My huge avocado tree has been attacked by ambrosia beetles. My tree trimmer says there is nothing to be done to save it. I’ve lived with this tree for 30 years and don’t want to lose it. Is there anything I can do?
Lois Wilson, North Long Beach
The lethal effects of ambrosia beetles in this country were first noticed in 2003, on the island of Hilton Head, South Carolina, when giant redbay (Persea borbonia) trees, close relations of avocado (Persea americana), began to wilt. Two years later, it was confirmed that tiny ambrosia beetles, which are less than one-tenth of an inch in size, were responsible for redbay tree death.
Ambrosia beetles get their name from their diet, which consists of golden Verticillium fungi. The relationship between ambrosia beetles and Verticillium fungus is symbiotic. The beetles bore through avocado bark carrying Verticillium spores in pockets on their mandibles (jaws). The spores are deposited in the tunnels created by the beetles and these tunnels provide the perfect microclimate for Verticillium growth. Damage to the trees is done when the verticillium clog water-conducting vessels in the tree, causing wilt and eventual death. Some have referred to this disease as laurel wilt since its primary victims are trees in the laurel family such as avocado, camphor (Cinnamomum camphora), and California bay (Umbellularia californica). Many other species of trees, however, including oak, sycamore, liquidambar, white alder (Alnus), box elder and maple (Acer), olive (Olea europaea), castor bean (Ricinus communis), golden raintree (Koehlreuteria), mimosa (Albizzia), black locust (Robinia), lychee, and persimmon, may become hosts to the ambrosia beetle.
Ambrosia beetles are native to Japan, Taiwan, and Mayanmar (Burma). They are thought to have arrived in this country in shipping containers on wooden pallets. Thus, one of the problems of preventing arrival of more beetles is control in their countries of origin or, failing that, monitoring of wooden pallets that arrive from those countries.
Unfortunately, there is no proven remedy for this disease as of yet. Research seems to indicate, however, that the beetles are especially attracted to tree wounds so it is advised not to prune avocado trees for the time being. Since avocado trees are infrequently pruned in any case, allowing them to just grow, for the time being, could be the best way of preventing beetle infestation. Chemical preventive treatments have been tried with limited success but, since the chemicals are systemic, it would not be safe to eat avocadoes growing from such trees.
Once a tree has been infested with ambrosia beetles, nothing can be done to save it and its removal is advised in order to prevent beetle infestation of neighboring trees.
Presence of ambrosia beetles may be detected by white fungal exudate, either dry or wet, around a beetle exit hole. The exudate, in turn, is surrounded by a large expanse of discolored bark. Locally, affected trees have been identified in Southgate, Downey, Pico Rivera, and Long Beach.
Driving south from Calabasas on Malibu Canyon Road, you may notice scores of fluffy botanical outbursts on both sides of the road. It may interest you to know that these eruptions are not flowers but clusters of cottony seeds. The plant in question is coyote brush (Baccharis pilularis var. consanguineus), a stout shrub that can grow over eight feet tall and nearly as wide.
California coyote brush is an abundant source of nectar to beneficial insects and butterflies. In the opinion of some, it just might be the best plant for attracting these winged visitors to your garden. Coyote brush is dioecious, which means it has separate male and female plants. Unfortunately, female coyote brush, the one with the fluffy seeds, is not widely available in the nursery trade. The coyote brush found in most nurseries is a clone of a male coyote brush ground cover, either ‘Twin Peaks’ or ‘Pigeon Point’ cultivars. As male plants, their flowers will not produce the quantity of nectar produced by their female counterparts. If you want female plants, you will have to visit a native plant nursery such as Theodore Payne or Las Pilitas.
The success of the coyote brush genus (Baccharis) in attracting pollinating insects is rewarded with enormous diversity. Baccharis is the most prolific genus, with more than 500 species, of the daisy family. Baccharis species are exclusive to North and South America, although their range extends from Canada to Chile.
Tip of the Week: Fiddle-leaf fig (Ficus lyrata) is a highly rewarding indoor plant. It manages to grow virtually care free with average to above average light exposure. For nearly thirty years, I have been admiring the giant specimens of fiddleleaf fig in the Casa de Cadillac showroom on the corner of Beverly Glen Boulevard and Moorpark Street in Sherman Oaks. Michael Kappel, my master gardener friend, has an eight foot tall fiddle-leaf fig growing in a corner of his house that gets all of its sun through a small skylight overhead. Several months ago, he cut back the terminal portion of a stem with five leaves attached. He filled a vase with glass marbles and water and then anchored the stem in the marbles. Eventually, roots started to grow from the stem base and now he has a hydroponically produced fiddle-leaf fig whose leaves are so perfect they hardly look real.