_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.
[Illustration: Fig. 22.—Nonpareil almonds. Branch on left free from Red
Spider and holding its full supply of leaves in green, healthy condition;
branch on right defoliated by Yellow Mite. Note premature ripening of
nuts on defoliated branch.]
[Illustration: Fig. 23.—Forty-three-year-old Languedoc almonds on peach
root, near Davis. This orchard has not been thoroughly cultivated or
irrigated. Mites have largely defoliated the trees. See contrast in Fig.
24.]
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.
[Illustration: Fig. 24.—Forty-three-year-old Languedoc almonds on
peach root, near Davis. This orchard has been irrigated and thoroughly
cultivated, and mites have not defoliated the trees. Note contrast in
Fig. 23.]
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.
[Illustration: Fig. 25.—Almonds infested with larvae of Indian Meal Moth
(_Plodia interpunctella_).]
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.[6]
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.