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.
|Pecan nut casebearer damage|
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|
|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.
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|
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
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