Although there
are many insects and diseases that can injure northern pecan trees, only a few cause economic damage on a regular basis. Pecan producers should learn how to
identify common pest problems and determine if and when those pests need to be
controlled. On this page, you will will find photos and descriptions of the most common pecan insects and diseases. Recommendations for chemical control of major pests are listed at the bottom of this page. These pesticide recommendations are primarily intended for pecan producers in Kansas,
Missouri, and Illinois.
Primary Pests
 |
| Pecan nut casebearer damage |
Two nut feeding insects and one shuck destroying disease are the primary targets for our pest control efforts. Annual
applications of pesticides made for these pests often help keep secondary pests in check.
Small, grey pecan nut casebearer moths are nocturnal and rarely seen in the orchard. However, these moths seek out newly pollinated pecan clusters for a location the lay their eggs. A larva hatches from the egg and the caterpillar bores into the base of a nut. As the larva feeds, it creates a pile of frass at the base of the nut and weaves a loose web that serves to keep the nut attached to the stem (photo at right) . A single nut rarely satisfies a larva's appetite and the insect quickly moves on to destroy the entire nut cluster. Growers should develop a regular scouting program to search for signs of pecan nut
casebearer damage. Make sure to inspect at least 300 nut clusters starting the 4th week in May. An insecticide should be
applied when 2% of clusters have been damaged.
 |
| Male (left) and female (right) pecan weevils |
Pecan weevil adults (pictured at right) emerge
from the soil starting in early August and continue emerging until early
September. Female weevils bore through the shuck and shell of a nut to lay 5-7
eggs. These eggs hatch into legless larvae which completely devour the kernel
of the nut. Left untreated, pecan weevil can completely destroy a pecan crop.
 |
| Circle pecan weevil trap |
Adult emergence is often irregular and related to soil moisture conditions. An extended dry period can delay weevil emergence while a good soaking rain in August will stimulate emergence. Growers should install trunk-mounted weevil traps (photo at right) to determine
peak adult emergence periods and apply an insecticide to kill adults before
they can lay eggs.
Pecan scab is the most serious disease of
pecan and can infect both leaves and nuts. Although scab lesions can be found on leaves of northern pecan trees, the infection rate is rarely sufficient to cause significant defoliation. In contrast, a scab infection on the shucks of northern pecans can
reduce nut size, inhibit kernel filling, and prevent proper shuck opening (photo at right). If
scab has been a problem in your orchard, a preventive schedule of fungicide
applications starting immediately after pollination will prevent economic losses. Recommended fungicides are listed in
Table 2 while a weather based schedule for scab control in given in Table 3.
There are several scab-resistant, northern pecan cultivars that can be grafted that can free a producer from the worries of pecan scab control (see pecan cultivars page). However, scab free cultivars are not necessarily disease free cultivars. Secondary diseases can become a problem during some seasons in the absence of regular scab sprays.
Secondary
Pests
Several
pecan insects fall into a category of secondary pests. These insects should be
controlled on “as-needed” basis. The key to keeping secondary pests from become
primary problems is to follow a strict orchard monitoring program.
 |
| Stem phylloxera with one gall cut open |
Two species
of phylloxera can create galls on pecan trees. Stem phylloxerans form large
galls on new stems and leaf mid-ribs distorting twig growth and inhibiting the
initiation of female flowers (photo at right). Leaf phylloxerans create smaller galls on the
leaf blades and can cause early defoliation. Once growers discover phylloxera
galls in their orchards it is too late to control the insect during the
current season. Growers need to mark phylloxera infested trees then treat those
marked trees the following spring during bud break. Timing for control of these
two species is slightly different. To control stem phylloxera, spray at inner
scale split or when the first bit of new green tissue starts to emerge. To
control leaf phylloxera, spray when the first leaf has burst from the expanding
bud.
Hickory shuckworm populations are often kept in check by insecticide
treatments aimed at controlling pecan weevil. However, if pecan weevil is not a
problem in your orchard, hickory shuckworm can build up to large populations
and cause a significant nut drop in July (2nd summer generation). You can identify hickory shuckworm damaged nuts by the tell-tale oviposition scar left on the outside of the nut (photo at right). Female moths cover newly laid eggs with white scales scaped from their abdomens. Growers
should monitor their orchards for signs of hickory shuckworm damage then plan
on making insecticide treatments the following summer if damage begins to
increase dramatically.
Fall Webworm and Walnut Caterpillar are two species of
caterpillars that feed in large colonies and can defoliate pecans. The fall
webworm spins a dirty white web over the colony (photo at right) while the walnut caterpillar
feeds without a protective web. Growers should scout for these insects and
apply an insecticide only if they find more than 5 colonies per acre. Each
insect has two generations per year. New colonies appear in mid-July and again
in late-August
Stink bugs are an increasing problem for pecan growers. Several species of plant-feeding bugs including brown stinkbug, green stinkbug, and leaf-footed bugs feed on pecans. During the water stage of kernel development, stinkbug feeding can cause nut abortion or the total cessation of kernel development and a blackening shell's interior. If feeding occurs after kernel fill, these insects will cause the development of bitter black spots on the nut meats (photo at right).
Pecan anthracnose is a disease that causes damage to both leaves and nuts. When symptoms of the disease occur on leaves the damage is often termed fungal leaf scorch. The disease first appears as a brown lesion on the edge of the leaf. As the lesion grows larger distinctive dark brown line
that separates healthy tissues from disease killed tissue (photo at right). Extensive infections can cause early defoliation.
Pecan anthracnose can also attack the nut causing a condition called Glomerella shuck rot (photo at right). Mid-summer infections can cause a reduction in nut size and prevent normal shuck opening. Infections that start later in the season have little impact on nut size or kernel fill.
Pecan cultivars resistant to pecan scab are often susceptible to this disease. However, this disease does not occur every year. Seasons of above average rainfall promote the spread of pecan anthracnose.
Tables for 2015 crop year
