi.gov/, (keyword “ER”).

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State Natural Areas The locations of State Natural Areas can be found online or by contacting the State Natural Area Program at (608) 266-0394. Check to see if your spray area is adjacent to a State Natural Area. Notification of the State Natural Area Program is required if spraying is adjacent to a State Natural Area.

Conserving rare animals and plants when planning a spray area

Avoiding certain habitats when designing spray blocks can help to avoid impacts to many rare and uncommon species, especially butterflies and moths. These habitats include forest openings, prairies, rock outcroppings and wetlands adjacent to spray areas. Planning an aerial spray near these habitats and State Natural Areas should be done carefully. Be very careful as you decide where to spray, and ensure that the spraying is done as planned. Spray drift, although not intended, can be harmful to many of the species mentioned in this Appendix (and other species as well). Use insecticides to only treat the pests, thus avoiding or minimizing impacts to rare species. Use small- scale or individual treatments if possible, to avoid impacts to unintended habitats. Report rare species if you encounter them as you assess your site. Additional information on rare species is available at: http://dnr.wi.gov/, keyword “ER”).

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Appendix II: Pest-Specific Information

A. Gypsy moth

These favored tree species will be fed on before less palatable species such as maples. For this reason, defoliation will be most severe and frequent on these favored trees:

Oak

Aspen

Birch, except for yellow birch

Basswood and linden

Apple and crabapple

Willow

Tamarack

Witch hazel Hazel shrub

Service berry

Gypsy moth caterpillars may defoliate conifers such as white and red pine, spruce or hemlock once the caterpillars are half grown. These and other conifers are at risk if they are adjacent to preferred broad-leaved trees that the caterpillars can feed on when small.

Predictive surveys and using them to determine the area to be treated

While gypsy moth populations can increase over large areas, the intensity of the population can vary considerably within that area. Predictive surveys can be used to focus aerial spraying on those areas likely to be damaged if the pest population is not suppressed.

If you are planning to sample egg mass numbers, wait until mid-August in southern Wisconsin and Labor Day in northern Wisconsin. This will ensure that allof the egg masses have been produced by the time you sample. For a description on how to conduct egg mass surveys to predict next year’s infestation levels, visit: http://gypsymoth.wi.gov/. Heavy defoliation (>50%) would be predicted if the sampling indicates that there are more than 500 egg masses per acre in a residential area, and if more than 1,000 egg masses per acre in a woodlot. Take a few samples throughout the area you are considering treating. If you see many egg masses on one end of the area but few on the other, you may want to expand your treatment area or retarget your spray area to center on the area with the highest pest population. Also be aware that large caterpillars can move short distances, up to 150

Gypsy moth egg masses.

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feet. If you have a concentration of preferred trees such as oak or aspen to one side of a heavy infestation, the gypsy moth caterpillars will likely move into these favored trees and cause damage even if there are few egg masses there at the time of survey.

Timing of gypsy moth spraying

When timing the spray application, take into account both the development of the caterpillars and size of the tree leaves.

Before the eggs hatch, the project coordinator or designate should identify 25 or more egg masses within the treatment area to monitor for hatching. Select new (firm) masses that are at eye level or lower and are at least 6 inches from other masses. Choose masses from a variety of positions around the trees, and avoid masses on buildings. Around mid-April (in southern Wisconsin) or late April (northern Wisconsin), begin to check the masses every few days until you see the first small larvae on the masses. Then, check every 2 days and count the total number of larvae on the masses you have chosen to monitor. Estimate numbers if there are more than 100 larvae on a mass. You will see that the hatch starts off slow, picks up, and then drops off. Normally, spraying occurs about 10-14 days after the peak of the hatching. Hatching should be complete by the time spraying is done, and most caterpillars should be about 3/8” to 1/2” in length. Look for the small caterpillars on the underside of tree and shrub leaves of favored species.

At the same time as hatch starts, monitor the oak leaf development in the area to be sprayed. Oaks will leaf out later than most species, but since oak is the gypsy moth’s favorite species of tree in most treatment areas, focus on its leaf expansion. Typically, spraying occurs when the oak leaves average 3-4” in length. Spraying too early results in too little leaf area to intercept the spray, and spraying too late results in the outer leaves intercepting most of the spray. When populations are high, expect to see some leaf feeding occur prior to the spraying. This amount of feeding should not affect the tree or spray effectiveness unless populations are extremely high.

Gypsy moth caterpillars hatching from egg masses.

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B. Forest tent caterpillar

Forest tent caterpillar (FTC) is primarily a pest in northern Wisconsin, and periodic outbreaks occur over a large area. Growth loss is the major impact, although trees can be weakened and become prone to mortality from other causes. The most common tree species affected are aspen and oak. Outbreaks and defoliation frequently occur for multiple years at a given site before the outbreak comes to an end. The presence of many large flies that often land on people is a sign that the outbreak is probably coming to an end. These flies attack the pupae of the forest tent caterpillar, leading to a decline in the caterpillar population. Note: gypsy moth caterpillars may be confused with forest tent caterpillars. Make sure the species is correctly identified before proceeding to organize spraying. Determining the area to be treated

FTC defoliation tends to be widespread and is less spotty in nature than gypsy moth defoliation. Landowners do not need to rely on local egg mass counts as much as they would with gypsy moth outbreaks. If landowners track FTC outbreaks by staying in touch with DNR Forest Health staff, they should have a good idea what the local populations will be like.

A guide developed by the Minnesota Department of Natural Resources, found on page 18, can be used to predict FTC population levels using local observations and does not require tree cutting. In residential areas, you could use other criteria such as nuisance caterpillars, increasing defoliation during the previous summer, or interest in treatment to determine the area to be sprayed.

Alternate method of FTC predictive surveys If you choose to do local prediction surveys using FTC egg masses, the most accurate way to predict next year’s forest tent caterpillar population is to cut down several aspen trees and count the number of egg masses found on the tree. Thus, this survey method may not be suitable for residential areas. This predictive survey should be done while the trees are leafless, between late fall and early spring.

Forest tent caterpillar egg mass (silver) and adult moth. Photo from www.forestryimages.org.

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When the potential spray area is less than 50 acres, select two aspen trees to cut. For each additional 50-100 acres, select an additional two trees. Trees should be at least one hundred feet away from a road. Since FTC tends to lay egg masses on tall trees, select the trees that are dominant or co-dominant (full crown and receiving full light from above). Choose trees that are at least 6 inches in diameter at breast height (dbh). Avoid trees with many dead branches, as FTC moths tend to avoid trees in poor health. Measure the diameter of the trees before you cut them down, and record this data.

Forest tent caterpillar prediction guide developed by the Minnesota Department of Natural Resources.

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After you cut each tree, count the number of new egg masses on it, and record the data on a tally sheet. Egg masses are sturdy, cylindrical structures that encircle fine twigs (see photo on page 17). They are ¼” to ¾” long, covered with a glossy brown material that protects the egg contents during cold winters. You may find some old egg masses from last year, which are lighter in color and feel soft. Count only new egg masses. To predict the level of defoliation for the sample area, plot the average tree diameter and average number of egg masses per tree on the graph below. Actual defoliation will be influenced by weather conditions, size of the egg masses, number of egg parasites, etc. The decision to spray should be based upon factors such as the impact of the predicted defoliation on the trees, cost, the use of the property, tree health and stand management goals.

Monitoring hatch If possible, find several trees where there are numerous egg masses within 8-10 feet of the ground. Find a total of about 25 masses to monitor. In mid-April, begin monitoring these masses every day or two and record when the hatching begins on

Forest tent caterpillar defoliation prediction system developed by Forestry Canada in Manitoba. Use the average tree diameter and average number of egg masses found on each tree.

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each mass. The hatching of the eggs should roughly coincide with the emergence of the leaves in the spring. Then, watch the development of the caterpillars, because the timing of spraying will be based on the size of the caterpillars and leaves. Monitor the size of the caterpillars on small trees, low-hanging branches and shrubs. The small larvae from an egg mass often cluster together on a group of small leaves.

If the area to be sprayed has a significant oak component (>25%), monitor the development of the oak leaves. Oaks will leaf out later than the aspens in the area. If there is only a minor oak component, monitor the aspen leaves instead. The optimal period for spraying occurs when the caterpillars are 3/8” to 1/2” in length, and the leaves are about half their normal length (oaks are 3-4” and aspen are 1 1/2” to 2”). Normally this would be sometime in May in northern Wisconsin. If a second spray is planned, it should occur 3-5 days after the first. When populations are very high, the small caterpillars may eat the foliage off as it appears. If this is the case, time the spraying only on the size of the caterpillars. Unfortunately, spray effectiveness will likely be reduced because of the reduced leaf area to intercept the pesticide. Alternative insecticides may be worth considering when planning the spray project.

C. Jack pine budworm and spruce budworm

Population sampling for these pests is more complicated than for gypsy moth or forest tent caterpillar, and the advice of a DNR Forest Health specialist is suggested. The hidden feeding habits of early instar jack pine budworm and spruce budworm make these species difficult targets for insecticidal control. The most common insecticide used to control budworms is Btk. For both budworms the first life stage that can be targeted by Btk is the relatively free-feeding 4th instar caterpillars. This stage would occur from late May to mid-June in Wisconsin. Since this is rather late in larval development for Btk applications, a single high dose approach is advised. Applications should also be high volume in order to get the Btk down to the base of the needles. This is necessary because even the free-feeding larvae tend to feed primarily by clipping through the needles at their base.

Forest tent caterpillars hatching from an egg mass. Photo from www.forestryimages.org.

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If Btk is the insecticide of choice, Jack pine budworms should be treated roughly two weeks after most of the male flowers stop shedding pollen. Spruce budworms should be sprayed about 7-10 days after all the bud caps have been shed from the new growth. If pollen cones are scarce, spray when the new needles are ½ to ¾ expanded. Btk has the advantage of being specific to caterpillars. Thus, it will not kill the parasites and predators of the budworms. Btk will not come close to a total kill of budworms but should provide enough control to keep the trees green and alive. A DNR Forest Health staff directory can be found online at: http://dnr.wi.gov/topic/ForestHealth/staff.html.

Agencies contributing to this guide: Wisconsin Department of Natural Resources; Wisconsin Department of Agriculture, Trade and Consumer Protection; US Fish and Wildlife Service.

Jack pine budworm (mature larva). Larvae should be sprayed when smaller than this. Photo from www.forestryimages.org.