Leaf Miners Attacking Veggies

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)

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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, 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  (//ucanr.edu/blogs/CCMGBlog/)

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