Master Gardener: Your plant and gardening questions answered

Q. I enjoyed your article on fruit trees in the newspaper. It’s been a challenge this year. An arborist suggested the referenced citrus leaf miner traps and they work really well. I replace them every 3 months and trap quite a few of the bugs. No pesticide needed and the trees are clear of the infestation.

A.  I’ve gotten several emails regarding the leaf miner traps, so I suppose I should have included them in my column about leaf miners.

These pheromone-baited traps can be found, after some searching, in farming supply stores or online (I’ve never seen them in our local stores). They are safer and easier to use than the soil drench because they only affect the problem insect and not the honeybees. I’m happy to hear that they have become easier to find for homeowners.

There are other versions of sticky traps that are environmentally friendly, including traps for apple coddling moths. Many of them look like little origami pyramids or houses, with a little entry hole just big enough for the target insect. The pheromones are species-specific, so only one type of insect will be drawn into the trap. Once inside, it can’t get out.

Other types of sticky traps, such as those for mice or rats, should never be used outdoors. Since they are non-specific, they can ensnare non-target wildlife such as lizards, toads, baby skunks and opossums, or birds.

Q. The directions on my Bonide Systemic Granules say that it should not be used on vegetables or other edibles. Will you please explain or clarify why you recommend it for citrus?

A. There are only a very few systemic insecticides that are approved for use on crop plants such as fruit trees. These will be labeled as such. Most systemics are not approved for edibles/crop plants.

When using these or any pesticide, it’s very important to follow the label instructions carefully. Most systemics can only be used within a very narrow time frame, usually after the flowers have fallen off and not too close to harvest time. Treating after the flowers are gone will protect the bees and other nectar feeders. Early treatment gives the pesticide a chance to clear before the fruit is harvested.

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Q. My 30-year-old magnolia tree has been losing lots of leaves and many top branches are bare. We tried adding more water but doesn’t help. Any suggestions?

A. Since you didn’t mention any other symptoms or signs (such as the presence of insects, oozing cankers, webbing, or mushrooms), my first guess would be bacterial leaf scorch. Trees affected by this will look like they need watering, but don’t improve with more irrigation. It’s caused by a bacteria that enters the plant’s vascular system and prevents water from reaching the leaves. Leaf dieback starts at the tips and proceeds down the branch. 

The bacteria is spread by the glassy-winged sharpshooter. In heavily infested trees sticky droplets will fall from the leaves – this is sharpshooter poop.

Unfortunately, there is no effective cure for bacterial leaf scorch. Sometimes you can prune the dead branches away, but if the infection has spread throughout the tree it is probably doomed.

Looking for more gardening tips? Here’s how to contact the Master Gardener program in your area.

Los Angeles County; 626-586-1988;

Orange County; 949-809-9760;

Riverside County; 951-683-6491 ext. 231;

San Bernardino County; 909-387-2182;

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