If Fruit Trees are Planted Correctly They Can Take the Heat

 Dig the hole three times WIDER than needed. Plant in a wet hole. Amend or mix that soil or bring in different soil.

The planting hole is dug three times wider than you need it.

Amend or mix the soil with about 20 to 30% of a very good compost.

Mix in a good compost when planting.

Stake all fruit trees. Make sure the trunk cant move when you are finished.

Stake fruit trees, all of them, so the trunk can't move.

Protect the fruit trees from rabbits with chicken wire for the first three to four years if you live near a golf course or an open desert.

Put at least two inches of mulch (wood chips that rot) on top of the soil. Three inches is better. Keep it 6 to 12 inches away from the trunk until the tree is six years old.

These are wood chips from whole entire trees, not bags of wood bark.

Water every other day or every third day, wide and deep.

Cure Yellowing Eucalyptus Tree

Q. I have a 20 plus year old eucalyptus tree. The leaves are very yellow. What is the cause of this?

Its not a simple answer when it comes to yellowing eucalyptus. Could be anything. Judging from the plants around it and recent water restrictions I am wondering if it is water related.

A. Yellowing leaves can mean many things. It could be a nutritional problem, watering issues, or damage from insects or disease. I need more information as well as leaf and tree pictures. Make sure it gets an iron application to the soil in the spring. To be on the safe side, apply an iron chelate such as EDDHA.

This is the iron chelate called iron EDDHA. Because of its chemistry it performs well in all soil pH if applied in the spring.

            Check for a watering issue or a leak that floods the soil in that area. Eucalyptus is “mesic” in their water use so an application frequency for large trees should be used. When water is applied it should be deep and wide or large shrubs that receive water should be located under its canopy. Once a tree is chosen its increasing water use as it gets bigger has also been chosen.

Borer Prevention

 Q. I have lots of borers in my trees. What can I do to prevent it from happening?

When borers are a problem it starts about mid summer. Often it begins in parts of the tree frequented by our intense sunlight like the upper sides of limbs that are not shaded.

A. First, prevent sunburn to all trees, particularly young fruit trees. Sun damage is a problem immediately after planting in our desert climate. Damage from the sun can lead to borer problems later down the road. If I were buying a fruit tree, I would buy a small tree and let it grow as a bush. This way the lower limbs will shade the trunk.

Let the Tree Grow Bushy

As soon as it starts to produce fruit, that next winter, I would remove the lower limbs only so the fruit does not touch the ground. Leave as many of the lower limbs as possible to shade the trunk. In fact, let it grow into a shrub.

The biggest mistake homeowners make with fruit trees is to buy large fruit trees with limbs high off of the ground. If lower limbs are present, they are removed to make a tree. Buy smaller trees and let them grow to the next size.

Shade the Trunk

It may be the right thing to do in other climates but not the desert. Desert fruit trees need tender trunk protection from the sun to about five or six years old. If you have a fruit tree and it is “limbed up”, then protect the trunk with diluted latex paint, tree wrap or protective collar that shades it.

A sign for a borer problem is limb death in the middle of summer; brown dried leaves clinging to one or more branches on the south or west side of the tree starting when it is hot. Use a borer soil drench with an approved pesticide for borers. You are not permitted to eat the fruit until 12 months have passed. This particular pesticide is best applied after flowering.

Use a Pesticide as the Last Resort

There are pesticides that can be used that will kill borers still in the tree. Be careful. Treat trees after they finish flowering to protect honeybees. Don't eat fruit from that tree for one season of production after you apply a pesticide. 

Ash Trees With Bark Lifting

Q. Our ash trees have “bark drop” as they got older. Should I worry that the light tan areas of bark are peeling in long sheets four feet long, and this bark seems to be coming away from the tree in small chunks?

Bark coming off or lifting from readers tree.

A. Worry only if your ash trees had the bottom branches recently removed and they were planted on the south or west sides of a building or wall. Try to leave the bottom limbs attached to the trunk as long as possible so the trunk is shaded by the limbs. Once the tree has gained some height and age, some of the lower branches can slowly be removed.

Beginning of ash sunburn after it was recently planted. The orangish-red color of the trunk or limbs is not normal for this tree and it was facing the sun. 

            Your job will be to discover if the trunk has been damaged either by the sun or by borers or both. Before you begin, establish which side of a wall or building the tree was planted on and make a mental note. South and west sides of walls and buildings are the hottest and most damaging.

Ash borers in the trunk of a young ash tree. Removing the loose bark will reveal their nasty work.

            Next remove any loose bark including those strips you mentioned. Use your hands first two pull off any loose bark. It won’t hurt the tree. Finally use a sharp and sterilized knife blade about 5 inches long to make the trimming cuts to undamaged wood just below the bark. The undamaged wood should be white or light green. The purpose is to hasten the healing either of the trunk or limbs and discover what did the damage.

Even though this is fruit tree it still demonstrates how to correct borer damage with a knife.

             It’s always a good idea to leave the lower living limbs for shading the trunk as long as possible. This shade helps protect trunk and limbs sunburn. Once these areas are sunburned, they will attract boring insects because these insects are attracted to damaged trees and shrubs. The sun burned areas are in the trunks and limbs where there is the most intense sunlight. This is usually the West or South facing sides or the tops of limbs and branches.

Reasons for Palo Verde Limb Dieback

Q. The palo verde tree in our daughter’s yard looks like it has damage. The top has some dead branches in it. We have had to remove some limbs because of this problem. Can it be saved?

A. There are several different kinds of Palo Verde used primarily in desert landscaping. All have tender new growth that can be severely damaged when exposed to intense sunlight. It is important these trees are pruned throughout their lives so that the tree’s canopy shades the trunk and limbs.

If desert adapted trees have limbs removed that expose the trunk or large limbs to direct sunlight and sunburn, borers can be a problem in these trees such as Palo Verde and acacia

            Pruning them in a fashion that exposes limbs and the trunk to intense sunlight causes damage that causes limb death that becomes visible a few years later. It’s a progression that usually starts with bad pruning practices. This progression begins when too much is removed from these trees. When too much is removed, the limbs and trunk are exposed to high intensity desert sunlight.

Exposing the trunk and lower limbs to direct sunlight and sunburn can create future problems to trees like the Palo Verde.

            Intense, direct sunlight on young limbs first causes a discoloration due to intense sunlight. As this direct sunlight repeats day after day, exposed areas of limbs and trunk facing the sun die. Water can’t through dead areas of the trunk and limbs.

            Unless this sunburn causes severe damage, the top of the tree probably looks fine. The tree can still move water around the damaged area from roots to tree branches. The damage could be as much is 50% of the limb and trunk area and the tree looks fine.

This is not Palo Verde but when the trunk and limbs are exposed to intense sunlight for a long period of time, year after year, the intense sunlight can damage or even kill the living part of the tree under the sunburned area. The beginning of this damage can be very attractive to some wood boring insects which can make the damage worse.

            This damage from sunburn attracts insects such as borers that feed on living parts of the tree close to the damaged area. This feeding by borers causes even more damage that reduces water movement to the limbs. Perhaps the first year or two, trunk and limb damage goes unnoticed because the canopy looks fine.

The first sign of sunburn is a discoloration or off-color to the trunk, limbs or even fruit on fruit trees.

            But at some point, damage becomes severe enough that water movement from roots to the canopy is reduced.  Limbs start dying back because the tree can’t get enough water past the damage. This usually happens during the heat of the summer when demand for water is highest.

            The homeowner now notices the limb death in the canopy. The homeowner removes dead limbs. This exposes the tree to more intense sunlight and further damage. Tree damage is so severe and unsightly the homeowner considers removing it. This is the tree “death spiral”.

            What to do? Damage to the tree may be already extensive. Decide whether you can live with this damage or not. If not, have the tree removed. If you decide to keep the tree, then encourage it to heal as quickly as possible. Contribute to this healing by giving it enough water on a regular basis and apply fertilizer in early spring.

Acacia Dropping Its Leaves

Q. My young acacia tree has abundant growth but only on the top half of the branches. Each of these branches are losing many leaves half way up the branch. There is a lot of growth at the top of the tree but not much below. Am I watering too much, too little? I water every five days during the summer.

A. Acacia trees are desert plants. Most desert plants are opportunists when it comes to using water. In other words, when water is present they grow like crazy. When water is absent, their growth slows and they then try to use as little water as possible. Desert plants may even stop their growth and drop their leaves when water is not available!

This is not Acacia but Palo Verde. Boring insects, or borers, may feed on a variety of trees and shrubs or very specific ones. Borers, like the flat headed apple tree borer, has a variety of trees they attack including the desert trees. Sometimes they attack trees with sun damage and other times they seem to attack trees without any cause at all.

            All plants are tremendous competitors for water, nutrients and light. They want to be “top dog” in their plant community by taking as much water, nutrients and light as possible when it’s available. By doing this, they take away these building blocks of growth from other plants.

            When water is present, trees try to get as tall as possible as rapidly as they can before they start to fill out. They grow upward first and then put energy into horizontal growth once they’ve established some height. This growth in height takes away light and shades competitors. This early growth in height, when there is a plenty of water and nutrients, oftentimes is at the expense of putting on lower growth .

We commonly see borers attack fruit trees and many different landscape plants. This flat headed Appletree borer infested a young Apple tree recently after was planted. The tree was so young that extensive damage was done by a single borer found feeding in the tree.

            Watering schedules take two different forms; how much water is applied and how often water is applied. It’s difficult to say with certainty without seeing the tree, but it sounds like it is receiving water too often.

            Watering every five days means nothing to me. I can take a sip of water hourly and someone might think I am drinking plenty of water. But another person might ask, how big are your “sips”? One teaspoon or 1 pint?

            How much water to apply? When watering trees, give them enough. Apply enough water to wet the soil at least 24 inches deep. Apply this water to at least half the area under the canopy of the tree. Once it enters the soil, the water spreads horizontally further than this.

Use 3 eighths inch rebar to estimate how deeply water has penetrated into the soil after an irrigation. Check the soil in 3 or 4 locations.

            Use 3/8-inch diameter rebar that is three feet long. After irrigating, push this rebar in the soil in three or four locations to check the watering depth. Wet soil allows the rebar to slip in easily to the same depth as the wet soil. Dry soil makes it hard to push further.

            It should slip into the soil at least 24 inches deep. Once you know how many minutes this takes, the amount of time you water won’t change. Each irrigation will be 24 inches deep.

            If using drip irrigation, space emitters about 2 feet apart. If using a basin or moat under the tree, the basin should be as wide as half the area under the canopy. Trees grow. This means the basin must expanded every three years. If using drip emitters, add more emitters every three years.

Basin under a tree used to capture the water for irrigation. If using a hose or some other delivery method that releases a large quantity of water rapidly, a basin is required to keep the water from going everywhere else but around the tree.

            How often to apply water? Look at the tree canopy. It will tell you. When the canopy of the tree starts to thin out, it’s time to irrigate! Desert trees tell you when to water when their canopies begin to thin out.

Random Thoughts Regarding the Desert and Our Hot Summer

Perhaps this summer has been brutal but plants like palo verde can handle “brutal” weather. 

 "Native" palo verde in Arizona in bloom

Be careful how these plants are pruned. The tendency is to prune them too high and this removes the shade that the tree naturally provides the trunk and limbs. Watering also helps. Plants like palo verde respond very nicely to increases in applied water very quickly..in just a few days. Water these plants with a hose to give them a shot of water and improve shading of the limbs and trunk. 

 

Sap coming from Palo Verde. Removing too many branches and exposing too many large limbs and the trunk can lead to sun damage of this thin barked tree.

Hopefully plants like palo verde were not pruned to allow excessive sunlight to shine on the trunks and limbs. Also, water in the soil helps keep limbs and the trunk from burning because these areas release water to the air and help cool the limbs and trunk through evaporation of water from microscopic holes that can open and close called stoma or sometimes called stomates. If water is restricted it cannot cool itself properly and they will burn. OR water loss can be faster than the plant can replace…as in the case of apple fruit…and burning occurs.

That is a wide variety of plants to have sunburn on. Sunburn on trees is usually restricted to trees with a think bark (palo verde fits this) and a lack of shade covering the limbs and trunk. Sunburn is on the sides of the trunk and limbs that face the sun and not on the other sides in the shade. If this damage extend into the side in the shade then it is something other than sunburn that is going on. 

 

In my opinion too many of the lower limbs were removed on this Palo Verde which can lead toward sunburn

You can apply the same logic to agave and desert spoon. Not enough water can contribute to sunburn. If they are droughty then will burn more easily than if they are getting enough water. 

A lack of soil improvement…poor soils that were not improved by adding compost at the time of planting…YES, this includes cacti!...may sunburn or turn yellow from intense sunlight. Sunburn comes in different degrees of severity…mild sunburn is a yellowing of leaves or fruit but not death of the plant tissues  beneath the damage. Medium damage results in yellowing with some brown or tissue death in or near the center of the yellowing…there is tissue death and this tissue death will attract bugs and other critters that sense the plant is damaged. 

Borers will attack sun damaged areas on the trunk and limbs of trees

These are bugs that are “decomposers” who want to break down these damaged plants and “recycle” them…naturally. The third stage is death of the tissues facing the sun, not only brown but cankered with bark or the skin dead and scaling or peeling back. This makes a pretty ugly plant. But the sides away from the sun are not damaged and the plant will survive unless some “decomposers” get in their and try breaking them down by feeding on them. Borers are in this category. They are goners if they look bad enough you cant live with them any longer. In most cases they will survive.

Prevent Plant Sunburn with Adequate Water and Wood Mulch

Some thin barked trees and shrubs will get sunburned if they don't have enough protection from strong sunlight.

This reddish-brown discoloration is sunburn. In the first stage of sunburn we see the beginning of death onsides exposed to the South and West

Plants that typically get sunburn include many of our fruit trees, mostly peach and apples. Ornamental trees and shrubs also get sunburn. I get a lot of pictures of sunburn sent to me with sunburn and include Japanese blueberry, locust trees, ash trees, Indian Hawthorn, and others. 

This is the trunk of an ash tree on its west side. It first got sunburn. After sunburn the borers attacked it. What you see now is loose bark covering dead wood killed by borers. You can take your fingers and just pull this bark off of the trunk easily. You should do it anyway. You will not hurt anything. That site is already dead. The tree is still alive because the trunk is alive on the other side of the tree.

The natural way to protect these plants from sunburn is to allow these plants to shade their own trunks and stems with leaves. Not providing enough water can thin out the canopy of trees and shrubs and encourages sunburn. 

When you pull this bark away from the trunk you will see oval-shaped holes in the wood. These are exit holes of the bores. Removing the bark also removes hiding places and birds have a better chance picking them off when they emerge.

Having rock mulch around plants that do not like rock mulch also reduces the number of leaves and increases the chance of sunburn. Plants that do not like rock mulch, like the ones I mentioned above, will develop an open canopy, leaf loss, and sunburn. 

This is sunburn on a bottle tree. The leaves drop from the canopy and expose the trunk and limbs. High sunlight intensity causes sunburn once the leaves are gone

What's the problem with sunburn? When we get sunburn we recover. When plants get sunburn, particularly in a desert climate, they frequently decline and die. Attack by boring insects, or borers, is the first phase after sunburn. The borers create more damage and more leaf loss and more sunburn. After that, the plant falls into a death spiral. 

Sunburn caused the top of this Japanese blueberry to die. Then the top had to be removed and it was pretty ugly. Japanese blueberry should not be in rock mulch. They should have wood chips around them.

Use surface mulches particularly wood chips and not bark. Don't water trees and shrubs daily but water them two or three times each week during the heat of the summer. Reduce the number of times per week during the cooler months. When you do water, give them adequate amounts so that the soil is wet to at least 12 inches and preferably 18 inches.

Pine Tree Dripping Sap from Holes

Q. I have a one-acre lot in east Las Vegas with large pine trees. One of the trees recently started dripping lots and lots of sap. Upon inspection, we found some horizontal lines of holes in the bark.  Other areas the sap is just dripping from the natural seams of the bark.  I looked online and it suggests a bird rather than a borer if the holes are in lines. Are there woodpeckers in Las Vegas?

A. Yes, we have the yellow-bellied sapsucker here which is in the family of woodpeckers. They cause the kind of damage you are seeing and drill holes in horizontal lines which can drip sap. It looks a little bit like someone took a drill and drilled holes in the tree close together and in a straight line.

There is not much you can do except to try to exclude these birds from the trunk which is difficult. The good news is that these trees can live many years with this type of damage from this bird if the tree is healthy and growing.

Big pine trees use a lot of water so make sure yours is receiving enough water in the spring and summer months so that it will grow enough and recover from the damage.

If damaged trees do not grow enough to recover from the bird damage then it can be a problem for the tree. 

Try looking here on my blog

http://xtremehorticulture.blogspot.com/2011/08/someones-drilling-holes-in-my-trees.html

http://xtremehorticulture.blogspot.com/2014/04/holes-in-trees-due-to-woodpecker.html

http://xtremehorticulture.blogspot.com/2015/01/what-caused-holes-in-my-tree.html

http://xtremehorticulture.blogspot.com/2015/01/time-of-year-for-holes-to-appear-in.html

Sap Coming From Peach Trunk to Top of Limbs

Q. Our peach tree has sap coming out from the ground level to the top of one of the limbs. Not sure if too much water, not enough water, too many bugs or what.

A. This is the time of year we start noticing borer damage in peach trees. Sap comes out from the limbs and possibly all along the trunk.

Branch dieback due to peach borer damage.

A clear indicator of borer damage will be that the bark around the sappy areas will peel off, leaving bare wood under it with clear feeding damage (looks like someone took a miniature sander to the wood with no clear pattern) and if you pull enough bark away you will see flattened, oval exit holes from the adult beetles.

Bark peeling away from dying branch due to borers.

You may even see some sawdust under the bark in these "sanded" areas from their feeding. Remove all loose bark all the way into good wood. You may even find a flattened, ugly larva of a borer just under the bark still feeding. Keep it for a pet if you want to.

Borer in removed dead branch

If damage is more than 50% around the limb, cut it off. Do not paint with black tree wound paint. Paint the trunk and remaining limbs with diluted white latex paint (50/50 with water) on the upper surface of all branches down to one inch in diameter and the trunk.

Borers like limbs and trunks exposed to the hot and intense sunlight. White paint keeps limbs and trunks several degrees cooler than brown limbs and trunks and helps to reduce damage to these parts by intense sunlight. 

Tops Dying Back in Japanese Blueberry

Q. I’m having a problem with my Japanese blueberry trees. Some are fine but the two on the end appear to be drying out from the top down.  Do you have any idea what’s causing this? The soil is not dry and they all get the same amount of irrigation.

A. The usual problem in damage or death to the top of a tree can be found on the main trunk just below the damaged area. I am guessing something has damaged the tree at that point.

            The reason for the damage could be several. Borers cause mechanical damage to the trunk and shut off the water going to the top. Diseases in this same location can do exactly the same thing.

            Because Japanese blueberry is relatively thin barked, sunburn from our intense sunlight can kill the trunk in that location and shut off water to the top. Humans can cause damage to the trunk and shut off its water supply as well.

Top of dead stem on readers Japanese blueberry

            I think we can rule out pathological diseases in our climate. The two most likely culprits are mechanical damage to the trunk by borers or the same type of damage caused by sunburn.

            Inspect the trunk at the location just above the healthy area of the canopy. Use your fingers and see if you can pull away any loose bark. Borers tunnel just under the bark usually on the side towards the most sunlight. This kills that part of the trunk and the bark peels away easily.

            If you don't see bark peeling from the trunk at this location, look for discoloration of the trunk on this side facing the sun. Sunburn to the trunk can happen in one hour of intense sunlight during the midday or late afternoon.

            If it is borers there is nothing you can do to raise the dead area back to life but you can protect the tree from extensive borer damage with an insecticide soil drench once a year.

            In any case, you'll be forced to remove the dead top from the tree with a pruning shears or saw this winter. Once you do this, it may open remaining branches for sunburn as well. Give them as much protection as you can.

            I would not do it now because the sunlight is too intense and will probably cause even more damage to the lower, healthier part of the tree.

Japanese Blueberry Tops are Dying Part I.

Q. I’m having a problem with my Japanese blueberries. Some are fine and the two on the end appear to be drying out but only towards the top? Do you have any idea what’s causing this? The soil is not dry and they all get the same amount of irrigation.

Japanese blueberries tops dying back

Poor Canopy Development in Newly Planted Large Tree Could Be Lack of Water

Q. I think I this might be a pink locust tree. I'm seeing a lot of dead branches. The tree was planted last Fall. Should I give it some fertilizer to help it push out new growth?

Holes in Trees Due to Woodpecker?

Q. Do we have woodpeckers in Las Vegas?  This is the north side on the trunk of my Carob tree, at about chest high.

Science in Action: Controlling Borers in Landscape Trees

Options available for controlling borers have actually increased over the past few years. While the traditional approach of spraying an entire plant with a chemical such as Lindane, a chlorinated hydrocarbon, has become less available to pest control operators other types of IPM (Integrated Pest Management) control strategies have blossomed on the commercial market. The problem for most applicators is that the "security blanket" of a traditional pesticide approach is disappearing and the research to support the newer products is not available to give applicators confidence that they will work.

The IPM model for borer control includes strategies such as cultural, chemical and biological methods. The most effective long-term control strategies are usually cultural in nature and should be our first consideration. Often times they are not used by commercial operators for a variety of reasons but usually get back to either economic reasons or lack of education on how to use them effectively.

 

Flat headed borer in small limb of peach tree. Sanitation would be removal of the small limb or cutting out
borers from larger limbs with a knife

When evaluating which method to use, we have to balance the efficacy of the control measure, it's economic benefit to the customer and the operator and impact of the control measure on the environment. Lets take a look at each component in the IPM scheme.

Cultural control options in traditional agricultural IPM include sanitation, crop rotation, tillage, host plant resistance and tolerance, mechanical or physical destruction of the pest and quarantine. Do any of these apply to controlling borers in landscapes?

Sanitation refers to the removal of infested plants or plant parts which helps reduce the level of plant pest in the urban landscape. This may mean removal of entire trees heavily infested or removal of limbs to reduce the infestation level. This can be done on an individual yard basis or community wide if there is a community "epidemic" of a particular pest.

Borer infested limb removed to save the tree from removal. A form of sanitation.

We have seen communities, or entire sections of a community, devastated by certain types of borers. Clear winged borers, like the ash or lilac borer, can be serious pests in this regard since these types of borers are known to attack healthy trees and the number of these insects in a community may dictate the degree of infestation and damage. Community-wide borer control efforts need the strategy of a community forester or city arborist to make these efforts work.

Crop rotation is the substitution of a crop (plant) with low pest susceptibility (host resistance) for a plant with high pest susceptibility. As an example, if we lose a tree to borers do we put the same type of tree back in that community or do we look for a reasonable alternative? As we begin planning a community or expanding a community are we checking to see what borers are problematic to the community or are we selecting plants only because they have aesthetic appeal? An example of this is the planting of weeping willows in climates like Las Vegas where they stress and become highly susceptible to attack by borers. These trees then become a source of infestation for other susceptible trees in the community. A proactive approach toward sound horticultural growth, balanced by future maintenance, requires public education and community coordination.

Weeping willow planted in Las Vegas with borer damage from clear-winged moth. For this reason
we never see weeping willows over about ten years old.

Quarantine is a legal restriction or exclusion of infested plants being brought into a community. On a state-wide basis, inspection stations are established that control the entry of infested plant material or documentation is required by the buyer that plant materials have been inspected, and found clean of, certain pest problems. Sometimes plant materials are simply not allowed into certain communities due to the highly virulent or infectious nature of certain pests. This has happened with elm varieties, and some of its relatives, known to be susceptible to Dutch elm disease.

Some arborists combine physical or mechanical control measures with their borer protection programs. Physical control can be as simple as noting borer activity in some young trees and carefully using a small knife to remove or kill the borer. This will work with borers such as some of the flatheaded types that that can be easily tracked and that feed near the surface of the trunk. A great deal of care has to be exercised so that the tree is not further damaged with the knife but with some experience it can be learned. Mechanical control includes barriers such as wraps that may help prevent sunscald and the physical entry of borers inside the tree. Some care has to be exercised that certain wraps don’t actually contribute to the problem by providing egg-laying sites for borers.

We are all most comfortable with cover spray applications of chemicals for borer control. This strategy was either to spray the plant periodically through the entire growing season or time the spray with some sort of insect trapping device. Cover sprays applied a poisonous, pesticide barrier to susceptible plants. The traditional approach was to apply a pesticide to the trunk and major limbs of trees either infested with borers or "threatened" with borer activity. This cover spray was a prophylactic treatment aimed at preventing the entry of the borer inside the tree. Once the borer entered the tree, cover sprays were ineffective.

Emerald ash borer damage to green ash which we do not have
 in southern Nevada

Our business practices, equipment and past education focused on chemicals for borer control. The problem with traditional cover spray applications of chemicals is that the chemicals traditionally used for this purpose pose a threat to the environment and human health, both by the nature of the chemical and how it was applied. This technique is still probably the most widely used one but is becoming more restricted with time. We have already seen Lindane become more restricted in its use and availability. Admittedly, using chemicals such as Lindane, Dursban, Thiodan and Sevin as cover sprays on large trees has its community environment and health drawbacks. The effectiveness of cover sprays always depended on a narrow window of time when the spray would be effective.

Applications of chemicals such as Metasystox R as a soil injection for borer control pose similar environmental problems. Applications of pesticides into the rootzones of plants pose an immediate threat to shallow groundwater supplies, wells and public health concerns.

 Application methods of pesticides such as trunk injection certainly minimize some of the environmental and community health concerns. Active injection systems exist, like Mauget, which rely on a pressurized system to inject pesticides such as Bidrin and Merit, into the tree's vascular system. Once inside the tree these chemicals become mixed with the vascular fluids and thus become systemically distributed. There are passive injection systems, such as trunk implants, that have no pressurized system but rely on the vascular fluids to carry the pesticide throughout the tree. This mixture of vascular fluid and pesticide poisons the immature borer feeding on the vascular tissue.
 

 How to Use Mauget trunk injection

 

In my opinion, never use systemic insecticides or inject insecticides systemically into fruit trees or other edible crops.

 

Entomologists have been concerned that trunk injections, made late in the protected borer's life cycle, would not be effective. They reason that borer feeding activity disrupts the flow of vascular fluids and prevent the pesticide from coming in contact with the borer. In the case of borers in an advanced stage of its life cycle, this may be the case. However in the very early stages of an infestation, injection may provide some measure of control.

The injection of pesticides into trees poses other problems such as the damage created when holes are drilled into the trunk. Research many years ago in the United States and Canada has both come to the same conclusions. If holes have to be drilled into trees then the holes should be as small as possible. The other piece of research conducted with injection equipment is that on larger trees, injection should be made as low on the trunk as possible. Injection holes drilled in the root flares provides better mixing and a larger trunk circumference to absorb the damage created from drilling the holes.