Help for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Situation: Client visited the Ask A Master Gardener (AAMG) Help Desk at a recent Wednesday morning program at MGCC's “Our Garden” asking for advice on the black spots on the fruit of his mature Meyer Lemon fruit tree. MGs on duty that morning couldn't give him a definitive answer at the time, but asked him to make some further observations about the tree and posed several questions about the health of the tree for him to answer and to send an email with his findings to the MGCC Help Desk.
Client's Response and Request: I appreciate your effort in determining the problems with my Lemon tree,
1. The tree is approximately 25 years old,
2. I bought it as a semi-standard tree. it's 18 feet tall and has a 15' canopy.
3. it's a great -year round producer of fruit.
4. The tree is located about 20' from a building, and it now gets sun all day.
5. I recently cut down a large olive tree that partly shaded the tree and blocked a lot of early morning sun.
6. I don't recall ever seeing spots on the rinds before, I have seen the inside of the fruit that looks darkened and not much juice before. I assumed that it was due to lack of water or fruit being old.
7. I fertilize the tree probably once a year with fertilizer spikes.
8. The bark looks fine.
9. The spotting on the fruit is about 20% of the total, and the leaves look good.
I'll examine the tree closer, but it's been a fantastic tree. I'll send you this now and if you need anything else from me let me know.
MGCC Help Desk Response: Thanks for coming to the UC Master Gardener Program Help Desk at Our Garden with your request for assistance with your Meyer lemon tree and fruit. Quite a few of us have spent time researching your inquiry in the past few weeks; unfortunately, we have been unable to pinpoint a specific disease or cause in order to give you a confident diagnosis.
Here's a list of what we think could be causes for your fruit decline based on our research:
- The change in the sun exposure is likely to have been a culprit, but we don't think that it is the only factor causing damage to the fruit. This problem may be resolved next year after the tree has had some time to adjust to the new light exposure.
- The high continual heat we've experienced this past summer may also have contributed to fruit decline.
- The cold wet winter last year may have caused some of the damage to the fruit.
- Oddly enough, actions you have taken to care for the tree may also have caused problems. See information in the attached link below.
We found an on-line UC article that includes many photos of various types of rind damage on citrus. There is mention in this article of many causes of fruit rind damage including: cold wet weather and frost, copper sprays, fertilizer sprays, wind damage, etc. Please take a look at this article to see if any of these causes may apply to your situation.http://ipm.ucanr.edu/IPMPROJECT/ADS/Fruit_disorders_in_citrus.pdf
We think that the best thing you can do now is to remove all the damaged fruit and give your Meyer lemon the very best cultural care you can and then you'll need to simply wait and see. Citrus are usually very hardy in our area and we think you may see recovery and improvement by next year.
Here are some tips on giving your citrus good cultural care:
- Citrus trees require moisture for growth and fruit production. Apply enough water at each irrigation to wet the soil three feet deep. This requires three to six inches of water depending on the type of soil. Here is a link to information on how to water citrus: http://ipm.ucanr.edu/PMG/GARDEN/FRUIT/CULTURAL/citruswatering.html
- A layer of organic mulch will help retain soil moisture and permits feeder roots to grow close to the surface. Mulch should not be placed close to the trunk of a mature tree.
- Mature citrus trees are given fertilizer to maintain their growth and fruit production. Nitrogen is the chief nutrient required by citrus and should be applied each year. Smaller quantities of phosphorus and potassium are required. These nutrients are held in the soil much longer than nitrogen. Here is a link to information on how to feed/fertilize citrus: http://ipm.ucanr.edu/PMG/GARDEN/FRUIT/CULTURAL/citfertilization.html
- Citrus may occasionally suffer from a deficiency of zinc or iron. When these nutrients are deficient, the tissue between leaf veins turns yellow, but the veins remain green, at least initially. Foliar sprays containing chelated zinc or iron can be used to correct these deficiencies. Iron deficiency can also be caused by excessively wet soil or by very alkaline soil (pH above 7).
- Citrus is ready to harvest when the fruit has colored and is mature. Your 25 year experience should suffice to know when the fruit is ripe... i.e. dark yellow. Fruit should be left on the tree until it attains a satisfactory "sweetness". Mature fruit should be carefully harvested. Any break in the rind will promote decay. Use sharp clippers to cut the stem close to the fruit. Fruit can be stored on the tree several weeks to several months, depending on variety, after it is mature. As you probably have experienced, fruit left on the tree too long will become overripe and can reduce the size of the following year's crop.
We hope you find this information helpful in bringing your lemon tree back to full production. Please let us know if you have any additional questions.
Help Desk of the Master Gardener Program of Contra Costa County (SLH)
Note: The UC Master Gardeners Program of Contra Costa's 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: firstname.lastname@example.org, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/)./span>/span>
Client's Situation and Question: My rhubarb tends to die back in the summer much earlier than I think it should or expect. I know that the soils where it is planted are marginal and I haven't fertilized the rhubarb. I do give it regular water. What is causing the early summer die back? and how can I improve the health, vigor, and survival of my rhubarb?
UC MGCC Program's Help Desk Response: We believe that the rhubarb's early die back may be due to a combination of lack of fertility and Contra Costa County's hot summer temperatures. Rhubarb plants do best if fertilized regularly. If you want to grow organically, you can use a six-inch layer of good compost around the base of the plant. The compost will provide a continuous nutrient source that may last for several months. Rhubarb also responds well to manure, but be sure that it has been well composted since applying fresh manure will burn the plant. You can purchase composted manure at a nursery or home supply store. It can be mixed into the compost before you put it around the plant.
Another contributing cause of the summer die back could be hot summer temperatures. Die back is a common response to temperatures that are too high. Although rhubarb likes plenty of sun, providing some shade on hot summer afternoons may help.
Hope this info helps your rhubarb thrive. It's a great perennial vegetable to have in your garden—does well in desserts but can also be used in savory dishes.
UC Master Gardener Program of Contra Costa's Help Desk (TKL)
Editor: Although this response is written for Contra Costa County gardeners, thanks go to the UC Master Gardeners of Sonoma County for input.
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Note: The UC Master Gardeners Program of Contra Costa's 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: email@example.com, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog at http://ucanr.edu/blogs/CCMGBlog/.