Fruit Tree Pest Update 2013 Notes for the PowerPoint
presentation
Robert Ll. Morris
University of Nevada, Emeritus
Desert Green is a conference held each year in Las Vegas for landscaping industry professionals. Here is a summary of my presentation on PowerPoint and my notes for my presentation.
Slide 3. Fruit growing can be very successful in the
desert because of our isolation from commercial orchards, our low humidity
which helps to suppress diseases, and our high light intensities which helps to
produce high levels of sugar in the fruit. Much of our plant material comes
from Dave Wilson Nursery in northern California which produces high quality
fruit trees for commercial orchards and nurseries. All of the fruit trees are
planted by bare root, usually in late January or early February. We produce our
own compost using local horse manure and green waste. The facility is a
distribution center for wood mulch which is recycled urban green waste,
primarily chipped trees removed from urban landscapes diverted from being
buried at our local landfills. Our principal supplier of green waste is First
Choice Tree Service, a Las Vegas based company. The management of the Orchard
is focused on none or reduced pesticide applications, integrated pest
management and ET-based irrigations.
Slide 4. Whitewash
reduces borer damage. We use whitewash painted to the outside of our trees
to reduce sunburn damage. Sunburn damage to the trunk and limbs can attract
boring insects such as the flatheaded Apple tree borer and the Pacific
flatheaded borer which are problem insects in Las Vegas landscapes. By spraying
the trunk and limbs with whitewash we can reduce the surface temperature of the
trunk and tree limbs by five or 6°F. Whitewash is made by diluting white latex
paint, or off-white latex paint, with an equal amount of water. In some cases
more water can be used but the resulting whitewash should leave the trunk and
limbs white in color. The most important sides of the trunk and limbs are West
and South facing as well as the top sides of limbs. These areas receive the
most direct and intense sunlight and usually show the most damage from boring
insects. The whitewash will need to be re-sprayed or renewed every 3 to 4
years.
Slide 5. Compost at
planting enhances growth. This planting is nopal cactus which is used in
Mexican culture as fresh vegetable, the fruit and animal fodder (feed). Once a
pad is planted in good soil, harvesting of fresh vegetable from young pads can
occur the following year. In three years, cactus fruits are ready to harvest.
Cactus pads were planted in 2006 on the right side of the picture using compost
applied to the soil after planting. The following year, 2007, pads were planted
on the left side of the picture by this time the same amount of compost was
mixed with the planting soil. Irrigations were every three weeks during the
summer. Fertilizer applications were identical. Cactus pads that were planted
with compost mixed in the soil exceeded the growth and production of cactus
planted with compost applied to the surface only. In our desert soils it is very
important to properly command soil at the time of planting for good growth,
even of cactus.
Slide 6. Staking
equals faster establishment. It is important to stake newly planted trees
to immobilize the roots so the tree can become established more quickly. If
trees are not staked properly and the roots are not immobilized, movement of
the plant due to wind can cause slower establishment. As trees begin to leaf
out in the spring their canopy acts like a sail and can catch the wind causing
the trunk to bend and possibly moving the root ball. Stakes should be driven
into solid soil beneath the planting hole and not just the loose soil used for
backfill. Trees should be tied to the stake so that the roots are immobilized
but allowing the canopy and upper trunk to move. If the stake is not driven
into solid soil, the root ball can move and root damage can occur with us
slowing establishment.
Slide 7. Wood mulch
improves tree growth and health. Applying wood mulch to the soil surface
has many benefits. Mulches help to keep the soil cool, moist, suppress weeds,
improve soil quality, provide nutrients as it decomposes, fosters animal
decomposers such as earthworms, lower soil pH and other benefits. Many plants
in the landscape prefer to grow in improved soils rather than raw desert soil.
Improved soils contribute to improved plant health. The best wood mulches come
from a mixture of different types of trees. Bark mulch is pretty to look at but
does not break down easily and contribute to the improvement of the soil and
plants. Bark mulches easily blow in light winds and move in surface water. Wood
mulch that has been chipped from trees does not blow easily in the wind and
interlocks because of its rough surfaces. Wood mulches should be applied to a
depth of 4 to 6 inches. These mulches should be kept away from the trunks of
young trees, a distance of about 12 inches, until these trees are at least five
years old. Wood mulches can be created from chipped landscape trees removed
from local urban landscapes. When this wood has been chipped it will not
contribute any disease or insect problems to landscapes where it is applied.
Slide 8. Wood mulches were applied to fruit trees
immediately after planting and the growth of these trees was compared to trees
that did not receive any surface mulch. All fertilizer applications and
irrigations were the same to all trees. As can be seen in the slide, the growth
of trees which received surface mulch far exceeded the growth of trees which
received none.
Slide 9. Rabbit
prone areas need rabbit fencing. Two types of rabbits are common in
southern Nevada; the desert cottontail and the black-tailed jackrabbit. Both of
these animals are serious pests to landscapes that are adjacent to their normal
range. Most damage to landscape plants occurs on landscapes close to golf
courses or the undeveloped desert. The jackrabbit is more damaging to landscape
trees because you can stand nearly upright and feed on trees with young shoots
or fruit within 3 feet off of the ground. In these areas where rabbits are
common, young trees need to be protected with fencing. Chicken wire with 1 inch
hexagon of openings and 2 feet wide is adequate protection. This fencing can be
cut and lengths of 3 feet and bent into a cylinder surrounding young trees. This
cylinder of fencing needs to be staked to the surface of the soil so rabbits
cannot get their noses under it and push it upward. Rabbits can dig but usually
do not unless it is easy digging.
Slide 10. Water,
not your foot, is the best way to remove air pockets. When landscape trees
are planted, water should be running into the hole when backfilled. The water
helps to remove air pockets from the backfill and settle the amended soil
around the root system or root ball. Using your feet to compress the soil
around the tree will damage the root system. If the soil is amended properly
and water is added at the same time as the backfill, the soil will fill the
voids and the tree will be firmly anchored. Never plant a tree in a dry hole
because this can cause severe root dieback and delay establishment. Creating
basins around trees, even though they may be irrigated with drip, will force
the water to fill the entire root zone and speed up establishment. The basins
can be removed after establishment if desired.
Slide 11. Regular
irrigations during fruiting improve fruit quality. This graph is for wine
grape berry development but this principle holds true for all developing fruits
and nuts. The growth of fruit follows what is called a double sigmoid curve.
The bottom of the graph shows increasing time moving to the right. If the fruit
takes four months to develop than the time will be four months on the bottom of
the graph. If the fruit takes six months to develop then the bottom of the
graph will be drawn out to six months. On the left side of the graph of
vertical line represents increasing weight of the fruit. When the fruit is very
young, starting in the bottom left corner, the fruit gains weight or enlarges
very quickly (I). Then there is a period of time when the fruit gains no wait
or size (II). There is a second growth spurt (III). It is extremely important
that the fruit is not water stressed or the tree under some sort of drought
during these two rapid growth stages or it will affect the quality of the fruit
produced. Of course these stages occur during the summer months when the demand
for water is already high.
Slide 12. Summer
pruning health and fruit production. Some varieties of fruit trees are fast
and vigorous growers while others are not. Fruit trees that are given a lot of
fertilizer and a lot of water will grow more rapidly than those which do not.
In any case, if there is excessive growth in the canopy it can affect fruit
production. This excessive growth can shade the interior of the canopy and
cause interior branches to die, leaves to drop off the tree and fruit fails to
develop inside. Fruit trees with dense canopies tend to produce the fruit on
the outside of the canopy where the fruit receives more damage from intense
sunlight. The amount and quality of the fruit produced can decrease a lot.
Summer pruning is done to allow better light penetration inside the canopy of
the tree. Light penetration inside the canopy allows for interior branched
development and fruit produced which can be lightly shaded. This tends to
produce better quality fruit with less damage. The act of summer pruning only
occurs in March and April when the new shoots are still soft and succulent.
Summer pruning only removes undesirable new growth. Most of this growth can be
removed without pruning shears, just by pulling downward on this young growth.
Summer pruning also tends to keep trees more dwarfed than if they were not summer
pruned.
Slide 13. Fertilizers
controlled growth and affect health. If a soil test has never been performed
it is a good idea to do one to obtain what we call baseline soil nutrient
values. This soil test can tell us if the soil is deficient in some major
nutrient and make those adjustments at the very beginning. For home landscapes
soil tests are not needed annually. Tests can be done several years part.
Generally speaking, if the soil was adequate at the beginning then annual
applications of fertilizer, with a ratio similar to a lawn fertilizer (3-1-2 or
3-1-3) is adequate. The fertilizer is applied near the source of water so the
water can move nutrients into the rootzone. Fertilizer stakes can be used and
slow release fertilizers are usually preferred with half of the nitrogen
available as slow release. If there is only a single application, it is normally
done in late winter or very early spring, late January or early February. If
two applications are to be made, half is applied in late winter and the other
half applied after harvest. Nearly all of the fruit trees in the rose family
(peaches, nectarines, plums, apricots, apples, pears, etc.) can develop iron
chlorosis. in our alkaline soils. It is best to apply chelated iron to the soil
at the same time as a late winter fertilizer application. The best chelate to
use is EDDHA due to its stability in a wide range of alkaline soils. Foliar
sprays of iron can be applied if this application is missed but foliar iron may
damage fruit growing on the tree. Calcium is sometimes applied as a foliar
spray multiple times while the fruit is growing to prevent bitter pit in apples
were corky spot in pears. These are talked about later.
Slide 14. Insects
and pests that can move. This slide lists pests that will be discussed.
Slide 15. Sanitation
reduces pest problems. It is highly recommended to pick up fruit that has fallen
to the ground as soon as possible. Fruit that is on the ground or damaged on
the trees will attract insects that contribute to do decaying process. These
types of insects can also attack fruit that is left to ripen on the tree.
Picking up fallen fruit and damage to fruit on the trees should be a daily
chore scheduled for the beginning of the day. Some people keep this fruit for
personal use while others will compost it. If this fruit is composted, it
should be buried in the compost. Fruit left exposed on top of a compost pile is
just like leaving the fruit on the ground; it will get infested and these
insects will spread to fruit ripening on the tree.
Slide 16. Borers
attack nearly any tree. There are two types of major boring insects that
infest landscape and fruit trees in the Las Vegas Valley. These are the
flatheaded Apple tree borer and the Pacific flatheaded borer. The adults are
beetles which can fly and mate outside the tree and the female lays its eggs on
the limbs of landscape and fruit trees. The usual sites for laying eggs are on
limbs which have been damaged from sunburn. Hence, preventing sunburn to limbs
helps to discourage, but not prevent, borer infestations. The eggs hatch and
the tiny larva or worm enters the tree. This larva feeds just under the bark in
living wood where it creates tunnels. In the fall when the weather cools, larva
may tunnel into the center of the limb or trunk where they pupate or turn into
the adult beetle. Some may spend the winter as a larva just under the bark.
Merit is an insecticide that is labeled for use to control borers in landscape
and fruit trees. It is a systemic insecticide applied to the soil and taken up
by the roots. Personally, even though the label does allow for the treatment of
fruit trees with this product, I would not use for fear of the pesticide
contaminating the fruit even in small amounts.
Slide 17. Borer
removal. Instead we use a sharp knife and remove loose bark from the tree
where we see borer damage. All of the loose bark is removed down to fresh wood
and left to heal without applying any sealer. If the borer damage is more than
50% of the limb, the limb is removed. If the tree is known to have good
suckering abilities, a stub may be left for suckering and no limb development.
Otherwise it is removed at the trunk or at the juncture of two limbs. In my
experience, this has helped to reduce borer problems in about 80% of the limbs
were this is done.
Slide 18. Birds
feed on ripe fruit. Bird damage to fruit can be a huge problem. Birds will
normally feed on fruit that is nearly ripe. They will usually damage a small
portion of the fruit and move on. Fruit that has been damaged cannot be stored
or sold. However, it is safe for personal consumption. Fruit does not ripen all
at the same time on the tree. When weather is hot, most fruit may ripen over a
period of one or two weeks. When weather is cooler, this can take three weeks
to a month. Birds will focus on fruit that is the ripest in the tree. As soon
as this damage occurs the fruit should be picked to stay ahead of Bird damage.
Otherwise the tree must be netted. The netting must extend all the way to the
ground with no gaps for bird entry or they will. I have not tested it but there
are reports that monofilament fishing line can be used to discourage birds from
entering your tree when fishing line is distributed like a teepee over the
tree. We have experimented with hanging CDs or DVDs in the trees, using
Christmas tinsel hanging from the limbs, devices which scare such as owls, and
even sound devices that make noises like distressed birds or predatory birds
like hawks. Generally speaking some of these devices work for short periods of
time until the birds figure out that it cannot harm them. At this point, they
ignore them. If these devices are used they should be placed in the trees just
before you expect bird damage and removed after harvest. If you have a long
harvest time as we do in the Orchard it is very difficult to use these types of
products.
Slide 19. Ground
squirrels. A lot of people call them chipmunks and think they are cute. But
these varmints can steal and damage a lot of fruit. I have seen ground
squirrels clean an entire almond tree of its nuts in one day and just a few
days before they were to be harvested. I have seen ground squirrels steal
grapes from grape bunches, clean out the inside of pomegranates which have
split, and damage vegetables. We usually set out poison baits to control these
animals. The baits are set in the spring without poison, the animals are
allowed to feed on the unpoisoned bait and, once they start feeding, poison
bait is substituted. Bait traps are constructed so other animals cannot gain
access to the bait and the traps are cleaned regularly.
Slide 20. Coddling
moth damages apples and pears. This is the insect responsible for wormy
apples. This moth is a serious pest of apples and pears throughout the entire
world. I would not say that coddling moth is a huge pest problem for Las Vegas
since we do not have any commercial orchards. We do get occasional damage from
the larva of this moth even though there appears to be large numbers of the
moths present. We set one pheromone trap with coddling moth lures in the Apple
and pear area around 1 March to monitor for the presence of this moth. The
pheromone lure is replaced on a regular schedule and extras are kept
refrigerated. Once we begin to catch moths in the pheromone trap we set other
traps in the Orchard as well hoping to cause confusion when they are mating.
This is called mating disruption. Even though the research tells us that it
should not work with our Orchard set up we never have coddling moth damage to
the fruit even though we catch hundreds of moths in the pheromone traps.
Normally in most operations sprays of BT or Spinosad are applied to the trees
to kill the larva and prevent it from entering the fruit. We do not use these
sprays.
Slide 21. Wormy
peaches. Worms in peaches and nectarines is from a different insect than
the coddling moth and requires a different pheromone lure. This insect is most
commonly the peach twig borer. Early in the season when fruit is not available
for this moth, this insect attacks new spring growth causing dieback or what is
called “flagging”. This might happen as early as early March. The same
procedure is used with pheromone traps and lures as we do with coddling moth.
However a different lure must be used since it attracts a different insect.
This insect is also a small brown moth very similar in appearance to coddling
moth. If pheromone traps are set out early enough we seem to be able to reduce
the damage by this insect to the fruit through mating disruption. Again, this
is contrary to what the research would predict. Again, we catch hundreds of
these moths in our traps. The same sprays that control coddling moth will also
control peach twig borer. We do not use these sprays.
Slide 22. Fruit
scarring on nectarine. This is a common complaint among people who grown
nectarines here in the Las Vegas Valley. The fruit can be extremely damaged and
disfigured usually with dried sap coming from it. This is damage from the
western flower thrips. This insect is extremely small and difficult to see
without a magnifying glass. They are not good flyers but they can fly from tree
to tree and fruit to fruit. I have seen this insect damage flowers of peach,
nectarine and plum. Because nectarine is a hairless peach, it gets damaged by
western flower thrips while the hair that covers the skin of the peach prevents
this from happening. We do see some slight damage to plums but nothing even
close to what the damage is on nectarine. Western flower thrips attack the
flower petals and ovary which forms the fruit when the flower is open. As the
petals fall from the flowers and the fruit begins to form from the ovary,
damage to the peach fruit stops because of the hairs but continues on the
nectarine fruit as it gets larger. If preventive sprays are not applied to
nectarine fruits, the fruits will be damaged. The degree of damage depends on
the amount of protection given the fruit. The fruit must be sprayed to protect
it. The best insecticide for controlling flower thrips is Spinosad. The problem
is with repeat applications of this insecticide. Repeat applications can cause
resistance to this product and only a certain number of applications are
permitted each season. Read the label. I alternate sprays of Spinosad with
soap, oils, and Neem. All are organic. The other sprays are not nearly as
effective as Spinosad in controlling Western flower thrips. By the way,
Spinosad is very effective at reducing leafhopper populations in grapes if
applied early when leafhoppers are still immature, usually in April and May.
Fruit with scarring is safe to eat.
Slide 23. Leaffooted
plant bug. This insect has become a serious pest in some parts of the
Valley on pistachio, almond and pomegranate. I'm sure it causes other damage as
well since it is a test of ornamentals as well as fruit trees. This insect has
a piercing sucking mouthpart that can cause deformity, fruit drop, nut drop and
nuts to form with a shell but no nut inside (blanks). These insects will
overwinter in landscape plantings and fruit trees. Dormant oil applications may
be effective at reducing their numbers. Otherwise insecticides such as Sevin
and synthetic pyrethroids have been noted to give control.
Slide 24. Diseases.
This is a short list of diseases to be discussed. Diseases can be categorized
as those caused by the environment (abiotic or caused by something “without
life”) or biotic (diseases caused by something living such as bacteria, fungi,
viruses and MLO’s and even includes nematodes). Diseases in fruit trees we are
most concerned about in the Las Vegas Valley are caused by the environment
(abiotic), bacteria and fungi.
Slide 25. Sunburn.
Because we have such high light intensity, sunburn is a huge problem on fruit
production in the desert. The damage from sunburn starts with slight discoloration
on the surface of the skin. As the damage progresses it becomes darker and may
even be black eventually. It is very noticeable on persimmon such as Fuyu and
apples. It will cause discoloration and reduces the visual quality of
pomegranates. To produce visually, high-quality fruit in our climate requires
some light shade from the canopy of the tree. Summer pruning helps to
distribute the fruit more evenly throughout the canopy and can reduce problems
of sunburn. Sunburn might also be reduced with spray applications of kaolin
clay such as found in the product Surround.
Slide 26. Brown
spots on apple and pear. Older trees of some varieties of apple and pear
can develop brown, corky spots to develop in the flesh or just under the skin.
This has been identified as a calcium deficiency known as bitter pit when it is
found in apples and corky spot when seen in pears. Apparently, when fruit is
forming there is a huge demand for calcium by the tree. Calcium is fairly
insoluble in the soil. The demand for calcium is higher than the soil can
provide and so the fruit and the tree becomes calcium deficient even though the
soil is loaded with calcium. The solution is to spray the fruit on the tree
with calcium chloride with five applications during fruit development. The
first application should be made when the fruit is small with continuous
applications about one week apart. The foliar calcium spray should have a
wetting agent to provide adequate uptake of the calcium chloride inside the
fruit. I have been using either food-grade calcium chloride or calcium chloride
suitable for an aquarium. I use about 2 to 3 lbs. of calcium chloride for every
100 gallons of water.
Slide 27. Fireblight
- a devastating disease of Apple, pear, Asian pear and Quince. This disease was
particularly devastating in 2013 due to a cold, wet and windy spring. Fireblight
can be a particularly devastating disease in Asian pear but occurs on a regular
basis and apple and European pear such as Comice, Bartlett and Hood. We can
normally expect fireblight damage to appear in the Orchard if we have a rainy,
cold, windy spring when these trees are blooming. This bacterial disease
appears to spread from flower to flower and may be aided in this spread by
birds, bees and people who prune. In other words it can be taken from an
infested tree by these animals or humans and spread to other trees through
physical contact. It is important that diseased parts of the tree be removed as
soon as it is seen, placed in plastic bags, sealed and, if possible, removed
from the property. This disease is extremely virulent or capable of spreading
easily. There are bacterial sprays available to apply to the plants as
preventive sprays but most people will just cut and remove infested wood when
seen. When cutting this wood from an infested tree it should be cut about 12
inches below the infestation. Pruning cuts should not need to be sanitized or
sealed if the pruning equipment has been sterilized. Pruning equipment must be
sanitized and sterilized after each cut on an infested tree and before pruning healthy
trees. There is a lot of debate on what to use to sterilize or sanitize
equipment but I typically use alcohol and heat. I will carry with me an
inexpensive lighter and heat the cutting blades with it. I also sanitize the
entire piece of equipment with soap and water, alcohol or Lysol. Air drying
equipment is not effective for sanitizing against bacterial diseases like this
one.
Slide 28. Shothole
fungus or Coryneum blight. Shot hole is a fungal disease that is widespread
among mostly peach and nectarine. The fungal disease will cause spotting of the
leaves in the early stages. These spots, about the size of a BB, die and drop
out of the leaf leaving holes in the leaves that resemble damage from a BB gun.
The difference is that these holes usually are rimmed with a purple or purplish
brown margin. Seldom does this disease get that enough like it does in wetter
areas that it attacks the fruit. When the fruit is attacked by this disease it
can leave the purplish spots over the skin of the fruit resembling measles.
This disease seems to be more severe on certain varieties then others. It also
seems to get worse if trees are stressed from drought. Usual control measures
include the application of a Bordeaux or copper-based fungicide applied to the
tree immediately after leaf drop. The disease can enter the wounds on the
limbs, (these are leaf scars or where the leaf was attached) that are created
when leaves fall from the tree. But the application of this fungicide has to be
immediately after leaf drop and before infection occurs. The second best time
to apply this fungicide is in the spring as the leaves are developing. This
helps to protect the new leaves from getting infected by the fungus.
Slide 29. Resources.
You can sign up for membership in my blog that answers questions from readers
about horticulture in the desert. It can be found by googling
Xtremehorticulture of the Desert. If you would like to be involved in a
discussion of desert horticulture, become a member of the Yahoo discussion
group on desert horticulture. To become a member you must be approved by the
administrators. You can find this discussion group by googling desert
horticulture Yahoo discussion group and send an e-mail to the group asking to
become a member. Other resources include the Dave Wilson nursery website at
davewilson.com and an excellent source of information on tests of fruit trees
can be found at University of California IPM online.
