Palm tree collapse


Dear garden guy, when we moved here 5 years ago, we had 3 big triangular palms in our front yard. They are 15 to 20 feet tall. We trim the bottom fronds when they start to die. Two days ago, one of these palms just fell over. The neighbor thinks it might be mold, since there was black stuff scattered in the base, which is about two feet high. We don’t want to lose our remaining palms, so am hoping you can tell us what caused the one to fall over & how to save our remaining ones.

Mahalo for your help, JB

A significant pest of Pritchardia palms is the banana moth, Opogona sacchari. The triangle palm is also attacked by this moth. It seems that the female moth targets wounded or stressed palm tissue to lay her eggs. Stresses can include drought, flooding, mechanical wounding, poor nutrition, and herbicide injury. The larvae generally feed on decaying and dead plant tissue but will feed on living tissue, too, causing extensive damage. In affected palms, larval tunneling, along with the characteristic frass (insect droppings), can often be seen. Fully developed caterpillars measure just over an inch. The adults have greyish brown wings are 3/8 to 5/8 inches long.

The main treatment is prevention: keep palms growing well; give them adequate fertilizer, and supplemental water during a drought. Gardeners also need to be careful with the weedwacker! Female moths are looking for wounds to lay their eggs. Bt (bacillus thuringiensis), an organic insecticide, can be applied to these wounds, as well as those caused during pruning.

For more information about this pest see the CTAHR Cooperative Extension Service publication, “Banana Moth – A Potentially Fatal Pest of Pritchardia and Other Palms,” by Scot Nelson and Mark Wright. For new readers, CTAHR is College of Tropical Agriculture and Human Resources.

Is it okay to fertilize a lychee tree that is in full bloom? How many times should a lychee tree be fertilized during the year? Thank you. ERG

Fertilizing fruit trees that are in full bloom is acceptable. Yet in order to maximize production, the fertilizer needs to be in the tree before bloom occurs, perhaps a month before. During the flowering period, trees need a rich complement of nutrients in order to fully develop the new fruit and produce a plentiful yield. A second application may be made in late spring when fruit has formed and a third time around the end of summer/beginning of fall. The pre-bloom application is the most crucial.

This is a general recommendation; fertility of soils varies greatly. Some soils will require the three applications while others may need only one or two. In addition, adding organic matter will always enhance the quality of the soil.

Tree appearance can also be used as an indicator for fertilizer applications. If the plant appears healthy and has dark green leaves, three applications may not be necessary. On the other hand, light green or yellow leaves may indicate a need for nitrogen (it may also indicate problems elsewhere). One note of caution: if excess fertilizer is applied during bloom, not only will the leaves be injured, but the bloom may be lost as well.

Class Announcement

I will be teaching a vegetable gardening class from 9:30 a.m.-12 p.m. on Saturday, April 20, at the University of Hawaii at Hilo campus. Call 974-7664 to register; or go online at http://hilo.hawaii.edu/academics/ccecs/fitness/ The website also contains a full description of the class. There is a fee.

Hilo resident Nick Sakovich is a professor emeritus of the University of California. He has worked in the field of agriculture for 30 years. Email your questions to Sakovich at askthegardenguy@earthlink.net.

 

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