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Thursday, November 14, 2013

Desert Green Presentation on Fruit Tree Pest Update for 2013

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 2.The UNCE Orchard was established in 1996 in North Las Vegas at UNLV's Center for Urban Horticulture and Water Conservation. The center is located 100 yards east of the intersection of North Decatur and Horse Drive. Visiting hours are every Tuesday and Saturday morning from 8 AM until noon. Volunteers at the Orchard are welcome. The Orchard was established as a research and demonstration facility through Cooperative Extension.

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.


  1. When I look at the Google Map aerial view of the MG Orchard (http://goo.gl/maps/GqhWv) I see the image roughtly divided into thirds running west to east. On the east side, the soil is white like the surroundings. In the middle in between brown and white, kind of grey and little to nothing planted. (Admittedly I didn't look to see what year the overhead was snapped.) And on the west a nice brown. What is up with that? East side represents newer expansion? Or non-mulched to compare?

    The Google street view seems to show the east side is planted with traditional Las Vegas landscaping trees rather than fruit trees...true or my eyes playing tricks.

  2. The UNCE Orchard is planted at UNLV's ten acre facility, Center for Urban Horticulture and Water Conservation. On that site, the Orchard occupies 1.5 acres on the West side of the Center. The Orchard trees are all mulched with recycled green waste from chipped trees diverted from the landfill. The non orchard area in the orchard 1.5 acre are vegetable plots running North and South and interplanted with palm trees because the palms were part of an earlier study before the orchard was established. So the vegetable plots were installed between the rows of palms. The soil is a "sandy loam" with about 1/10 of 1% organic matter and is as hard as rock. It is naturally a light brown (tan) to light grey in color. Of course the wood mulch is medium to dark brown. Digging in that soil is done with picks or irrigation trencher until we can wet and modify it enough to get a shovel in it. Salts in the raw desert land were running with an EC of about 40 mmhos/cm (about 25,000 ppm). The soil was leached to remove salts. The soil is naturally high in gypsum and boron. Salts are dominated by caclium as the cation and sulfates, carbonates, chlorides, borates, etc. This soil took about three years to reclaim it and see good production from the vegetable plots.This type of soil is not uncommon in Las Vegas.
    When planting fruit trees, all trees are bare root and the backfill for the trees is the same soil taken from the hole, large rocks removed and modified with 50% compost which is contrary to the recommendations by the University of Arizona and others. They are concerned with the backfill being to dramatically different in texture from the surrounding soils and creating a "bowl" that does not drain. We have never found this a problem with well over 750 trees that we have planted there. Irrigation for nearly all of the fruit trees is "bubbler and basin" using a 2 gpm bubbler filling a basin around the tree about six feet in diameter. Trees are planted 10x10 in rectangular spacings on the south side and 10x10 triangular spacing on the north end. Green waste, wood mulch chipped from urban trees, is used on the surface to a depth of 4 to 6 inches.