Bananas, Grapefruits, and Oak Tree Beetles

“I have banana trees that bloom and produce fruit of the ‘Ice Cream’ (also known as ‘Blue Java’) variety. I have heard that I should trim the flower off after a single cluster of bananas has formed or, alternatively, that I should let the flower continue to grow after fruit formation.  What is your opinion?”
Don Whitlatch, Laguna Beach
Once bananas in the initial cluster have reached full size, even while still green, you should cut the still growing flower stalk several inches below the cluster.  Subsequent growth on that flower stalk, including new banana clusters, will diminish the sweetness of fruit in the first cluster.
Your question goes to the heart of understanding the issue of quantity versus quality of fruit on any plant or tree.  That is, each tree has a limited amount of resources for fruit growth.  On apple or apricot or plum trees, you will get larger fruit on any given shoot if you thin the fruit on that shoot when it is still small.  On the other hand, if you allow all the fruit on a shoot (or stem) to develop, you will have a larger quantity of fruit but of lesser quality — meaning less sugar content — than if only a few fruit on that shoot had been allowed to develop.
Incidentally, this principle also holds true where flowers are concerned.  For example, suppose that, during the winter, you prune a rose bush back to a height of 6 inches, allowing just 3 or 4 canes to remain.  The following spring you will have much larger blooms, although fewer in number, than if you had cut back your rose bush to a height of 24 inches and left 10 or 12 canes in place.
Bananas are not just for seaside locations such as Laguna Beach.  At Papaya Tree Nursery ( in Granada Hills, eight banana varieties are on sale.  Moreover, there is even a super hardy banana hybrid (Musa basjoo) that can grow almost anywhere in the United States.  Where its rhizomes are heavily mulched, it can survive temperatures as low as -10 degrees Fahrenheit. It is sometimes called Japanese banana, although it actually comes from China.  You can find hardy Japanese banana trees through suppliers on eBay and
There is a catch:  these hardy trees are strictly ornamental and it is only in mild winter climates where they produce bananas which, in any case, are inedible.

prolfic grapefruit tree, photo by Eric Peterson

“Each year in July, I strip a large grapefruit tree in my front yard. The tree is around 60 years old and bears approximately 1500 fruit, or so it seems. I strip it because I am under the impression that it is healthy for the tree. Could I be mistaken? When I drive around my neighborhood and CSUN campus I see trees with fruit all year long.”

Eric Peterson, Granada Hills
The advantage to stripping the tree in the summer is that you will promote a large crop again next year.  By the same token, the fruit will get sweeter the longer it is left on the tree.  The disadvantage of a later harvest, which can be extended into the winter and beyond, is a smaller crop next year.
Once again, the issue is resource allocation.  The longer the grapefruit remain on the tree, the more carbohydrate (sugar) they will pull from the surrounding evergreen foliage, giving them more sweetness but at the expense of a smaller crop next year.  There will simply be less sugar — depleted in sweetening the existing crop — available for next year’s reproductive (flower and fruit) development.

oak tree infested with bark beetles, photo by Duane Potts

Tip of the Week:  Duane Potts has several oak trees in Castaic which are infested with beetles and he seeks suggestions for their eradication.  These beetles are about the size of a grain of rice and hide under or bore into bark.  If you have a stressed oak tree and see woody dust or frothy exudate coming from small holes in the bark, you probably have a beetle problem.

The only non-chemical approach to this problem that I have seen is solarization.  Wrap the infested trees in clear, thick (10 mil), air-tight plastic.  The heat inside the plastic roasts the beetles.  This may not be a practical solution for large trees, especially since you need to keep the plastic in place for several months.
Chemical treatments are not effective on heavily infested trees but such treatments may be undertaken as a preventive measure where healthy or lightly infested trees are concerned.  Locally, I know of two landscape pest control companies that render such treatments:  National Tree Service in North Hollywood (818-984-3670) and Mitchell Pest Control in San Gabriel (626-287-1106).
It is likely that the long period of drought that we experienced may be responsible for your beetle problem since stressed trees attract insect pests.  Even native trees such as oaks may suffer in a drought.  It is wise to soak all trees, including natives, once or twice a month during a drought.
Meanwhile, it is essential that you wrap log piles on your property in clear plastic in full sun so that any beetles residing in them are killed through solarization. You should also dispose of any dead trees or tree limbs because they are favorite beetle domiciles.

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