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Pecan Insect Pests

(Click on images to see pests lists and description)

NUTS


Nuts
FOLIAGE


Foliage

TRUNK, BRANCHES, TWIGS

Trunk










PESTS ASSOCIATED WITH NUTS

Pecan Weevil

Pecan Nut Casebearer

Stinkbugs and Leaffoted Bugs

Spittled Bug

Hickory Shuckworm

Red Imported Fire Ant

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Nuts











PESTS ASSOCIATED WITH FOLIAGE

Black Pecan Aphid

Yellow Aphids

Pecan Phylloxera

Sawfly

Fall Webworm

Walnut Caterpillar

Spider Mites

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Foliage











PESTS ASSOCIATED WITH TRUNK, BRANCHES, TWIGS

Asian Ambrosia Beetle

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Trunk











PECAN WEEVIL    
Where it is found in Texas, 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 kernel. Full-grown larvae emerge from the nut in late fall or early winter through a round hole chewed through the shell.

The life cycle of the pecan weevil egg, larva, pupa and adult usually is completed in 2 years but can 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 suitable 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. 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 a cell, 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 cell for an additional (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.

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PECAN NUT CASEBEARERAdult pecan nut casebearer.  Click on image to enlarge. - Adult
Pecan nut casebearer adults have been collected in pheromone traps in Texas as far north as College Station, TX as of April 19. During this time of year pecan bud moth adults occasionally are collected in PNC pheromone traps. Proper identification of PNC adults is important for determining scouting time. PNC adults have a ridge of scales that sticks up that appears as a band across the forewings approximately 1/3 the distance from where the wings attach to the body. This is a key identification character for PNC. The picture shows a PNC adult on the left and a pecan bud moth adult on the right. 

Pecan Nut Casebearer - EggPecan nut casebearer egg
Female casebearer adults will deposit singular eggs on the stigma end of small nutlets. Oviposition or egg lay will begin 7 and 10 days after the initial catch of adults in pheromone traps. New eggs are a pearly white color but as eggs mature, red spots will form and the egg will take on a pink or red color prior to hatch. Time from egg lay to larval hatch is 3 to 5 days.

More information check our publication "Controlling the Pecan Nut Casebearer"

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STINK BUGS AND LEAFFOOTED BUGS
Several species of stink bugs and leaffooted bugs feed on pecan nuts. Infestations often develop on field crops or weeds and then move into pecans.

Stink bugs and leaffooted bugs suck sap from developing nuts. Nuts injured before the shells harden fall from the tree. Feeding after shell hardening causes brown or black spots on the kernel. Affected areas taste bitter.

As adults, these bugs overwinter under fallen leaves and in other sheltered places on the ground. Adults lay eggs on many crops and weeds, where populations increase in summer. Fields of soybeans, other legumes and sorghum may be sources of adults that fly to pecans. Infestations are usually greatest from September through shuck split.

Weed control in and near the orchard helps suppress stink bugs and lower the possibility of their moving into pecans. Cypermethrin (Ammo ® , Cymbush ® ), esfenvalerate (Asana ® , azinphosmethyl (Guthion ® ) or carbaryl (Sevin ® ) applied for other pests may also control stink bugs and leaffooted bugs.

These kernel-feeding insects can also be managed by planting certain host or "trap crops," which lure adult stink bugs and leaffooted bugs away from pecans in September, October and November. Planting plots or single rows of peas (blackeye, purple hull, crowder, etc.) along the edge of the pecan orchard in the last week of July through the first week of August produces an attractive trap crop for these pests.

The trap crop does not have to be continuous around the entire orchard. Small plantings in several selected locations can be enough. To help ensure having an attractive trap crop longer into the fall, stagger the plantings by a couple of weeks. Monitor the peas for adult leaffooted and stink bugs when the plants begin to bloom and set pods.

Apply an insecticide to the trap crop to kill stink bugs and leaffooted bugs once the crop stops blooming and setting pods. This treatment is necessary to kill the bugs before they have a chance to leave and fly into the pecans. Before planting a trap crop, consider these factors: having available water to obtain a stand; planting a variety of pea suited to the soil type and soil pH of the orchard; weed control; and grazing of plots by wildlife and livestock.

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SPITTLE BUG Spittlebug. Click on image to enlarge.
White spittle masses are produced by the nymphs of spittle bugs. This sucking insect is frequently seen on nutlets and tender stems.

High populations on nut clusters can result in nut loss. Currently there are no well defined guidelines for treatment thresholds. Provado ® is a selective insecticide for sucking insects and could be used to treat spittle bugs and not disrupt beneficial insects.

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HICKORY SHUCKWORM: 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 occurring 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 pecan 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 1/2 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 shuck-worm 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. Asecond application 10 to 14 days later may be needed. Cultivars such as "Pawnee" and other early-maturing varieties that reach half-shell hardening earlier than other varieties must be treated earlier for hickory shuckworm. Removing and destroying old shucks and dropped nuts, where shuckworms overwinter, can reduce shuckworm infestations. Pheromone traps are available that attract and capture hickory shuckworm moths. Guidelines for using trap catches to determine the need for treatment have not been validated in Texas.

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RED IMPORTED FIRE ANT
Fire ants can lower pecan production when they interfere with such operations as grafting, mowing and harvesting. They also may damage drip or sprinkler irrigation systems. Chlorpyrifos (Lorsban ® ) is registered for use in pecan orchards as an orchard floor spray for fire ants. Logic Fire Ant Bait ® is registered for use only in nonbearing pecan orchards.

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BLACK PECAN APHID
The black pecan aphid is much more destructive than the two species of yellow aphid. Three black pecan aphids per compound leaf can cause severe leaf damage and defoliation. Like yellow aphids, the black pecan aphid feeds on the undersides of leaves and occurs 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. Infested leaves soon fall. Premature defoliation reduces nut fill and the next yearÕs production.

The black pecan aphid is pear-shaped. Nymphs are dark olive-green while 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.

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 two to three per compound leaf. In most cases, black pecan aphids are easier than yellow aphids to control with insecticides. Natural enemies are important in maintaining low numbers of black pecan aphids.

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YELLOW APHIDS
Aphids are small, soft-bodied insects that suck sap from pecan leaves. There are two species of "yellow" or "honeydew" aphids, the blackmargined aphid, Monellia caryella , and the yellow pecan aphid, Monelliopsis pecanis .

The blackmargined 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.  Blackmargined aphid infestations typically increase to large numbers during 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 season. Outbreaks of this species can cause defoliation and reduce yield and quality on most cultivars. Both species of yellow aphids have piercingsucking 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 serves as a food source for sooty mold, which can cover leaves when humidity is high. The shading effect of sooty mold can reduce photosynthesis. Studies have also shown that aphid feeding can reduce leaf efficiency; 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 from eggs 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 that reproduce without males during spring and summer. In late September and October, males and females develop, and females deposit overwintering eggs.

Control : 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. 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 normally needs no protection with insecticides.

    Consider treatment when infestations of yellow pecan aphid exceed 25 per compound leaf, indicating the onset of an outbreak. Scouting the orchard on a 4- to 5-day schedule will determine if 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.

    Insecticides do not consistently control either species of yellow aphids. Aphids may become tolerant to an insecticide used frequently in an orchard. An insecticide that is effective in one orchard may be ineffective in a nearby orchard. Studies have shown that in some cases, applications of pyrethroid insecticides (Asana ® , Ammo ® , Cymbush ® ) to control casebearers or aphids may be followed by large increases in yellow aphids.

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PECAN PHYLLOXERA: Feeding by the immature stages of the pecan phylloxera, Phylloxera devastatrix causes galls or knots to form on the woody portion of the new growth. This includes stems, leaf petioles and midribs, nutlets and catkins. Heavy infestations of this insect can cause nut loss and defoliation.

The immature stage hatches from eggs in the spring that have overwintered on the tree. The immatures, also known as "stem mothers" migrate to the new growth where they settle and begin to feed. As the phylloxera feed, gall formation is initiated with tissue forming around the insect. If an insecticide is needed, it should be applied before the immatures become embedded in the new tissue. Insecticides only need to be applied to a tree if a tree had galls the previous season. The time of treatments should be when the foliage is at the stage shown in the picture. Recommended insecticides can be found in the Texas Agricultural Extension Service publication "Managing Insect and Mite Pests of Commercial Pecans in Texas" B-1238. Since the last printing of the pecan insect control guide, the insecticide imidacloprid, (Provado 1.6F or Admire 2F) has received a label for pecans. Provado 1.6F, the formulation for foliar application has provided good control of phylloxera. In addition, this product does not have a grazing restriction.

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SAWFLYSawfly damage to pecan tree leaves
Adult sawflies are small, bee-like in appearance and are about 1/4 to 1/3 inch long. Larvae feed on foliage and leave holes in the leaves or consume the whole leaf.

Sawfly larvae resemble caterpillars but are actually larvae of a wasp. Larvae of moths and butterflies have 1 to 4 sets of abdominal prolegs, whereas sawfly larvae have 6 sets. Once larvae finish feeding, they drop to the ground and burrow into the soil to overwinter. There is only one generation per year.

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FALL WEBWORM: 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 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. The insecticide spray must penetrate the web to be effective.

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WALNUT CATERPILLAR : 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 caterpillar have occasionally occurred in Texas.

Walnut caterpillar moths emerge in spring, de-positing eggs in masses of 500 or more on the undersides 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.

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SPIDER 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 ® ) 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 if spot treatment is practical.

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ASIAN AMBROSIA BEETLEAsian ambrosia beetle.  Click on image to enlarge.
Infestations of the Asian ambrosia beetle can be identified by the toothpick-like projections from the trunk or the main scaffold limbs. Infested trees should be removed and surrounding trees should be treated with lindane or chlorpyrifos (Lorsban ®). This is an early season pest with most infestations observed in April or May. Infested trees should be burned or shredded to prevent the adults from from emerging from the wood.

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For more information, contact:
Bill Ree
Pecan Pest Management
P.O. Box 2150
Bryan, TX 77806-2150
Phone: 979-845-6800
Email: w-ree@tamu.edu
Department of Entomology at Texas A&M University
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Texas A&M University
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