Some Common Pecan
Diseases and Their Control
in North Carolina
Ornamental Disease Information Note 3
R.K. Jones, Extension Plant Pathologist
D.F. Ritchie, Extension Plant Pathologist
Information] [Scab] [Powdery Mildew] [Blotch] [Wood Rots]
[Rosette and Bunch] [Internal
Breakdown] [Crown Gall] [Spanish
[Back to Ornamental Disease Notes]
are widely grown in North Carolina both for shade and nuts. Pecan trees
have several disease problems which reduce both the shade value and the
nut crop but seldom kill a tree. These diseases are difficult for the
homeowner to control with chemicals because of tree height. Therefore,
spraying pecan trees usually is not feasible for homeowners.
Scab is the most common and
damaging pecan disease. It is caused by a fungus that affects rapidly
growing leaves, shoots, and nuts. Symptoms on all plant parts are similar.
Velvety olive-brown to black spots occur on the husks. Several spots may
develop to form black blotches or may blacken the entire surface of the
husks. Severely affected nuts of susceptible varieties may drop prematurely
or they may stop growing, die and remain attached to the shoot. Leaf symptoms
first appear on the underside as tiny olive-brown lesions on the veins.
Later, leaf symptoms appear on the upper surface as small olive-brown
to black spots. Severely infected leaves may be shed prematurely and weaken
the tree, thus reducing the crop next year.
practical method of scab control is to plant varieties having some degree
of resistance to scab such as: Desirable, Cape Fear, Elliott, Chickasaw,
Gloria Grande, and to a lesser extent, Stuart. Varieties severely affected
by scab are Schley, Mahan, Success, Van Deman, and Mohawk. Use of "resistant"
varieties does not necessarily assure complete absence of the disease
as no variety is totally resistant. If possible, removing and destroying
all leaves and husks may help reduce the amount of scab the following
A spray schedule
is available for growers who have spray equipment adequate to cover the
trees, or for growers who hire custom spray applicators. The following
fungicides are registered on pecans: benomyl (Benlate 50WP), propiconazole
(Orbit 3.6EC), fenbuconazole (Enable 2F), and thiophanate methyl (Topsin-M
70WSB). Spray applications should be made every 2-3 weeks beginning when
leaves first emerge until shell hardening (early August). Spray at 2-week
intervals when the tree is growing rapidly or during wet periods.
Check fungicide labels for restrictions on grazing in sprayed orchards
and the need to use tractors with enclosed cabs while spraying.
states the scab fungus has become resistant to some of the fungicides.
This may not be true in orchards that have rarely, if ever, been sprayed
is occasionally a problem on highly susceptible seedling trees and can
be identified by the white powdery growth on the surface of nuts and young
shoots. Powdery mildew usually does not cause serious damage to most pecan
varieties. Scab sprays usually provide adequate control of powdery mildew.
several other leaf diseases can occasionally cause defoliation in late
summer. Generally blotch occurs only on trees low in vigor or deficient
in zinc. Nursery trees are especially susceptible. These diseases appear
as circular black spots or large, irregular yellow blotches on the leaves.
Removing or plowing under old leaves helps reduce the infestation from
one year to the next. Scab sprays usually will control leaf spots.
Wood or heart
rots can cause extensive wood decay and thus weaken the branches or trunk.
These fungus diseases occur following mechanical damage, commonly caused
by ice, wind, improper pruning, or mechanical damage during construction.
Damaged trees should be properly pruned to ensure normal healing and treated
with asphalt-base wood dressing.
occurs on pecans in North Carolina. This problem is caused by zinc deficiency
or by certain soil types where zinc is unavailable to pecan trees. Initial
symptoms occur mostly on the branches in the top of the tree. Leaves are
yellowish and mottled. In advanced stages, leaflets become narrowed and
crinkled on lower branches. New shoot growth is inhibited. Eventually
twigs and branches die back from the tips. Zinc deficiency can be corrected
by spraying the leaves twice with zinc sulfate alone or added to other
sprays at the rate of 2 pounds per 100 gallons of water (1 tbsp per gallon).
The zinc also may be applied to the soil around trees by spreading the
material from near the trunk outward to the drip line. A soil test is
desirable to determine the amount of zinc required but in general can
be applied at the rate of 1/2 pound for each inch of trunk diameter. A
disease called bunch disease can produce similar symptoms but differs
from rosette in two ways: leaflets of bunch diseased trees neither become
yellow between the veins nor extremely crinkled like those affected with
rosette. Bunch disease is thought to be caused by a phytoplasma. There
is no known effective control for bunch disease, however the following
practices will reduce spread. Use only graft wood from bunch disease-free
trees for propagation and do not top-work affected trees. On mildly affected
trees, prune the affected shoots several feet below the region of symptoms.
Candy, Lewis, Caspiana, and Georgia seem to be highly resistant.
breakdown of almost mature nuts in late summer occurs each year. The inside
part of the nut becomes soft and watery. This is a physiological disorder
the cause of which is not known. Its severity varies from year to year,
but appears to be most prevalent on certain varieties such as Moneymaker
Crown gall is a disease that
results in round to irregular swollen tumors or galls, usually found at
or near the soil line on the trunk or roots. Infected trees show a lack
of vigor, foliage lacks normal green color, and occasionally the tree
may die. To prevent crown gall, plant disease-free trees. For individuals
with a small pecan nursery, it is important not to locate a nursery in
an area where crown gall has been observed previously. As a preventative
control measure, it would be advisable to treat the seed with Galltrol-A
and coastal areas, Spanish moss can occasionally become thick enough in
pecan trees to increase ice and wind damage. A small amount of Spanish
Moss does little or no damage to trees. Where it is a problem, spray the
moss with copper sulfate at the rate of 10 pounds per 100 gallons (6 tbsp
per gallon) during the dormant season.
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Carolina Insect Notes
Carolina Agricultural Chemicals Manual
with a specific problem, contact your local North
Carolina Cooperative Extension Service Office.
Carolina, look for your state extension service
of specific chemicals are based upon information on the manufacturer's
label and performance in a limited number of trials. Because environmental
conditions and methods of application by growers may vary widely, performance
of the chemical will not always conform to the safety and pest control
standards indicated by experimental data. All recommendations for pesticide
use were legal at the time of publication, but the status of registration
and use patterns are subject to change by actions of state and federal
Published by the North Carolina Cooperative Extension Service Distributed
in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment
and program opportunities are offered to all people regardless of race,
color, national origin, sex, age, or disability. North Carolina State
University at Raleigh, North Carolina A&T State University, U.S. Department
of Agriculture, and local governments cooperating.
Last update to information: January 1999
Last checked by author: January 1999
Web page last updated Nov. 2000 by A.V.