D. R. King

“ 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. ”

“ In older trees, the borers can be removed with a sharp knife. Care should be taken to injure as little of the healthy wood as possible. If the wound is extensive, it should be trimmed and then painted with a commercial tree paint or with a mixture of one part creosote and three parts coal tar. Dead and dying limbs and trees should be removed from the orchard each year and burned before the following spring. If they are not burned, the borers in them may mature and re-infest surrounding trees. Commercial tree borer preparations are of little value in controlling this insect. ”

“ The insect overwinters as a pupa in lightly woven cocoons in debris on the soil or under the bark. In the spring the adults emerge and lay masses of greenish white eggs on the leaves. The caterpillars which hatch from the eggs feed on the leaves in colonies under webs which they construct. After feeding for a month to 6 weeks, the larvae crawl down the tree and pupate in loose cocoons in debris, under bark, or in loose soil. Adults appear during the summer and deposit eggs for the second generation. ”

“ 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. ”

“ 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 winter is passed in the egg stage in crevices in the bark. In the spring, the egg hatches and the tiny nymph feeds on the tender, young growth, apparently secreting a substance which stimulates the plant tissues to develop into galls. ”

“ Immediately behind the head is a broad, flattened expanded area from which the insect takes its name.
The winter is passed by larvae in varying stages of development within the tree. In the spring, they change to pupae in their burrows, emerging as adults during the spring and summer. The female beetles deposit their eggs in cracks or bruises in the bark. The larvae which hatch from these eggs feed during the remainder of the season and pass the winter. There is only one generation each year. ”

“ In highly alkaline soils, or soils that readily fix zinc and make it unavailable to the tree, foliage spray applications of zinc sulfate are more economical because of the excessive rates required to supply available zinc through the soil. ”

“ When possible, fungicides for disease control and insecticides for insect control should be combined in the spray tank and applied to the trees in one operation. The spray materials should be applied evenly and thoroughly to all the leaf and nut surfaces to provide a chemical barrier to disease organisms and insects. Do not neglect the tops of the trees. Diseases and insects can harbor and multiply in all unsprayed areas of the tree. ”

“ Pupation is accomplished in a cell which is constructed in the ground in the fall of the second year. The beetles emerge the following spring. Both larvae and adults may be found in the soil during the winter.
Control.—May beetles are usually a problem in orchards which are not cultivated because the larvae feed on the roots of the sod cover. Cultivation of the orchard periodically will reduce the food supply of the grubs, and smaller infestations of adults will appear the following year. Where cultivation is not feasible, sprays will control the adults. ”

“ Rosette is a nutritional deficiency disease caused by certain soil conditions which make zinc unavailable to the pecan tree. All pecan trees require zinc for growth.
Trees showing the first symptom of zinc deficiency have yellowed tops. The individual leaflets when examined are yellowish and mottled. The next season the foliage may be yellowish and the leaflets narrowed and crinkled. More severely affected trees produce foliage which is a yellowish to reddish-brown overall color, and the leaflets are very narrow with reddish-brown spots and may be perforated. ”

“ Pecan scab, caused by the fungus Cladosporium effusum (Wint.) Demaree, is the most destructive disease of pecans in Texas. The fungus invades the young rapidly growing shoots and leaves and later the developing nuts. Severely infected nuts on highly scab-susceptible varieties fall or fail to develop, resulting in a total nut crop loss. Early season defoliation often occurs in seasons of frequent rains and high humidity which facilitate the rapid development and spread of the scab fungus.
The scab fungus overwinters in infected shoots and in old shucks and leaves in the trees. ”

“ 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. ”

“ Although the majority of catocala larvae reach maturity before the time to spray for the nut casebearer, a number of them will be killed when the recommended spray is applied for the latter insect.
PECAN SPITTLEBUG
In the spring and early summer a number of buds and small nuts may be covered with foamy white masses. Inside these masses are several small insects called spittlebugs, Clastoptera obtusa (Say) . The white froth is produced probably to maintain an artificial high humidity, which is required for development. The adults resemble leafhoppers and fly actively during the summer. ”

“ Mites usually are light green and are just large enough to be seen without the aid of a hand lens. They are wingless and feed principally on the underside of the leaves along the midrib. Colonies of them produce webs in which molted skins and eggs may be found. The life cycle of mites is very short and several generations occur each year. ”

“ Plant bugs and stink bugs overwinter in the adult stage in debris on the ground. In the spring, the adults are attracted to growing vegetation such as cover crops or weeds, where they deposit their eggs. The immature bugs develop on low-growing vegetation. ”

“ The females never move again from the spot they have selected, but the adult males develop wings and emerge from their scale coverings to mate with the females. Only one generation is produced each year.
Control.—When damaging populations develop, a spray application of 31⁄2 gallons of 97 percent miscible dormant oil per 100 gallons of water during the dormant season will keep this pest under control. ”

“ When they reach maturity, their wings are fully developed and they fly to pecan trees. A few eggs may be deposited on pecan trees, but the young bugs apparently are unable to develop on them. Only the adults are present in sufficient number to inflict economic injury. There may be as many as four generations each year.
Control.—Although certain insecticides will control these pests, the number and frequency of spray applications necessary for control would not be economical.
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Care should be taken to keep weeds down in the orchard during the growing season. ”

“ The immature larva is reddish brown with narrow yellowish lines that extend the length of the body. The full-grown larva is almost black with two grayish lines on the back and two on the sides. Many long, soft gray hairs are distributed over the body. ”

“ The scale covering over a full-grown female is about one-eighth inch long and is usually dark gray, and closely resembles the bark of the tree. Infested limbs appear to have had wood ashes sprinkled over them, Figure 23. Numerous pits appear in the bark where the insects feed, producing a roughened appearance. ”

“ The shucks stick to the nuts and fail to open, thus increasing the difficulty of harvest.
The adult shuckworm is a dark, grayish-black moth with a wing span of a little over one-half inch. The larva is white with a light brown head. It attains a length of three-eighths inch at maturity. ”

“ The trees must be kept in a healthy, vigorous condition by proper fertilization and watering. On young or transplanted trees, wrapping the trunks in early spring before the adults appear is the only effective control known for these insects. ”

“ When infection is severe, the entire nut surface is black in appearance, development is arrested and the nuts drop prematurely.
Figure 1. Scab lesions on leaves and nuts of Delmas variety. Note concave lesions and overall scabby appearance of severely infected nuts.
Pecan varieties vary in their susceptibility to scab disease. Among the highly susceptible varieties are: Burkett, Delmas, Schley, Moore, Halbert and most western varieties. Moneymaker, Success and Curtis are moderately resistant. Mahan, Stuart and Desirable varieties are highly resistant to the scab fungus. ”

“ Usually, these insects are not present in sufficient numbers to cause serious injury until mid or late summer. Infestations earlier in the season rarely assume damaging proportions. As is the case with mites, aphid populations may increase, following the application of certain insecticides applied for the control of the pecan nut casebearer or following treatment with bordeaux mixture for pecan scab disease control. ”

“ Various types of spray machines for application of fungicides and insecticides to pecan trees are available. The spray machines employ 19 either a high pressure hydraulic pump, high pressure centrifugal pump or low pressure high air velocity systems. All the machines are portable and are equipped with a gasoline engine or operate from a truck or tractor power takeoff shaft. ”

“ After the nymph reaches maturity, a number of eggs are deposited inside the gall. The young nymphs of the succeeding generation develop within the gall, which splits open in 1 to 3 weeks, liberating them. ”