Pecan Shuck Rot Treatment: How To Control Pecan Kernel Rot

By: Mary Ellen Ellis

A grand, old pecan tree in your yard is a wonderful anchor for the space, a good source of a large shady patch, and of course a bountiful provider of tasty pecan nuts. But, if your tree gets struck with pecan phytophthora rot, a fungal infection, you could lose the entire harvest.

What is Pecan Shuck and Kernel Rot?

The disease is caused by a fungal species, Phytophthora cactorum. It causes rot in the fruit of the tree, turning the shuck into a mushy, rotted mess, and rendering the nuts inedible. The disease is most common after it has been wet for several days and when the temperatures remain below 87 degrees Fahrenheit (30 Celsius) during the day.

Pecan shuck and kernel rot infections usually occur in late August or early September. The rot begins at the stem end and slowly covers the entire fruit. The rotten part of the shuck is dark brown with a lighter margin. Inside the shuck, the nut will be dark and bitter tasting. The spread of the rot from one end of a fruit to the other takes about four days.

Pecan Shuck Rot Treatment and Prevention

This fungal infection is not that common and tends to occur in only sporadic outbreaks. However, when it does strike, it can ruin half or more of a tree’s crop. It’s important to provide pecan trees with the best conditions for preventing the disease and to look for signs of it in order to treat immediately.

The best prevention is to simply make sure the tree is trimmed adequately to allow for airflow between branches and around fruits.

To control pecan kernel rot in trees that already have signs of the infection, a fungicide should be used right away. If possible, apply the fungicide before the shucks split. This application may not save every nut on the tree, but it should reduce the losses. AgriTin and SuperTin are two fungicides used to treat pecan shuck rot.

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Pecan Shuck And Kernel Rot – Learn About Pecan Phytophthora Rot Disease - garden

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Fruit and Tree Nut Research: Byron, GA


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Interpretive Summary: A new pecan nut disease was discovered during the 1988 growing season. This disease was caused by the water mold Phytophthora cactorum. The fungus infected nearly mature pecan fruits from early September through harvest causing yield losses up to 50 percent. The disease also reduced the quality of the remaining kernels by darkening the seed coat. Conditions associated with disease development were prolonged periods overcast, high humidity, cool temperature, and frequent rainfall. Disease was observed more frequently in irrigated orchards.

Technical Abstract: Phytophthora shuck and kernel rot infection usually started at the stem end of the pecan fruit and progressed distally to encompass the entire shuck within 4 to 6 days. Rotted shucks turned dark brown leaving a distinct margin between necrotic and healthy tissue. Phytophthora cactorum was isolated from the rapidly rotting pecan fruit. Two to three weeks after the symptoms appeared, the diseased shucks dried and stuck tightly to the shell. The seed coat of the kernels turned dark brown and the endosperm rotted. The new disease of pecan was first observed during September 1988 on maturing pecan fruit in central Georgia in the vicinity of the town of Byron where growers estimated losses of 50 percent or greater in some orchards. In south Georgia, near the cities of Albany and Cordele, the disease was present but less severe. The causal agent was identified as P. cactorum and deposited with The American Type Culture Collection as isolate B1, ATCC No. 66186. Laboratory and field inoculations using B1 isolate produced typical symptoms on nut clusters. Symptoms of the disease were observed in 13 orchards brought to our attention by state pecan extension specialists, and the pathogen was isolated from the soil of 10 of these orchards in south and central Georgia.

Selecting a Site

North Carolina is on the northern fringe of the commercial improved pecan-producing region of the United States. The limiting factor is the length of the growing season. The probability of spring frost damage to early and midseason varieties and the limited selection of late-maturing varieties for North Carolina are both limitations of pecan production. North Carolina’s northern-fringe location makes proper site and varietal selection crucial for consistent, profitable production.

Pecans do not grow well in all areas of the state. The best area is the North Carolina coastal plain, extending to the eastern edge of the North Carolina piedmont. Although pecan trees can be grown further west, nut production may be inconsistent.

The selected site should ideally have well-drained, deep soils (3 to 4 feet) with moderate soil-moisture-holding capacity. Pecan trees are native to river valley soils and have a relatively high water requirement. They do best on sandy loam soils but also can be grown on heavier soils such as clay loams if the soils are well-drained. In areas where the soil is lighter and relatively dry, irrigation is required.

To reduce the potential for frost or freeze damage, select a site at a higher elevation or one on a gradual slope. Do not plant in low areas where cold air tends to settle these areas are frequently referred to as frost pockets. As cold air settles, the moist air is frequently seen as fog or dew. Orchards planted on a slope also dry more quickly after wet periods, decreasing the wetting period of the orchard and minimizing conditions that favor disease development. Climatological maps can be used to determine potential sites for growing pecans. Information on the length of the season for a particular area, indicated by the number of frost-free growing days and the probability of frost in the spring, is readily available. For help with sites and season length, contact your county Cooperative Extension Center.

A site’s history is also a very good indicator of how well pecans will grow. Does the site frequently have frost in late spring or in early fall? Does it have standing water during wet periods, and is water readily available during very dry periods if irrigation is needed? What has been planted on this site in the last several years? Have herbicides or pesticides been used that may still be present in the soil? If so, will they reduce pecan tree growth when planted? Are pesticides or growth regulators applied to nearby fields that may harm pecan trees? Are homes or public areas nearby that might restrict spraying? All of these questions should be answered before you plant pecan trees.

Hickory Shuckworm

Cydia caryana

The hickory shuckworm targets two hosts – pecan and hickory trees. It is said that the hickory shuck worm is second only to the pecan weevil in terms of damage caused to pecan trees. They can be found throughout most of the eastern pecan growing region from Texas, Oklahoma, and Kansas east to South Carolina.

The hickory shuckworm has an unusual life cycle that allows for 2 – 3 generations of larvae each season (depending upon location). The first generation result from eggs laid in the hickory nuts, pecan nutlets or phylloxera galls. These larvae develop in May and June, with adults exiting the nuts and galls in late June and July. They lay eggs that become the second generation of larvae and they begin to feed inside the nuts in July and August. The second generation of larvae cause the greatest harm to the crop.

Symptoms of hickory shuckworm infestation include: poor kernel development, shuck sticking, scarred and discolored shells, and delayed nut maturity. The damage can be identified by a powdery white stain around entry points.

Controlling the 3rd generation of adult moth is the most likely path to success with the hickory shuckworm. Use of contact insecticides such as Neem Oil will help to control next year's population.

Photo courtesy of Clemson University Department of Entomology, Soils & Plant Sciences, Cooperative Extension Service.

Trattamento e prevenzione del marciume del pecan

Questa infezione fungina non è così comune e tende a si verificano solo in epidemie sporadiche. Tuttavia, quando colpisce, può rovinare metà o più del raccolto di un albero. È importante fornire agli alberi di noci pecan le migliori condizioni per prevenire la malattia e cercarne i segni per curarli immediatamente.

La migliore prevenzione è semplicemente assicurarsi che l’albero sia tagliato adeguatamente per consentire il flusso d’aria tra i rami e intorno ai frutti.

Per controllare la putrefazione del nocciolo di pecan negli alberi che hanno già segni di infezione, si dovrebbe usare immediatamente un fungicida. Se possibile, applicare il fungicida prima della divisione degli shuck. Questa applicazione potrebbe non salvare tutti i dadi sull’albero, ma dovrebbe ridurre le perdite. AgriTin e SuperTin sono due fungicidi usati per trattare la putrefazione del pecan shuck.

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