Pest Management Principles
Chemical Use Precaution
Policy Statement on Pest Management Suggestions
Pecan Insect Pests
Protecting Bees and other Pollinators from Insecticides
Allen Knutson | Professor and Extension Entomologist
Bill Ree | Extension Program Specialist III IPM (Pecan)
Texas A&M University System
Many insects feed on the leaves, nuts, branches, and buds of the pecan tree, reducing the tree’s nut production potential. Some insects lower production directly by feeding on the nuts. Other pests cause indirect damage, as their feeding depletes the tree’s reserves, so that nut production is reduced the following year.
This guide discusses the management of insect and mite pests of commercial pecans. Extension publication ENTO-083, Pecan Pests in the Home Orchard (available from your local Texas A&M AgriLife Extension office and online at http://agrilifebook store.org) describes how to control pests attacking pecans in home landscapes and in other non-commercial orchards.
Pest Management Principles
For many years, growers minimized pest damage to pecans by spraying pesticides on a regular schedule based on crop development. This effective, relatively inexpensive approach paired well with a preventive fungicide and zinc spray program. However, applying pesticides according to a schedule can:
- Increase the risk that pests will develop resistance to pesticides;
- Reduce populations of beneficial insects that keep pests in check;
- Result in secondary pest outbreaks; and
- Overuse of insecticides can negatively impact human health and the environment.
“Integrated Pest Management,” or IPM, is a philosophy used to design pest control programs. It uses the most compatible and ecologically sound combination of pest suppression techniques available to sustain profitability. These management techniques include:
- Cultural control – such as destroying crop residues where some pests overwinter;
- Host plant resistance – selecting pecan varieties that are well adapted and, when available, have genetic resistance to pests;
- Chemical control – using insecticides only when pest densities exceed economically damaging levels and, when available, selecting effective insecticides that have the least impact on natural enemies and non-target organisms; and
- Biological control – recognizing and protecting, when possible, natural enemies that suppress pest populations.
Insecticides are important in managing pecan pests, but they should be used wisely and only when needed to prevent economic loss. Base the decision to apply an insecticide on established treatment thresh-olds of insect density or damage, as determined by systematically conducted orchard surveys. Do not add insecticides to fungicide or zinc sprays unless it has been determined that an insect pest has or will exceed a treatment threshold. Choose insecticides and application rates carefully according to their effectiveness, the hazard they pose to the applicator and their impact on beneficial insects.
Application of insecticides classified as pyrethroids, carbamates, and organophosphates may be followed by outbreaks of aphids, other insects, or spider mites. Outbreaks may result from the destruction of natural enemies that were holding these secondary pests in check. If these products are used, limit their use to control late-season pests. Pyrethroids used in orchards where mite or aphid outbreaks have occurred following their use may exacerbate problems with those same pests.
The frequent use of some insecticides can cause some insect pests to become resistant, especially aphids. These resistant insects survive and pass on their genes for resistance to their offspring. Each time the insecticide is applied, the proportion of resistant insects in the population increases. As a result, the insecticide is no longer effective.
Insecticides are classified according to their modes of action, or the ways they kill insect pests. The development of insecticide resistance can be managed by using them only when necessary and rotating their use with other pesticides with different modes of action. It is difficult for an insect to develop resistance to two insecticides that have different modes of action. Therefore, rotating insecticides with different modes of action is a good resistance management tactic. The mode of action of labeled pecan insecticides is identified by its IRAC number or group number as listed on the label. To rotate insecticides, choose effective insecticides with different modes of action numbers.
Adverse weather, inadequate food supply, or natural enemies may hold insect and mite populations below damaging levels. It is important to recognize the impact of these natural control factors and, where possible, encourage them.
Biological control is the use of living organisms (parasites, predators, and diseases) to reduce pest numbers. Important natural enemies of pecan pests include lacewings, spiders, lady beetles, assassin bugs, predatory mites, and many kinds of tiny wasps that parasitize insect pests. Biological control includes con-serving, augmenting, and importing natural enemies.
Conserve existing populations of natural enemies in the orchard by minimizing insecticide applications and by using insecticides that are the least toxic to the natural enemy. As example, Confirm®, Intrepid®, Spinosad, and B.t. formulations are less toxic to most beneficial insects and other non-target species than carbamate, pyrethroid, and organophosphate insecticides. Ground covers such as legumes can provide food and shelter for natural enemies. Augmentation involves periodically buying and releasing natural enemies. However, research to date has shown that releasing convergent lady beetles, lacewings, or Tri-chogramma wasps does not provide significant pest control in pecans.
Thorough tree coverage is essential for maximum pest control. Low-volume sprayers (mist blowers, air blast sprayers, speed sprayers, etc.) use forced air to deliver a concentrated spray mix and require proportionately less water than high-volume hydraulic sprayers. Concentrated low-volume spraying saves water and time. The amount of pesticide applied per acre must be consistent with the label and is the same regardless of how much water is applied.
To calibrate a sprayer, fill the spray tank with water only and spray a known acreage of trees (e.g., 5 acres). Measure the amount of water remaining in the tank to determine the number of gallons of water applied. To determine the number of gallons applied per acre, divide the amount of water applied by the number of acres sprayed. For example, if 300 gallons were used to treat 5 acres, then the sprayer is delivering 60 gallons per acre. In this example, a 500-gallon sprayer would treat 8.3 acres.
Then add the amount of formulated insecticide needed to treat the number of acres the spray tank treats. For example: If the label rate was 1 pint per acre, add 8.3 pints of pesticide to 500 gallons of water.
Recalibrate sprayers for different tree sizes and spacings, as these factors change the volume of spray required for coverage. Carefully follow the sprayer manufacturer’s directions for mixing spray materials and for calibration.
Chemical Use Precaution
Select the suggested insecticide that provides the most effective, safe, and economic control. All suggested materials are poisonous, but proper handling reduces the hazards associated with their use. Comply with the manufacturer’s label directions for handling all toxic chemicals.
Residues: The Environmental Protection Agency (EPA) has established pesticide residue tolerances on pecans. These regulations establish the amount of a specific chemical that can be present in or on pecans at harvest. Always consult the product label for specific restrictions. Be sure the pesticide is registered for use on pecans and is used only in accordance with specific application instructions.
Caution: All pesticides are potentially hazardous to humans, animals, and non-target crops; use them with caution. Store all pesticides out of the reach of children, irresponsible people, livestock, and household pets. Properly dispose of leftover spray materials and containers. Provide proper training to any orchard worker who is engaged in mixing, spraying, or entering orchards after they have been sprayed. Use appropriate signage in orchards when trees have been sprayed to communicate proper reentry times to all persons coming and going through the orchard.
Pesticide drift: Do not let the pesticide drift to nearby land or contaminate ponds and streams.
Poisoning symptoms: Some symptoms of pesticide poisoning are headaches, nausea, cramps, diarrhea, weakness, blurred vision, and muscular twitching. If you notice any of these symptoms during or after handling any pesticide, consult a physician immediately.
Policy Statement on Pest Management Suggestions
The information and suggestions included in this publication reflect the opinions of Extension entomologists based on research, field tests, and user experience. Our management suggestions are a product of research and are believed to be reliable. However, it is impossible to eliminate all risks. Unforeseen or unexpected conditions or circumstances may result in less than satisfactory results even when these suggestions are used. The Texas A&M AgriLife Extension Service assumes no responsibility for risks, and such risks shall be assumed by the user of this publication.
Suggested pesticides must be registered and labeled for use by the Environmental Protection Agency and the Texas Department of Agriculture. The status of pesticide label clearances is subject to change and may have changed since this publication was printed.
The USERS are always responsible for the effects of pesticide residues on their livestock and crops, as well as for problems that could arise from the drift or movement of the pesticide from their property to that of others. Always read and follow the instructions on the container label carefully.
Pecan Insect Pests
Phylloxera are tiny, soft-bodied insects closely related to aphids. These insects cause noticeable swellings, called galls, to form on leaves, twigs, and nuts. The two most important species attacking pecans are pecan leaf phylloxera and pecan phylloxera. Pecan leaf phylloxera form galls on leaf tissue only; extensive infestations may cause some defoliation. The pecan phylloxera is the most damaging species because it attacks shoots and nuts. Widespread infestations of this species can reduce yield and the tree’s vitality and subsequent production.
Both species of Phylloxera survive the winter as eggs in bark crevices. In spring, tiny nymphs emerge during bud break and feed on new growth. As they feed, nymphs secrete a substance that stimulates plant tissue to develop abnormally, creating galls. The young phylloxera are soon completely enclosed in the galls, which range from 1/10 to 1 inch in diameter. Phylloxera feed and complete development inside the gall. Galls then crack open and winged, adult phylloxera emerge.
Some adult female leaf phylloxera deposit eggs, and the hatching nymphs result in a second and sometimes third-generation of galls if new growth is available during the season. Other females overwinter and deposit eggs the following spring. The more destructive pecan phylloxera form no additional galls. These females hide in protected places on the bark and die, their eggs remaining inside the mothers’ protective bodies throughout the winter.
Native trees and improved varieties vary in susceptibility to phylloxera. Because phylloxera cannot fly long distances, infestations move slowly from tree to tree. You can often control them by treating only those trees with phylloxera galls. Survey the orchard in May and mark trees with galls to treat the next spring.
Insecticides for phylloxera must be applied after the eggs hatch in the spring but before nymphs are protected inside galls. Treat after bud break when growth is 1 to 2 inches long.
Sawfly larvae feed on the underside of pecan leaves in the spring. Sawfly larvae resemble caterpillars, but they are actually wasp larvae. Sawfly larvae have six sets of prolegs, while larvae of moths and butterflies have anywhere from one to four sets of prolegs. Two species are often found on pecans. The larva of one species is shiny green and its feeding results in small, neat holes cut in the leaf. Full-grown larvae are about ½ inch long. The larva of the other species ranges from yellowish-brown to orange with black spots along the body and generally consume the entire leaf. These larvae only produce one generation a year. There are no guidelines for making insecticide treatments. However, leaf damage is usually minor, and insecticidal control is rarely needed. Very few insecticides list sawfly on the label. However, if an insecticide is needed to prevent excessive defoliation during outbreaks, malathion, or chlorpyrifos labeled for pecans can be effective. Scout for aphids and other secondary pests which may increase to damaging levels when using these and other broad-spectrum insecticides.
June beetles are brown to brownish-red, hard-bodied beetles about ½ to ¾ inch long. June beetles feed on pecan leaves at night, and large numbers of beetles can defoliate pecan trees almost overnight. Look for beetles feeding on leaves during the night. As the beetles hide just below the soil surface during the day, it is often difficult to identify them as the cause of the leaf-feeding in pecans. Damage occurs in the spring when beetles emerge from the soil. Immature June beetles, called white grubs, feed on grassroots and are not a pest of pecans. Very few insecticides list adult June beetle on the label. However, if an insecticide is needed to prevent excessive defoliation, malathion, or chlorpyrifos labeled for pecans can be effective. Scout for aphids and other secondary pests which may increase to damaging levels when using these and other broad-spectrum insecticides.
Pecan Nut Casebearer
The pecan nut casebearer is found in all pecan-growing areas of Texas and can cause severe crop loss almost every year if left uncontrolled. Case-bearer larvae or caterpillars feed inside pecan nuts. First-generation larvae feed inside small nutlets from April to June. This generation is the most damaging, as a single larva often destroys all the nutlets in a cluster. Larvae of later generations require just one or two nuts to complete their feeding, as pecans are larger at that time.
The adult casebearer is a gray moth about 1/3-inch long with a ridge of dark scales across the forewings. The moths are active only at night when they mate and lay eggs on pecan nuts. Most eggs are found on the nutlet tips. Each female can lay 50 to 150 eggs during her 5- to 8-day life. The greenish-white to white eggs change color to pink or red before hatching.
Casebearer eggs hatch in 4 to 5 days; young larvae crawl to nearby buds below the nuts to begin feeding. The empty white eggshell remains on the nut. After feeding for 2 to 3 days on a bud below the nut cluster, the tiny larvae enter the pecan nut, often tunneling in at the base. Silk and black frass (excrement) are usually visible on the outsides of infested nuts. Larvae feed inside pecan nuts for 3 to 4 weeks, depending on the temperature. They are olive-gray and reach a length of about 1 inch. Full-grown larvae pupate in the pecan nut; adult moths emerge about 9 to 14 days later.
The pecan nut casebearer completes several generations each year. Adults that develop from the overwintering larvae emerge in April and May and lay eggs on pecan nutlets soon after pollination. First-generation larvae feed on nutlets and mature to moths. These moths lay second-generation eggs in grooves on the tips or bases of nuts, or on buds. Second-generation larvae attack the nuts in midsummer about 42 days after nut entry by first-generation larvae.
Third-generation eggs are deposited on nuts from late July to early September. These larvae feed only in the shucks if the pecan shells have hardened to prevent penetration into the kernel. Many third- and later-generation larvae do not feed, but crawl to the base of a dormant bud and build tough, tiny, silken cocoons where they spend the winter. In spring, these immature larvae leave the cocoon, called a hibernaculum. They feed on buds and tunnel in developing shoots until they are full-grown. Larvae then pupate in shoot tunnels or bark crevices. Casebearer moths soon emerge to lay first-generation eggs on nutlets.
Often a single, carefully timed insecticide application adequately controls the first-generation case-bearer. A second insecticide application may be required if unhatched eggs are found 7 to 10 days after the first application, depending on product and rate. Time insecticide applications accurately to control newly hatched casebearer larvae before they enter the nuts. Once inside nuts, larvae are protected from insecticides. See Table 2 for insecticides.
To determine whether treatment is needed and when to apply insecticide, examine nuts carefully in the spring for casebearer eggs. Infested clusters can be flagged to monitor egg hatch. Once they emerge from the egg, the tiny larvae feed for 2 to 3 days on a secondary bud just below the nut cluster and then tunnel into a nutlet. Delaying treatment until observing the first nut entry maximizes the insecticide’s residual activity. However, consider the time required to treat the orchard, including possible weather delays, so that insecticide is applied before most larvae have entered nuts.
Peak egg-lay often occurs during a 2-week period in late April to early May in the southern and coastal areas, or mid to late May and early June in North Texas. Spring temperatures influence casebearer development; cool, rainy weather can delay moth activity and egg-laying. Thus, the egg-laying period can vary as much as 2 weeks from year to year, depending on spring weather. Knowing when to scout the orchard for eggs and when to apply an insecticide, if needed, are two important components of managing pecan nut casebearer.
Walnut caterpillars feed together in large numbers on pecan leaves but do not build silken webs like fall webworms. Larvae eat leaves, leaving only the mid-ribs and leaf stems. Large infestations can defoliate entire trees. This insect is found throughout Texas east of the Pecos River. Although economic infestations are uncommon, severe and widespread outbreaks of walnut caterpillars have occasionally occurred in Texas.
Walnut caterpillar moths emerge in spring and deposit eggs in masses of 500 or more on the under-sides of leaves. The egg masses are round, about the size of a half-dollar, and are not covered with hairs or scales. Eggs hatch in about 10 days; larvae feed for about 25 days. Young larvae are reddish-brown with yellow lines running the length of the body. Full-grown larvae are about 2 inches long, black with grayish lines, and are covered with long, soft, gray hairs. Larvae congregate in large masses on the trunk and scaffold branches to shed their skins before crawling back to complete feeding on leaves. These final-stage larvae consume most of the foliage, and defoliation can occur very quickly. Mature larvae crawl to the soil to pupate. A generation is completed in about 6 to 8 weeks. There are two to three generations each year.
Because walnut caterpillars do not build tents or webs, infestations often go unnoticed until leaf damage becomes obvious. To detect infestations early, look for egg masses or leaf feeding. Egg masses can be detected at night by shining a flashlight on the undersides of leaves and looking for white spots about the size of a half-dollar. Caterpillars cause 80 percent of their damage during the last 3 to 4 days of feeding. Smaller larvae are easier to kill with insecticides than larger larvae; controlling this stage prevents severe damage. Insecticide treatment may be necessary if large infestations threaten to defoliate trees.
Aphids are small, soft-bodied insects that suck sap from pecan leaves. There are two species of “yellow” or “honeydew” aphids—the black margined aphid, Monellia caryella, and the yellow pecan aphid, Monelliopsis pecanis.
The black margined aphid has a black stripe along the outside margin of its wings, which are held flat over the body. The yellow pecan aphid holds its wings roof-like over its body and lacks the black stripe along the wing margin. Immature aphids are difficult to identify because they lack wings. Infestations may contain both species.
Black margined aphid infestations typically increase to large numbers from June to August and then decline after about 3 weeks. Outbreaks on most cultivars (except possibly “Cheyenne”) usually decline without causing measurable damage to foliage or yield.
The yellow pecan aphid occurs later in the sea-son. Outbreaks of this species can defoliate trees and reduce yield and quality on most cultivars.
Both species of yellow aphids have piercing/suck-ing mouthparts for removing water and plant nutrients from leaf veins. As they feed, aphids excrete large amounts of excess sugars. This sticky material, called honeydew, collects on leaves.
Honeydew is a food source for sooty mold, which can cover leaves when humidity is high. The shad-ing effect of sooty mold can reduce photosynthesis. Studies have shown that aphid feeding can reduce leaf efficiency and large, persistent infestations of the yellow pecan aphid, M. pecanis, can defoliate trees. This leaf injury and loss can reduce current and subsequent yields and quality because of lower carbohydrate production.
Yellow aphid eggs survive the winter hidden in bark crevices on twigs and tree trunks. Immature aphids, called nymphs, hatch in spring and begin to feed on newly expanded leaves. Nymphs mature in about a week and give birth to live young. All individuals are females, which reproduce without males during spring and summer. In late September and October, males and females develop, and females deposit overwintering eggs.
Aphids have a short life cycle and high reproductive capacity, so infestations can increase quickly under favorable conditions. Natural enemies, including lacewings, lady beetles, spiders, and other insects, can suppress aphid infestations if there are enough of them. However, insecticides applied for aphids or other pests can sometimes destroy these natural enemies, allowing aphids to increase to even greater densities than before treatment.
Inspect leaves frequently to monitor yellow aphid densities. Treatment of either species of yellow aphid may be justified on “Cheyenne” when aphid densities are high and persist for several weeks. “Pawnee” is the least susceptible cultivar to yellow aphids, and insecticide treatment for yellow aphids is not normally needed on this variety.
Consider treatment when infestations of yellow pecan aphid exceed 25 per compound leaf. Scouting the orchard on a 4- to 5-day schedule will reveal whether yellow pecan aphid numbers are increasing or decreasing and indicate the need for insecticide treatment. Do not base the need for treatment on the amount of honeydew alone, as infestations often decline rapidly (“crash”) because of weather or physiological effects.
Hickory shuckworm is an important mid- and late-season pest of pecans throughout much of Texas.
Shuckworm larvae tunnel in the shuck, interrupting the flow of nutrients and water needed for normal kernel development. Infested nuts are scarred, late in maturing and of poor quality. Damaged shucks stick to the nuts and fail to open, creating “sticktights” that reduce harvesting efficiency. Infestations before shell hardening may cause nuts to fall.
Adult shuckworms are dark brown to grayish-black moths about 3/8 inch long. They are active in spring before pecan nuts are available.
Adults deposit eggs on hickory nuts and pecan buds. Larvae on pecans feed-in phylloxera galls in spring. Later in the season when pecan nuts are present, moths deposit eggs singly on the nuts.
The egg is attached to the shuck with a creamy white substance visible on the shuck surface. The tiny larva hatches in a few days and burrows into the shuck to feed for about 15 to 20 days. Mature larvae are about ½ inch long and cream-colored with light brown heads. Pupation occurs in the shuck, and the moth soon emerges.
Several generations are completed each year. Shuckworms overwinter as full-grown larvae in old pecan shucks on the tree or the orchard floor.
Pecans are most susceptible to hickory shuckworm damage during the water through gel stages. If the orchard has a history of shuckworm damage, treat with insecticide when pecans reach the half-shell hardening stage (see the chart of Development Stages, page 19). A second application 10 to 14 days later may be needed.
Fall webworm caterpillars build large silken webs in pecan trees. A hundred or more caterpillars may be found inside the web, where they feed on pecan leaves. Large infestations may cover the tree with webs, causing severe defoliation.
Mature larvae are about 1 inch long, pale yellow or green, and covered with tufts of long, white hairs. The adult is a white moth with dark spots on the wings. Female moths emerge in spring and deposit eggs in masses of several hundred on the undersides of pecan and other tree leaves. The greenish-white eggs are covered by gray hairs left by the female. There are two to four generations each year, depending on the location in the state. The last, or fall, generation is usually the most damaging.
Many insect parasites and predators feed on and reduce the number of fall webworm larvae. Also, insecticides applied for other pecan pests help reduce webworm densities. If webs are common and the potential defoliation appears unacceptable, spot spraying of infested trees may be practical.
Pecan Leaf Scorch Mites
The pecan leaf scorch mite is the most important spider mite attacking pecans.
Large numbers of these tiny mites feed on the undersides of pecan leaves. Mites suck plant sap, causing irregular brown spots on infested leaves. Infestations often develop first along the leaf midrib. Damaged leaves appear russeted or scorched. Large infestations can result in leaf loss, especially if trees are under moisture stress.
Scorch mites overwinter as adults in the rough bark of limbs. Adult females begin laying eggs in spring. Mites can complete a generation in 5 to 15 days and are more numerous during hot, dry weather. Natural enemies of scorch mites, including predatory mite species, are important in controlling these pests.
Because scorch mites prefer the shady, interior portion of the tree, significant damage can occur before infestations are detected. Check water sprouts and shady, lower branches to detect early mite infestations. Mites may increase after some insecticides (e.g., Sevin® and other carbaryl formulations) are applied for hickory shuckworm, aphids, or other pests. Monitor the orchard for mites when the weather is hot and dry and after insecticides are used. Spray when mites are present and damaging leaves. Mark infested trees or areas to determine whether spot treatment is practical.
Black Pecan Aphid
The black pecan aphid is much more destructive than the two species of yellow aphid. Three black pecan aphids per compound Black aphid leaf can cause severe leaf damage and defoliation. Although they sometimes can be found on the upper side of the leaf, black pecan aphids feed primarily on the undersides of leaves and occur throughout the pecan-growing region of Texas.
While feeding, black pecan aphids inject a toxin that turns the leaf tissue between major veins bright yellow. These damaged areas, up to 1/4 inch across, turn brown and die, and infested leaves soon fall. Premature defoliation reduces nut fill and the next year’s production.
The black pecan aphid is pear-shaped. Nymphs are dark olive-green and adults, which may be winged, are black. Like yellow aphids, all summer forms are females that reproduce without mating. Male and female forms appear in fall and females lay eggs that overwinter on branches. Densities often are very low until August or September, when infestations often increase rapidly. Note that parasitized yellow pecan aphids will turn black and can be confused with black pecan aphids. Parasitized aphids are dead and stuck on the leaf surface and do not move while live black pecan aphids quickly fly when disturbed.
Monitor the orchard frequently for black pecan aphids and their characteristic leaf injury. Because these aphids feed singly and can be damaging in low numbers, examine leaves closely. Examine the interior of the canopy where infestation often begins. In general, treat when black pecan aphids average three per compound leaf. Black pecan aphids are easier to control with insecticides than yellow aphids. Natural enemies are important in keeping the number of black pecan aphids low.
Stink Bugs and Leaf-footed Bugs
Several species of brown and green stink bugs and leaf-footed bugs feed on pecan nuts. Infestations often develop on soybeans, sorghum, and other field crops or weeds and then move into pecans in late summer and fall.
Stink bugs and leaf-footed bugs have piercing-sucking mouthparts and penetrate the shuck to feed on the developing kernel. Nuts injured before the shells harden fall from the tree. Feeding after shell hardening causes brown or black spots on the kernel. The affected areas taste bitter.
These bugs overwinter as adults under fallen leaves and in other sheltered places on the ground. Populations increase in summer when adults lay eggs on many crops and weeds. Fields of soybeans, other legumes, and sorghum may be sources of adults that fly to pecans. Infestations are usually largest from September through shuck split, but low numbers not necessarily requiring treatment may occur throughout the growing season in pecan orchards.
Look for stinkbugs feeding on pecans during kernel development. Guidelines for determining when an insecticide is needed to prevent stinkbug dam-age have not been developed. Brown stinkbugs are more difficult to kill with insecticides than are green stinkbugs and leaf-footed bugs. Field studies indicate bifenthrin is more effective on brown stinkbugs than other pyrethroids.
Weed control in and near the orchard helps suppress stink bugs and lower the possibility of their moving into pecans. Some growers also have planted “trap crops” to lure adult stinkbugs and leaf-footed bugs away from pecans. Black eye, purple hull, crowder peas, or millet planted in plots or a single row along the edge of the pecan orchard in the last week of July through the first week of August are attractive crops for these pests. To maintain a trap crop longer into the fall, stagger the plantings by a couple of weeks. Monitor the peas or millet for adult leaf-footed and stink bugs when the plants begin to bloom and set pods. Apply an insecticide to the trap crop to kill stink bugs and leaf-footed bugs once the crop stops blooming and setting pods. This treatment is necessary to kill the bugs before they leave and fly into the pecans. Before planting a trap crop, make sure you have enough available water to obtain a stand and are planting a variety of pea suited to the soil type and soil pH of the orchard. You will also need to control weeds and prevent livestock and wildlife from grazing plots.
Grasshoppers can move into pecan orchards from adjacent crops, pastures, and weedy areas and feed on pecan leaves and developing nuts. Weed control in and around the orchard can deprive grasshoppers of food. Pyrethroid insecticides (lambda-cyhalothrin, zeta-cypermethrin, bifenthrin), chlorpyrifos, and carbaryl labeled for use in pecans kill grasshoppers. However, their residual control is limited, and frequent re-application may be required when grasshoppers continue to move into the orchard from adjacent areas. Treat the orchard floor, fence rows, and areas surrounding the orchard to create a buffer zone.
The pecan weevil is found throughout most of Texas. Where present, the pecan weevil is the most damaging late-season pecan pest. Infestations are often localized and vary greatly within orchards.
In August, adult weevils begin to emerge from the soil and feed on nuts in the water stage, causing them to drop. After the kernel has entered the gel stage, the nut is susceptible to egg-laying and attack by pecan weevil larvae. Infested nuts remain on the tree while the developing larvae consume the kernels. Full-grown larvae emerge from nuts in late fall or early winter through a round hole chewed through the shell.
The life cycle of the pecan weevil from egg, larva, pupa and to adult usually is completed in 2 years but may require 3. Adult weevils begin emerging from the soil in August; their numbers peak from late August through early September. Rainfall, soil moisture, and soil type influence the ability of the weevils to emerge from the soil. Drought can delay adult emergence until rain or irrigation loosens the soil.
Adult weevils feed on nuts and live for several weeks. Once nuts reach the gel stage, they are suit-able for egg-laying. For this reason, early maturing varieties are infested first. The female weevil drills a hole through the shell and deposits one or more eggs within the developing kernel. A single female lays eggs in about 30 nuts.
Larvae hatch from the eggs and feed inside the nut, destroying the kernel. Larvae emerge from the nuts about 42 days after the eggs are deposited. The emergence of full-grown larvae from nuts begins in late September and continues as late as December.
Larvae burrow 4 to 12 inches into the soil and build cells, where they remain for 8 to 10 months. Most of the larvae then pupate and transform to the adult stage within a few weeks. However, the adults remain in the underground cells for a second year before emerging from the soil the following summer. Those larvae (about 10 percent) not pupating after the first year remain as larvae for 2 years and then emerge from the soil as adults the third year. Monitoring In most years, economic damage occurs if pecan weevils are left untreated.
In most years, economic damage occurs if pecan weevils are left untreated. Monitoring weevil emergence from the soil helps determine the optimum timing of insecticide treatments and the need to reapply insecticides.
Depending on environmental conditions, the emergence of adult weevils may be completed in a week or less or last for 4 to 5 weeks or more. These variations are caused primarily by differences in soil hardness, as influenced by soil texture and rainfall or irrigation. Peak emergence typically occurs from August through mid-September.
There are several methods of detecting and monitoring adult weevils. One involves jarring limbs to knock adult weevils onto a sheet placed on the ground, where they are easily seen. Fallen pecans can also be examined for feeding and egg-laying punctures made by adults.
Trapping weevils is the most reliable way to determine adult weevil emergence. The pyramid trap can be bought, but it and the other types of traps can be built easily following instructions found at http://factsheets.okstate.edu/documents/epp-7190-monitoring-adult-weevil-populations-in-pecan-and-fruit-trees-in-oklahoma/. Begin monitoring traps about 1 to 2 weeks before the first pecans enter the gel stage. In Central Texas, begin trapping about the first week of August and continue through shuck split.
Wire cone traps. Wire cone traps are built from ⅛-inch mesh hardware cloth. Place traps on the soil beneath “scout” trees known to have a history of high weevil numbers. Weevils emerging from the soil beneath the trap crawl up the sides of the trap and are captured inside the jar at the top.
Inspect traps every 2 to 3 days, record the captured weevils and remove them from the traps. The number of traps you will need depends on the orchard size and weevil density. Ten to 15 traps per orchard are often enough to monitor weevil activity.
Pyramid or “Tedders” traps. Pyramid traps are built of two triangular pieces of ½-inch hardboard that interlock to form a 4-foot tall pyramid. The trap is painted a dark color and fitted with a container at the top for capturing weevils.
When placed in the orchard, pyramid traps simulate a tree trunk and attract adult pecan weevils emerging from the soil. Weevils walk or fly to the trap and crawl up the sides until captured in the container at the top. Place one trap beneath the canopy of each scout tree. Remove grass, weeds, and fallen branches from around the tree and trap to increase its attractiveness. Painting the adjacent tree trunk with whitewash or paint decreases its attractiveness to weevils and increases the number of weevils attracted to the dark pyramid trap.
As with cone traps, record the number of captured weevils and remove them and other insects and spiders from the traps every 2 to 3 days. The number of traps needed to monitor weevil emergence depends on orchard size and weevil density. Ten to 15 traps per orchard is often enough to monitor weevil activity.
Circle trap. Because wire cone and pyramid traps are placed on the orchard floor, they interfere with mowing and can be damaged by grazing cattle. Circle traps were designed to avoid these problems, as they are placed on the tree trunk. Also, these traps can be left in the orchard, unlike other types that require removal for harvest.
A circle trap is built much like the wire cone trap and fastened to the trunk of the pecan tree. Adult weevils crawling up the tree trunk are funneled into the trap and captured in a container at the top.
Trapping indicates the presence and relative abundance of adult pecan weevils. The pattern of trap catches, as described above, helps determine when adult weevils begin to emerge and when insecticide should be reapplied to protect nuts from later emerging adults.
Pecan weevils are controlled by foliar insecticides, which kill adults. Once nuts reach the gel stage, apply insecticide if adult weevils are present. A second application 7 to 10 days later is usually necessary unless drought has delayed weevil emergence from the soil. If weevils are late-emerging, continue to monitor the emergence and reap-ply the insecticide at 7- to 10-day intervals if weevils continue to emerge. Aphid infestations may increase following insecticide application for pecan weevil control.
Pecan weevil infestations spread slowly unless aided by humans. Do not transport infested nuts to weevil-free orchards, as they can be the source of
a new infestation. Also, destroy infested nuts after harvest.
Harvesting early, before weevil grubs have exited the nuts, physically removes grubs from the orchard and can reduce weevil infestations if done each year.
Red Imported Fire Ant
Fire ants’ stings can be a serious problem for orchard workers and interfere with pecan operations such as grafting, mowing, and harvesting. They may also damage equipment such as electrical motors and irrigation systems. Some formulations of chlorpyrifos are labeled for application as a broadcast spray to the orchard floor and temporarily reduce fire ants. Methoprene, pyriproxyfen, and hydramethylnon are baits that are broadcast across the orchard. Fire ants collect the bait particles and carry them back to the colony. The colonies die over a period of weeks or months, depending on the bait product used. For additional information on fire ants, download the publication E-628, Broadcast Baits for Fire Ant Control from the Texas A&M AgriLife Bookstore (www.agrilifelearn.tamu.edu).
Protecting Bees and other Pollinators from Insecticides
Pecans are wind pollinated and therefore do not rely on insects for pollination. Pecan flowers do not produce nectar, and the pollen grains are very small and of poor nutritional content; therefore, they are not collected by honeybees. Honeybees sometimes collect aphid honeydew, a source of sugar, from pecan leaves. Bees may be killed if cover crops such as clovers, alfalfa, or vetch are flowering in the orchard during insecticide application. Insecticide applicators and beekeepers should cooperate closely to minimize bee losses.
To prevent bee losses, do not spray colonies or allow the insecticide to drift onto colonies. Bees cluster on the fronts of their hives on hot evenings and can be exposed to pesticide drift or direct spray. Read the “Directions for Use” section of the pesticide label for directions and restrictions on protecting honeybees and pollinators. New labels include this information in a bee advisory box highlighted by the bee icon.
Additional information on commercial pecan management can be found at the following websites:
- Texas A&M University Entomology Department httpsw://entomology.tamu.edu/
- Texas Pecan IPM http://pecankernel.tamu.edu
- Texas Pecan Growers Association http://tpga.org
- Texas A&M University Horticulture Department http://aggiehorticulture.tamu.edu
- The publications below can be downloaded or ordered from http://agrilifelearn.tamu.edu:
- ENTO-083, Pecan Pests in the Home Orchard
- E-173, Controlling the Pecan Nut Casebearer
- ENTO-089, Controlling the Pecan Weevil
For more information and pesticide recommendations, download the full PDF.