Bulletin [No. 70 (Jan. 1928)]

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GEORGIA STATE BOARD OF ENTOMOLOGY
E. LEE WORSHAM, State Entomologi t, Atlanta, Ga.

BULLETIN 70

JANUARY, 1928

Control Measures For
PECAN SCAB
WITH SPECIAL REFERENCE TO DUSTING
BY 0. C. BOYD, Ph. D.
Plant Pathologist

ATLANTA, GA.

Georgia State Board of Entomology
Organization Eugene Talmadge, Chairman
Atlanta

J. P. Hogg Buena Vista

Lyman B. Veeder Cornelia

E. Lee Worsham, Sta te Entomologist and Secretary of t he Boa rd Atlanta

Staff

Chas. H. Alden, Entomologist Cornelia

R. M. Seeley, Entomologist Atlanta

0. C. Boyd, Plant Pathologist Thomasville

W. L. Neese, Asst . Sec.-Treas. Atlanta

B. M. Gaddis, Inspector Valdosta

M. S. Yeomans, Inspector Cornelia

A. B. Hamlen, Apiary Inspector V. C. Durham, Inspector

Macon

Savannah

C. H. Gaddis, Inspector Albany

J. H. Girardeau, Inspector McRae

J. C. Maness, Field Agent Atlanta

TABLE OF CONTENTS
Page Introduction___________________________________________________________________________________________ 5 Varities to dust for scab_________________________________________________________________ 6 .Minimum size of orchard to dust for scab__________________________________________ 7 Kind of dusters to use___________________________________________________________________________ 7 Dusting materials to use________________________________________________________________________ 7 Control measure for scab____________________________________________________________________ 9
Orchard sanitation_________________________________________________________________ 9 Orchard cultivation____________________________________________________________:_lO
Tree protection-----------------------------------------------------------------11 Dustinfl------------------------------ ------------------------------11 Time and frequency of application_______________ll Effect& of wind and moisture on dusting______l2 Amount of dust to' use______________________________l3
Other important points and precautions in dusting-------------------------------------------------------13 S p r a y i n g_ ___ _ _ _ _ _ _ _________________________ _______ ___________________ __ l 4 Add poison for the leaf case-bearer_____________________________________________________l5
In the spraY-----------------------------------------------------------------16 In the dust__________________________________________________________________l5 Cost of dusting and spraying for scab_____________________________________________l6
Summary -----------------------------------------------------------------------------------------17

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FULTON PRINTING COMPANY ATLANTA, GA.

CONTROL MEASURES FOR PECAN SCAB WITH
SPECIAL REFERENCE TO DUSTING
By 0. C. Boyd, Plant Pathologist
The disease known as pecan scab, caused by the fungus, Fusicladiurn effusurn Winter, is responsible for more injury and crop loss to the cultivated varieties of pecans in Georgia than any other malady of parasitic origin. More important still is the fact that susceptible varieties are rapidly becoming more susceptible, and many choice varieties that were considered highly resistant or immune a few years ago, are gradually yielding to the inroads of the scab fungus. As a result, at the present time in the principal pecan growing sections of the state, at least two varieties are considered entirely too susceptible .to scab for profitable propogation, even when protective measures are employed; the varieties occupying an intermediate position in susceptibility are at the point where they must either be replaced by more resistant ones or be protected against the disease; and several of the lesser susceptible varieties are threatening to enter the intermediate class.
As a means toward meeting this situation, dusting and spraying experiments for .,he control of pecan scab have been conducted in the so-called Albany section over a period of three years, 1925, 1926 and i927. The objects of the experiments was to test the effectiveness of some promising dust fungicides against the scab fungus, and to test generally the possibilities of dusting pecans with present orchard equipment, with a view of working up a dusting program that might supplement to advantage or replace the spray program already in effect, which program the growers seemed reluctant to continue or adopt. At the time of the beginning of the project, and at the present time, the method generally recommended by other workers is the use of Bordeaux mixture spray.
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Although the dusting and spraying project is still under way, the results of which. will be published in detail in bulletin form at a later date, it is felt that the results of the three years' experimentation justify the offering of definite recommendations in dusting for scab prevention. During the seasons that represented both light and heavy scabbing years, effective and profitable control has been realized in commercial orchards in which the dusting schedule was followed, as well as in the more limited and better controlled experimental tareas. As a macter of fact, it was the intention not ;o offer recommendations for either dusting or spraying until it had been demonstrated that the methods were practical and profitable in the hands of the growers.
It is not the intention to discourage entirely, or to condemn, the practice of spraying as now recommended in the scab control program. On the o'ther hand, it is suggested that growers of comparatively small acreages of scabbing varieties who already own good spray outfits, keep and use them. For the larger growers, however, especially those who do not own sprayers and who contemplate adopting a scab control program, it is recommended that the dusting method be adopted.
VARIETIES TO DUST FOR SCAB
The recommendations that follow apply to Georgia conditions where such varieties as Alley, Schley, and Van Deman are accustomed to losing 25 per cent or more of their crop from scab. Highly susceptible varieties, as Georgia and Delmas, might be included only in sections of the state where they ordinarily undergo losses amounting to 25 per cent to {5 per cent. Those varieties in the more heavily scabbing sections of the state, are no doubt rightly being replaced by or topworked to more resistant ones. In some of the more thickly populated areas of the southern part of the state, such varieties as Moneymaker, Moore, and
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Pabst have shown evidence of rapid approach to the list now requiring protective fungicid.,.s.
MINIMUM SIZE OF ORCHARD TO DUST FOR SCAB
In determining the minimum size of an orchard that will justify a grower to undertake dusting for scab, such factors as the size and yielding capacity of the trees, together with their past record in, or their probable danger of loss from scab, should be considered. In the case of the grower witit a limited number of scabbing trees, the cost of the dusting machinery and
materials, also, would enter. On the other hand, it
should be remembered that our budded varieties are rapidly becoming more susceptible to the disease, and therefore that growers of young or lightly scabbing orchards in or near comparatively heavy scabbing sections, might be justified in beginning to dust for scab as a matter of general prevention, even though t he operation of protection for the first two or three years might be rather expensive. The cost of protection with dusts and sprays is treat~d in a subsequent t opic.
KIND OF DUSTERS TO USE
Since the performance of the dusting machine is as important a factor influencing the effectiveness of the job done, as the kind of . dust used, or as any other major factor in dusting, only the best types of machines should be considered for use on pecans. To date, as far as the writer is aware, only two companies manufacturing fruit dusters have demonstrated the satisfactory service of their machines in our pecan orchards, namely, the Niagra Sprayer Company, Middleport, N. Y., and the Bean Spray Pump Company, Lansing, Michigan.
DUSTING MATERIALS TO USE
After comparing sever~il kinds of dusts against scab, it has been found that a copper dust consisting of a
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mixture of 20 per cent partly dehydrated (monohydrated) copper sulphate and 80 per cent hydrated lime is not only the most adhesive and effective, but also is safe to use on pecans as regards possible toxic or injurious effects to the foliage. That kind of dust is ordinarily referred to as a "copper-lime dust." The material may be purchased from a number of firms for prices ranging from $5.80 to $7.50 per hundred pounds (1927 prices).
If mixing facilities are on hand, such as the standard
makes of rotary sifter-mixers, or the mixing devices in
the duster hoppers, and if they are under competent
supervision, the grower can make this dust himself at a
cost varying from $3.55 to $4.00 per hundred. When
purchased in carload lots, the ingredients cost considerably less than when purchased in smaller quantities from either the manufacturer or the local dealer. In 1927 one company furnished the monohydrated copper sulphate in 122 pound bags, the correct amount to mix with one bag of lime (50 pounds ). If the grower should attempt to mix this dust, he should be sure that he is securing a high grade of hydrated lime, that is, one that is finely ground and that analyzes over 95 per cent calcium hydroxide. Air-slaked lime, stone lime, and hydrated lime with high magnesium content, should be avoided. The ordinary hig.h-grade ~buildert; lime or finishing lime is satisfactory. In mixing the dust at home, the mixing machine should run about five minutes to insure thorough mixing, or about two minutes in case of the duster-hopper mixer. If there is any question regarding the quality of the ingredients or the thoroughness in the mixing, it would be much safer for the grower to purchase the dust already mixed, for one of the principal factors contributing to leaf and nut protection is the quality of the dust, which property in turn depends upon the quality and fineness of the ingredients, together with the thoroughness with which they are mixed.
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CONTROL MEASURES FOR SCAB
In the successful control of pecan scab, it is necessary to perform three major orchard practices, namely, orchard sanitation, orchard cultivation, and tree protection. The first one concerns the destroying of such parts of the former year's crop that might be harboring the scab fungus over the winter, and that would serve as a source of spores for early infection of leaves and nuts. The second one refers to a regulation of the ordinary cultural practices in such a way as to make the first and third measures most thorough and effective. The third one provides for the covering of the susceptible parts of the tree with a fungicide that will protect those parts against possible infection. As these three measures are equally important, it would be entirely unsafe and unprofitable for the grower to attempt the control of scab by employing only one or two of them.
ORCHARD SANITATION
Pruning, and destroying sources of inoculum.-In the winter or spring before the buds begin to swell, the orchard should be properly pruned, and rid of old nuts, shucks and leaf parts in the following manner: First cut away all low-hanging branches, for they not only interfere seriously with proper cultivation, but also serve as early and ready starters of scab infection. Then knock from the trees all shucks and mummies (dead, shriveled nuts) and leaf-stalks by flailing with bamboo poles and jarring with heavy, well-padded mallets. Carefully sweep old shucks and leaves away from the tree trunk. Mter removing all prunnings and coarse refuse from the orchard, bury the old shucks, nuts, and leaves that remain, by plowing at least six inches deep with a turning or mold-board plow. If tractors are used in plowing, in order to insure coverage of the refuse under the trees, particularly around the trunks, and in order to avoid cutting the bark and large roots near the trunks, make the first four furrows next to the trees
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with a two-horse walking plow. This deep winter plowing is not only a recommended cultural practice but also serves to bury the scab affected nuts and leaves, and to bury the old shucks containing the shuck-worm larvae.

ORCHARD CULTIVATION

Since the young leaves and shoots are highly subject to scab infection, and as their susceptible period extends fr0m four to five weeks before the first application of dust can safely be made, up until the leaves assume the dark-green, more matured color, ordinarily around the time for the second application, all cultivation during that period under the susceptible varieties should be made as shallow and at as long intervals as possible, without neglecting the important practice of conserving ~oil moisture. At this time of year, ordinarily du;ring April and May in the southern part of the state, spring-tooth and spike-tooth harrows might better be used instead of the disc harrow. Even in later cultivations with the disc harrow, it would be highly advisable to use depth gauges in order to avoid a greater depth than three inches. Tlfese .precautions are meptioned in order that the probability of turning up old shucks and leaves, and stirring spores into the air, might be reduced to the minimum. Then, throughout the remainder of the season, at least until the first of August, orchard cultivation should be made, if possible and practicable, just following the applications of fungiCides while the leaves and nuts are freshly and completely covered with the protective material.

It will be noted that the above recommendations con-

cerning sanitation and cultivation cover orchards that

have been, or that can safely be plowed. As the execu-

tion of sanitary measures is as important in the scab control program as the application of dusts or sprays,

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it is doubtful if the grower will find it profitable to

dust the varieties mentioned above unless he plows the

orchard as suggested, or otherwise properly disposes of

the old nuts, shucks, and leaf-parts. For the benefit of

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those who have not been plowing deeply, and who intend to begin dusting or spraying, it might be suggested that for the first year as much of the old shucks and leaves as possible should be raked and burned, and that a deep, thorough discing be employed under one side of the trees and plowing under the other side. It would then be doubly important to observe the precautions mentioned in regard to cultivation with harrows during the susceptible period of the leaves, for disc harrows do not cover the trash thoroughly. At the beginning of the second year, plowing could safely -be done under both sides. The grower would thus avoid serious -injury to his trees that might occur if he plowed deeply under both sides of the trees in the same season, following a system of shallow cultivation.

TRF;E PROTECTION
One reason for observing the sanitary measures mentioned and the precautions in early cultivation, is to prevent a greater part of the early leaf and shoot infection that would otherwise occur before it is safe to make t4e first application of protective fungicide. After the period of the danger of injurying the young foliage and flowers is over, that is, after pollination in the orchard is complete, then applications of fungicides should be made to protect further the leaves, and the nuts throughout their period of susceptitbility.

D1JSTING

The important factors to he observed in making the

dust applications are: The time and frequency of appli-

cations as determined by the growth of the tree, the

amount of rainfall, and by the habits of the fungus; the

relation of the amount of wind and tree moisture to

the effectiveness o'f dusting; the amount of dust to

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use per tree in order to insure protection, and other factors that will be treated collectively.

Time and frequency of applications.-Make the first application of dust as soon as pollination in the orchard is complete, in other words, after the receptive end of

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the pistillate flower, the stigma, turns brown and be-

comes dry. If it is the first year in the control of scab,

especially if the Delmas variety is concerned, or if

scab infection is already evident on the leaves, make

the second application two weeks after the first. Other-

wise, the interval between the first two applications

might be three weeks, but not longer than three weeks.

In both the first and second applications, make a spe-

cial effort to cover the under sides of the leaves, for

at that time of year the foliage is subject to infection.

Subsequent applications should follow at three to four

week in_tervals, depending upon the amount and fre-

quency of rainfall and upon the amount of scab infec-

. tion that occurred before the first application was made.

In case the season is unusually rainy and the dust

washes off, it may be necessary during such periods to

shorten the interval to two weeks. This is often the

case during the latter half of June and the first of

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.

.

Ordinarily, the scabbing season for Schley, Alley,

and Van Deman, in the southern half of the state, ex-

tends to the first or tenth of August. Therefore,. the

grower should plan to make his last application late

enough to insure protection to the nuts through their

susceptible season, i. e., during the latter half of July

or first of August. The second growth of foliage that

usually appears during the latter half of July should be

protected in order to prevent leaf and twig infection

that might occur at that time. Otherwise, scab lesions

would develop that readily pass the winter and fur-

nish spores for early spring infection. Ordinarily, the

last application serves to protect this growth as well as

to complete protection to the nuts.

Effect of wind and moisture on dusting.-Dust applications should be made only when there is a noticeable film of moisture on the under side of the leaf or on the nut, and while there is little or no wind. Moisture from dew or fog is more satisfactory than rain moisture. Dew
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rarely appears until shortly before daylight, and ordinarily lasts from two to three hours. The dusting operation should cease when the wind becomes strong, even though there is moisture on leaves and nuts. While the requirements of damp foliage and nuts and a quiet atmosphere constitute the chief handicaps in dusting, yet it is possible to dust from two to three times as many trees in an hour as to spray them.
Amount of dust to use.-The amount of dust that should be delivered to trees. depends largely upon the size of the trees and upon the amount of moisture present. It requires less dust to furnish coverage with an abundance of moisture on the foilage than if only a slight amount is present. As to the size of the trees, ordinarily it requires from 12 to 2 pounds of dust per tree per application for seven-to-nine-year old trees; 3 to 4 pounds for ten-to twelve-year old trees ;5 to 6 pounds for twelve-to fourteen-year old trees; 7 to 8 pounds for sixteen-to eighteen-year old trees; and 9 to 10 pounds for nineteen-and twenty-year old trees. This provision covers dosages for trees that are normal in size for their age.
Other important points and precautions in dusting.-
1. There should be a competent white man in charge of the dusting program, either the grower himself or a dependable foreman. On his judgment depends the choosing of days with conditions suitable for dusting, and of the time for starting and ending the day's operation, together with the purchase and mixing of the dusting materials. There should be a dependable white man in charge of the machine, operating the discharge pipe, or an unusual colored hand working under the close supervision of the foreman.
2. Each laborer should by all means be supplied with a dust respirator. It is a marked imposition on the hands to require them to operate a dusting machine without one.
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3. The trees, :Whether large or small, should be dusted from two sides. It is the direct, forceful drive of the dust that proves effective. Drift-dust is of little consequence against pecan scab. Sufficient time, therefore, sho1,1ld be spent at each tree at close range to insure coverage of all parts of the tree. One should not be satisfied with enveloping a tree by shooting a cloud of dust into it frQ.m a distance; for the result will be disappointing to tJ:le grower. While small trees may be dusted thoroughly as the machine passes by, large trees require from one to two stops on both sides. The rapidity in dusting depends mostly upon the blowing and feeding capacity of the duster.
'' SPRAYING
Although pecan scab can generally be controlled with one less application of Bordeaux mixture spray than with the dust, particularly whelie badly scabbing orchards are being protected for the first time, yet, due to the many difficulties in and handicaps to spraying, the latter operation on the whole is less practical for the grower than dusting. For the benfit of those growers, however, who own sprayers or who intend purchasing same, the following recommendations are offered:
The same practices in regard to orchard sanitation and cultivation should accompany the spray program as outlined for the dusting program. The formula, 3-4-50 should be used in all Bordeaux applications, that is, 3 pounds of blue vitriol (copper sulphate ), four pounds of stone lime. (or 6 pounds of hydrated lime ), and 50 gallons of water.
The time of the first application should correspond with the first dust application, and the second one, three to four weeks later, instead of two to three weeks as in case of the dust schedule. Subsequent applicatons, also, should be made at three to four week intervals. It is not advisable to make more than three or four applications of Bordeaux mixture on pecans in a single season, lest foliage injury occur, resulting in premature defolia-
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tion and small, lightly filled nuts. Where a heavily scabbing orchard is being sprayed for the first time, or if the season is unusually rainy, thus calling for more frequent applications, all applications in excess of four should be made with lime-sulphur solution, one gallon of the concentrate to 50 gallons of water, in order to avoid possible foliage injury from accumulating copper deposits. Even in the ordinary year after scab infection in the orchard has been reduced in preceeding years, the fourth application might better be made with the lime-sulphur spray.
The pecan sprayer should be equipped with a shortdistance spray gun for close work, and a long-distance, solid-stream nozzle for spraying the tops of the trees. If the trees to be sprayed are 45 feet in height, or higher, a tower on the tak will facilitate spraying the topmost parts. A pressure of not less than 300 pounds is necessary in order to convert the liquid into a fine mist or spray with the short-distance gun, and to force the material to the highest parts of the tree through the long-distance gun.
ADD POISON FOR THE LEAF CASE-BEARER
Inasmuch as the leaf case-bearer is becoming distributed over a greater part of the pecan sections and causing sufficient damage to warrant control measures, it is recommended that the grower include an effective poison in the scab dust or spray in order to eliminate the necessity of making a separaate application of insecticide alone for this pest.
IN THE DUST
Although the experiments on the use of dusts for the control of the leaf case-bearer are still under way and not yet conclusive, it has been found that two applications of dust containing 10 per cent of arsenate of lead will not only produce satisfactory control, but will cause little or no injury to .the foliage. When this ar-
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senate is included in the scab dust, the formula of the latter then becomes 20 per cent monohydrated copper sulphate, 70 per cent hydrated lime, and 10 per cent arsenate of lead. The arsenate should be used in the last two applications of the scab-dusting schedule. In dusting for the leaf case bearer, it is as important that leaf moisture be present as it is in dusting for scab alone.
IN THE SPRAY
It has been demonstrated over a period af three years that one thorough application of spray containmg 1 pound of powdered arsenate of lead and four pounds of hydrated lime to 50 gallons of water, or 1 pound of the arsenate to 50 gallons of Bordeaux mixture, will give commercial control of the leaf case-bearer. When combined with the scab spray, the arsenate should be applied in the last application of the scab schedule.
. In either dusting or spraying for the leaf case-bearer, it is necessary that the under sides of the leaves receive a thorough covering of the insecticide, for the feeding areas of the larvae are restricted to that region.
. COST OF DUSTING AND SPRAYING FOR SCAB
The cost of either dusting or spraying for scab control varies considerably with the size of the trees, the number of applications necessary for protection, the amount of labor and equipment in the particular orchard, and the cost of the materials. The total cost should ' also take into account the purchase price and depreciation of the machines, as well as the water pumping facilities, suply wagons, etc., necessary in the spray outfit. Although the spray materials are generally less expensive than dusting materials, yet the cost of good sprayers is just about twice that of the best dusters, and the cost of the additional time and additional man and mule labor, together with the extra pumping and hauling equipment, no doubt raise the cost of spraying to, or beyond that of dusting. The operation of dusting is
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practically three times as fast as spraying, i. e., in considering the use of equal numbers of dusting machines and spray machines.
In 1927, the cost of dusting with the orchard-mixed 20-80 copper-lime dust was about two-thirds the cost of dusting with commercial brands of the same kind of material. Including the price of the lead arsenate for the leaf case-bearer in two applications of the scab schedule, the cost per tree of dusting five times with the orchard-mixed dust ranged from $1.35 to $1.50 for 12 to 14 year old trees, to $2.00 to $2.50 for 17 to 19 year old trees.
SUMMARY
The following control measures are effective and practical in preventing loss from pecan scab on such varieties as Schley, Alley, Van Deman, and even on the more susceptible varieties under limited conditions.
1. In the winter or early spring, before the buds start growth, prune out all low hanging branches; knock from the trees the old shucks, nuts, and leaf-stalks; and sweep all such trash away from the trunks. Remove the prunings and coarse refuse from under the trees and burn.
2. Before the buds swell, plow the orchard at least six inches deep. This step is advisable not only as a good cultural practice, but also for the purpose of burying the tree parts that are harboring the scab fungus and the shuck worm larvae.
3. Practice shallow cultivation, two to three inches, during the remainder of the season, particularly . during the period from the time of plowing through the unfolding of the leaves and up to the time the leaves assume the dark-green color. Otherwise the buried refuse will be turned up, and severe scab infection may occur on the young leaves before the first application of fungicide can safely be made.
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.4. Make the first application of dust, or spray, immediately after pollination is complete; the second application of dust, from two to three weeks later, and the subsequent ones at three to four week intervals, until the latter part of July or the first of August, depending upon seasonal conditions. The second and subsequent applications of spray should be made at three to four week intervals.
5. More than three or four applications of Bordeaux mixture spray may cause injury to leaves and nuts. Provisions are made for substituting lime-sulphur solution for Bordeaux mixture under certain conditions.
6. The leaf case-bearer may be controlled by including arsenate of lead (10 per cent ) in the last two dust applications of the scab schedule, and in the last spray application.
7. The cost of dusting or spraying varies greatly with: the size of trees; the cost of machines, material, and accessory equipment; the number of applications, and the type of labor. All factors considered, there is little or no difference in the cost of dusting and spraying for scab control. Dusting, however, is considered less troublesome and .disagreeable, and about three times as fast as spraying. The chief handicaps in dusting are the requirements of moisture on leaves and nuts, and of little or no wind.
8. With reasonable precautions, the grower may mix his own scab dust with a saving of from one-third to one-half of the price of factory-mixed dusts.
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