Nursery and Floriculture Alliance
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Nursery and Floriculture Alliance

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Who's Been Mining My Citrus?

Advice for the Home Gardener from the Contra Costa Master Gardeners Help Desk

Description of the client's problem:

Typical Leafminer damage to
young citrus leaf
The client has citrus trees that are not doing well. It looked like a pest, but she couldn't detect any insects. There are deformed and curling leaves with curvy track marks, especially on the new growth.

Advice From the CCMG's Help Desk:
The pest that is causing the new leaf growth on your citrus trees to curl is most likely the Citrus Leaf Miner. The adult stage is a very small moth, which lays eggs on young citrus leaves. When the larvae emerge from the eggs a week or so later, they bore into the leaves and begin feeding, leaving minute trails observable on the surface of the leaves. As the larvae grow, the trails become more pronounced and noticeable.

Adult Citrus Leaf Miner
Phyllocnistis citrella
size: ~ 1/4"

After feeding for two to three weeks inside the leaf tissue, the larva emerges and enters a pupal stage. At this point, the leaf curls over the pupa to protect it. The pupal stage lasts from one to three weeks. Because the life cycle moves so quickly (between three and seven weeks, depending on the ambient temperatures), multiple generations of the pest can develop in warm weather.

You can see photos of the leaf miner moth and the damage it causes at this website: website also contains information about management of this pest.

Typical damage to
young citrus shoots
Except for the aesthetics of the damage, mature citrus trees (those over four years of age) can usually sustain damage from leaf miners with relatively little effect on the overall health of the tree and without loss to fruit production. Less mature trees (under 4-5 years) or trees that are heavily infected may sustain bigger setbacks, but leaf miner attack is rarely fatal.

Since the leaf miner pest typically attacks only the new leaf growth regardless of the age of the tree, there are some cultural strategies that you can use to reduce the prevalence of the new growth, such as limiting pruning to once a year (pruning encourages new growth), going easy on fertilizing, and not over-watering. Past experience with this leaf miner indicates that we might see a year or two of damaged trees as it has only just arrived in our area, but as the natural enemies develop, it should be less of a problem. Use of pesticides is not recommended at this time and in most instances would be ineffective because the miner is inside the leaf and it may kill off beneficial insects.

Hopefully this information answers your question and will help you managing this pest. Please do not hesitate to contact us again if you have questions.

Contra Costa Master Gardeners Help Desk

Note: The Contra Costa Master Gardener Help Desk is available year-round to answer your gardening questions.  Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA  94523. We can also be reached via telephone:  (925) 646-6586, email:, or on the web at


Posted on Monday, December 22, 2014 at 12:27 AM

Daily Life For Master Gardeners



Bat Blind

By Andrea Peck


The topic of bats came to me while perusing Facebook.  I was scrolling away in that semi-conscious stupor that accompanies non-intellectual internet pursuits and there it was: a little cutie patootie. Or in actual English, a cute animal picture. This was unlike any other animal picture I've seen before. This one was a bat. Sure, it was a baby bat, but seriously when did bats get so cute? When I was a youthful teenager, all bats were menacing creatures with rabies. They even flew down low and got caught in your hair. On purpose. That's what my dad told me, anyway. The only cute bat that I know is Stellaluna, but then again, she thought she was a bird.

Well, I stand corrected. Bats have cuteness potential.

Most gardeners are aware that the horror flick version of aggressive, blood-thirsty bats is a slightly hysterical view. That doesn't change the fact that bats are simply unappealing. It's probably those crescent-shaped claws and rubbery wings – oh, and the freaky color. The skeletal physique that wraps around contortionist-style doesn't help. The picture below illustrates my point. I mean, the anatomy!


On the other side of the spectrum, bats are prized for their voracious insect appetite. They'll eat what happens to be on the menu for the night whether that be cutworm moths, chafer beetles, potato beetles, spotted cucumber beetles (yum!) or the dregs, mosquitos, midges and flies (yuck!). An average colony of insect-eating bats can eliminate 100 tons of insects in one season. Per night, the average bat consumes ¼ to ½ its body weight in insects.

Bats serve a significant ecological purpose particularly in the rainforest. Fruit eating bats disperse seeds over miles as they fly during the night hours. Nectar feeding bats pollinate fruits such as, bananas, mangoes, dates and figs. In desert areas, bats are the main pollinators of the pipe organ cactus and the agave. Insect eating bats protect plants by controlling pests that are out past their bedtime. California is home to 25 types of bats, 23 of which are insectivores. The other two survive on pollen and nectar.

Perhaps part of the dark mystique that surrounds the bat is its hours of activity. Bats are nocturnal creatures, leaving the roost when you're just heading in. Insects, their main meal source, are most active during the early evening hours. Echolocation allows them to use sound vibrations to determine distance, speed and even identification of some prey. Rainy weather stops the bat short, however. Apparently the rain interferes with their ability to echolocate.

Because of the bats ability to hunt insects, many gardeners erect a bat house and hold an open invitation to the local bat society. It is important to remember before you purchase a bat house for, say, $3.00 at a yard sale, that you know about bats – the whole picture, not just the glorified version.

First, bats don't like their houses placed on poles. That answers the question that I've had for the last few years: why have no bats moved into my bat house? I have it in the yard. It's on a pole. I painted it black like that one article 4 years ago told me to do. No takers.

Bats like to live on a structure. The pole is cold and when they have their hairless young, they get cold and you know that moms of all species do not settle when baby isn't happy. The bat home must be 12-18 feet above the ground. Not in a tree, though. Too many predators.

But, we're skirting the issue. After reading a bit about bats, I am somewhat happy that my black-bat-house-on-a-pole did not lure in Ma and Pa bat. This is why: bats do carry disease. Yes, rabies is a reality – though a slight one. But, because I have kids and they (or one of their friends) would probably climb that pole and grab those bats by their hook-wings, I am probably very lucky that we did not get any renters.

The chances are low that 1) your cute bat has rabies and 2) you will be bitten by this rabid bat, but the chance is there nonetheless. And if you are pretty relaxed like me, you'll think, oh, its nature and they have those stomach shots. We have modern medicine, right? Yes and yes, but rabies can be fatal. In fact, it is always fatal unless treated.

So that stopped me short.

Bats are wonderful and necessary animals. Currently, the number of bat colonies is in decline and if you have a large garden or own land where you can place a bat home, then your story is different. But, for me, in a small home, with a small garden, kids and pets, it is best not to encourage that close of a connection.

If you happen upon an injured bat, or one that is on the ground, let it lay there protected for a while and see if it recovers on its own. Sometimes bats will tire during migration. If it is cold, place a box or other simple structure over the bat until it is able to warm up and continue on. Never touch a bat, rabies is transmitted through a bite. Use gloves if you must handle a bat. If you have come into contact with a bat, seek medical attention. Often a bite goes unnoticed, so don't take any chances.

Now, if you are in the clear and you want to attract those night stalkers, there are a couple of other things you can do to your garden to make it more welcoming. Plant night blooming or night scented flowers. Below is a list:

Salvia Nicotiana


Evening Primrose
Nightflowering/Silene catchfly
Purple coneflower
Four o'clocks
Aromatic herbs
Butterfly Bush

Place a bird bath or source of water within a ¼ mile of the bat house. Change the water regularly. Encourage the growth of sheltered areas along fences where vines or hedges meet; these may provide additional roosting sites.

Also, keep the nightlight on – it will serve as a bat buffet. Just make sure to keep a little distance.

For more information take a peek at the UCIPM pest notes:





Posted on Sunday, December 21, 2014 at 12:23 PM

Tree Pruning


Prune With a Purpose

By Kim McCue  UCCE Master Gardeners


Several of my neighbors trim all the branches off their Mulberry and Crepe Myrtle Trees.  I think it's unsightly, but should I be doing the same?  Ann M., Paso Robles


The answer is no; emphatically, no!  Based on aesthetics alone the argument can be made against pruning trees to within an inch of their lives, but you should know such severe pruning of mature trees actually does jeopardize the trees health and creates more work in the long run.


The practice of topping trees, sometimes called “hat racking”, is usually done to reduce size by cutting all branches to a stub.  Ironically, topping actually stimulates vigorous upright growth all around each cut.  That new growth is anchored in just the top layers of parent tissue.  As a result, a single sturdy branch is replaced by multiple branches that are weakly attached to the tree.  As you can imagine, this creates a dense canopy of branches that are easily broken off making them hazardous and messy. 


Topping trees is detrimental to the trees health in many ways.  Large, open cuts are ripe for disease and pest invasion.  Drastically reducing the canopy exposes bark that was previously shaded, possibly resulting in sun scald.  The ensuing flush of dense, new growth inhibits air circulation, again making the tree more susceptible to disease.  All that tender, new growth is also preferred by many insect pests that are not able to feed on the mature, hardened wood that has been cut away. 


If handled properly and planted in a suitable site, mature trees rarely need much pruning.  If reducing size is a must, thinning cuts produce the best results by removing a branch at its origin or shortening it to a lateral growth bud.  This allows the tree to maintain its natural growth habit and does not usually encourage a flush of vigorous growth. 


Aggressively topping leaves you with an unattractive tree that now requires frequent pruning to manage the abundant growth and ensuing issues that go along with it. So be kind to your landscape trees and prune with the purpose of maintaining their natural beauty and their health.  For more information on pruning techniques please visit:

Posted on Sunday, December 21, 2014 at 12:09 PM

Daily Life For Master Gardeners

Weedy Weather

By Andrea Peck


Hot, cold, drizzle. Hot, wind, rain! Make up your mind, weather! This year has been the most schizophrenic of years. One minute it is apocalyptically warm, my face purple-red from sun irritation. Rapid aging is imminent. The next we are getting monsoon-style rains that partner with gale force winds. Make no mistake about it, this year we have Weather.

And there's one thing that's lovin' it: my weeds.

By loose definition, a weed is any plant that you pretend does not exist in your yard. It is an uninvited intruder that sucks the very marrow out of your soil, stealing nutrients, water, soil and space. Often the term is associated with a certain strength, an incalcitrant insistence that it reside where you least want it to. Weeds are plants on the spectrum. They are prone towards oppositional defiance disorder. They proliferate assiduously (one small plant can have 1000 seeds). Their large families appear here, there and everywhere. They are formidable, tolerating your conditions with aplomb. You have to admire their pluck.

But, how do we handle them?  I thought I was doing the right thing during the summer by loading on the mulch, but these new weeds are undeterred. They are thriving.

The first step in weed reduction, (I say reduction, because you are unlikely to eliminate all weeds) is to identify your enemy. One way to do this accurately is to utilize the UCIPM Weed Photo Gallery:

This link allows you to identify your plant with a series of categorized photos and descriptions.

After you identify the offending weed, you can glean information about its lifecycle and habitat. From there you can decide on a course of action. Knowing whether your weed is annual or perennial makes a difference. For example, you may have a particular nuisance weed that you are ready to waste a whole pound of herbicide on. But, if you find out that this weed is at the end of its lifecycle you might save the effort and allow it to run its course.

Most weeds, no matter the sort, are best plucked early on. Whatever your method, strike early - ignoring the problem and allowing the weed to grow into a large, robust and fertile plant is a mistake. Certainly letting it get to the point of flowering is a recipe for disaster.

Mowing, hand picking, hoeing, tilling, mulch and landscape fabrics fall under this blanket term of mechanical methods, though mulch and landscape fabrics are preventatives also.  We all know that mulch is a must, but did you realize that the particle size of your mulch is important? Choose mulch that is medium sized. Large blocky wood chunks allow water and light through. The larger spaces also accommodate those wind-blown seeds, allowing them to settle in and sprout. Mulch that is made from material that is overly small provides a nice bed for seed germination.  One problem is that perennial weeds are often able to overtake the suppressing power of mulch. Be aware that some varieties of mulch deplete soil of nitrogen temporarily.

Mowing is a good solution for broad leaf plants and annual weeds. Perennials often take several years of mowing before the problem is controlled. Tilling and hoeing are suitable methods, but care must be taken with neighboring plants that you want to keep – over tilling can damage roots which slows plant growth or destroys the plant.

Black plastic is a fine solution for annual plants, but perennials may suffer because the plastic does not allow for adequate air and water circulation. Weed cloth adds an extra layer of protection underneath your mulch. The thickness prevents light penetration and is usually made from material that resists weeds underneath the surface.

Chemical methods or herbicides, are used to control, suppress or kill weeds by interrupting plant growth. Before using an herbicide, it is important to read and understand the label and follow directions carefully. Only recommended amounts should be used. Herbicides should not be used on plants that are not included on the label.

As a last note, there are many more methods that work towards reducing weeds in your garden. But when the weather is tumultuous, the chance of weed growth rises exponentially. Suddenly you find yourself unable to control what is watered and what is not. Weed seeds get pulled into the atmosphere, fly for miles and somehow land in your own Garden of Eden. Ah, the circle of life.

Certainly, you cannot control Mother Nature and this year she travels via the Pineapple Express, so batten down your hatches and watch for strange growth in spring.

Posted on Wednesday, December 17, 2014 at 9:05 PM

5 Ways NOT to Poison Friends & Family During the Holidays

Guacamole and salsa shouldn't be left out for longer than 2 hours.

‘Tis the season for gathering with friends and family and eating. Whether you celebrate Christmas, Hanukkah, Kwanzaa or Festivus for the rest of us, many of us invite people to our homes during the holidays and leave food out to graze. Leaving...

Posted on Wednesday, December 17, 2014 at 1:25 PM

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