The Harbingers of Spring and Pest/Disease Control

At the time of my last correspondence (New Year’s Message) we were experiencing drought conditions and our rainfall totals were virtually non-existent. As it stands now (beginning of March) with the spate of recent storms which contained significant measurable rainfall, we have almost caught up to our average amount for the year thus far. In addition, it appears we have more storms on the horizon.

You may have noticed that the rainfall has already made a positive impact on landscapes: the renovated turfs have completed germination and are quite lush, while in general all the plant material has benefited from the leaching of salts from the soil and deep irrigation of the root zones. We are now in position, with most of our late winter pruning, cultivation and fertilization completed, for spring growth as the soil temperature rises.

Anaerobic conditions

With the harbingers of spring around the corner, it also brings up the issue of increased pest infestation and disease activity in the landscape. With all the good things rain does for the landscape, for a short period of time it creates anaerobic (lack of oxygen) conditions from the amount of moisture we have in heavily clay-laden soils (typically the type of soil we have in this area), which can be detrimental to certain species of plants and trees sensitive to this condition. Usually this condition abates without too much noticeable adverse effect to most of the plant material.

Chlorosis and phytophthora

In those species sensitive to the condition, it can create both short-term problems such as ‘chlorosis’ — a yellowing of the leaves due to nutrients (chiefly iron) in the soil being unavailable to the roots because of the lack of oxygen which is required for their uptake. This is usually a short-term condition that can be corrected with pH adjustment and/or the drying out of the soil. Plants in low areas or areas of poor drainage will be susceptible to this condition longer.

A more serious condition to be concerned about is various ‘phytophthoras’ (root rot), which can affect mainly trees and — of more concern — palms. If left untreated, phytophthora can kill a tree or palm. If the trees or palms in question have ‘french drain’ or ‘breather tube’ systems adjacent to the root ball, we can combat the effects by pumping out the excess moisture from around the root ball and injecting a ‘fungicide’ to kill the harmful organisms present. With trees that do not have any of the aforementioned drain systems, we can either install a drain system, or we can still inject and drench the root balls with fungicide.

Aphids, giant whitefly and lerp psyllid

The conditions outlined above, in conjunction with the warm, humid weather of May, June and July and the tender new growth of spring, contribute to a prolific increase in the activity of aphids, giant whitefly, and — new to the area since last fall — lerp psyllid. The anaerobic conditions above contribute to the increased pest activity in that they temporarily lower the natural defenses a plant or tree has to normally ward off the pests. The pests can more easily attack a plant or tree when it is under stress of this kind. Combine this with the humid weather and inviting new tender foliage, and you have all the conditions in place for the infestations we usually experience. Each of these pests affects specific plant/tree material, with the aphids having the broadest spectrum of infestation.

Aphids

Aphids will attack plants such as Hibiscus and Hemerocallis (Daylilies) and trees such as Jacaranda ‘mimosifolia’ and Platanus ‘acerifolia’ (London Plane). They usually will not kill the material they infest, but they can defoliate a plant or tree and lead to ancillary problems such as ‘sooty molds’ on, or ‘honeydew’ dripping from, the foliage and attracting ants. Aphids can be controlled at a minimum or eradicated completely in some cases — but in either case they can be controlled. Like every type of pest infestation, anticipating the emergence and treating the material with controls that have a residual effect, or treating as soon as an outbreak occurs, is key to containing the infestation.

Giant whitefly

Giant whitefly has been around for a couple of years and is distinguished from normal whitefly both by its size and by the sticky, web-like substance it quickly covers the foliage in. It can also be more detrimental than normal whitefly, which usually does not have any long-term effect on plants or trees, and is nearly impossible to effectively treat. Giant whitefly mainly affects Hibiscus, Fatsia ‘japonica’ and Tupidanthus ‘calyptratus’. Currently we are using a combination of chemical controls, rotating their use to make them more effective. At worst we can at least keep them under control, while in some cases we can virtually eradicate them. The industry is still looking for a more effective control. Again, the key in containment is early and continual control. Most of you who have had giant whitefly on your projects are aware of it and of our efforts to control them.

Lerp psyllid

Lerp psyllid is a new pest to the area, which last fall exploded into the region, infesting mainly Eucalyptus ‘globulus’ (Blue Gum) trees, but also to a lesser degree Eucalyptus ‘polyanthemos’ (Silver Dollar), Eucalyptus ‘rudis’ (Flooded Gum) and Eucalyptus ‘sideroxylon’ (Red Gum). On the Blue Gum trees it causes massive defoliation (you may have noticed a lot of bare Eucalyptus trees along the freeways which have been infested) and large amounts of ‘honeydew’, which stain the ground under the tree(s). We contacted our clients last year who had lerp psyllid infestation on their projects and treated them with fairly good results. Once again the experts are trying to find better means of treatment, including natural controls using predator insects; however, to date, even with some predator insects (two types of ladybeetles), the lerp psyllid is still proliferating.

The main lerp stage is found to be between May–June to November. Their development, as with a lot of pests, is slowed during the winter months, accelerating through the spring. We do expect another substantial outbreak this spring. As this pest was most widespread and virtually went unchecked last year, before anybody was geared up to treat it, we recommend early treatment — in terms of both its effectiveness in killing the pests and limiting the damage it can do to both the trees infested and the property underneath. We have two options for treatment this year: one using the traditional spray application, in which we use a contact/systemic pesticide; while the other, more effective means is through injection directly into the trunk of the tree.

The spray application, while less expensive, is primarily a contact kill, whereby it only deals with the lerp psyllid existing on the tree at time of treatment. That will usually knock down the pest sufficiently to protect the tree through summer, at which time there is a risk of reinfestation when the summer growth replaces the leaves that originally defoliated during the spring infestation. Unless another application is made in the fall, the tree will remain infested, defoliating the fall foliage and dripping ‘honeydew’ until the colder weather decreases their activity.

The more effective treatment, through injection, uses “Merit” systemic, which is injected into the tree itself and penetrates the entire tree through its ‘vascular’ system — not only killing the initial infestation but continuing to protect the tree from reinfestation later in the year. The key to the effectiveness of this treatment depends upon injecting the tree early enough in the year (March–April), so that the systemic is in the tree when its sap begins to flow, as the weather begins to warm, and can therefore be distributed throughout the entire tree. The amount injected depends upon the size of the tree. The other consideration for using the injection method is that it can, depending upon the size of the tree(s), cost two to three times more than the traditional spray application.

Your project supervisor will be contacting you in the coming weeks with regards to your project’s exposure to any of the aforementioned pests, or for that matter any other pests, that may affect your landscape. They will present you with the scope of the problem and your options for treatment. If you have any other questions, please feel free to contact me or my staff.

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