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Citrus Leafminer: Diagnosis and Treatment

Citrus Leafminer

(Phyllocnistis citrella)

 

Citrus Leafminer Overview:

Citrus Leafminer is a common pest for nearly all citrus growers.  The disease deforms leaves and reduces the plants ability to photosynthesize.  Citrus Leafminer can stunt the growth and fruit production of young trees.  In severe cases, Citrus Leafminer infection can even cause total tree defoliation and eventual tree death to a young tree.  The disease has been spreading around the world from its native Asia.  In the year 2000 it was discovered in California for the first time and now it is widespread.

Citrus Leafminer larva

Citrus Leafminer infection: Pictures from UC Davis http://anrcatalog.ucdavis.edu/pdf/8321.pdf

 

Citrus Leafminer Diagnosis:

  • Infected leaves are deformed, rippled and curled but generally remain green.
  • On closer inspection, you will see a squiggly whitish line (sometimes a dotted dark line) on the leaf surface which is a cardinal sign of Citrus Leafminer.  This thin line represents the parasites feeding trail and feces of the Citrus Leafminer.  This fecal streak (yuck) is most commonly found on the under surface of young leaves (see images above and below).
  • However, in cases of severe infections even older old hardened off leaves can be infected.
Citrus Leafminer (Phyllocnistis citrella)

Citrus Leafminer Diagnosis: Pictures from UC Davis http://anrcatalog.ucdavis.edu/pdf/8321.pdf

 

What causes Citrus Leafminer?

  • The disease is caused by the larva of a tiny moth (Phyllocnistis citrella).
  • The larva feeds just under the surface of the leaf.  The thin line that you see is the path where the larva has been… and the poo it has left behind.
  • Since this path of the parasite is located just below the surface of the leaf, this is the larval mine (and thus leafminer has become the name of the bug).  The actual culprit larva can often be found at one end of this mine (see arrow in the picture above).
  • There are often several leafminer larva per leaf; commonly 2 to 3 larva per leaf.
  • At the end of the larva stage, the leafminer will emerge from the mine and will curl the leaf around itself, apparently as a form of protection as it enters its pupa stage.

 

Biological control of Citrus Leafminer:

  • There are many predatory insects that will feed on the citrus leafminer larva. In California many of these parasitoids are generalists.
  • However, there are more-specific leafminer enemies that are found in other parts of the world.  These leafminer specific eating insects are currently being evaluated for importation into the United States.
  • The enemy of my enemy is my friend. – Ancient Proverb

 

Cultural Control of Citrus Leafminer:

  • Since the citrus leafminer larva thrive on young leaves, eliminating new growth during the time that the larva are around may help to protect your tree.
  • Therefore, another important option to control the citrus leafminer is to reduce a summertime leaf flush.
  • The proper timing of pruning and fertilizing will help to prevent the tree from having a flush of new growth during the vulnerable time of the year (summer and fall).
  • Although this option may help, I do not believe it will be enough to fight the onslaught by itself.

 

Pheromone traps for Citrus Leafminer:

  • There are Citrus Leafminer traps which emit a pheromone/chemical that attracts the male moth and then traps the moth.
  • These traps are most often used to monitor the amount of leafminer moths in the environment so to optimize treatment times.
  • However, some people have advocated using them as a primary means of defense.  The rational is that if you pull the males out of the population, there will be no mating and therefore no larva to hurt the plant.  This sounds good, on paper; in fact it was my own personal first step in the battle.  However, for me using the pheromone traps didn’t seem to do anything to protect my plants.   There are just too many moths in the environment for a few traps to do anything significant to the mating population.

 

General considerations regarding insecticides for Citrus Leafminer:

Some people have suggested that you can just leave the leafminer alone and the plant will survive.  However, this option is definitely not my experience.  I have several young citrus trees that took a major hit a few years back and this ‘hands off’ approach is not in any way recommended by me.  Therefore, in my strong opinion, chemical control may be your only option.  None the less, many insecticides are nonspecific and can/will reduce the populations of beneficial insects.  This is always a difficult balance to be mindful of.

 

Citrus leafminer insecticides (options):

Systemic chemicals:

There are several systemic chemicals that you can put directly in the ground to be absorbed into the trees through the roots.  However, I am not thrilled with this option because I am not confident about how long it will be in the plants system or to what degree it will be inside the fruit that I eat.   I would also expect this type of insecticide to dramatically change the soil microbial environment for the worse.

Topical Sprays:

Since the larva is found just below the leaf surface, many topical sprays will not reach the pest.  However, the topical/spray spinosid (which is a natural insecticide) is able to penetrate this leaf barrier and kill the parasite.  In addition, spinosad is supposedly safe for the leafminers natural enemies.  Unfortunately, spinosad doesn’t last that long in the environment and needs frequent reapplication.

Azadirachtin is another natural insecticide that is said to be effective against the leafminer larva.  However, I have not tried that one.

General spraying considerations:

Whatever spray method you use, don’t spray when it is windy outside.  This will waste chemicals and you will likely end up spraying yourself in the process. For me, the air seems to be the calmest around or just after dusk.

There are several scientific papers that say spinosid is safe for bees as long as it is allowed to dry for several hours before bees come in contact with the chemical. This is another good reason to spray in the late evening/dusk.

Also make sure to spray the bottom of the leaves as this is a favorite spot for the leafminers to live. Although I tend to spray the entire plant, new tender leaf growth is the favored target for leaf miners (and most parasitic bugs for that matter). Therefore, if you only had one place to spray, it should be on the young leaves.

I recommend that you get (and label) a separate garden sprayer for each of your different garden needs.  That way you don’t have to worry about leftover residue in the bottle doing damage. For example, you dont want to have leftover toxic herbicide in the bottle mixing in and ending up on a plant that you would actually like to keep around.  It is also nice to have a spray bottle with an angled spray nozzle so you can easily get the bottoms of the leaves.

 

My method of controlling Citrus leafminer:

  • For me, I am most comfortable with the balance struck with the spinosid option.
  • I use to use volck brand horticulture oil with the spinosad to the help the spinosid to stay on the leaf.  I also use the horticulture oil because this oil also helps to protect the plant from a large variety of other parasites.  The mix is kind of a one two punch for the bad bugs.  Overall, horticultural oil is an awesome alternative to systemic pesticides.

 

UPDATE 1/20/14:
Well, I am really disappointed to learn that Ortho Volck Oil Spray has been discontinued by the manufacturer.  I know a lot of loyal customers are bummed at Ortho for discontinuing Volck.   Fortunately, the main/active ingredient in this product is simple mineral oil.  Several other brands have basically the same ingredients.  

Therefore, I am now using “Bonide All Seasons oil” for the same indications that I used Volk oil for in the past (which is basically everything).  

Anyhow, if you are really interested in learning more about the fine details of oil insecticides, the “Using Oils as Pesticides” article is a rather complete outline reference from “agrilife extension” of Texas A&M University. 

  • Specifically, I now mix spinosad and Bonide All Seasons oil  in one spray bottle (by recommended amounts of each as seen on the label).
  • I mark my calendar and spray my citrus leaves every 3 weeks during leafminer season.
  • I was once under the impression that leafminer season was  from mid-June to mid-October.  However, this year, I learned the hard way that the season actually lasts into late November (at least where I live).  This lesson was learned when I stopped spraying in October and a new flush on my beloved Tahitian Pummelo was ravaged by those little suckers (see recent pictures below). I am also hearing reports that the season is starting earlier as well.  Therefore, my new recommendation is to spray your plants from mid-May to mid-November. 
  • That being said, I sometimes spray more frequently when I see a flush of new growth between scheduled spraying times. The new leaves are the main target for the leafminer and if they emerge in that time between spraying then they will be totally unprotected. Also, if it happens to rain between spraying, you might what to spray again, because the rain may wash off the spinosad.

Since I had some trouble finding spinosad in the big box stores, I go to amazon.  This Monterey brand spinosid has worked extremely well for me.  I have also found horticultural oil  to be totally awesome way to address just about every sap sucking bug.

 

spinosid

White leafminer trails and yellow leafminer larva.

New untreated flush attacked by leaf miners on left. Compared to older-protected treated leaves on the right. This damage taught me the lesson to spray with spinosid until November.

New untreated leaf flush attacked by leafminers on left side of this picture. Compared to older-protected-healthy treated leaves on the right. This damage taught me the hard lesson to spray with spinosid until November.

This damage taught me the lesson to spray spinosid untill November.

New untreated flush attacked by leaf miners look sad and curled on the right-forground. Compared to older healthy protected-treated leaves on the left which are not damaged. This damage taught me the lesson to spray with spinosid until November.

Leaf uncurled to show white leafminer trails and yellow leaf miner larvae

This leaf was uncurled to show white leafminer trails and yellow leaf miner larvae

When to treat for Citrus Leafminer:

  • In California, the disease is most active in the summer and fall.  If you are using a ‘natural insecticide,’ such as spinosad, you will have to respray at regular intervals.
  • For example, spray every 3 weeks (as directed on the label) from mid-May to mid-November (see above discussion).

 

Insecticide warning:

  • There are many warnings on every pesticide label.  Read them.
  • Even though spinosad is a natural chemical, it should still be treated with respect.
  • The number one goal is to protect yourself and the people around you.
  • Spray when it is not windy outside to reduce the chance of spraying yourself.

 

Your vulnerable bees:

  • Another insecticide warning that I would like to draw your attention to (which may not be on the label of insecticides)  is about bees.
  • There is a mysterious disease that is killing bees called ‘honeybee colony collapse disorder’.  There are a lot of different ideas about the cause of this disease.  Theories include ideas about habitat loss, parasites, bacteria, viruses, fungi, stress, and pesticides.
  • As a result, I have done some reading on the subject of bees and spinosad.  There are some interesting conclusions from several scientific papers.  Below is a summary from what I have read.
    1. In laboratory conditions, high concentrations of spinosad is toxic to bees.
    2. However, in field studies, spinosad is relatively safe to bees.
    3. More specifically, several papers state that spinosad is harmless to bees if bees come in contact with spinosad after it has dried.

Here are a few scientific papers to reference:

In the 2002 scientific paper, An ecological risk assessment for spinosad use on cotton from the journal Pest Management Science “Spinosad is acutely toxic to bees under laboratory conditions, but toxicity of residue studies and field studies indicate that under actual use conditions the impact on bees is minimal.”

In 2003 scientific paper The effects of spinosad, a naturally derived
insect control agent to the honeybee from Journal the Bulletin of Insectology  “In field studies dry residues of spinosad were safe to foraging worker honeybees, with no adverse effects seen on mortality, foraging behaviour, brood or queen.”

Here is a similar reference from The BCPC Conference: Pests and diseases, Volume 1. Proceedings of an international conference held at the Brighton Hilton Metropole Hotel, Brighton, UK, 13-16 November 2000.

  • All of this seems to basically say that it is best to spray spinosad when the bees are not around.  This will allow spinosad to dry and be safe before the bees are exposed.  Since bees go to their hive at night, this is another great reason to spray your plants in the evening/dusk.
  • To be extra extra kind to your bees, avoid spraying plants that are currently flowering to further reduce any remaining risk.

 

Further Citrus Leafminer reading:

http://anrcatalog.ucdavis.edu/pdf/8321.pdf

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74137.html

http://ag.arizona.edu/crop/citrus/insects/leafminer.pdf

About Thomas Osborne, MD

Dr. Osborne is a Harvard trained Radiologist and Neuroradiologist who loves to share his insight about medicine and gardening.

53 comments

  1. I liked this article so much that I bought Sinosad right away from Amazon and have sprayed several of my citrus trees which have been damaged by leaf miners. I will repeat again monthly. I am very impressed by your knowledge and willingness to share. I will reciprocate over the coming months. Thanks.

    • Thomas Osborne, MD

      Hey Sateesh
      Thanks for the great feedback.
      I am happy to hear that you have found it helpful.
      Looking forward to reading your other comments.
      Thanks!

    • I just found your article and read every word. I have several young tree that were tore up by leaf miners two years ago. I came across the same recipe you use and my trees are great. I’m reall worried as they all have new growth but are also flowered out. I have recently taken up bee keeping and I really want to spray the tree because we have had extreme heat early in Southern California this year. I’m afraid the leaf miner season may start early. I have beautiful new growth but I’m afraid to spray because the trees are loaded with bees. Watching daily for evidence of infestation and have not seen any. Do you have any advice with my predicament?

      • Thomas Osborne, MD

        Hey Mike.
        Thanks for the note.
        Sounds like you and I are on the same page here.

        Possible early leaf miner season:
        I am also concerned that leaf miner season might come early this year with the amount of warm weather we have had.
        However, to date, I have not seen any evidence yet either.

        Bees and Spinosad:
        I also have the same concern about spraying with insecticides when there are flowers to be pollinated.
        Although spinosad is a natural compound, it does not necessarily mean it is safe.

        There are many reports that state that spinosad is harmful to bees.
        However, there are several academic papers that explored this in detail and there is apparently a bee-safe way to use it.

        Their general conclusions are that spinosad is safe to bees if allowed to dry for 3 hours before bee exposure.

        For more info, check some of the academic articles below:

        Spinosad toxicity to pollinators and associated risk.
        Rev Environ Contam Toxicol. 2003;179:37-71.
        http://www.ncbi.nlm.nih.gov/pubmed/15366583

        “The collective evidence from these studies indicates that once spinosad residues have dried on plant foliage, generally 3 hr or less, the risk of spinosad to honeybees is negligible.”

        Heres another journal article with the same conclusion:
        The effects of spinosad, a naturally derived insect control agent to the honeybee
        Bulletin of Insectology 56 (1) 119-124, 2003
        http://www.bulletinofinsectology.org/pdfarticles/vol56-2003-119-124miles.pdf

        So based on those articles, it seems that it is ok to use spinosad as long as you time your spraying so it has 3 hr to dry before the bees are around.
        Therefore, spraying at dusk, after the bees go to bed, seems to be one good option that would give plenty of time for spinosad to dry and be safe for bees before they come out again the next morning.

        Please let me know if you hear/see anything more on the topic.

        Best,
        Tom

  2. Hi Dr. Osborne.

    Love your article about leaf miners. I planted a few citrus last year and a few had been damaged by leaf miners. I also ordered your treatments from Amazon. I’ll treat the citrus next week.

    Thank you for your research and articles.

    Betty

  3. Hello !! I live in La Crescenta and have read what you say about the citrus leaf miners with great interest. I am wondering when you would say is the proper time to fertilize and prune the citrus trees to try to avoid the leaf miner infestation. I have had my trees for several years and have been fertilizing per package instructions once monthly from January to September. As for pruning, I snip off a few leaves or a little branch or two or three about once or twice a month, mostly removing the disfigured leaves. Since it’s always the new growth that I have been removing, I’m thinking that maybe I am interrupting the trees’ cycles, and that it’s not good for the trees to be forced to depend only on their old leaves. How harmful is it, do you suppose?

    • Thomas Osborne, MD

      Hey Kathy

      Thanks for the great questions.

      What is the proper time to fertilize your citrus?
      The idea of managing your fertilizing schedule in relationship to the leaf miner season has to do with the timing of new leaf growth.
      Young leaves are the most susceptible to leaf miner infection… and fertilization will encourage new leaf growth (flush).
      Producing young leaves is costly for a plant and if those leaves are not working to their full potential because of a leaf miner infection), then the plant gets a poor ROI (Return On Investment).
      So if you can time the fertilization in such a way to avoid the leaf miner season (June to October), you can avoid a lot of negative issues (in theory).

      However, this is a tricky issue because depending on the type of fertilizer you use, there may be a variable amount of lag time for its growth stimulating effects on your tree.
      Different citrus trees also respond differently to the growth stimulating factors of fertilizer.
      So to use this technique, you really need to know how your particular plants responds to the specific fertilizer you use… so you can schedule and account for the lag time of the trees growth response.

      Hot weather:
      However to further complicate things,
      Warm/hot weather will stimulate a leaf flush regardless of your fertilizer timing.
      Furthermore, when it is really hot your trees will need/demand additional watering, which may also stimulate new growth.
      Finally, since the summer is the best time to get your trees to grow, you may not want to put the brakes on that growth opportunity.

      Important side note:
      Young leaves are also the most susceptible to the damaging effects of cold weather.
      Therefore, I try to avoid fertilizing in a way that would promote a cold weather (winter) flush.

      So what do I do?
      I try to do the major fertilizing in early spring and right about now (early fall).
      I do give smaller amounts of fertilizer through out the growing season.
      I also will fertilize or augment at just about anytime if I notice signs of a particular nutrient deficiency.

      I also spray with the spinosad-oil mix that I have outlined in the article.
      I spray every 3 weeks during the leaf miner season (however, if you get a flush of new growth after you spray then those leaves that popped up between spraying will not be protected… Therefore, I am starting to think that more frequent spraying (at least for the new growth that come out just after spraying) might be a good idea.

      The most important thing to do is spray the young leaves, esp the under-surface of the leaves.
      However, I spray the whole tree because that spinosad-oil mix will also take care of other pests such as scale, aphids, etc.
      This spray is by far the best thing I do to fight leaf miner.

      Pruning citrus leaf miner infected leaves:
      Pruning plants (of any kind) can stimulate new growth.
      This is not the best option during leaf miner season (see above discussion).

      However, this brings up the issue of pruning leafminer diseased leaves.
      In general, I would leave the leaf miner infected leaves alone.
      Even though they look sad, and likely don’t bring in half the amount of energy as a non-infected leaf, they do bring in some energy.

      Very early on in my growing experience, I red somewhere on line that you should remove citrus leaf miner infected leaves (I dont do this now).

      Therefore, at that early time, I tried to remove all of the leaf miner infected leaves on a tree (this is before I discovered my spinosad-oil spray mix).
      By the time I was half way through the process, I realized that this was a loosing battle and I stopped.
      However, as a result I my pruning, a new flush of leaves came out soon after that and all of those leaves were systematically ravaged by those freekin leaf miners.
      You just can win this way.

      Pruning citrus at all:
      Overall, pruning a citrus tree is a rather controversial topic.
      There are people who stand strongly on both sides of the issue.
      Some people say you don’t ever have to and/or shouldn’t trim a citrus (except to remove dead branches).
      There are also others that have outlined extensive methods of creating the ‘perfect’ pruned structure for a citrus tree.

      So where do I stand?
      I dont think you can lump all citrus trees into the same bucket when it comes to this issue. I think there is a lot of variation in the way each different citrus tree grows and responds to environmental factors.

      However, if I was to generalize…
      I will always remove dead branches and suckers below the graft union.
      I will trim/prune a citrus tree if it is getting in my way (making it difficult to walk on a path for example).
      I will trim off broken branches (broken branches can often be prevented if you remove some fruit from a heavily-weighted down over-burdened branch).
      I will not trim a citrus to ‘open it up’ to the air in the way you would for a stone fruit (peaches, plums, apricots, etc).

      I don’t intentionally trim to expose the trunk of my citrus trees to direct sunlight. Many have advocated this method, but I think it is a terrible idea. Citrus bark is thin and can easily become sun burnt. If you must expose your citrus trees trunk to direct sunlight, I would paint the trunk white to protect it from the sun. I would use the same method that I use on fig trees (I talk about this in my Mission Fig Tree Cultivation article.

      Hope this helps.

      Best,
      Tom

      • I’ve tried treating my citrus leaf minors with 1/3 cup Murphys Oil soap per gallon of water. I’ve been spraying once a week. It seems to be helping. It is also very cheap. Have you heard of this? Thanks Keith

        • Thomas Osborne, MD

          Hey Keith
          Interesting question.

          A lot of people use diluted soap to treat plants for various bug infections.
          However, I have not heard of anyone using this method for leaf miners.
          The problem with leaf miners is that they do their damage just under the surface of the leaf and therefore most topical applications wont touch them. I suspect this would be the same issue with soapy water… it just would not penetrate the leaf surface to get at them.

          If you are not seeing evidence of leaf miner infection now (and you live in the Northern Hemisphere) it is because this is not leaf miner season. Fortunately, you dont have to spray at this time of the year for leaf miners. However, we will start spraying soon… Spraying times are outlined int he article

          Best,
          Tom

  4. Sorry !! Forgot to give you my name. Kathy

  5. You went to so much trouble to write this detailed response. Thank you so, much !! So much information. I made myself a little calendar to help me remember all the dates (times of year) you mentioned. Fortunately, just from my own instincts I have already been following the do’s and dont’s of your pretty conservative pruning instructions. It’s going to take some serious self-discipline on my part though, to resist taking off those ugly leaves when I see them in the summer. You’re asking a lot !! :^)

    Thanks again !!
    Kathy

  6. I just wanted to say it was a pleasure to read your websiteand thank you for sharing your wisdom

  7. I just found that spray you bought on amazon.com for $33.99 at a different place for $16.95 on the link below with spinosad in it.

    http://www.ghorganics.com/ghsmailfaxorder.html

    • Thomas Osborne, MD

      Hi Valerie
      Sorry that I am just getting back to you now-I was out of town giving a lecture.

      Thanks for the info, it is always great to have more options.

      However, the spray you are looking at for $16.95 is for a 16 oz bottle.
      The one I have linked to on Amazon is a 32 oz bottle and (at the time of this note) is selling for $33.25.
      Therefore, the one on Amazon is a tad cheaper per unit volume.

      In addition, the one you have shared the link to has a shipping charge of $8.
      The one on amazon ships for free for orders that are over $35.
      Therefore, if you spend another $1.75 on Amazon when you buy the spray that is already cheaper… you then also save an additional $6.25 ($8 – $1.75).

      Best,
      Tom

  8. I guess I’m banned from here every time I try to comment it says I can not comment. What did i do????

    • It says that I already made a comment so a person can only make one comment on this website? Is this prejudice or not? I thought I would help and find a cheaper place to purchase Spinosad, but I guess I’m not welcome here. And note it said that the first time I tried to make a comment I’m surprised it let me make this comment and the one above. PREJUDICE or what????

      • Thomas Osborne, MD

        Hi Valerie

        I do have my website comments set up so I have to approve the comments before they are published.
        I do this to prevent spam… and there is a lot of it out there.
        However, if a comment is not spam and not offensive I am pretty open to publishing any sincere comment.

        Every nice plant lover is very welcome here.

        There is definitely no prejudice here, just trying to create a collegial and open platform for the sharing plant knowledge.
        I am sorry to hear about your technical problems, this is the first that I have heard of it.
        I was out of town for a bit, so this would be a result of a delay in your comment being published but not a total block.

        best,
        Tom

    • Thomas Osborne, MD

      I am not sure what you did.

  9. A question about your Spinosade to oil mix: If the Spinosade ratio is 2 fl oz per gallon and the Oil ratio is 5 fl oz per gallon, do you mix a combined total of 7 fl oz per gallon, or mix them separately and then combine them for a total of 2 gallons?

    thanks,
    Justin

  10. Is the fruit from a tree infected with Citrus Leafminer safe to eat?
    Thank you for all the help!

  11. Hi Dr. Osborne,
    Thanks for your advice about citrus leaf miner management. Since it is early in the season, it sounds like I can plan ahead and spray the spinosad/all season oil in late May/early June to protect my citrus in San Diego. It’s mid-February and I’m already seeing a lot of tender new growth on my citrus. I will follow your plan to continue until the end of November, at 3 week intervals with the spray. <– hopefully I am understanding your advice correctly. Please let me know when you have a minute!

    My other question is this; can you tell me about what is called, 'cocktail grapefruit'? From what I read on the plant label, it is a cross between a grapefruit and a sweet orange. Have you tried any? This is the first time I've heard of it. Just wondering. Thanks!

    • Thomas Osborne, MD

      Great questions Cynthia

      Leafminer season:
      There is definitely a leafminer season… Which is basically every season but winter. However, I have noticed that the season is getting a little longer each year. I am not sure if this is the bugs adaptation or global warming or something else. Just an observation. I try to keep the article up to date, so if you follow whats in the article, you should be in good shape. But yea, spray every 3 weeks as described. If it rains, you may want to reapply in the interim.

      New winter growth:
      I have noticed the same. Its because of the unseasonably warm weather we have been having. Warm weather stimulates citrus growth. On one hand this is great because no leafminers to worry about this time of year. However, if we suddenly get a cold spell then those young leaves will be the most sensitive to damage.

      Cocktail Grapefruit:
      I dont have one of those but my neighbor does.
      Heres some info from the UC Riverside website: it is a hybrid cross between a Siamese Sweet pummelo and Frua mandarin that was developed at UC Riverside in the 1950s and never intended to be released to the public. The fruit tends to be very seedy and juicy. Apparently some people either love it or hate it.
      http://www.citrusvariety.ucr.edu/citrus/cocktail.html

      • You might want to check the pages on Tahitian pomelo and Valentine pomelo for some info on growing pomelos or persuasion to grow these two.

  12. You have an excellent website. Are there any temperatures that would cause you to refrain from spraying? I have read that horticultural mineral oils aren’t recommended when it’s very hot. Thank you for your experience.

    • Thomas Osborne, MD

      Hey Brett

      Thank you for the great feedback and your excellent question.
      I have read the same about how you should not spray oil in the heat of the day because it can burn leaves.
      Although, I havent tried to spray horticulture oil during the day to test this idea.
      None the less, since I have seen this warning in so many places, I would think there is some merit to it.
      Better safe than sorry.
      For me, I only spray in the evening because its is more pleasant for me to do when it is cooler outside.

      Best,
      Tom

  13. My tree specialist told me about this site, after diagnosing a heavy leafminer infestation. Here in Phoenix we had a very warm February, the pesky little critter hit my lime tree in early to mid-March. By the time I noticed it (tree is in an out-of -the-way place in the yard), I’d completely lost an entire branch, including some fruit that had already set. This was a major hit to the tree, and will require some good fortune to recover and develop another main branch. Moral of the story, start looking early in the season.

  14. Hello Dr. Osborne,

    First and foremost, thank you for taking the time from your busy schedule and sharing so much valuable information so thoroughly. I have not seen this level of knowledge and detailed instructions in most gardening sites where I used to look for answers. well, no more! I have found my new home. Thanks to you.
    I came across this site and your blog quite by accident. I was searching for ways to make my beautiful 4 year old Bearss Lime tree to produce again. It produced nicely the first year and some in the second year and has been fruitless for the past 2years.
    It is in a nice full sun location, in well drained soil. I have not fertilized it much. Just an occasional Citrus and Fruit tree food. Should I fertilize it to force it to flower?
    Also, three weeks ago I purchased this beautiful Myer Lemon from my local nursery in a 2X3 feet huge wooden container. At purchase time the tree had some interior leaves that were yellowing. Just a clean solid yellow. No dots or blemishes. They told me it may be due to stress. I suspected overwatering may have been an issue as well. A few days ago I fed it the proper amount of Ironite and am carefully monitoring it. I see some faint greening, I think! Some of the younger fruit are yellowing and falling off, but the tree has a few stages of fruit on it. The larger ones are doing alright. Any advice?
    Sorry for the long dissertation. Looking forward to hearing from you soon.
    All the best.
    Raffi
    P.S. Is it possible to upload photos to our comments?

    • Thomas Osborne, MD

      Hi Raffi

      Your very welcome
      Thank you for the kind comments.

      What part of the world do you live in?
      I ask because some potential citrus problems could be regional.

      Bearss lime:
      Unfortunate dilemma you have.
      Fruitless for 2 years is a sad situation.
      In optimal conditions, they should produce all year.

      Few questions:
      Do you get flowers on your Bearss lime?
      What do the leaves look like?
      Is the bark ok, is the bark pealing?
      What growing zone are you in?

      How often do you water and how much… How moist is the soil?
      When is the last time you fertilized it?

      Meyer Lemon:
      The tree does sound a bit stressed.
      Growing in containers is challenging… less room for error with watering, fertilization, etc.
      Is the tree root bound?

      Photos:
      Photos would be great. However, I do not have that option. Do you have some other way to upload images on the internet such as pinterest?

      Best,
      Tom

  15. Hi Tom, Have my spinosad and oil ready to go and a leafminer male trap out on the Washington Navel. Have noticed some minor activity so have been spraying any new flush with “pre-mixed” bottles from Armstrong. Somebody made a comment on another website and said to be sure and put “surfactant” in the mix of oil and spinosad when used in a sprayer. Not even sure what he is talking about. Any comments on that? Thanks in advance.
    Paul

    • Thomas Osborne, MD

      Hey Paul.

      Good question.

      Beads of water on the surface:
      When you spray water on something waxy (like a leaf) you might see little beads of water form on the surface of the leaf.
      This might look something like a car wax advertisement.
      Many leaves are built this way so they will stay dryer and cleaner (like a car after it is waxed).
      When a leaf is clean and dry, a leaf will be able to receive more sunlight and at the same time be less susceptible fungal infections because the leaves dry quickly.

      Surface tension:
      So part of the reason why water does this is because there is surface tension on the outer surface of a water droplet.
      This physical property of surface tension becomes most noticeable when water interacts with a hydrophobic material such as wax or oil.
      A surfactant will reduce the effects of surface tension… and therefore when you add in a surfactant, there will be less beading of water on the surface.

      Practical issue:
      This is important when you want liquids to stick to the surface of a leaf and be applied evenly.

      Types of surfactant:
      There are many different types of surfactants that work differently.
      However, soap is probably the most common type of surfactant.

      Specific plant treatment example:
      When I spray to kill weeds with vinegar, I add in some soap to the vinegar.
      This makes a huge difference in the effectiveness of the vinegar.
      See my article on organic weed control for more specific info on this technique.

      Necessary?
      So, in theory adding a surfactant to a spinosad spray would help to apply the treatment more evenly on a leaf surface.
      However, in practice, I have not found this to be necessary.
      I have been using the leafminer spray as described in the article for years and it has always done the job without a problem.

      Hope this helps.

      Best,
      Tom

      • Thanks Tom. Excellent explanation. Kind of like unwaxing your car so more of the sun and elements get into the paint. (<:

  16. I have a flush of growth right now and have been spraying every 5 days or so. What is the maximum frequency tht you have sprayed? Every night? At Raffi, I too have a Bearss lime tree that hasn’t produced. I blame it on the leaf miners, because at first it tried but they attacked it incessantly and it hasn’t dome anything since (about 2 years). Dr. Osborne, I’m surprised that the Argentine ants don’t cause you more problems. You can’t put Tanglefoot on everything.

    • Thomas Osborne, MD

      Hey Brett
      Thanks for the note.

      Citrus Leaf Miner:
      Yea, leaf miners are a real problem.
      Most of the time I spray every 3 weeks.
      If it rains or there is a new flush I will spray more frequently.
      I try not to spray more than once every 2 weeks.

      Bearss Lime producing:
      Massive leaf miner attack can definitely do a lot of damage to a tree.
      So I would not be surprised if this was part of your dilemma.
      However, it could also have something to do with the age of the tree.
      I have a Bearss lime tree that wasnt doing much for about the 1.5 year after planting.
      Then it got settled in and really took off.
      Now it is about 10 feet tall (started at 3 ft tall 3 years ago) and produces nearly all year round.
      My methods are outlined in the Bearss lime article below.

      Ants:
      Yes we have ants… lots of them.
      They do cause a lot of problems with the aphids, scale, etc they carry around and farm.
      However, that leaf miner spray mix (kills a lot of bad guys) as well as tanglefoot keep them in check.

      Best,
      Tom

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