Eucalyptus Pests? Try Proper Care

Do You Feel Lucky?

Driving over a downed eucalyptus branch can lead to this

Drought. Psyllids. Borers. Whiteflies. Caterpillars. Root rot. Improper pruning. Sudden Limb Drop. As if the local eucalyptus trees don't have enough problems. Now entering Northern California is another pest problem for this widely planted tree, the eucalyptus tortoise beetle, first discovered in Riverside County seven years ago.

There are those who would have you remove eucalyptus trees, especially the blue gum (E. globulus) and red gum (E. camuldensis) due to their invasiveness. Eucalyptus trees can be messy, susceptible to wind damage and tough to plant anything else beneath them. Eucalyptus trees have their place in California, especially rural areas where their fast growing, evergreen qualities can serve well to prevent soil erosion as a windbreak. In urban areas, tall eucalyptus trees are more problematic. There are better choices for backyard trees in cities and suburbs.

While the red gum lerp psyllids are sucking away along the undersides of eucalyptus leaves and the longhorned eucalyptus borer is tunneling its way into the tree's branches and trunk, the eucalyptus tortoise beetle is chewing semicircular or irregular notches along the leaf margins, leaving only the mid-vein when its done dining.

Eucalyptus long horned beetle

eucalyptus tortoise beetle

red gum lerp psyllids on E. camuldensis

The psyllid is inside the lerp, well protected

Although beneficial insects have been introduced to battle the red gum lerp psyllid, eucalyptus long-horned borer and the eucalyptus tortoise beetle, it may be years before the beneficials population is large enough to control these pests. In the meantime, homeowners can help out their suffering eucalyptus trees with a few simple steps:

* Water eucalyptus trees, once a month, during the summer. Soak the area beneath the outer canopy of the tree. Don't flood the area near the trunk, though; eucalyptus are susceptible to root rots. Drip and soaker hoses are preferable to sprinklers.

* Don't fertilize these trees. Nitrogen-induced tender, new growth is especially susceptible to these pests.

* Clean up any dead branches on the ground, remove dead trees. This could be a breeding area, especially for the eucalyptus longhorned beetle.

*  Prune in December or January to avoid borer attacks to freshly cut limbs.

* Don't plant pest-susceptible eucalyptus species. The varieties most susceptible to damage by these critters include the blue gum (Eucalyptus globulus), manna (E. viminalis) and the widely planted river red, E. camaldulensis.

* Choose eucalyptus varieties that have shown some resistance to these pests. This list would include the Australian beech (E. polanthemos), silver dollar eucalyptus (E. cinerea), gray ironbark (E. paniculata), the narrow-leaved eucalyptus (E. spathulata), and the hybrid E. trabutii. Several more are listed here.

* Read and follow all label directions if using a soil drench systemic insecticide whose active ingredient is imidacloprid, which may control the red gum lerp psyllid; studies aren't in yet if it is effective on the tortoise beetle. The University of California reports mixed results on the efficiency of imidacloprid in controlling the red gum lerp psyllid; for best results apply this soil drench in early spring.

* According to the UC Davis Integrated Pest Management Project, limit any chemical treatments to situations where damage is intolerable or pests threaten tree survival. Most pesticides are at least somewhat harmful to beneficial predators or parasites. Imidacloprid applied to flowering plants or the soil beneath them may move to nectar and poison the nectar-feeding adult parasites, which during their larval stage partially or completely control other pests. Be aware that imidacloprid application may contribute to outbreaks of spider mites and other pests.

Use pesticides rarely and always as a last resort. Most tortoise beetle infestations do not require pesticide treatments, and pesticides disrupt biological control of other pests.

For more Information:

The Eucalyptus Tortoise Beetle:

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74104.html

Red Gum Lerp Psyllids:

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7460.html

Eucalyptus Longhorned Borers:

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7425.html

The most diverse collection of eucalyptus trees in North America is at the UC Santa Cruz Arboretum. Plan a visit!

E. laeliae

What Plant Is Your Horse Eating Right Now?

   
 A caller to the radio program awhile back asked a good question, one that livestock-owning country dwellers ought to also consider:
    

     "I want to plant some trees or shrubs that will grow quickly to hide the view of a new house going in next to us," said the caller. "But I don't want to plant anything that might be poisonous to our horses, which will eat just about anything. Any ideas?"

    "There definitely are some plants that you should avoid," advises Dr. Frank Galey, now with the University of Wyoming, formerly the toxicologist at the California Veterinary Diagnostic Laboratory Systems at UC Davis. 

Highly poisonous plants that should not be planted within the reach of horses include:

                                         oleander 
The book, "The UC Davis Book of Horses", says that the oleanders (of which all parts are toxic) can cause horses to develop diarrhea, colic and an irregular heartbeat.

                                            yews

"A yew can kill a pile of horses in a heartbeat," says Dr. Galey.

                                     rhododendrons

                                   

                                          azaleas

Rhododendrons and azaleas, which can cause severe colic or diarrhea, can often be found while on wilderness expeditions with your horses. They will be become hungry during prolonged treks and may eat any forage available at rest stops or campsites. A good piece of advice? Don't picket your horse near any shrubs.

                                Privet with berries

                                         pieris 

 There are many, many more plants that can be toxic to horses, a list of which you can probably get from your veterinarian. "Toxic" has a wide meaning, from gastric distress to death. Among the other highly toxic plants that are commonly found in California: 
the twigs and leaves of deciduous fruit trees, including apricot, cherry, peach and plum;
Foxglove
Lupine
Mountain Laurel
Nightshade
Oak acorns (in large quantities)
Sweetpea seeds
Tomato vines

   

PLANTS THAT ARE LEAST TOXIC TO HORSES





There are a number of trees and shrubs that can provide a quick screening effect; here are a few that will do well in our area of California and are the least toxic to horses:

* Eucalyptus. "Horses tend to leave eucalyptus trees alone," says Dr. Galey. For a quick, bushy screen, plant the Eucalyptus globulus 'Compacta', the dwarf blue gum, about six feet apart.

* Bottlebrush (Callistemon citrinus). This evergreen shrub can reach 15-20 feet tall, and is dotted with colorful, bright red bottlebrush-shaped flowers several times throughout the year. "We haven't had any poison reports about the bottlebrush, so it should be pretty safe," says Dr. Galey. "But because the plant attracts bees, it's possible the horse could be allergic to bee stings."

* Coast redwood (Sequoia sempervirens). Given ample water, this evergreen tree can grow several feet a year. It also has a low incidence of toxicity. Horses, though, may trample the lower branches.


     It's up to the horse owner to be vigilant, patrolling the pasture regularly for unfamiliar plants, especially those that may pop up seasonally. Look for toxic plants near water tanks or ponds; along fence rows; or, roadside gullies that a hungry horse might reach.

    This word of caution: anything eaten in mass quantities by a horse may cause medical problems. A good book that goes much more in depth on this topic is "The Horse Owners Field Guide to Toxic Plants". And check your horse insurance policy. Make sure you have thorough coverage if your pasture is surrounded by a field full of mystery plants. Some companies may drag their feet if the horse is suffering due to human error.
So, if you have horses that have never missed a meal, you may want to install a horse fence or hot wire between the screening plants and your ravenous friends.