The (small) Elm Leaf Beetle (ELB), or Xanthogaleruca luteola can have a disastrous effect on Adelaide gardens. First identified in December 2011 by Arborist, Guy O'Donnell in Malvern, Adelaide; the Elm leaf beetle causes damage to trees by skeletonization of the leaf during feeding. It is important to control the beetle as both the larva and beetle can cause significant damage to our Elms. After 6 years and 12 generations, the ELB is now endemic across Adelaide, it cannot be eradicated: the beetle and the damage it does can only be controlled. Its spread is by vector: people, vehicles, trains and less so by flight. Putting them alive into a bin and sending them to the tip only helps them spread by garbage truck from the tip.
URGENT BULLETIN September 2019!!!
NOW is the time to drench the ground beneath your elm tree(s) and though September, October and November until ALL leaves have opened.Water is absolutely necessary to help the tree distribute the injected chemical now. Despite the rains we have had, water is required immediately. Do not let the ground dry out. Unless we have heavy rains, I expect that continued watering will be necessary throughout spring and summer.
Would all customers and intending customers please drench the complete area beneath their elms NOW and at least three times per week whenever a dry week is forecast until ALL leaves are fully open.
A Below average rainfall is forecast for this month of October & November.
Water is absolutely necessary to help the tree distribute the injected chemical now during winter and before leaf burst in Spring.
Despite the rains we have had, water is required immediately. Do not let the ground dry out. Unless we have heavy rains, I expect that continued watering will be necessary throughout winter, spring and summer.
Would all customers and intending customers please drench the complete area beneath their elms NOW and at least once per week whenever a dry week is forecast.
Water must penetrate to a depth range of 150-250mm. This is an arbitrarily chosen range. Take depth samples of the soil under the canopy to be sure.
It is unavoidable using arbitrary and general terms here, as using volumetric terms here will not help the reader.
I cannot inject your tree if the ground beneath it is dry. It must be at least damp.
Readily available Soil Water is critical in order to produce a repeatable treatment result, particularly in Golden Elms.
Use a high volume, low pressure revolving sprinkler, left on for hours so the water penetrates at least 150mm deep. Do not rely on microsprays or drippers.
The point of watering now is to reduce one of the variables that cause inadequate protection against beetle attack.
Note that I am seeing the occurrence of chemical resistance in certain locations across the Adelaide Metro. This means that strains of the beetle have developed a level of resistance to the currently used chemical.
One cause of this is underdosing, currently employed by many practitioners in Adelaide, another is the process of natural selection.
WINTER IS THE BEST TIME TO INJECT AND THEN INTO SPRING /SUMMER.
FOLLOWING A 220-TREE TRIAL LAST WINTER ACROSS SOTH AUSTRALIA, I HAVE HAD STAGGERINGLY SUCCESSFUL RESULTS.
What trees does the Beetle Attack?
The Elm leaf Beetle prefers the European Elms and the Japanese Elm, a species of the Genus Zelkova, which is closely related to the Elm (Genus Ulmus).
It does not attack the original form of the Chinese Elm, Ulmus parvifolia, but does attack the 4 grafted forms of the Ulmus parvifolia, such as "Frosty", "Geisha" and "Todd".
Most commonly at risk in Adelaide are the 3 types or cultivars of Golden Elm, each grafted onto a different rootstock; these have been planted for their ornamental value and foliage colour across the metropolitan zone and extensively throughout the higher altitude areas; and the English Elm: Ulmus procera, for its potential height and form, as it is typically planted in parks and along roadsides creating tall tree lined vistas.
In the mature forms of Ulmus glabra "lutescens", found in Adelaide, 2 rootstocks have been used to graft the Golden Elm scion (the bud) onto: the Ulmus parvifolia (Chinese Elm) and the Ulmus glabra (the Wych or Scots Elm), ; these rootstocks have a have a notable effect on the form of the resultant Golden Elm, and this may also have an effect on the way the insecticide is translocated through the canopy. There is certainly a different method for treating each due to the varying internal structure of each type. The latter is often referred to as the Golden Wych Elm. Hence, there is the Loius Van Houtte and the Golden Wych Elm, but those speciments grafted onto the Chinese Elm are only referred to as a Golden Elm, which also encompasses all 3 grafted forms. (Just to cause more confusion!)
The rootstocks have been chosen to impart certain characteristics to the grafted bud when it grows into a tree. A knowledge of the rootstock, canopy form and growing habit is required to identify each, which Guy has learnt during his early days owning and managing a wholesale growing nursery.
Other less common species include the grafted form of the Weeping Elm : Ulmus glabra “Camperdownii” , the Horizontal Elm: Ulmus glabra "Horizontalis", The Wych or Scots Elm : Ulmus glabra, and the Variegated or Silver Elm : Ulmus minor "Variegata".
When are they most active?
The short answer is usually from September through to April. Though there is no specific date of commencement, late September is most typical.
Understanding their life cycle gives us an insight into when it is most active and the best time to eradicate it. October tends to be the heaviest month due to coinciding with the beetle's emergence from shelter combined with an increase in leaf burst and leaf size for them to eat. Initially you will notice hole damage in your leaves. Damage to the trees increases throughout November, when more foliage is available as a food source. This is also the month they lay eggs. You can spot the eggs by looking on the underside of the leaves, they are yellow and look like lemons and can be in rows of two or three. One beetle lays up to 20 eggs, so 100 beetles on your tree in the first generation i.e. in spring, will produce up to 2000 in the next generation, starting around January.
In 7-12 days the eggs will hatch and the larvae will begin eating the leaves. There are 3 larval instages, the larvae increase in size through summer reaching a length of 12 mm, when they are black and yellow and ‘caterpillar-like’.
Throughout December, it is the larvae that cause the most damage leading to skeletonization of the leaves. (Please see the two blow up photos below).
Near the end of December the larvae crawl down the tree to the ground to pupate, the pupae are lemon yellow and not quite circular. Often the larvae will pupate in the deep bark furrows or in the branch and trunk crotches or at the base of the tree, or beneath anything that’s there, otherwise you'll find them in large visible clusters nestled against the base of the trunk, which indicates they are gregarious, producing a pheromone, (a chemical attractant).
After pupating into beetles, they will either crawl back up the trunk or alight into the foliage, and the second wave of attack begins. It’s the damage to the foliage from this wave that is most often noticed, around late January and February, when it’s the second year after the first ever attack.
Its not unusual to find some Trees heavily defoliated with their leaves skeletonized by Christmas, depending on the beetle numbers first attacking your tree in spring that made it through the previous winter in the garden.
Hence garden pressure is very real, and thinning or removing plants beneath the canopy of your Elm reduces the over-wintering sites (e.g.: my not-so-favorites: the Agapanthus and the Clivea!) and also reduces competition for gas-exchange and water penetration, as the 2 plants above produce thicket-like root balls.
SO: There two generations per growth season but a third generation is possible into late May, if climatic conditions are conducive.
How Can We Identify an Elm Leaf Beetle Problem?
1. Shot holes through the leaves. Usually the lower canopy skirt is attacked first because the beetles alight from the garden straight up into the foliage closest to the ground.
2. Small "grubs" on the underside of the leaves, which are the larvae, and which appear black but change colour as they mature to pale yellow with green or grey markings reaching a length of 12mm.
3. The mature beetles to be seen on both surfaces of the leaf, yellow and green in colour (see photos) and 5-6mm long
By treating the tree in Winter you can beat their reproductive cycle and exterminate them before they lay eggs.
Please Call Guy for urgent advice before spending your money.
Below is a seriously defoliated tree as photographed by Guy O'Donnell in 2016.
This damage below can occur as early as Christmas time, at the end of the first generation, and from then on to the end of the season in April.
If your tree looks like these photos (below) then it may be more economical not to inject until the following winter. Please call Guy for more clarification on the best course of action.
If your tree looks like this (below) then it's not too late to inject now.
If your tree looks like this (below) then it's not too late to inject now.
At the moment entomologists and Plant Pathologists have been unable to find a way to biologically control the ELB (economically), but research continues.
Natural enemies that parasitize ELB are still being tested and evaluated. These include Oomyzusgallerucae (a small wasp) and Erynniopsisantennata (a small fly). A spray made of the naturally occurring bacterium Bacillus thuringiensis subsp. tenebrionis has been trialled and found to be effective against elm leaf beetle larvae. This spray could become available in the near future.
Currently, Stem injection is the best method.
Guy is an authority on Elm leaf Beetle Injection. He recently made a presentation on the subject to a National Arboricultural conference here in Adelaide in 2012.
Further Information on the Control Techniques Used by Guy
Guy uses the Bayer Product “Silvashield”, containing Imidachlorprid and chemical carriers, which is registered Australia-wide for ELB treatment. He suggests NOT to use “home made” concoctions due to the massive liability issues, as you will have no legal protection should your tree be damaged by a chemical not registered specifically for ELB control in your state or Australia.
Guy only practices sterile stem injection, as it is the safest for the environment and the safest for your family and pets. The active ingredient, Imidachlorprid, is in the group of chemicals referred to as Neo-nicotinoids. This chemical has been banned for use in many countries through Europe due its affect on bee populations. It is an indiscriminate killer of any insect i.e. anything with 6 legs. Fortunately Elms are wind pollinated i.e. they do not require bees for pollination.
For this reason he does NOT undertake spraying of trees due to likely spray drift. When you think about it--Perfectly still conditions are almost an impossibility. The drift will settle on any surrounding plant/ tree foliage and for instance your freshly washed clothing hanging on the line.... This is one of the reasons this group of chemicals has been banned in Europe.
In some cases where the trees are juvenile and their trunk diameter is too small to be injected, Guy recommends application using a watering can or hand spray, provided there is no breeze blowing.
Secondly, Guy does NOT undertake soil injection because of the long term bonding effect by the chemical to the organic matter in the soil; it has a half-life of 1.5 years. It also an indiscriminate killer of all soil-borne insects. Additionally, large amounts of water are needed to be effective and the chemical needs to be inserted where there are roots, which can be hit and miss.
The chemical trunk banding is unproven and the trunk bands covered in sticky gelatenous substance bleed and impregnate the bark and stop the bark from breathing. As well as leaving an unsightly stain for years afterwards.
Stem injection, provided STERILE EQUIPMENT is used, is the best control currently available.
Guy uses stem injection and calculates a base volume of the insecticide to be used in your Elm to create the required level of foliage protection, which will last at least over 2 growth seasons. However, he regularly obtains 2.5 seasons; and in this case he recommends the tree be allowed to be attacked during the 3rd growth season and inject in the Winter immediately, following his principal of less is more and the fact that this is the most cost effective. the premature skeletonised leaf drop during the summer months after Christmas and the numbers of beetles present in the garden and around the house. Guy creates a database for each customer's tree which is used for comparison purposes which can be used in successive trips should chemical top ups be required.
Beware Slime Flux or Wet Wood
Sterile equipment has to be used to avoid spreading the Bacterial disease SLIME FLUX: Caused by Erwinia nimipressuralis (Carter, 1945) Dye, 1969, (also known as Enerobacter) which reduces the life of any Elm infected by it. It is very easily spread by mechanical vector—a drill bit, an injector, chainsaw or secateurs. It begs the question if the beetles can spread it??
When you hire an Arborist ask “is your equipment sterilized and with what EXACTLY?” The same may be asked of any pest controller BEFORE any of your trees are drilled, to avoid the spread of wood decay pathogens.
Principles of Chemical Use
As the Elm leaf beetle is now endemic across Adelaide, one of Guy’s principles of control is to "MANAGE THE DAMAGE" as the ELB cannot be eradicated. He does not wish to create a perfectly protected tree. He prefers to see some holes in the canopy at budburst and moreso in the autumn of the second season.
Using only tiny holes, and as few holes as possible, vertically staggered, the chemical is injected. These holes are then filled with a sterile material. Plastic sleeves, are NOT left in the tree by Guy, as can be often seen by other practitioners nor are 8-10 mm diameter holes drilled and left unsealed in a ring around the trunk.
It should be noted that tree injection is a highly technical procedure and Guy takes great responsibility and care of his clients' trees based on the principle of chemical usage that LESS IS MORE, wherever possible. Further notes are provided to his customers to further enhance their understanding of his approach, methodology and goals in the use of chemical injections.
Underdosing and underuse of the chemical will ultimately lead to chemical resistance within the strain of Elm leaf beetle now in Adelaide. Additionally, there can be some variation in distribution of the chemical by the tree, so that all beetles who ingest the chemical do not die and in this way resistance or tolerance can build up between each successive generation.
Whatever the cause, chemical resistance is inevitable where only one chemical is used to control one insect with one foodsource. Presently we only have the Bayer product "sivashield" for use to control ELB. The efficacy of any chemical is only as good as the time it takes for a given insect strain to develop a tolerance to a chemical.
Remember: use a trained arborist for control of ELB because it requires technical expertise. Trained arborist, Guy O'Donnell, has a very thorough knowledge of tree physiology, which is absolutely necessary when injecting trees.
There are plenty of cowboys out there who are jumping on the ELB wagon with contaminated drill and contaminated injector in hand. These people couldn't care less if they underdose or overdose your tree and some are telling people to inject annually, all of which of course, is utterly unprofessional.
Use Duct Taping
When you see caterpillars crawling down the trunk from mid November. This is one simple non-chemical method to interrupt the life cycle:
Use plastic duct tape double wrapped and sticky side out around the most circular section of the trunks and/ or major branches. The larvae on the tape below were caught overnight.
Use mapping pins to hold the tape in when there is a depression in the trunk, or the caterpillars will crawl between the tape and the bark and pupate there.
Where the bark is deeply fissured, replace the tape with fresh tape every 3 days.
Throw the tape into the bin because the larvae will die when stuck. Any larvae on the bark can be swept off with a hard broom into a bucket of water. No chemical needed.
GUY DOES NOT RECOMMEND using ANY form of sticky glue, Vaseline, or gelatinous substance, as these block the lenticels of the bark and look unsightly for many months after.
Watch this space: There will be a film clip here shortly
Guy O'Donnell's Credentials
Guy is highly trained, fully insured and has been a practicing arborist for over 35 years. He has a Bachelor of Science in Botany, and Post Graduate studies in Viticulture and Oenology. Guy is a long standing member of the Aboriculture Australia and the International Society of Aboriculture. He is very passionate about Elm trees.
Guy is an authority on Beetle Injection. Having treated elms in Melbourne having identified and treated the mother tree in Malvern in December 2011, and lectured on the subject to a national Arboricultural conference here in Adelaide in 2012.
Call Guy today for more information on how he can help you.