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.
Pecan Nut Casebearer
PECAN NUT CASEBEARER – 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 – 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.
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.
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.
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.
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.