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Tuesday, August 12, 2014

Preventing Olive From Dropping Flowers

Q. I have an older olive tree that is very messy. Is there a way to prevent it from blooming in the spring and dropping all its yellow flowers? It also sheds a lot of leaves only during the spring but all year-round. Is there any way to prevent that also?

A. The only consistent way to eliminate or reduce flowering is to spray an olive tree with an appropriate chemical before it blooms. In the past, the most effective timing has been in mid to late February or March using a chemical called Maintain. It needs to be applied by a commercial applicator.
Olive flowers. Some chemicals must be sprayed when the flowers are open to get good fruit drop.
            Commercial applicators have access to other chemicals as well but they usually are not as effective as Maintain. The less effective chemicals are sprayed at the time the olive tree is blooming. These are primarily aimed at fruit elimination, not flower elimination.
            These other chemicals cause the flowers to abort after they are open. It should be obvious if the chemical has to be applied when the flowers are open, it will not do much to eliminate flowers or reduce the release of pollen.
            This is an important question to ask a commercial applicator: when does your chemical need to be applied? If the response is during bloom, then this is not the right chemical to use to eliminate flowers.
            There are two very different products available to homeowners which might be useful to some as a spray. One is fairly effective at eliminating flowers. The other does not do much to the flowers but is fairly good at eliminating fruit.
            When you go to your favorite nursery or garden center, look for sprays that eliminate fruit from trees. Read the label. If the label says it must be sprayed when the flowers are open, it will not be effective as a “flower eliminator”.
            The other spray has a label which tells you to apply it just before the flowers are open. This spray has a much better chance of eliminating the flowers. Again, read the label.
            Regarding leaf drop, olive is evergreen so some shedding is normal since it drops leaves primarily as it puts on new growth. But some leaf drop will occur season-long.
            Excessive leaf drop is not normal. The primary reason for excessive leaf drop throughout the canopy would be lack of enough water. When there is not enough water, then it is normal for a plant to drop leaves to reduce its need for water.
            Make sure your water sources are not plugged, restricted or the clock has not been changed for some reason. Make sure olive trees received enough water during irrigation. You might have to add emitters.

            If the leaf drop is coming from only one or two branches, this is also not normal and could be a sign of disease and you will need to investigate this further.


  1. Lab results are in on tissue samples taken from olive trees on my property. I'm sad to say that we have one of the first known cases of Phyophthora Neiderhauserii in olive trees in Las Vegas. We have contacted our gardeners and told them to sterilize all of their tools right away. We are preparing to restrict irrigation, lay gypsum and a deep layer of course wood mulch within the drip lines of each tree. Can you recommend anyplace that carries wood mulch (not bark) here in LV. I'm assuming that I can get the gypsum at most nurseries. We'd prefer to stay away from the pesticide treatments unless absolutely necessary. Any recommendations or input you can provide would be appreciated.

  2. Who diagnosed this disease problem?