Advice from the Help Desk of the
UC Master Gardener Program of Contra Costa County
MGCC Help Desk Request:I am located in Central County. I am having issues with my lemon tree. I have attached some photos. I was hoping you could give me some advice.
I have never sprayed pesticides. I am hoping for a more organic solution to the issues. I know it might not be possible.
I have not fertilized it this year. It is on our sprinkler system so it gets water daily. Some of the leafs have spiderweb looking substance under the leafs. Some leafs are yellow. I have also noticed the spikes are very large. Thank you so much for your help.
MGCC Help Desk Response: Thank you for contacting UC Master Gardener Program with your lemon tree questions and for sending the photos. The symptoms you are seeing could be the result of various minor problems that occur on citrus. The curled leaves show signs of citrus leaf miner. Citrus leaf miners are moth larvae that create shallow tunnels in young leaves. They can distort the leaves but are generally not harmful to the tree. You are probably seeing the end result of leaf miner damage that was done previously. For more information on citrus leaf miners, see: http://ipm.ucanr.edu/PMG/PESTNOTES/pn74137.html.
We are not sure about the spiderweb type substance. It could be from an insect, e.g., whiteflies, but if so you should also find sticky areas on the leaves. Also, any pictures of the insect would be helpful. It is also possible that there are spiders on your tree. If that is the case, I would not worry. If you want the spider identified, see if you can get a photo and we will try to identify it.
The fruits look like they may have been damaged by the thorns which you indicated are very large. That would happen if the fruits were rubbing against the thorns. Is that possible? If not, another possibility would be herbicide damage. Is it possible that herbicides were used anywhere near the citrus tree? Even your neighbors? Make sure you remove the damaged fruits from the tree before we have any more rain. The damaged areas provide an opening for fungi and other diseases to get into the tree. Also, large thorns might indicate that the branch is a juvenile branch or is coming from below the graft, the "bump" near the bottom of the trunk. If from below the graft, you should consider removing that branch as it probably will not produce edible fruit.
The spots on the leaves may be from a fungus. The fungus may be the result of the watering, especially if the sprinkler system is putting water on the leaves. Make sure that the sprinkler is set low and also make sure that the sprinklers are not dampening the tree trunk. Wet tree trunks can lead to root or crown rot from fungus growing around the roots and crown (where the roots and trunk meet). Root and crown rots are serious diseases that are difficult to treat and can ultimately kill the tree.
The daily sprinkling may also be causing other problems for the overall health of your tree. Daily watering might not be supplying the citrus with enough water. Citrus, like most trees, do best with less frequent, and deep watering to promote stronger roots. To give you an example of how infrequent the watering should be, watering in the heat of summer should be done about every seven to ten days. This would be for citrus planted in the ground and with several inches of mulch under the tree out to drip line. In a pot you would need more frequent watering as they dry out faster. If other plants on your irrigation system need frequent watering, you should consider setting up a separate irrigation system on a different timer for the lemon. For more information on watering citrus, see: http://ipm.ucanr.edu/PMG/GARDEN/FRUIT/CULTURAL/citruswatering.html.
You mentioned that you had not fertilized the tree this year. Yellow leaves are a common sign of a lack of nitrogen. Citrus trees require regular fertilization, especially with nitrogen. The fertilizer should be applied in January or February (prior to bloom) with a second application in May and perhaps a third in June. This link has more information on fertilizing citrus: http://ipm.ucanr.edu/PMG/GARDEN/FRUIT/CULTURAL/citfertilization.html.
Finally, I thought that you might be interested in this general write-up on growing citrus in Contra Costa County: http://ucanr.edu/blogs/slomggarden/blogfiles/4260.pdf
Please let us know if you have any remaining questions. You are also welcome to bring plant samples into our office if you want more information. We are open Monday to Thursday, 9am to 12 noon.
Good luck with your lemon tree..
Help Desk of the UC Master Gardener Program of Contra Costa County (ECS)
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: ccmg@ucanr.edu, 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/).
Advice From the Help Desk of the UC Master Gardener Program of Contra Costa County
Client's Question: The photos show what several of my dwarf lemon tree's leaves look like. I had several leaves look the same last year, but I thought it was just a one-time occurrence and would go away when I took them off the tree awhile ago. However, as you can see on the picture, the condition is back. What is it and what can I do to protect the tree and fruit.
Response from the UC MGCC Program's Help Desk: This condition n the photo is not a disease. It is caused by an insect that,during its immature stages, burrows (“tunnels”) in the leaves. The insect is called a Citrus Leaf Miner. When it becomes an adult and exits the tunnels, it is a moth. Although the burrowing causes the leaves to become distorted, the leaves still provide food for the plant, so you should not remove them. There will not be any lasting damage from this insect. There is not any spray that can prevent this, because the insect larva is protected inside the leaf. The best way to reduce the infestation is to not fertilize your citrus during summer or fall, since this is the time the moth is active. Fertilizing causes new growth, and the new leaves are much more susceptible to the Leaf Miner than older, hardened leaves. Citrus should also not be pruned during this time, again because pruning also causes new leaves to emerge.
Citrus should be fertilized before bloom (January or February), and again in May. If fertilizer is needed (e.g., if the leaves are not a deep green color), apply additional fertilizer no later than June. Always follow label directions when applying fertilizer. More recommendations regarding fertilizer for Citrus can be found here
http://www.ipm.ucdavis.edu/PMG/GARDEN/FRUIT/CULTURAL/citfertilization.html
Additional information about Citrus Leaf Miner can be found at this University of California website http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74137.html
Help Desk of the UC Master Gardener Program of Contra Costa (JL)
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Editor's Addendum: The Citrus Leaf Miner has been in California for many years, mainly in Southern California. However, it became very obvious in Contra Costa County only a few years ago. I've seen Citrus Leaf Miner in my various citrus trees in Martinez for the last several years, and we've had many questions about Leaf Miner at the Help Desk for the last 2-3 years. In my citrus, it hasn't been a significant impact, but it is noticeable due to the obvious tunneling and distortions. Per the referenced Pest Note, I haven't really done anything to prevent and/or “cure” the infestation other than normal care. Anecdotally, the impact didn't seem to be as significant last year (2015), and I haven't really noticed any impact so far this year. The Pest Note indicates that there are natural predators that often follow the Leaf Miner so maybe they have finally arrived (woke up?) or some other predator has discovered this new “food”? We'll soon see as warmer weather arrives.
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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: ccmg@ucanr.edu, 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/).
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