Read Diseases. Insects: CHAPTER XIV of The Pecan and its Culture , free online book, by H. Harold Hume, on ReadCentral.com.

FUNGOUS AND OTHER DISEASES OF THE PECAN.

The fungous diseases attacking the pecan have not been thoroughly investigated. They have not, however, become so numerous or common as to cause serious damage except in a few instances. The true fungous diseases are usually propagated and disseminated by means of spores, and the most effectual method of control usually consists in spraying with Bordeaux mixture or some other fungicide. For all fungous diseases of the pecan which may be controlled by spraying no substance will give better results than Bordeaux mixture, and directions for preparing it are given at the end of this chapter. Paris green, at the rate of four ounces to each fifty gallons of liquid, may be added to the mixture for the destruction of biting insects. For effectual work in spraying large trees, a platform should be erected on the wagon-bed to make it possible to reach the tops with the spray.

PECAN LEAF BLIGHT (Cercospora Halstedii): This disease of pecan leaves causes them to turn brown, wither up and drop prematurely. At first, small brown spots are noted. These become larger, and at length the whole leaf is destroyed. When attacked by this disease the tree makes no progress. An examination of the discolored areas, under a microscope, shows the presence of tuft-like growths of spores upon short conidiophores. As they become matured the spores are scattered by the rain or wind and so the disease is spread. It probably lives over from one season to another on the diseased leaves.

The most effective remedy is to spray thoroughly three times with Bordeaux mixture. The first application should be given just when the young leaves are expanding, followed by two others at intervals of two or three weeks. The fallen leaves should, if feasible, be gathered and burned.

Pecan Scab (Fusicladium effusum): This disease attacks the fruit, leaves and twigs. The husks of the diseased nuts become covered with dark spots or specks. They become hardened and crack open in places. As a result of the attack, growth is stopped, the fruit does not fill out and mature, but drops prematurely or, in some cases, remains attached to the trees long after the leaves have fallen. Round, black spots form on the leaves when attacked by the fungous. These become dead and brown and in most cases the whole leaf is destroyed. When attacked, the trees are usually so badly injured that they make little progress. Not all varieties are subject to the disease in the same degree and some appear to be entirely exempt.

Those varieties which are not attacked should be given preference in propagating work. The disease may be further controlled by spraying with Bordeaux mixture, as directed under leaf-blight.

PECAN ROSETTE:"The earliest symptoms are a peculiar crimping of the leaves at the ends of the branches. These leaves are smaller with crimped margin, and when held to the light show light green or yellow streaks between the veins. The leaf tissue in these light-colored areas is thin and undeveloped and often breaks away leaving angular holes in the leaves. A tree usually shows the disease over the whole top at once, though sometimes only a single branch is affected at first. As the disease progresses, the foliage assumes a bunched appearance, due to the formation of tufts of leaves at the ends of the branches. This characteristic has led us to use the term “Rosette” as a name for the malady.

“The next stage of the disease which is observed the second year or later, is a dying-back of the branches from the tips. This is followed by the development of numerous small, lateral branches from adventitious buds. These are short, producing thick clusters of small, unhealthy leaves, sometimes reduced to mere skeletons, so that the rosetted appearance of the tree is intensified. This goes on from year to year. The growth of the tree is checked and these abnormal branches are formed only to die back each year. Trees in the earliest stages of rosette have been observed to have light crops of nuts, but, when badly diseased, are barren and unsightly or worse. Rosette has been found in all ages, from nursery stock to trees forty feet high.

“The cause of the disease remains a mystery. No fungous or other parasite can be detected in the earliest stages. The appearance of the trees leads us to infer that the trouble is internal, due to some derangement of the nutritive or assimilative functions of the plant, but we are unable to correlate this with any corresponding external conditions. That is to say, that so many cases have been observed on fertile soil, when cultivation, drainage and plant food had all been provided, that it is impossible to conclude that the disease could be due to starvation or to the lack of any single element in the soil, nor can it be due to over-feeding, since it occurs in light soils and in neglected orchards.

“It seems probable that it will be classed by the plant pathologist with peach rosette, peach yellows, and related diseases, the causes of which still remain unknown after years of investigation. The indications are that it is contagious, though a complete demonstration of this point remains to be made; at any rate, it must be regarded with concern until more knowledge is available.”

Dissolve the copper sulphate in two gallons of water, place it in barrel N and add water to make twenty-five gallons. Slack the lime, reduce it to a very thin paste, place it in barrel N and add water to make twenty-five gallons. To mix the solutions of lime and copper sulphate, dip a bucketful from each barrel, and pour together into the barrel of the spray pump. The two mixtures should flow together as they are poured into the barrel. This is one of the secrets of making a first-class mixture. The best arrangement is to have the barrels, Nos. 1 and 2, elevated, and use a piece of rubber hose to run the liquids into the pump barrel.

If a large amount of spraying is to be done, a somewhat different policy should be pursued. Too much time would be taken up in preparing the ingredients in small quantities. Instead, large amounts of copper sulphate should be dissolved and large quantities of lime slacked beforehand. This may be done as follows:

In a fifty-gallon barrel place about forty gallons of water. Put one hundred pounds of copper sulphate in a sack and suspend it in the water. As soon as dissolved, fill up to the fifty-gallon mark. When well stirred, each gallon will contain two pounds of copper sulphate. Each time some of the solution is dipped out, the height of the remaining portion should be marked on the inside of the barrel. Before taking more of the solution out of the barrel, any amount of water lost by evaporation should be made good by filling up to the mark last made.

As soon as procured the lime should be slacked, placed in a
barrel and kept covered with an inch or two of water. In this
way it can be kept indefinitely.

To prepare Bordeaux mixture from these stock solutions, dip out two and a half gallons of the copper sulphate solution, place it in barrel N and dilute to twenty-five gallons. From the slacked lime take fifteen pounds, or thereabouts, to allow for the water it contains, reduce to a thin paste, place it in barrel N and add water to make twenty-five gallons. Pour the contents of barrels Nos. 1 and 2 together, as already directed.

Tests: If free copper be present, severe injury may be done
to the foliage or other tender parts of the plants. Sufficient
lime should be added to neutralize it.

Dip out a small quantity in a porcelain saucer or shallow bowl, and holding it on a level with the mouth, blow the breath gently into it. If a thin pellicle forms on the surface, more lime must be added. Add and test until it does not form. An excess of lime will not hurt.

Another test is to dip the blade of a clean knife into the
mixture. If a thin film of copper forms on it after holding it
there a minute or so, more lime must be added.

Use good materials and prepare the mixtures thoroughly.

In making up the various mixtures, never use iron vessels, but
use glass, wood or crockery receptacles instead.

Strain all mixtures thoroughly into the spray pump to prevent
clogging of the pump or nozzles.

Spray thoroughly and in good season. Be in time.

Do not use mixtures which have been leftover and allowed to
stand for some time.