Farm Contingency Plan for MRLS Risk Reduction for Kentucky Horse Farms

Eastern Tent Caterpillar Recommendations - 2002

By Lee Townsend, Extension Entomologist

USDA Insect and Plant Disease Slide Set

The presence of moderate to high numbers of eastern tent caterpillars (ETC) in mare areas was one of the risk factors identified in a Mare Reproductive Loss Syndrome (MRLS) survey of 133 Kentucky horse farms. Consequently, minimizing or eliminating exposure of pregnant mares to ETC has been identified as one part of an overall risk reduction plan. However, the toxicological and biochemical mechanisms of MRLS have not been fully defined so application of insecticides to control ETC may have no impact upon incidence of MRLS in 2002. This information is presented as an aid to decision- making. If an ETC control program is implemented, it must rely upon on well-timed and properly delivered applications of an insecticide.

What Is The Possible Role of the ETC in MRLS?

There are 2 potential ways in which ETC could have been involved in the syndrome, a direct effect or an indirect effect.

Direct effect

Leaves of the wild cherry tree contain a material that releases cyanide when the leaf is physically damaged. Initially, it was thought that pregnant mares could have eaten enough caterpillars to receive a dose of cyanide that would be passed to the foal with lethal effect. Research in the lab of Dr. Bruce Webb, University of Kentucky Entomology Department, has shown that cyanide does not accumulate in caterpillars and thus they are not likely to deliver appreciable amounts of cyanide to horses.

Indirect Effects

Feeding ETC produce large amounts of frass (feces) that rains to the ground under infested trees. This nutrient-rich material could serve as food for specific fungi that in turn produce toxins. These toxins could be ingested by grazing mares and affect their fetuses. Also, diseases can rage through insect populations during outbreak years. It is possible that a pathogen which infects the ETC could in some way have been ingested by mares and contributed to MRLS.

Experiments to investigate these hypotheses will be conducted early this spring. Results are not likely to be available in time to resolve whether or not the ETC is involved in MRLS. Since ETC cannot be discounted as a contributing factor, reduction of their numbers is one part of an overall program of risk reduction for MRLS.

ETC Control Program

There is no preventive approach to ETC control. If insecticides are to be used, they must be applied after egg hatch is complete and tents are visible in trees. The recommended insecticides do not have long residual lives on foliage. Premature applications may result in the need for an additional spray.

There are 4 elements of an ETC control program:

• Timely detection of active ETC nests and feeding caterpillars in trees
• Application of an appropriate insecticide with proper equipment if ETC populations are judged to be moderate or greater.

• Protection of applicators, animals, and the environment.

• Follow up inspections of treated areas 5 to 7 days later to evaluate results and to check for additional tents.

When Should ETC Scouting Begin?

Forsythia bloom is a phenological event that can be used to determine when to scout trees. Egg hatch of ETC coincides with 50% bloom of Forsythia so FULL BLOOM is the right time to be scouting trees for the small tents and starting the sprays.

An insecticide application to control ETC should be made after egg hatch has occurred and when small tents are visible in the trees. The spray should be applied after egg hatch and directed to foliage within about 3 feet of the nest, or where caterpillars are feeding. Most of the products must be eaten by the caterpillars to work so they need to be applied to feeding sites, not the nest.

What Are "Safe" Control Alternatives?

Confirm Turf and Ornamental (tebufenozide) is labeled for ETC control on shade trees and ornamentals. Tebufenozide is a molt-accelerating compound that disrupts caterpillar development. Because it has no target site in vertebrate animals, it is classified as a low- hazard insecticide. Although environmentally friendly, tebufenozide is toxic to aquatic invertebrates, so it should not be allowed to drift or run-off into streams or ponds. A 6-hour drying time is needed for optimum results. The label recommends use of LATRON B-1956, a spray adjuvant, for optimum initial deposit, redistribution, and weatherability of the residue.

Conserve SC (spinosad) is a new type of microbial insecticide that is labeled for caterpillar control on trees. It, too, poses little or no hazard to vertebrates and is regarded as a reduced risk or biorational insecticide. It is toxic to some aquatic organisms. The label cautions against spraying to the point of excessive runoff. This is a turf and ornamental product.

Bacillus thuringiensis - Bt based insecticides (Dipel, etc.) are derived from a toxin produced by a soil microbe. They are specific to caterpillars, disrupting the digestive tract of the insect. The caterpillars generally stop feeding within hours after feeding on treated foliage but may not die for several days. Bt is essentially nontoxic in the environment.

Timing of application is very important with all three of these products. They are most effective against small larvae and less effective against large caterpillars.

Some synthetic pyrethroids can be used for ETC control. These products have an advantage over the previous products in being active at lower temperatures. However, they have a much broader spectrum of activity and can cause more “off target” effects. These include:

DeltaGard T & O (deltamethrin) is extremely toxic to fish and aquatic invertebrates. Use care when applying in areas adjacent to any body of water. Skin contact can result in transient tingling and reddening of the skin. Eye protection is required on the label, in addition to standard personal protective equipment.

Talstar Lawn & Tree Flowable (bifenthrin) is toxic to fish, drift and runoff may be hazardous to aquatic organisms in nearby bodies of water. It is an eye irritant.

Tempo 20 WP (cyfluthrin) is toxic to fish, drift and runoff may be hazardous to aquatic organisms in nearby bodies of water. Tempo causes moderate eye irritation.

Scimitar SC or GC (lambda-cyhalothrin) is extremely hazardous to fish, drift and runoff may be hazardous to aquatic organisms in nearby bodies of water. It is an eye irritant. Scimitar SC is for use by individuals/firms licensed and registered by the state to apply pesticide products. Scimitar GC is a Restricted Use pesticide.

What About Grazing Restrictions?

These products are to be applied to tree foliage, not to pastures. There will be some drip from treated foliage on to the grass below. Confirm and Conserve have specific statements on the label indicating that livestock must not graze on treated areas and must not be fed hay or cover crops grown in treated areas. The same instructions apply to the synthetic pyrethroid insecticides. There are no such restrictions for Bt- based insecticides.

Regardless of the product used, it would be prudent to keep the “drip” area clipped closely and to feed hay away from the tree line to draw horses out of the area.

What About Spraying Pastures?

Several insecticides, such as Sevin (carbaryl) or Bt products, are labeled for application to pastures to control several caterpillar pests. There is no benefit to spraying pasture grasses to kill wandering ETC.

Pesticide Exposure Considerations

The application of any insecticide to medium to large-sized trees provides the potential for applicator or animal exposure through spray drift or runoff. Read and follow label instructions before buying and applying any pesticide. Pay particular attention to protective equipment and other guidelines.

Shade Tree Spraying Equipment

Application equipment can be as simple as a pump up or backpack sprayer for small trees but a very different equipment is needed for large trees. The following information was written by D. R. Daum and Thomas F. Reed, College of Agriculture, Extension Service, The Pennsylvania State University.

A successful pest control program has four objectives; diagnosis of the problem, the right chemical and rate, proper timing, and thorough coverage. These are essential and cannot be overemphasized. Any one component is worthless without all the others.

Thorough coverage is probably the most difficult objective. Weather, size of trees, and available spray equipment all influence application. Weather conditions and tree size are beyond control, but you can select the proper equipment to meet your needs. Repeated applications are often uneconomical. Therefore, you must use equipment which gets the job done right, the first time.

Types of shade tree sprayers

A hydraulic (liquid) sprayer uses water as a diluent and carrier. The pressure developed from the pump is used to atomize the spray mix at the nozzle and deliver it to the target. An air-blast sprayer uses water as a diluent and both air and water as a carrier. Pressure from the pump provides atomization and a high-velocity air stream carries the droplets to the target.

Hydraulic (liquid) sprayers are used for all sizes of trees. Tree sprayers are available as trailer models to be towed or skid-mounted models for use on pickup trucks or other vehicles. They vary in size from a 2.5-gpm pump and 2-HP engine to units with a 60-gpm pump and a 60-HP engine used by municipalities, institutions, or custom-spray operators. Tank sizes vary from 10 gallons up to 1,000 gallons. Some of the large trailer units can be powered from a tractor power-take-off shaft. Between these extremes there is a wide range of sizes and options.

The hydraulic sprayer uses large volumes of water and high pressure. The taller the tree, the higher the required pressure. However, since higher pressures tend to produce smaller droplets, larger orifices must be used to offset this effect. Droplets must be relatively large to have sufficient momentum to carry to the tree tops and to adhere to the surfaces.

The table below provides some information to consider in determining sprayer needs.

As the tree height increases, the spray angle at the nozzle is decreased to concentrate the pressure in the spray stream. In spraying tall trees, a solid stream may be used with most of the liquid breakup being produced by the resistance of the air after the liquid leaves the gun.

Nearly all hydraulic tree sprayers use a hand-held gun. For short trees and shrubs a multiple-outlet gun may be used but the single-outlet gun with a pistol-grip valve is the most common. Many applicators use a variable discharge-angle gun; with a twist of the handle the spray angle can be controlled from a wide angle for short trees and shrubs to a solid stream for tall trees.

The working pressure at the gun is very important for satisfactory operation. Often the gun is a considerable distance from the pump. Runs of 200 feet or more are common where the sprayer must be parked away from the tree being treated. Whenever liquid flows through a hose, friction loss is unavoidable. However, this loss can be minimized by choosing the proper diameter hose for the desired flow rate. Of course the choice is a compromise among friction loss, cost, and handling ease (size and weight of hose with water).

Since friction (pressure) loss is directly proportional to length, you can extend the information to any length, i.e. a 100-foot hose has twice the loss of a 50-foot hose. Select hose size based on flow of the gun or other delivery means being used, not the rated pump capacity. It is interesting to note that for a given flow, a change of one commercial hose size has a big effect on friction.

Additional pressure losses occur at fittings, valves, and turns. To check pressure at a gun, simply 'tee' a gauge into the line at the gun and read pressure while spraying at the desired rate. No friction loss occurs when the gun is off because there is no flow present. As you start spraying, you may observe a quick pressure drop at the gun; this drop is the friction loss in the hose as the flow initiates.

Generally, coverage by a hydraulic sprayer is relatively good with a high volume of water; if there are problem areas, they are usually in the tops of very tall trees. Height of effective coverage can be increased by using elevated truck-mounted platforms, gun extensions, or ladders.

The spray mix is relatively dilute and therefore relatively safe. Although the droplets are larger and more resistant to drift than those from an air-blast sprayer, drift can still be a serious problem. To insure adequate coverage, trees are usually sprayed to the point of runoff.

Air-blast sprayers

The air-blast (mist-blower) sprayer applies a concentrated pesticide mixture using a high- velocity, large-volume airstream. Since air is the carrier, the air-blast sprayer uses only a fraction of the water used by hydraulic units. With air providing the transport energy, the droplets must be relatively small. To accomplish this, air-blast sprayers are usually equipped with cone nozzles. If the air velocity is greater than droplet velocity at the point of injection, additional atomization takes place.

The small droplets give the necessary coverage for good insect control. Although small droplets are desired for good transport and coverage, they must be large enough to deposit on the foliage. This balance between size and deposit establishes a minimum volume per area rate. Research has shown that more spray volume should be directed toward the top of the tree than the lower portions to obtain uniform coverage. The larger droplets, containing most of the spray volume, settle out of the air stream very rapidly.

The larger air-blast sprayers have capacities up to 20 gallons per minute. The combination of engine size, fan size, and type of air tunnel allow some sprayers to reach trees 80 feet tall.

Competent operation is essential when using air-blast sprayers since the spray pattern is almost invisible. It is also impossible to determine the extent of coverage since there is no runoff. Trees to be sprayed must be directly accessible to the sprayer unit because best coverage and distribution is obtained by spraying up through the canopy. If the distance from the tree to the sprayer is too great, the velocity will be insufficient to penetrate the canopy.

Most airstreams lose 75 percent of their velocity in the first 25 feet after leaving the sprayer. Therefore, the sprayer should be immediately adjacent to the tree.

Two factors affecting the coverage obtained with air-blast sprayers are airstream velocity and volume. In addition to canopy penetration, velocity is important in getting the spray to the top of tall trees.

Spray material must be forced into the foliage with a turbulent force. To achieve this, air velocity is nearly 100 mph when leaving the sprayer, and must be at least 15 mph at the tree surfaces.

Generally, increasing the volume of air applied improves the spray distribution. The blower must displace the volume of air in the tree with air from the sprayer containing spray droplets. When the available energy is fixed, the higher the ratio of volume to velocity, the better the distribution.

Air-blast sprayers are not trouble free. In addition to wind conditions, a potential problem during cold weather is freezing of the spray droplets both on the nozzles and while air-borne. Evaporative cooling may cause ice to accumulate on the nozzles. This can alter the droplet size as well as the distribution patterns. Also, sometimes after leaving the nozzle droplets will form ice crystals and coverage is negligible. To avoid freezing problems, air-blast spraying should be done only when the temperature is above 45 degrees Farenheit.

Although air sprayers can reach tall trees, their energy consumption far exceeds that of hydraulic sprayers. The energy need is greater because air-blast sprayers must move both air and liquid. Some air sprayers require as much as a 140-HP engine. O

n the other hand, air sprayers cover trees faster and require less refilling, than hydraulic sprayers. When spraying large numbers of trees, timely operation can result in pest control equal to hydraulic sprayers, with lower overall costs.

Application

The first key to good application is coverage. In other words, delivering the pesticide to all surfaces of the tree as uniformly as possible. This requires proper equipment and a competent operator.

Training and experience are very important. A limiting factor with shade tree spraying is the wind. Utmost attention must be given to wind speed and direction. Winds as low as 5 mph can disrupt the spray stream and should be avoided. Small droplets are very susceptible to drift and certain mixtures, such as dormant sprays, can be a problem on non-target areas.

Also, operators should avoid spraying during periods of low relative humidity; evaporation causes a significant reduction in droplet size from sprayer to tree. This can cause loss of momentum and impingement resulting in reduced coverage and control. Ideally, tree spraying is done during times of no wind and high relative humidity; often these conditions occur only at night or very early in the morning.

Mixing is an important part of spray application. Always carefully and accurately measure the correct amount of pesticide for the mix. Stay within approved rates. If recommendations are in active ingredients, be very careful in determining the amount of formulated product. Technical materials may be formulated in more than one percentage of active ingredient, even by the same manufacturer. If you have trouble getting a uniform suspension with wettable powders despite agitation, try premixing as a thin slurry before adding to sprayer. In all cases, the agitator should be operating before any pesticide is added to the sprayer tank.

Always try to end the day with an empty tank. Do not mix more pesticide than is needed. Always flush with clean water and drain, even if you plan to apply the same material the next day. Also rinse the outside of the sprayer.

Safety

Exposure to a large amount of almost any pesticide can cause illness. Some pesticides are so toxic even a small quantity can be dangerous to the operator. To apply any pesticide safely, your most important source of information is the label on the container. Read and follow the directions on it.

Avoid exposure to pesticides when mixing and spraying by using protective clothing and equipment. Applicators should wear long-sleeve shirts and trousers, gloves, waterproof boots, brimmed hats, goggles, and if necessary respirators. Consult the pesticide label for specific recommendations. Do not smoke or eat when handling pesticides. Apply chemicals at the recommended rate and time and only on the recommended crops. Avoid contamination of water sources due to runoff from trees or wash water from cleaning equipment.

When not in use, chemicals should be stored in their original, labeled containers. Place the containers in an approved locked storage building or room.

Surplus pesticide mixes are a serious problem, also. Mix only what you need. Prevent contamination of food and water sources by disposing in an approved manner, preferably by applying in a labeled use.

Summary

The degree of success in any pest control program depends to a large extent on the equipment. Can you reach the tops of small trees? Does your sprayer give uniform, complete coverage.? Is a hydraulic sprayer or air-blast sprayer best suited for your needs? Careful consideration must be given to these questions when under taking a tree spraying program.

Information on the biology of the ETC is available in EntFact 423 - Eastern Tent Caterpillars

Trade names are used to simplify the information that is presented. No endorsement by the Cooperative Extension Service is intended, nor is criticism implied of similar products that are not named.