MAY | JUNE 2016
Almond Facts
35
begin to split in the interior of the orchard. Most reduced-
risk pesticides need to be applied prior to egg laying or
hatching, supporting this earlier timing. Pyrethroids (e.g.
Brigade, Warrior), organophosphates (e.g. Lorsban), and
chlorantraniliprole (e.g. Altacor) have shown adult activity
and may be suitable for later timed hull-split sprays.
Although lower in cost, pyrethroids have been shown to
impact spider mite predators for at least six months after
the application, increasing the risk of spider-mite flare-
ups into the following year. Second sprays for ‘Nonpareils’
and coverage for later splitting pollinators may be needed,
especially in areas with higher temperatures and NOW
populations. Work with your pest control advisor to determine
the best strategy for timings and pesticide selection.
Ants
Ants are a serious problem where they are present. If in
high populations, they can consume between 1 to 2 percent
of the crop within four days. Fields should be scouted in
mid-May. Baits containing growth regulators, if needed,
must be applied one month prior to harvest for maximum
effectiveness. If bait wasn’t applied, and fire or pavement ants
are present, a broadcast spray of organophosphate should be
applied as close to harvest as allowed to reduce foragers. Nuts
should also be picked up as soon as possible after shaking.
Be mindful that not all ants present within the orchard feed
on almonds. A quick trick to distinguish “good ants” from
“bad ants” is to throw potato chips or a hot dog near the
mound. If consumed, it can be assumed that the colony will
also feed on almond kernels. Another trick is to stomp near
the mound to bring ants to the surface. If they swarm out
of the mound, are red in color with a black butt and bite,
they are mostly likely fire ants. Monitoring and treatment
information can be found at
/
selectnewpest.almonds.html).
Webspinning Spider Mite
Management in Almonds
As summer approaches almond growers need to be
monitoring for webspinning spider mites. The most common
species during the summer are Pacific and twospotted spider
mite, though on occasion strawberry spider mite can be
found. As adults, all three mites look and behave similarly,
even though control of Pacific spider mite is more difficult.
Webspinning spider mites overwinter in the orchard under
rough bark and ground litter. During the spring, usually
in March and April, migration will occur from these
places into the lower areas of the tree. These early-season
populations are typically small, do not reproduce quickly,
and often become prey to early-season natural enemies.
However, as temperatures warm in late May through
September, the populations increase rapidly, particularly
if natural enemies are absent. In favorable conditions, a
lifecycle can be completed in seven to ten days, with eight
to ten generations a year.
Spider mites damage leaves by sucking cell contents.
Damage initially appears as a light stippling. As populations
increase, mites and their eggs become more visible, and
eventually “webs” will appear around spurs and leaves.
Leaves with high populations will fall from the tree, reducing
carbohydrate production. If leaf loss becomes severe there is
a potential for crop loss the following year. Spider mites are
most problematic in orchards that are dusty or where the
trees are stressed. Stressing factors can include insufficient
irrigation, nutrient deficiencies, or excessive crop load.
The most important factor in spider mite management is
biological control. When natural enemies are abundant,
miticides are not needed. When natural enemies are absent,
control with even the best miticides can be short-lived.
Figure 2: Bacterial spot infection of ‘Fritz’
almonds. Note the amber colored gum and
severity of infection. Treatments for bacterial
spot have to occur in the dormant and spring
of the following year.
Photo credit: David Doll.
Continued on page 36.
