Ornamental or landscape trees are often planted to improve the aesthetics of your property or to improve environmental conditions such as shading a sunny area, providing a wind-break, etc. Because trees are long-term investments, it is important to select trees that are suitable to the climate, soil type, site, and light/ wind conditions of the planting location. Initial placement, planting method, and ongoing care can all influence the health and longevity of the tree.
Ornamental Trees and Shrubs
Question:
I have elm trees that have beetles that become quite a pest. They eat the leaves. How can I get rid of them?
Answer
A sure way to get rid of elm leaf beetles is to cut down your tree(s) and those of your neighbor's! The larva of the beetles are eating the leaves so you must get rid of them. You can spray Bacillus thuringiensis or B.T., the San Diego strain. This product is sold under several trade names and is an organic insecticide that kills insect larva only and is not harmful to other insects or animals. B.T. is a natural occurring soil bacteria that must be sprayed on the leaves and the treated leaves eaten by the larva. B.T. is washed off by rain and must be reapplied. Another solution is to spray a 2 foot band of Sevin insecticide around the tree trunk 6 to 8 feet above the ground. The elm leaf beetle larva travel down the tree trunk to pupate on the lower trunk or near the soil line. Crossing the Sevin strip will kill the larva and over time reduce the insect population according to University of California entomologists. This treatment also will not destroy adults so if there are a lot of elm trees in you neighborhood other elm leaf beetles will fly to your trees and lay eggs. However, these treatments can significantly reduce larval populations and damage to tree leaves.
Question:
My ash, plum and pomegranate leaf margins are turning brown and drying up. The leaves are yellowish in color with some green remaining between the veins. I have been watering the trees using a well. They are planted in my lawn. I used "Weed and Feed" on the lawn this spring and again during the summer. The trees are just looking sick and I am feeling like the trees.
Answer
The trees are showing the signs of herbicide damage. "Weed and Feed" products contain fertilizer and 2,4-D herbicide. Inert particles like clay are coated with the herbicide which releases into the soil when watered. The herbicide 2,4-D will kill many broadleaf weeds in the lawn. However, the herbicide also can damage or kill other broadleaf plants. These trees are showing symptoms but did not receive a large enough dose to kill them. The herbicide reached the shallow rooted trees, was absorbed and you see the symptoms in the leaves.
Control
Do not apply 2,4-D type herbicides, (as a spray or in a "Weed and Feed" product), where desired broadleaf plants will absorb them through the roots or leaves. Many broadleaves like roses and grapes are very sensitive to 2,4-D type herbicides. The trees will most likely not show symptoms in the spring. For now the leaves will have to drop so that the trees will not look sick.
Just a note on the herbicide 2,4-Dichlorophenoxyacetic acid, (the chemical name), or 2,4-D for short and related compounds. This herbicide comes in several different formulations. If it is to be used around plants that are susceptible, i.e. broadleaf plants, use an amine formulation. It is less volatile than an ester formulation. You must read the label and find the chemical name. If amine or ester appears in the chemical name you will know the type of formulation.
Question:
I have a number of cottonwood trees, (Populus fremontii), that are growing around the edge of our pond. The younger trees that I planted over the past two years are doing fine. The trees that are older, with trunk diameters of 18 to 24 inches have been dying or dead limbs that appeared this summer. We saw some black beetles under the bark in channels carved out of the wood. What are these and what can we do to save these trees?
Answer
After seeing samples of the branches it was determined that damage was caused by a large larval stage of the carpenterworm moth, Prionoxystus robiniae (Peck). The black beetles you saw were secondary pests and not causing the damage. This insect attacks weak trees. Your trees were weakened by three spring frosts that defoliated the trees. This stress allowed the hatching insect larvae to enter the trees. This wood- boring insect takes one or two years to complete its life cycle in warm areas but in cooler areas as long as four years. The eggs are laid shortly after the moths emerge in the spring and continues for about a month. The female can lay 300 to 600 eggs in a sticky mass on host branches or trunk. The larvae hatch and bore into the sapwood where it remains most of the larval stage, going through eight to 31 instar stages. As they mature they extend their tunnels into the heartwood. As the larvae bore they produce large amounts of frass, (droppings), and sawdust. In fact the frass looks like excelsior from cooler pads. This clings in mass to the external bark. Tunnels maybe up to 18 mm, ( 3/4) in width. This boring can be disastrous to host trees by killing limbs which are subject to wind breakage, also ruining the wood for saw-log purposes. Host trees include elm, ash , birch, black locust, oak, cottonwood, maple, willow, apricot, pear and an occasional ornamental shrub. The carpenterworm is distributed all over the United States and all bordering Canadian Provinces."
Control
Remove all dead or dying limbs and burn them to kill the larvae. Make sure that the trees are receiving adequate water and nutrients, because the best defense is a healthy tree. Applying a small amount, (1/16 to 1/8 pound per inch of trunk diameter) of nitrogen fertilizer will help strengthen the tree this fall. Too much will invigorate the tree that is preparing for winter dormancy. This next spring apply four times the fall amount in two or three applications. Place fertilizer around the drip line and water in. Insecticides applied in the spring might help destroy other eggs that will be laid, but will do little to destroy the larvae that are feeding underneath the protective bark. Systemic insecticides are of little worth with such large trees.
Question:
An Arizona oak tree that is growing in the middle of my patio has dead branches under the living branches and its leaves that are falling. The tree is quite large with a trunk diameter of close to three feet. Natural rainfall is the only water it receives. The patio was build two years ago. Why is this happening? Don't oaks stay green year around?
Answer
The oak tree is a very large and old specimen. An oak that has a diameter of nearly three feet must be at least 100 to 150 years old. The dead branches are those that are under the living ones. When new growth occurs older branches can be shaded out and not produce leaves; they have served their function and die. Prune out the dead branches to make the tree more sightly. Leaves of evergreen do not live forever but their don't fall all at once. During certain times of the year it is natural for some evergreen leaves to fall. By placing a patio around the tree perhaps some of the roots do not have the access they once did to rainfall. However, it must be remembered that mature trees normally have actively feeding roots only 40 to 60% of the distance in from the drip line towards the trunk. Remember that trees do not live forever. Only some species will out live humans.
Question:
I have some Eldarica pines that have funny curling needles. They occur on last years needles but form nearly complete circles. What is happening to these needle and will it affect the future growth of the trees?
Answer
The damage to the needles is caused by eriophyid mites. There are probably more unknown and undescribed species of these mites than any other group of arthropods. They are very small and are measured in micrometers or microns. They are worm-like and slow moving. Injury in conifer species is expressed by chlorotic needles, and/or dwarf, distorted, or short needles. Also by rosette bud/needle clusters similar to a witches broom, by galls, and by partial defoliation of old as well as the current season's needles. Eriophyid mites are found in or on the buds and foliage of all North American conifer species. Many other plants are affected by these animals including deciduous trees and shrub.
Control
There are no control measures that are recommended for eriophyid mites on conifers. The effects of the damage will not cause the plants to die, however, they can cause unusual growth.
Source
Insects That Feed on Trees and Shrubs. Warren T. Johnson and Howard H. Lyon. 1991. Cornell University Press. page 122.
Question:
I have a pine tree that has masses of sap that look like large bubbles or balloons. These occur on small branches near the tips. Some of the needles are dead or dying. What is causing this and what can I do to prevent it?
Answer
The mass of sap you see is the result of an insect larvae that is living inside of the blister-like bubble. If you burst the bubble" you will find a pitch twig moth larvae. There are several species of pitch moths, however the one you have is most likely Petrova comstockiana (Fernald). Eggs are laid singly on the bark of limbs, the hatching larvae tunnel into the bark and cambium region and establish feeding sites. The pine tree exudes pitch and the larvae then uses the pitch to construct a "home" which includes frass or insect droppings. A mature larva is about 25 millimeters long and has a brownish head and light yellow body. Pupation takes place within the pitch mass and adults emerge during the summer months. In some species about half the population requires one year to complete a life cycle; the other half requires 2 years. In the case of this larvae it will feed on one site for one year then move to a new site, usually a branch crotch, and feeds for another year. Thus two years are required for full development from the feeding stage to a pupal stage. Adult moths emerge only in the summer."
Control
Normally there is no need to control these insects. Populations in our area rarely if ever reach economically damaging proportions. If they are really a problem then killing the larvae by pruning out and burning the bubbles"; or open the bubble and impale the larvae on a wire will decrease the population."
Source
Insects That Feed on Trees and Shrubs, 2nd Edition. Warren T. Johnson and Howard H. Lyon. 1991. Page 72.
Question:
What are these fussy brown spots about 1/8th to 1/4 inch in diameter on the underside of oak leaves? The affected oak trees were planted last spring.
Answer
At first it looked like an egg mass of a lepidoptera, that is the moth and butterfly family. After further examination of the sample leaf it was determined to be a gall of the woolly leaf gall caused by cynipid wasp. Other gall forming insect are other wasps, aphids, psyllids or other insect. Most galls are formed as a reaction of the plant to larval feeding or adult egg laying. Most of the time the gall is formed from the reaction of chemicals that the insect secretes which produces mutation of plant cells. This abnormal tissue many times provides cover over the newly laid or hatched eggs. Also many times the inside gall tissue is a food source for newly hatched insects.
Question:
We live up in the mountains and have many oaks on our property. We have noticed brown growths near the end of branches that looks as if someone had thrown cow manure into the trees and it stuck! Also, we have some round balls" hanging from the oak trees as well as some growths that are near the end of young twigs that look to be impaled on the twigs. What are these and where do they come from?"
Answer
Wherever oaks occur, they are attacked by a small group of insects called galls makers. These insects cause deformities of plant tissue. The majority of gall making insects that attack oaks are wasps. Galls are produced by powerful plant growth-regulating chemicals or other stimuli produced by the insect that react with plant hormones. Some stimuli are feeding or egg laying. The inner walls of the galls are rich in protein and thus provide the larvae living in the gall a concentrated food source. The larvae are somewhat protected from predators while they are in the galls. Galls come in several shapes and sizes. They can be globular, dish-shaped or look like thorny, spiny balls. Galls are specific as to the kind of oak they occur on. For example, those found on the black oak group do not occur on the white oak group. Many galls exhibit a characteristic gall alternation of generations. That is that the offspring of a gall wasp may produce galls that are completely different from those produced by their parents, but identical with those by their grandparents. Also, the site of the galls usually will be produced on a different part of the tree than those of their parents. It is reported that 717 species of gall wasp are found in North America. That number is decreasing as biologists unravel the mystery of alternating generations pairs and identify single species.
Source
Insects That Feed on Trees and Shrubs, 2nd Edition. Warren T. Johnson and Howard H. Lyon. 1991. Page 440.
Question:
I have some juniper trees whose tips are turning brown. The trees were planted over 20 years ago and they receive enough water. When the branches are moving a yellow powder falls out of the infected" area. What is causing the browning of the tips. Is it an insect or a fungus of some kind?"
Answer
After examining a sample of the plant it was determined to have normal growth. The small brown tips are the developing male portion of the trees and when mature will produce pollen. The yellow power that falls off the plant when disturbed is indeed pollen.
Question:
The cottonwood in our back yard has several limbs that are dying in the center of the tree. It is growing in a fescue lawn. What is causing this to happen?
Answer
Cottonwood trees are native to rivers, streams and washes in Arizona. They require a lot of water. You need to water the lawn and then deep soak for the cottonwood tree. If you water shade trees with only the 1 to 2 inches of week per water required by the lawn you will not supply the 3 to 6 inches of water per week that large trees will need. This is because lawn roots are primarily in the first foot of soil. The majority of tree and shrub roots will be in the top two to three feet of soil. During the hot summer weather trees will extract large amounts of water from the soil each day. Shallow watered tree roots will tend to be closer to the surface of the ground. However, the genetics of the tree has a lot to do with the depth of rooting. I have known of several cases where the tree roots where growing up to the soil surface and the owners cut the roots out so they would not have to run over them with the lawn mower. By doing this you sever the roots that uptake nutrients and water to specific limbs of the tree causing them to die.
Question:
I have several trees, shrubs and bushes that have leaves that are turning yellow but the veins remain green. I water them every other day and feel that they are receiving enough water. What can I do to correct this problem?
Answer
The leaf yellowing is called iron chlorosis and is caused by insufficent iron in the plant leaves. If you look closely you will see that the older leaves are not effected. Iron is necessary in the formation of chlorophyll, the green pigment of plant leaves and stems. Our soils are alkaline, meaning that they have pH's above 7.0. As soil pH increases above 7 iron forms other molecular complexes which are not taken up by plants. Water logged soils or anarobic conditions can cause iron to be unavailable.
Control
Decrease the amount of water given plants, checking the soil to see if watering is necessary. Lowering soil pH will make iron more available. Changing soil pH is a long term proposition but can be accomplished by adding acidifing materials such as soil sulfur and/or gypsum. Iron can be applied to the soil or the leaves to help correct this problem. Iron applied to the soil is slower acting but is longer lasting than iron sprayed on the foliage. There are several dry products that can be soil applied; these include Ironite", iron sulfate and other forms of iron. These products are poured into holes that are about poked into the soil one to one and a half feet deep, placed around the drip line of the affected plant and serves as a reservoir of available iron. Foliar applied irons are usually liquids and can also come in chelated forms. Chelates are "chemical jaws" which protect the iron from becoming bound up with other chemicals before it is inside the plant. Once near or inside the plant the chelating agent is dissolved and the chelated chemical is available. Chelates can be applied to the soil also but only Sequestrene 138, (6% iron), will work well in our alkaline soils. It is red in color as a powder and when added to water has the color of blood and is expensive as blood! The Sequestrene 330, (10% iron), is yellow in color and is applied to the foliage only. It should only be soil applied to acid soil, if not it will become bound up and not available to the plant. Look at the product color to know which chelated iron is being used and how to properly apply it. Always read and understand the label before using chemicals."
Question:
My mesquite tree has mistletoe in it. Is there any way to rid my trees of this growth?
Answer
There are several genera and species of mistletoe. In Arizona we have 5 species of Phoradendron (leafy mistletoes) and 3 species of Arceuthobium. The latter, called dwarf mistletoe, infests only conifers. Leafy mistletoes are considered as hemi-parasites, which means that they produce some or all of their own energy through photosynthesis but depend on the host for water and minerals. Mistletoes elicit a disease response from most hosts and are considered pathogens. However, mistletoes seldom kill healthy hosts except dwarf mistletoe, which can cause severe damage in coniferous forests. Severely infested trees usually have been subjected to other stresses that increased their susceptibility such as drought, flooding, soil compaction, nutrient deficiencies, etc.
The "root" of a leafy mistletoe is directly connected to the host's xylem (that part of the plant's plumbing that conducts water and minerals from the roots to the leaves). The "root" of a dwarf mistletoe is connected to the host's phloem as well as the xylem. The phloem conducts sugars and other products of photosynthesis from the leaves to other parts of the plant. So the dwarf mistletoe is highly parasitic, depending on the host, for photosynthate as well as water and minerals.
Leafy mistletoes can occur on several hundred host species. Mistletoe creates a drain on host resources that reduce growth, decreases vigor, and increases susceptibility to other diseases and insect pests. Local symptoms can include dieback, formation of witches' broom, and weakened branches. Dwarf mistletoe, in particular, can cause spiketop, where the entire host crown dies and also causes witches' broom which increases the diversion of water, minerals, and nutrients to the site of infestation.
Control
Removal of the branch below the mistletoe remains an economical and fairly efficient method of mistletoe control. However, control by pruning requires diligence. Birds eat mistletoe berries and spread the seed which is unaffected by the digestive tract. So any fruiting mistletoe that survives pruning is a source for reinfestation. Chemical treatment has not been effective to date. In one study 2,4-D was injected in infected eucalyptus trees. The chemical killed 70% to 100% of the mistletoes, but partially defoliated all trees and killed 5% of them.
Recent research efforts have focused on interrupting fruit set with hormone sprays combined with pruning. Resistant cultivars and biological control remain as possible long term solutions.
Wrapping the mistletoe and infected branch with black plastic to block light and increasing heat has proven somewhat effective. The plastic must remain around the branch for several months.
Source
Paine & Harrison. 1992. HortTechnology 2:34-330.
Question:
My mesquite trees have brown round bumps on many of the limbs. In fact some of the branches have ooze dripping from them. Is this scale?
Answer
Yes the problem is scale, soft brown scale in fact. Scale are a super family" of over 200 insects that feed on plant sap while females protect themselves with a soft or hard "shell" body covering. Males can be winged. Scale produce young by eggs or by bearing live young. The young, called crawlers, may crawl out from under mother's covering and move to another location, usually close by, and then set up "housekeeping". One to five generations will be produced each year depending on the species and environmental conditions. Scale are protected by the covering they make for themselves and it is very hard to penetrate with pesticides."
Control
Physical removal by spraying a hard stream of water may work, however many times they are stuck on the plant very tightly. Even rubbing off the scale with a stiff brush can be effective. Using systemic insecticides can help control scaled but many times does not work very well. Suffocating or penetrating their shell" are methods also used to kill this pest. Dormant oil sprays are used when plant leaves are no longer than a half inch in early spring. If used later leaf damage may occur. Rubbing alcohol applied to scale will penetrate their waxy shell covering and kill them. Use 70% isopropyl (rubbing) alcohol, mixing 1 to 2 cups of alcohol per quart of water. Since alcohol can damage some plants first test spray on a small area. Wait for a day or two to see if damage occurred, if not it is safe to spray. You can mix insecticidal soap up according to the label directions but substitute rubbing alcohol for half of the water. A recipe a that has proven effective in the past for scale control and other insects is made by mixing one cup cooking oil plus 1 Tablespoon of dish detergent (non-citrus). Mix one to two teaspoons of this solution with one cup of water. Spray mixture on the infected plant until it drips off. It is best to spray a few leaves and then check for leaf burn the next day before spraying the entire plant. With many of these treatments the scale will not drop off of the plant but will remain attached even though they are dead. Pry some off several days after treatment to determine if the scale are dead. If not treat again."
Question:
I have several 12 year old Arizona cypress trees with needles that are turning brown. The middle to center of the limbs on the lower branches are affected. What disease is causing this? What can I do about it?
Answer
As evergreen trees get older the leaves, called needles or scales, on older branches, (those that are close to the tree trunk or base of the tree), will naturally brown and fall off. These leaves are old having served the tree well but have become shaded out and are not contributing to the tree's growth. During normal winters adequate moisture falls. This winter however was unusually dry. Because of little or no moisture supplemental water was necessary. Several people have called with questions about browning evergreens. Usually people will state that they did not water their trees last winter. Evergreens need about one third the of water during the winter compared to the rest of the year. Therefore, water the trees and watch for new growth. The tips of the branches should be green and healthy because that is where shoot growth takes place. Also, water at the tree drip line and out from that point. Feeder roots are located usually out from the drip line not next to the tree trunk. I trees are planted through plastic that has crushed granite or gravel on top, take a pitch-fork and poke holes through the plastic to allow rain fall into the soil.
Question:
I have several Arizona Cypress trees that are dying. There are holes in the trunks and the tips are breaking off. What is happening to my tree?
Answer
The problems observed on your tree are two different insects. Both are aggressive pests of stressed cypress and junipers on Arizona. The first is Western Cedar Borer. This borer will attack and seriously injure or kill trees. It seems to prefer older, large trees. Adults are bright emerald with serial dark areas on the wing covers. Flatheaded larvae bore from the branches into the main trunk where they feed on the heartwood for several years.
The second insect is the Juniper Twig Pruner. It causes dieback on the tips of tree branches. The insect is a small long-nosed beetle. The adult has a reddish-orange head and brownish to black body. Eggs are laid on the branches, often near an intersection of twigs, one to two feet from the branch tip. Larvae are small, white, cylindrical, legless grubs that kill the twigs by boring though the centers. The life cycle may take as long as two years to complete.
Control
No practical controls or preventive measures have been developed for Western Cedar Borer or Juniper Twig Pruner. The Juniper Twig Pruner damage can be unsightly when populations are high but this pest rarely seriously injures trees. However, the Western Cedar Borer will kill trees.