THE EUCALYPTUS MESS by Randy Newhard

As I'm walking around my garden this morning, I can't help but mutter to myself about the sticky mess underneath my Eucalyptus trees. The fallen, dried out sticky leaves are adhering to my shoes and get carried everywhere I walk. You can bet my wife has lectured me about taking off my shoes before I enter the house. Approximately half of the thousands of leaves that were once on my trees now lay on the ground. The leaves are coated with this funny looking, white, cone shaped substance.

WHAT'S GOING ON?

The culprit of this unfortunate situation is a pest called the Redgum Lerp Psyllid (RLP). The scientific name of this pest is Glycaspis brimblecombi. The RLP was initially found in Los Angeles and San Bernardino counties. The RLP has traveled fast. This pest also occurs in San Francisco Bay area and the San Joaquin Valley in Central Valley. It is expected to spread throughout California where susceptible species of eucalyptus are grown. RLP heavily infests Red Gum Eucalyptus, Eucalyptus camaldulensis, but also occurs on sugar gum (E. cladocalyx), blue gum (E. blobulus), Eucalyptus rudis and three other species.

A characteristic feature of this pest is that it forms a protective cover or "lerp". This protective covering, which is small, white and cone shaped, is composed mostly of crystallized honeydew, the sugary liquid that sap-feeding insects secrete. This secretion stains the ground beneath trees.  A blackish sooty mold grows on the honeydew-covered surface. In severe infestations, thousands of lerps cover the ground and understory, giving the appearance of hail. Heavy infestations cause severe leaf drop.

Honeydew and sooty mold are bothersome to people (especially me), but probably do not have a serious adverse effect on tree health. However, extensive defoliation weakens trees and increase susceptibility to wood boring pests such as eucalyptus longhorned beetles. These beetles, if successful in attacking trees weakened by RLP, can kill branches or entire trees. Successful attacked eucalyptus will turn completely brown. This presents another problem. These attacked trees provide fuel for fires in the hot, dry California summers.

WHAT'S BEING DONE?

Towards the end of summer last year, Dr. Don Dahlston, an entomologist from UC Berkeley, headed to Australia. That's where these pests came from. He was looking for a predator capable of controlling the unchecked RLP. He eventually gathered six different promising wasps. Many difficulties were overcome in the pursuit of the elusive dark, pepper-grain-sized wasps, including funding and numerous permit requirements. Of the six wasps collected, one is a hopeful prospect.

The 'good guys" are being bred at a quarantined insectory. They have to be carefully studied to ensure they won't sting humans and will only pick on the pesky RLP and no other insects, so as not to upset nature's balance. So not to worry that there will be more wasps out there to sting you. The wasps have been released in Los Angeles last month and they hope to breed more and a release is scheduled for San Diego in July.

This biological control method has been effective against other psyllids, including the acacia psyllid and blue gum psyllid, and it gives partial control of the eugenia psyllid. But don't expect miracles right away. This biological control may take up to a few years to establish itself.

WHAT CAN I DO NOW?

Cultural control - Minimize the amount of tree stress by providing the eucalyptus with proper cultural care and protecting the trees from injury. Nitrogen levels in foliage may increase when eucalyptus is stressed. Increased foliar nitrogen increases reproduction and survival of psyllids. To minimize stress, consider providing trees with supplemental water during periods of prolonged drought, such as summer and fall when rain is infrequent or nonexistent. Drought stress increases damage to trees from both RLP and eucalyptus longhorned borer.

When irrigating trees, apply water beneath the outer canopy, not near the trunks. Avoid frequent, shallow watering. A general recommendation is to irrigate eucalyptus infrequently (possibly 1x per month during drought periods) but with sufficient amounts so that the water penetrates deeply into the soil. This can be achieved by applying water slowly through drip emitters that run continuously for several days.

Avoid fertilizing eucalyptus. Use slow release nutrient formulations if other plants near the drip line of the eucs require fertilization. Psyllid larvae and egg laying females prefer the abundant, succulent new shoot growth stimulated by excess nutrients that occur following the application of quick release fertilizer formulations.

Chemical control - Many trees may need help in surviving until the beneficial wasps can achieve control. Recently Cal Poly University conducted clinical trials of two systemic insecticides for control of the RLP - Imicide (imidaclorpid) and Metasystox R (oxydemetonmethyl). These Doctors tested the micro-injection system using the chemicals Inject-A-Cide and Imicide.  A total of 40 trees at random sites were tested. Three injection treatments were evaluated, Imicide alone, Inject-A-Cide alone and a combination of the two chemicals. Imicide injected alone provided the best overall control. The Imicide treatment was active in one week, and was active after more than four months. The Doctors related that Imicide residues would not harm the beneficials. Imicide label includes use for control of psyllids, but you should check with your local Agricultural Commissioner. Imicide has been submitted for label amendments to specifically include RLP and the eucalyptus longhorn borer. Federal EPA registration amendments have already been completed.

Over at Bayer Chemical Company, they report another formulation of Imidacloprid, Merit, gives long-term control of RLP. It can be applied by soil drenching, soil injection or micro-injection. Imicide provides long term RLP control, assists biologicals and controls defoliation, sooty mold and honeydew. Imicide use will also reduce twig and limb dieback, fire hazard, freeze damage and tree mortality.

Until beneficials are released in San Diego County and their effectiveness documented, we're fortunate to have the option of three different chemical delivery methods. Micro-injection may be used on stressed high value trees, in even the most difficult to reach locations. Micro-injection knocks down the psyllid quickly, and puts the entire chemical directly in the tree. Soil injection formulations can be used for large numbers of infested trees that accessible to equipment. Soil drenching is valuable for treating single or small numbers of isolated trees.

Imicide application for RLP control is cost effective, when weighed against the costs of tree trimming, removal and possible fire outbreaks. Overhead chemical foliar treatments are not effective. It is hard to pierce the lerp cone with the chemical and the potential for spray drift is great.

Randy Newhard is President of New Way Landscape & Tree Services in San Diego. Randy has his Qualified Applicator License and is a Certified Landscape Technician in Maintenance and Irrigation.