Dormant Spray for the Control of San Jose Scale in Almonds
Mario Viveros
UCCE Farm Advisor, Kern County
Deciduous Tree Fruits and Nuts
December 22, 1999
Dormant Spray for the Control of San Jose Scale
in Almonds
A dormant spray is made up of a
dormant oil plus an organophosphate or synthetic pyrethroid. This spray
traditionally has been effective in controlling San Jose scale, peach twig borer
and European red mite eggs. However, in the last few years, it has been under
the scrutiny of regulatory agencies and growers. Regulatory agencies are looking
at the dormant spray because the organophosphates are causing environmental
problems. Growers are thinking twice about using dormant sprays because it may
not effectively control peach twig borers and San Jose scale.
San Jose scale, three years ago, showed us what it
can do to almond trees. This insect infested and killed big tree limbs in some
orchards. The death limbs were located not on the top but on the bottom part of
the trees. This indicates that dormant spray didn't control the scale. The
reason is not known at this time. However, if a grower has San Jose scale in his
orchard, we recommend a dormant spray with oil and an organophosphate
insecticide.
The best time to apply a dormant spray is in the
winter, during the first week of January. If by this time, there has been no
rain, irrigate your orchard. Oil sprays can be phytotoxic to water-stress trees.
Before a dormant spray is applied, irrigate your orchard using two- to three-
acre inches of water. This will allow you to wet the soil profile 24 to 36
inches. This water is not wasted water since root growth and development starts
between Christmas and the New Year. Furthermore, if the water that is not used
by the roots, it will be stored in the soil profile for use in the early
spring.
The application of the dormant spray should be
properly done. The sprayer should be well calibrated. It should deliver
two-thirds of the spray to the upper one-half of the tree. Speed should be kept
below two mph. The faster you travel, the greater the bending effect on spray
droplets. Concentrate applications are particularly susceptible to the effect of
speed due to the fine particle size of these sprays.
The dormant spray should be diluted because San Jose
scale occurs in dense colonies. A diluted spray consists of 300 to 500 gallons
of water per acre. This is not a popular spray because it takes a long time to
do one orchard. However, this is the only spray that is going to cover all the
parts of the tree.
The amount of oil should be 1.5 to 2 gallons in each
100 gallons of water. For example, if you are applying 300 gallons of water per
acre, you will be using 4.5 gallons of oil. If you are applying 500 gallons of
water per acre, you will be using 10 gallons of oil. The oil alone will control
low to moderate infestations of San Jose scale. However, if the infestation of
scale is high, add an organophosphate insecticide such as Diazinon® to the oil
mixture. If you have resistance to Diazinon® or Lorsland®, Seven® is a good
alternative. Please read and follow directions of all insecticide
labels.
Copper in the dormant spray has been controversial.
Some researchers believe that copper aids in the control of shothole disease and
"blast" in almonds. Others believe that copper has no value in a fungicide
program for almonds. Dr. Beth Teviotdale and I have studied dormant copper
sprays for seven years in an almond orchard in Kern County.
Based on seven years of data, I will make the
following statements are on the use of copper in the dormant spray.
· Dormant
copper alone does not control shothole disease, therefore, it is not a
substitute for a good fungicide program in the spring;
· In years with heavy
shothole infestation, dormant copper has increased the effectiveness of the
fungicide program in the spring;
· Even though copper in the dormant spray
decreases the amount of shothole disease, it did not show an increase in
yields.
In conclusion, if a grower wants to have a clean orchard, (especially
during a heavy disease pressure year), he needs to include copper in his/her
dormant spray. The grower needs to keep in mind that copper in the dormant spray
is not a substitute for a good fungicide program in the spring.