Pecan Diseases and Pests and Their Control

Part 1

MP-313 NOVEMBER 1958

PECAN DISEASES AND INSECTS AND THEIR CONTROL

TEXAS AGRICULTURAL EXPERIMENT STATION ... TEXAS AGRICULTURAL EXTENSION SERVICE College Station, Texas

Key to Pecan Diseases

DISEASES OF THE LEAVES Olive spots on underside page 5 Scab Downy, buff, or greenish-yellow lesions page 7 Downy Spot Small, reddish-brown to gray spots on page 6 Brown Leaf Spot underside Dark brown to black lesions on veins page 6 Vein Spot and stems Tiny white tufts of fungal growth on page 9 Articularia Leaf Mold underside Small olive green velvety spots. By page 7 Leaf Blotch midsummer, black pimple-like dots appear in the spots Leaflets yellowish, mottled, narrowed page 8 Rosette and crinkled with reddish-brown spots, may be perforated Broomy type of twig growth, bunching of page 8 Bunch Disease leaves DISEASES OF THE NUTS Small black sunken or raised spots page 5 Scab which may fuse to cover entire surface of shuck Pink spore masses on shuck surface page 9 Pink Mold DISEASES OF THE ROOTS Galls of various sizes on larger roots page 7 Crown Gall Splitting and deterioration of bark of page 10 Cotton Root Rot infected roots, strands of buff-colored fungal growth may be present NONPARASITIC PLANTS ON THE LIMBS AND BARK Whitish-gray mosslike masses on the bark page 9 Lichens Accumulations of grayish strands page 9 Spanish Moss, Ball Moss hanging from limbs and twigs or ball-like growth on limbs and branches

Key to Pecan Insects

INSECTS ATTACKING THE NUTS Olive-green caterpillars up to ½ inch page 10 Pecan Nut Casebearer long feeding in the nuts, or later in the season, in the shucks White caterpillars up to ⅜ inch long page 11 Hickory Shuckworm tunneling in the shucks White legless grubs feeding in the nuts page 12 Pecan Weevil in late summer Green or brown bugs sucking the sap page 12 Stink Bugs and Plant from the nuts Bugs INSECTS ATTACKING THE FOLIAGE Soft-bodied yellow insects producing page 13 Aphids honeydew or small black insects causing yellow blotches on the foliage Tiny green arthropods in webs near the page 13 Mites midrib, leaves appear scorched Caterpillars feeding in gray cases page 14 Pecan Leaf Casebearer about ½ inch long in the spring; small winding blotches produced in the leaves in the summer Olive-green caterpillars tunneling in page 10 Pecan Nut Casebearer the shoots in the early spring Tiny caterpillars in light brown page 15 Pecan Cigar Casebearer cigar-shaped cases about ¼ inch long Galls on the leaves, twigs and nuts page 14 Pecan Phylloxera Leaves eaten in the early spring by a page 14 Sawfly light green caterpillar which leaves the midribs and veins intact Beetles feeding on the foliage at night page 15 May Beetles Caterpillars in large white webs page 15 Fall Webworm encasing entire branches Caterpillars with long soft hairs page 16 Walnut Caterpillar feeding in colonies on the foliage without producing webs Dark gray, active caterpillars up to 3 page 16 Pecan Catocala inches long feeding on the foliage in early spring Masses of frothy white foam enclosing page 16 Pecan Spittlebug tiny, light green insects in the spring Tiny greenish caterpillars feeding in page 16 Pecan Bud Moth the terminals and axils of the buds on young pecan trees INSECTS ATTACKING THE LIMBS, TRUNK AND TWIGS Beetle girdling twigs and limbs in late page 17 Pecan Twig Girdler summer and fall Holes about ⅛ inch in diameter in dying page 17 Red-shouldered limbs Shot-hole Borer White borers with an enlargement behind page 17 Flatheaded Borers the head tunneling underneath the bark of trunk and limbs Limbs encrusted with scales, which page 18 Obscure Scale closely resemble the color of the bark

CONTENTS

Key to Pecan Diseases 2 Key to Pecan Insects 2 Spray Schedule for the Control of Pecan Diseases and Insects 4 Introduction 5 Pecan Diseases and Their Control 5 Scab 5 Brown Leaf Spot 6 Vein Spot 6 Leaf Blotch 7 Crown Gall 7 Downy Spot 7 Bunch Disease 8 Rosette 8 Lichens 9 Articularia Leaf Mold 9 Pink Mold 9 Spanish and Ball Moss 9 Cotton Root Rot 10 Pecan Insects and Their Control 10 Pecan Nut Casebearer 10 Hickory Shuckworm 11 Pecan Weevil 12 Stink and Plant Bugs 12 Aphids 13 Mites 13 Pecan Leaf Casebearer 14 Pecan Phylloxera 14 Sawflies 14 May Beetles 15 Pecan Cigar Casebearer 15 Fall Webworm 15 Walnut Caterpillar 16 Pecan Catocala 16 Pecan Spittlebug 16 Pecan Bud Moth 16 Twig Girdler 17 Red-shouldered Shot-hole Borer 17 Flatheaded Borers 17 Obscure Scale 18 Application of Fungicides and Insecticides 18 Spray Equipment 18 Literature Cited 19

SPRAY SCHEDULE FOR THE CONTROL OF PECAN DISEASES AND INSECTS

Name of spray and Insect or Spray materials, Remarks time of application disease to be per 100 gallon controlled

Prepollination Scab, downy Zineb, 2 pounds If phylloxera is a spray, when first spot, vein spot problem, see page leaves are 14. one-third grown First cover spray, Scab, downy Zineb, 2 pounds when tips of small spot, vein nuts have turned spot, leaf brown and nut blotch, brown casebearer eggs are leaf spot observed Pecan nut 3 pounds 50 percent casebearer, wettable DDT, or 1 pecan leaf pound 25 percent casebearer wettable parathion, or 1 pint nicotine sulfate plus 2 quarts summer oil, or 5 pounds 40 percent wettable toxaphene, or 3 pounds 25 percent wettable malathion Rosette Zinc sulfate, 2 If rosette is a pounds problem, include zinc sulfate in spray. Second cover spray, Scab, downy Zineb, 2 pounds 3 to 4 weeks after spot, vein Zinc sulfate, 2 first cover spray spot, leaf pounds blotch, brown leaf spot Rosette Third cover spray, Scab, brown Zineb, 2 pounds If aphid or mite 3 to 4 weeks after leaf spot, infestations are second cover spray liver spot, severe, use aphids, mites insecticides recommended on page 13. Walnut If walnut caterpillar, caterpillars or fall webworm fall webworms are a problem, use insecticides recommended on pages 15 and 16. Rosette Zinc sulfate, 2 pounds Fourth cover spray Pecan weevil 6 pounds 50 percent For control of wettable DDT weevils, apply spray when as many as three weevils can be jarred from a tree. If scab is present add 2 pounds zineb to DDT spray.

Zineb. Zinc ethylene bis dithiocarbamate. Manufactured by Rohm & Haas Co., trade name Dithane Z-78: E. I. DuPont Co., trade name Parzate.

Pecan Diseases and Insects and Their Control

David W. Rosberg and D. R. King

Respectively, associate professor, Department of Plant Physiology and Pathology, and associate professor, Department of Entomology.

The pecan tree must be protected from attack by the many destructive diseases and insects that affect it to produce a bountiful nut crop.

The diseases that affect the pecan, especially those caused by fungi, are rapidly spread throughout the trees in an orchard in the early spring. During this season of frequent rains, the spores of the disease fungi germinate and invade the young tender tissues of the shoots, leaves and nuts. Under conditions of prolonged damp weather, when the humidity remains high, the disease organisms reproduce at a rapid rate and cause severe shedding of leaves and nuts.

Pecans are attacked by more than 20 species of insects that cause damage to leaves, nuts, twigs, buds, branches and even the bark. The development of commercial pecan acreages has provided ideal conditions for the increase in severity of both disease and insect damage because of the abundant food supply in a concentrated planting of pecans. In its natural habitat the pecan is less subject to the devastations of diseases and insects.

The many destructive insects and diseases must be controlled for successful pecan production. The pecan grower must also understand the nature and habits of the various disease and insect pests that threaten his crop and use certain cultural practices which help to reduce damage from diseases and insects.

Pecan Diseases and Their Control

The diseases which affect the pecan are of four different types: namely fungus, bacterial, virus and physiological. The fungus diseases, the most numerous and widespread, are caused by small microscopic molds. Approximately 12 different fungus organisms cause harmful diseases of the pecan.

The bacterial disease organisms, unlike the disease producing fungi, are single celled and can be seen only under a microscope. Bacterial diseases are fewer and of less economic importance than fungus diseases.

Virus diseases are caused by extremely small agents which can be seen only under special ultra-microscopes such as the electron microscope. Plant viruses are protein substances, but their exact nature is unknown.

Physiological disorders (sometimes called physiological diseases) are caused by a variety of environmental conditions. A physiological disorder in a pecan tree may result from infertile soil, excessive moisture, or the absence or degree of available nutritional mineral elements to the growing tree. These various environmental factors have special adverse effects, manifested by specific symptoms caused by insufficient levels of a given nutritional mineral element or elements, which are easily corrected by supplying the tree the necessary mineral elements either through soil application or foliage sprays.

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