Citrus trees need care throughout the year, including cultural practices to keep trees healthy and pest management. During the fall season, several pests can attack citrus trees in many California regions.
Brown Rot
Monitor for this disease by checking for damaged fruit on your tree, as well as fruit in storage. Sometimes affected fruit develops a pungent odor and can ruin fruit held in storage. See the UC IPM web page on Brown Rot to learn more.
If you see what look like small “tunnels” on your citrus tree leaves, your tree might have citrus leafminer. The adult stage of this pest is a small, light colored moth; the larval stage feeds and develops inside the leaves of young citrus and other closely related plants.
Citrus leafminer rarely causes problems for mature trees, however, it can seriously damage very young trees. Read the UC IPM Pest Notes: Citrus Leafminer for recommendations for prevention or management.
Snails and Slugs
Asian Citrus Psyllid and Huanglongbing
You may have heard of the Asian citrus psyllid (ACP) and the deadly disease huanglongbing (also called citrus greening) that has been featured in the news. This disease doesn't pose a threat to humans or animals, but is deadly to citrus trees. Once a tree develops huanglongbing, there is no cure, so for this disease prevention is key.
UC IPM Web Site
For information on managing other citrus pests in the garden, see the UC IPM webpage on Pests in Gardens and Landscapes: Citrus.
- Author: Ben Faber
A new pest for avocado? Old pest? How much damage will it do? Don't know yet.
Tracy Ellis, the San Diego County Ag Commissioner Entomologist has partially identified what appeared to be two pest and a parasitoid, as only one pest and a beneficial that is doing it's duty going after the pest.
The insect determination has come back for both larvae (one a leaf miner and one a leaf roller) as the same insect! It has been determined to be C-rated gracillariid miner Caloptilia sp. (Lepidoptera: Gracillariidae) at this time. An image of the adult moth is not yet available.
Apparently, the larval stage transitions from a miner to a roller, in what's called hyper-metamorphosis. Starting as a miner and abandoning the mine to roll the leaf. CDFA scientist Marc Epstein is taking a closer look at this insect . Marc does not know if it is a local insect that adapted to avocados or is an import, as many in this family have not been studied or sequenced.
The leaf roller/folder has appeared down in San Diego and Santa Barbara. It's not clear whether it will be a pest of the fruit at this time.
The results for the parasite came back as Hymenoptera. That too needs greater study.
Above is a photo of both insect stages. They can be found together in the same habitat.
The damage from the leaf miner generally looks like this
And miner looks like this
The damage from the leafroller looks like this:
Larval leafroller with the parasite on it.
And the parasite , once it grows up from being a maggot, looks like this
It's still not clear what damage this might do. Maybe nothing significant. Maybe this is an aberration only for this year. Stay tuned.
- Author: Elizabeth E Grafton-Cardwell
- Editor: Elaine Lander
[This post has been modified from the article originally published in the Fall 2018 issue of the Retail Nursery and Garden Center IPM News.]
Citrus leafminer is a moth that arrived in California in 2000 and has invaded citrus throughout the state. This small moth lays its eggs on new, succulent citrus leaves. The larvae burrow through the soft leaf tissue, creating shallow meandering tunnels, or mines (Figure 1). Larval feeding causes the leaf to curl and distort. Mature citrus trees are less frequently attacked since most of their tough leaves are resistant to the leafminer, but very young trees with their higher proportion of young, tender leaves, are more susceptible. This can slow growth of young trees but even those with heavy leafminer damage are unlikely to die.
In home landscapes, citrus leafminers are killed by many natural enemies—other insects and spiders that attack pest insects. Insecticides don't work very well on this pest because it is inside the leaves. If you can, try to ignore leafminer damage since citrus can tolerate it. The leaves damaged by leafminers will continue to produce food for the tree, so they do not need to be removed. If you remove them, it will stimulate the tree to produce more new leaves, which will be attacked by the leafminer and more damage will appear.
For more information about management techniques, see the Pest Notes: Citrus Leafminer.
Looking for other citrus insect pests? Check out our related posts on mealybugs and cottony cushion scales, Asian citrus psyllid, and ant control for Asian citrus psyllid.
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Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Client' Request: Hi! What bug (or other cause) is responsible for my “Bright Lights” Swiss chard leaves to look dry and brown? (See pictures below) What can I do to fix this?
MGCC Help Desk Response: Thank you for contacting the UC Master Gardener Program's Help Desk with your problem with Swiss chard leaves turning brown.
It's likely that the issue is caused by leafminers. On vegetables, the most common leafminers are the larvae of small flies in the genus Liriomyza. Adult leafminers are small, active black flies. Their eggs are inserted into the leaves and the larvae feed between the leaf surfaces.
Leafminers can attack many different vegetables, including chard, tomatoes, peas, beans, spinach and lettuce. In warm weather, leafminers may be more active and there are as many as ten generations per year. The most obvious evidence of leafminers is the twisting trails (or mines) the larvae leave as they feed beneath the leaf surface. Mining usually has little impact on plant growth and rarely kills the plants. Damage will not be serious on most plants older than seedlings, though it makes chard or spinach leaves unsightly. The unaffected leaf areas are still edible.
Leafminers rarely require treatment in gardens. Be sure to provide proper care to the plants, especially irrigation, to keep plants vigorous. Clip off and remove older infested leaves. Small seedlings can be protected by a protective (i.e., frost) cloth. Leafminers are often kept under good control by natural parasites. Because the larvae are encased and thus protected in the leaves, insecticides are not very effective for leafminer control.
More information can be found at the UC ANR's integrated pest management website at http://ipm.ucanr.edu/PMG/GARDEN/VEGES/PESTS/vegleafminers.html.
Help Desk of the UC Master Gardener Program of Contra Costa County (LRF)
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, although we will be moving this summer. We will notify you if/when that occurs. 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 Biog (http://ucanr.edu/blogs/CCMGBlog/)
- Author: Ben Faber
Hats Off.
The Orange County Master Gardeners have lived up to their name with their website information on citrus. It's a truly impressive information site for not only homeowners, but also growers:
http://mgorange.ucanr.edu/Edible_Plants/?uid=108&ds=530
The “Citrus Problem Diagnosis Chart” is especially work perusing: