Wednesday | September 28, 2016
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When to prune?

Dear Garden Guy,

Thank you very much for your reply about avocado flowering from a few months ago. It was extremely helpful for me in understanding my avocado trees and how best to care for them. Now I am thinking about the timing of pruning, in particular for my guavas, but also for my avocados, citrus, and mango. When you have two crops at once (or even three crops in lemons), when is the best time to prune? If you choose to prune, it seems you will have to sacrifice at least some of the flowers one of those crops.

Is there a period of time prior to a natural cycling of flowering that is useful for pruning, i.e., prune at least one month prior to the natural time of flowering? If so, does this apply to most trees I am thinking about, namely guava, citrus, avocado, and mango. Many thanks for your assistance. — M.

When it comes to pruning, timing can be important, but it isn’t always critical. Pruning at the wrong time will not necessarily harm the tree, but it can lower the yield.

In guavas, pruning will influence flower bud formation and is usually initiated after harvest. And since pruning can influence flower bud formation, specific dates can be chosen to manipulate harvest dates. In guavas, the crop harvest will begin approximately 7 months after pruning. For a detailed discussion on pruning guavas to influence harvest dates go to the CTAHR website

Mangos are generally pruned after the harvest. With avocados, pruning is done only to shape young trees and remove dead branches.

As you mentioned, some citrus present a problem in pruning because there will be two crops present on the tree at the same time. When should pruning occur without sacrificing fruit? It can’t be avoided; whatever the timing, some fruit will be removed. As a rule, it is recommended to prune after harvest. With lemons, the timing of pruning is difficult since there are always multiple stages of fruit growth on the tree. For vigorous varieties like Lisbon and Eureka, it is best to prune after the last harvest of the year. This is also true with limes and calamondins, though they will need minimal pruning. Meyer lemons require little pruning; this can be done at any time.

Hi, Nick! My vegetable seedlings have thousands of tiny spots on top (of the leaves). Is it a mite? — Merle

From your description and from the pictures, it is clear that the seedlings show a condition called stippling. These are tiny, yellow dots where the insect inserts its mouthpart into the plant to suck up the juices. At the point of insertion, the plant cells die, and the area becomes a yellow speck. With mass feeding there are numerous specks, or stippling. From a distance it looks like a leaf turning yellow. But upon closer examination, individual tiny yellow spots can be seen.

Some insects that produce stippling have piercing-sucking mouthparts and include aphids, leafhoppers and lace bugs, which are common on azaleas. In addition, mite feeding creates the same symptom.

Most of these insects and mites can be detected by examining the plant. Inspect both sides of the leaves; lace bugs are usually found on the underside. Mites are tiny and may need magnification for viewing. Leafhoppers are difficult to observe since they feed and hop around quite a bit.

An oil/soap solution is good for mites, aphids, and lace bugs; sulfur is also good on mites.

Class Announcement:

Growing Citrus in Hawaii

I will be teaching a citrus class Nov. 3 from 9:30 a.m.-noon. Topics to be discussed are preparing the soil, planting, pruning, fertilizing, diseases, insect problems and troubleshooting; learn basic information for the backyard gardener. Call 974-7664 to register; or go online at There is a fee. Location: UH Hilo Campus UCB 118.

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


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