January 24, 2002

News from Autumn 2001

 

AUTUMN BLOOM

Japanese anemone, anemone hybrida, is a long-lived, fibrous rooted perennial which provides fall color in partially shaded locations.  Although it can be slow to establish, the sprays of graceful flower stalks waving two to four feet above the basal clumps of soft, lobed leaves make the small effort worthwhile.  After planting, do not disturb the roots by weeding or cultivating (hand pull weeds and apply mulch), and keep the plants moist.  You will be rewarded each September by a dainty yet abundant display of flowers.  Varieties include white, rose, and pink flowers.

 

                                             IT'S SPIDER SEASON

 

One sure sign of autumn is an abundance of spiders.  The spider shown here, the green lynx or peuctia viridans, is one of my favorite common garden spiders.   As you can see, it is beautifully colored and marked.  The green lynx waits among flowering plants to pounce on unsuspecting visitors such as wasps and flower flies.  Green lynx are easily found this time of year as they are maturing.  The adult females are about 3/4" long.  In autumn they lay their eggs in silk sacs attached to foliage.  The mother spider actively defends her nest and assists the spiderlings as they emerge.

        Spiders play the important role of general predator in ecosystems.  They hunt in various ways, including laying in wait, active pursuit, and snaring prey n various types of webs.  As general predators, spiders apply environmental pressure on the prey populations, helping to keep their numbers in balance.  When observing spiders, always use caution and do not annoy them.  Any spider may bite to defend herself or her nest, and the bites can be painful and irritating.  The bites of several spiders, including most famously the black widow but also the violin, some orb weavers, some wolf spiders, and others, can be dangerous to humans.  Look, learn, but don't touch.

 PSYLLIDS IN THE NEWS AGAIN.

 

 

 

 

An article which ran in the OC Register Tuesday, 9/11/01 about damage to eucalyptus trees from redgum lerp psyllids.   

A few comments or responses follow.  Please note, for the sake of brevity, rglp=red gum  lerp psyllid and lglp=lemon gum lerp psyllid.

Lerp Psyllids

Our lerp psyllid experience this summer has been that of much heavier infestations by lglp than rglp.  In our experience, the rglp has had a favored set of eucalyptus species to feed on  which did not included lemon gum or spotted gum.  many of the trees initially and repeatedly infested with rglp are dead or dying.  Now the lglp populations are exploding on the previously uninfested lemon gum trees, and (in our experience) to a lesser extent on the spotted gum trees.  The infestations that we have seen are all primary, and most of them very recent (small lerps, leaves still green, no sooty mold developing).  I've seen some primary rglp infestations, but not as explosive as lglp.  This is probably due to the locations and species of eucalyptus I've observed, but I am not sure.  There is no person or agency collecting data on imported pests from field observers, as far as I know, so busy field personnel have no efficient, day to day resource to find out what other people are learning or observing..

Plant Diversity

1.  By planting more species on a site, instead of a monoculture, the risk of the entire planting being damaged by a single infestation or disease is reduced.  Of course, no species of plant is free of pests . . . that is what we once thought of eucalyptus. Brisbane box (tristania conferta) is a beautiful evergreen tree that even looks sort of like eucalyptus.  And well it should, since it's closely related and also native to Australia.  Perhaps the pest that will decimate our tristanias is lurking in the cargo hold of a jet right now.  So a monoculture of tristania is as ill-advised as were the single species plantings of eucalyptus.  

2.  More first hand information and research is needed on host species preference of these two psyllids.  Instead of erasing eucalyptus (a plant genus that includes over 500 species) from our plant lists, we could be gathering information on the relative susceptibility of each species to psyllid infestation.  With this information, we might be able to plant a workable diversity of eucalyptus.

3.  The suggestion of using native plant materials, since they grew up in this neighborhood and the bullies are tired of picking on them is good.  Unfortunately, the overwhelming majority of landscape plants currently used are non-native to California.  Several great nurseries have been promoting the expanded use of natives, but they have not caught on to a large extent.  One reason is plant palettes being burned into master plans.  Another is availability.  Another is cultural needs and growth cycles of some natives are different, and when they are planted, their needs are sometimes not met, they don't thrive, and so they get a bad reputation.  And, natives can have pest problems, too.

4.  Every replacement tree has its pluses and minuses, so any proposed tree planting should receive careful evaluation.   Pears can get fireblight, sycamore (native) get spider mites and grow rather large; non-native sycamore get anthracnose; both of them drop copious amounts of leaves early in autumn.  Oaks are subject to root rot and various insect pests.  Tristania has no faults whatsoever (see #1 above); liquidambar drops not only leaves but spiky seed pods.  Each of these species is a beautiful tree finely suited for the proper location and management situation.

Management Options for Eucalyptus

Even though dead trees provide valuable perch habitat for a variety of birds, they should be removed from most landscapes, as mentioned in the article, because of the safety hazard as well as our aesthetic sense.  Other options for trees not yet dead do exist:

1.  Assessment.  Decide the value of your trees to your property.  List the trees, rating their level of infestation, likelihood of survival, and quality of branch structure.

2.  Pre-emptive removal.  Are there trees you just really do not need or want?  Why wait for them to become infested, drip honeydew all over your place, and die?

3.  Treatment.  Chemical treatment of good candidates (young trees, valuable trees, easily accessible trees, newly infested trees) can be successful enough to be worth trying. Call a licensed pest control operator or advisor for information on your particular situation.

4.  Wait and see.  WIth cooler weather coming, psyllid feeding should slow down.  I don't have any first hand information, nor any other sources yet, on the lglps' winter activity.  I suspect, however, it will be like the rglp.

On Other Imported Pests

 1.  The article does not mention the tortoise beetle, trachymela sloanei.  We have observed certain eucalyptus species (ie e. rudis) with heavy infestations of these, but no sign of psyllids of either kind.  Tortoise beetles hide under bark or in cracks, coming out after dark to chew large notches along the leaf margins.  The insects themselves are actually rather cute, if you get a chance to see one.  Again, it would be good to document which trees these insects prefer, and the relative likelihood of severe damage among the species.  Biological control efforts are under way for this pest.

2.  The glassywinged sharpshooter is the vector of Pierce's disease, which threatens California's grape industry as well as other crops and ornamentals.  The state government, grape growers and the nursery industry report they have spend millions of dollars in research, control, and quarantine in an effort to limit the spread of this disease.  And, by the way, oleanders in Orange County are still succumbing to the bacterial infection.  Maybe they are not as noticeable since so many have already been removed, or possibly they are overshadowed, so to speak, by infested eucalyptus.

 

 

April 2002

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