Plant Health Care and Integrated Pest Management
Pest, diseases and disorders are a component of urban landscapes. Control measures will be required at times to maintain healthy and aesthetically pleasing trees and other vegetation.
Treelogic recommends that the principles of Integrated Pest and disease management (IPDM) are implemented to address pest and disease management with a focus on problem prevention through appropriate tree selection, soil improvements, planting and tree maintenance.
When selecting tree species all effort should be made to select species that are known to be pest and disease resistant. However, there will be situations where the existing tree species may be under threat but their on-going use is important considering that they may be significant landscape elements.
It would also be very difficult to select a palette of tree species for urban landscapes that are immune to potential infestation from pathogens, particularly when some potential threats could impact on entire plant families.
Constant monitoring of your trees will allow timely and appropriate responses to pathogen infestations.
The predicted change in our climate is also likely to inflict particular stresses on the trees and vegetation in our urban landscapes, which may in turn increase their susceptibility to certain pests and diseases.
Elm Leaf Beetle (ELB) was accidentally introduced into Australia in the late 1980s. Since then the beetle has rapidly spread throughout Victoria. Both the adult and the larval stage of ELB feed on Elm trees and can cause complete defoliation in the course of a single summer.
While local government strives to control the pest in public areas, more must be done to control the beetle on private properties. Speak to one of our plant health care consultants today and help to control this pest and protect Victoria’s Elm trees.
This method is undertaken between August and October just prior to leaf burst. The procedure employs a purpose designed soil probe that this inserted into the soil around the drip line of the tree. A low-toxicity systemic insecticide is then pumped into the soil where it is taken up by the tree’s root system. The insecticide is then transported via the trees vascular system to the newly emerging leaves where it is ingested by feeding beetles and larvae. Soil injection treatments are guaranteed for 12 months.
This method is undertaken between October and December after leaf burst and is particularly useful in situation where it is difficult to access tree roots. The procedure employs specialised trunk implants that are inserted directly into the trees vascular system where they deliver a dose of low-toxicity systemic insecticide. Once in the tree, the insecticide is transported via the trees vascular system to the leaves where it is ingested by feeding beetles and larvae. The delivery system is self-contained and greatly reduces chemical exposure to the surrounding environment. Once the treatment is complete the implants are removed and your Elm will be protected against ELB. Trunk injections are guaranteed for 12 months.
Watering your Elm may help to improve the efficiency of the treatment. This is particularly important after treatment as additional soil moisture assists with the translocation of the insecticide from the roots to the canopy. Watering is most effective if it is applied to the soil from half way between the trunk and the drip line to 3-5m beyond the drip line. Water loss through evaporation can be limited by watering trees early in the morning or in the evening. Tree Logic encourages responsible water usage and recommends that additional watering be compliant with current water restrictions and the use of recycled water is recommended where possible.
Some Elm species develop suckers from their roots, particularly if the trees are drought stressed or have been damaged by mowers. Elm suckers are not protected from ELB even if the primary tree has been treated it is therefore important that all suckers are removed as they can provide a safe food source for the ELB. Suckers should be removed with a clean, sharp cut as close as possible to the root; the use of herbicides is not recommended as it may also kill the tree.
Psyillid (lerp insects) are common on many native plants, including Eucalyptus spp., Acacia spp. and Syzygium spp. Native figs (Ficus spp.) are often attacked by the fig psyllid (Mycopsylla fici), which produces a white sticky material underneath the leaves; heavy infestations can cause premature leaf fall. Kurrajongs are sometimes affected by the star psylla (Protyom sierculiae).
Every eucalypt has its own group of psyllid species. The nymphs of many species secrete protective waxy or sugary coverings called lerps. The lerp helps to protect the nymph from natural enemies and dehydration. A few species form galls or pits on leaf surfaces, and some make leaves curl. Others are free-living and protect themselves by producing fluffy white threads between the young shoots and buds on which they are feeding. There are at least 10 genera of lerp-building psyllids on eucalypts, but the most common species belong to the genera Cardiaspina and Glycaspis.Cardiaspina species produce characteristic shell-like or lacy lerps, while Glycaspis species tend to produce white sugary lerps.
Some species occasionally have population explosions. Although psyllids have similar life cycles, the conditions necessary to initiate and maintain high populations can differ between species. Climate is one of the main factors influencing psyllid populations. High psyllid populations always collapse eventually, either as a result of changes in the weather conditions or the depletion of suitable foliage due to feeding damage and premature leaf fall. Once the population starts to decline, the influence of natural enemies increases. Natural enemies include parasitic wasps, hoverflies, lacewings, ladybird larvae, ants and spiders. Many birds also feed on psyllids, including honeyeaters, thornbills, pardalotes and rosellas.
Psyllids feed by sucking sap from leaves and shoots. Although this may cause local discoloration or malformation, they cause little damage to their host plants at low population levels. Unfortunately, in Australia a few species occasionally undergo population explosions, particularly species of Cardiaspina and Glycaspis. When feeding, Cardiaspina species secrete substances that cause localised death of the leaf cells. Initially this appears reddish-purple but later turns brown. This discoloration is usually more obvious before new foliage appears giving the tree a scorched or burnt appearance.
Most eucalypts can cope with high psyllid numbers for a couple of seasons, and recover after the population declines. Repeated defoliation, however, will deplete a tree’s reserves faster than they can be replaced by photosynthesis. This can result in crown decline and die-back that may lead to the eventual death of the tree. Apart from feeding damage, psyllid infestations can cause further problems for trees. They can become more susceptible to attack by other insects such as borers and termites. Some feeding psyllids also attract ants and other insects that feed on the honeydew exudate they produce. Sooty mould may develop on these secretions, blackening the leaves and reducing the rate of photosynthesis.
Population explosions of insects are rare in undisturbed natural environments. Human intervention has altered the balance between psyllids and their natural predators, which allows population explosions.
Healthy, vigorously growing eucalypts can usually outgrow the damage caused by psyllids, and psyllid attack can be a sign that trees are under stress. Wind, frost, root damage, compacted soil, salinity, drought or waterlogging are all important sources of stress.
Action can often be taken to reduce the stress on the tree, if the cause is known. Proper watering can reduce the effect of drought, and improving the drainage can help waterlogging. Removing the cause, loosening the topsoil and mulching can improve compacted soil.
Increasing plant density and diversity, including understorey, is one way of improving the control exerted by natural enemies.
Insecticides can be used to control psyllids, although by the time damage is noticed it is usually too late to take effective action. If a valued tree has been attacked heavily by psyllids over consecutive seasons however, an insecticide, correctly applied, can give the tree some respite, and allow the canopy to recover. The tree must first be monitored, and the insecticide applied when new foliage has developed and the psyllids appear to be increasing.
Recommended chemical control is soil drenching or stem injection with a systemic insecticide with imidacloprid as the active constituent.
The City of Greater Dandenong has experienced extensive psyllid damage on eucalypts within its municipality and has partnered with La Trobe University to complete a study on Psyllid leaf type specificity and die back of River Red Gums (Eucalyptus camaldulensis) in Fortheringham Reserve. Results from the study will increase Council’s understanding of Psyllids, their impact on Council’s River Red Gum population, which will allow for improved management practices in the future.