Part 9

(2) Cercospora circumscissa is another fungus causing much the same effect as the Coryneum. It is difficult for an untrained person to distinguish between them. The same sprays used for Coryneum are effective in controlling this, though if this form alone is present the Bordeaux mixture or lime-sulphur spray in the spring should be sufficient.

(3) Gloeosporium amygdalinum, while apparently uncommon in this state, has been found to exist in some places. Further work must be done on this to determine its behavior and the most satisfactory methods of control, but it is believed that the control measures mentioned for the other forms of “shot-hole” will also be applicable to this.

Prune Rust (Puccinia Pruni).—This fungus is worst in the southern coast sections where almonds are not extensively grown. It is not serious on thrifty trees well supplied with moisture. The disease is characterized by reddish pustules on the under-sides of the leaves, appearing generally about July or August and causing a premature yellowing and dropping of the leaves.

Ordinarily the only treatment needed is to supply the necessary moisture in the soil to keep the trees healthy and vigorous.

Heart Rot.—This is one of the most insidious of tree diseases, for it works inside beneath an apparently healthy exterior until the decay has progressed so far that the tree commences to break down, and then it is too late for remedial measures. The almond is not as susceptible to this as most other kinds of orchard trees, but where large wounds have been exposed to the weather, infection may take place readily, and after it is once well started it continues at a comparatively rapid rate. Decay is caused in most cases by one or more of about a dozen different fungi, of which the oyster-shell fungus is by far the most common.

Control consists in taking care to leave no open wounds exposed to the air to dry and crack, thus permitting the entrance of decay organisms. Much of this can be avoided by care in pruning the young tree so that the removal of the large limbs will not be necessary later on. Where such wounds must be made, measures should be taken to prevent infection. This can best be done by making smooth, clean cuts close to the part from which the branch to be removed emanates, leaving no stub. Stubs dry out and crack more quickly and require very much longer to heal over, if this is possible at all. Further, all such wounds which will not heal over the first season should be covered with some good disinfectant, such as corrosive sublimate, one part to one thousand parts of water, and then painted over with some elastic coating, such as “Flotine” or asphaltum, grade D, applied with a brush. The entire wound must be covered or the work is largely wasted.

Die-back.—This is serious in many orchards where moisture is insufficient to carry the trees through the growing season, and the trees show considerable dying-back of the branches. Unfavorable soil conditions, such as hardpan, gravel or sand may be the direct cause of such moisture shortage. Lack of soil fertility is also a common cause. Control measures consist in remedying the defective conditions and where this cannot be done economically it is better to abandon further attempts at almond culture on such land.

Sour-sap.—This is one of the so-called “physiological diseases” and is quite common with the almond. It is most frequently found where trees are planted in heavy or poorly drained soils. The inability of the almond to endure standing water around its roots for any length of time and particularly so after growth commences in the spring, renders it especially liable to sour-sap when planted in soils where excess water from the late winter and spring rains cannot be readily drained away. The direct cause of the trouble is sudden changes in weather from warm to cold after growth commences, which checks the flow of sap very suddenly, causing stagnation, cracking of the bark and then fermentation. With an unusually strong flow of sap in trees in wet soils, such climatic changes cause unusually severe disturbances in the normal functioning of the trees.

The affected trees ordinarily show the disease first in the spring when gum may be seen oozing from the bark of the trunk or main branches, and sometimes even from the smaller branches. Small or large branches may die, and in severe cases the tree may die soon after having commenced to leaf out strongly. On cutting through the bark to the wood and peeling back, a strong sour odor is noticeable. The cambium layer appears brownish or reddish in color and often masses of gum may be found between the bark and the wood. Mild cases may not be serious enough to show on the outside of the tree and only portions of the cambium layer may die. The sudden dropping of the blossoms or young fruit may in some instances be attributable to sour-sap.

All affected parts on smaller branches should be cut back to healthy wood, while on the main branches or trunk, where only a small portion or one side is affected, it is best to clean out the dead bark and paint the bared wood with a protective covering until new bark can cover the spot. At the same time every effort should be made to remedy the soil-moisture conditions which were largely responsible for the trouble in the first place.

Fruit-drop.—The same conditions which cause sour-sap may cause fruit drop. It may be caused by lack of pollination due to improper mixing of varieties or to rain during blossoming. Frost may also produce the same thing by killing the germ in the young fruit. In such cases, the fruit may remain on the tree for one or two weeks after the injury occurs before falling, and in some cases, may even appear to continue its development for a short while.

INSECT PESTS

Mites.—Commonly called red spiders. There are two kinds of mites that do much damage in almond orchards, the brown or almond mite and the yellow or two-spotted mite. Both are common in all parts of the state and are the worst pests the almond grower must regularly face.

The brown mite (Bryobia pratensis) is the larger of the two, is dark red or brown in adult stage, has very long front legs, and a flattened back. It does not spin any web and works on the green bark of the small twigs as well as on the leaves, sucking the plant juices from beneath the bark. It causes a mottling of the leaves which eventually fall, although not as readily or in such large numbers as when attacked by the yellow mite. The injury to the tree is equally as great because of the serious drain on the vitality as a whole and because it commences work earlier in the season. This mite may spend its entire life on the tree; the very small, round, red eggs being laid largely on the under-side of the branches and in cracks and crevices in the bark and twigs. These remain on the tree throughout the winter and hatch early in the spring soon after the trees have their leaves half developed, leaving the white egg-shells in place. Most of their work is done in the spring and early summer.

The brown mite may be controlled satisfactorily by means of a dormant spray of lime-sulphur solution, 1 gallon to 10 gallons of water, applied just before the buds open in the spring. Crude oil emulsion as a dormant spray is also effective, if thoroughly applied over the entire tree under high pressure. This also applies to applications of the lime-sulphur spray.

During the growing season a milder material must be used. Dry dust sulphur, using only the very finest grade of “flowers of sulphur,” is often very effective, provided weather conditions are satisfactory, but generally this must be applied a number of times if best results are to be obtained. The work is done by blowing the sulphur dust into the tree with blowers in the early morning when there is little or no wind.

A more satisfactory method is the use of “Atomic sulphur” or other sulphur pastes or similar material. “Atomic sulphur” is a prepared spray whose value consists in the fact that the sulphur is held in suspension in water so that it may be applied as a liquid spray. By this method the material may be more effectively and thoroughly applied. “Atomic sulphur” is applied at the rate of 10 pounds to 100 gallons of water.

The use of lime-sulphur, the commercial strength of 33 to 34 degrees Beaumé being diluted 1 part to 35 parts water, is another effective method. For such use a flour paste may be added at the rate of 4 gallons to each 100 gallons of the spray mixture to act as a spreader. This paste is made by cooking one pound of flour with enough water to make one gallon of the mixture.

The yellow mite (Tetranychus telarius) is much smaller than the brown mite and is of a pale yellow color with occasionally a reddish tinge and sometimes with two darker spots on either side of the body. Unlike the brown mite, the winter is spent in concealment somewhere, presumably off the tree. During the warm days of early summer, generally in June, the mite makes its appearance on the trees, spinning a fine web on the leaves, generally on the upper surface, and then works under this web. The mite sucks the plant juices from the leaves giving them a yellowish mottled appearance. These leaves soon die and drop to the ground. In serious infestations the trees are often almost completely defoliated by the end of August. (See figure 22.)

The use of dormant sprays is not effective for controlling the yellow mite, but the summer sprays mentioned above are all satisfactory, and for best results, must be applied under high pressure, preferably 200 pounds or more.

The mites are much easier controlled where a comparatively high percentage of moisture is kept in the soil by frequent cultivations, or, if necessary, by irrigation (figures 23 and 24).

Peach Twig Borer (Anarsia lineatella).—In the larval stage these borers work on the young buds and shoots in the early spring. They are especially troublesome in newly planted orchard trees when a comparatively small number may kill most of the new shoots which are needed to make the desired framework of the tree. In some years they may be serious in large trees also. Dormant spray of lime-sulphur applied under high pressure just as the buds are opening in the spring will control the borers very effectively. This same spray may be used to control the brown mite, thereby accomplishing double control.

California Peach Borer (Ægeria opalescens).—The larvae are serious in many parts of the state where they burrow just under the bark near the surface of the ground. They may be detected by the small bits of frass and gum at the entrance of their burrows. If allowed to continue, they will eventually girdle the tree.

The surest means of control is to dig out the worms with a knife or kill them with a wire probe. This work should be done systematically once or twice every year and very thoroughly if it is to be effective. The application of hot “Flotine” or asphaltum, grade D, after the worms are killed should help considerably to prevent the entrance of the larvae. To be effective it must be applied at least twice a year on young trees and probably the same on old trees.

Thrips.—These are most serious on the almond leaves, their attacks being serious enough to cause considerable defoliation in late spring or early summer. They may be controlled by spraying with lime-sulphur, 1 to 30, to which has been added black-leaf 40 (40 per cent nicotine) at the rate of 1 part to 1500 parts of water or other spray-mixture. It is possible that other than the pear thrips have been doing damage, but the same spray as described above should be effective against all.

Grasshopper.—Grasshoppers have been serious in orchards in outlying foothill districts in some years, and especially so in young orchards where it has been almost impossible to get trees started properly. In such locations special means must be employed on a large scale to protect orchards from their devastations, of which poisoned bait and hopper dozers are the most effective.

Indian Meal Moth (Plodia interpunctella).—The larva of this moth feeds on the kernels of the harvested almonds when they are stored. Infestation usually takes place in storerooms or warehouses in which the nuts have been placed for a time. The warehouses become infested from old grain bags which have been kept there at one time or another. So far as known, infestation does not take place in the field. The larvae will continue to work in the stored almonds for a long time, doing a very great amount of damage (fig. 25). They may be controlled by thoroughly cleaning out the corners of the warehouse and thoroughly disinfecting. The nuts should be disinfected with carbon bisulphide (explosive when in the form of a gas mixed with air), or other means used to control insects in grain. Prevention is far easier than the cure in this case.

Scale, aphis, diabrotica and other insects are sometimes found on the trees, but are generally not sufficiently troublesome to require special attention. Most of them are held in check by the control measures used for the more serious pests.