Advice from the Help Desk of the
UC Master Gardeners Program of Contra Costa County 

Client: I'm having some early summer problems in my garden. I'm reluctant to use pesticides in my garden since I have several small children. Would you please provide some recommendations to either cure and/or minimize the problems:

1. Tomato plants are doing reasonably well but there are some funky looking lower leaves that I'm concerned about.
2. My roses' leaves are mottled with brown-red markings.
3. The flowering pear tree's leaves are mottled and dropping; an arborist recommended injecting a chemical into the tree to cure the problem
4. I suspect that my garden soil is too alkaline (i.e. previously tested pH@7.1). How can I test it and what can I do to reduce pH? Will just adding compost reduce pH? 

UCMGP's Help Desk Response: Thank you for the photographs, which were very helpful. Our responses follow:

Tomatoes:  Your tomato plants look mostly healthy, but do have a very common disease called early blight seen on a lower leaf. This disease is caused by a fungus, and is spread by wind and splashing water. Disease development is favored by cool, humid conditions. To reduce the spread of the disease, avoid overhead irrigation. You may want to cut off the diseased leaf at the bottom of the plant to reduce spore production. These cultural methods should be sufficient to reduce the impact of the disease on your plants. Since you have small children and are concerned about the toxicity of pesticides, you probably will not want to use any pesticides on your tomato plants. Additional information about early blight can be found here http://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/tomearlyblight.html. 

Roses:  Your roses are infected with rust, another common fungal disease in our county. Rust is favored by mild, moist conditions, and is less common during hot weather. However, once a leaf has become infected, it will not recover, and many infected leaves will drop prematurely. Avoid overhead watering or splashing onto leaves. Fungicides can protect new growth but do not eradicate the fungus from leaves that are already infected. Commercial products (when labeled for the care of rose rust) as well as Neem oil should be effective as a preventive when used before infection starts. Clean up all fallen leaves and put them in your green waste container (i.e. do not add to the compost pile). Since one of your roses is almost completely defoliated, you may want to consult with a rose specialist. You can find one here: http://www.ncnhdistrict.org/CRs/districtcr.html. Rust resistant roses are available. Additional information on rusts can be found here: http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISEASES/rusts.html. 

Flowering Pear Tree:  The photograph from the flowering pear confirms that it is infected with Entomosporium, another fungus that is spread by splashing rain. http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISEASES/entomoslfspt.html. We do not think that this disease warrants fungicide treatment. I do not know what chemical the pest company was

recommending for injection, but any chemical that has systemic activity would be transported to the leaves.  The infected leaves do fall prematurely, but the tree grows a new set of leaves later. Hot dry weather protects the new leaves from infection. The fungus survives from season to season in the fallen leaves, so it is recommended to clean up all the fallen leaves and put them also in your green waste container (i.e., again do not compost). This cleanup is made easier if there is no other vegetation under the tree and the soil is left bare. The University of California says that in special cases fungicides can be applied, but neither of the UC recommended fungicides have activity when injected, only when sprayed on the leaves. Generally, we do not recommend spraying any type of pesticide on large trees, because the chemical, applied under pressure, is bound to drift onto other plants where children, pets, beneficial insects and wild animals can be exposed. Further, since this disease is mostly a cosmetic problem and not likely to kill the tree, using fungicide is hard to justify.

Soil pH:  Home test kits for soil are fairly reliable as long as the instructions are followed carefully. A pH of 7 - 7.5 is borderline satisfactory, but may go up over time because our municipal water tends to have high pH. We recommend that you wait until the plants have been harvested and then add garden sulfur to the soil in the fall according to label directions. Lowering the pH with sulfur takes time (i.e., months), so you must be patient. Adding compost will not lower the soil pH.

I hope that this information is helpful. Please do not hesitate to contact us again. Good luck on a successful summer garden.  

Editor's Notes:  It is likely that the tomato, rose, and flowering pear tree problems may have been caused by the late rains creating conditions conducive to fungus: cool, humid conditions. Warmer, drier weather should minimize these types of fungus infestations provided there is adequate air circulation and not overhead watering early evening.

Help Desk of the UC Master Gardener Program of Contra Costa County (JL)

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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/). 

 

Master Gardeners of Contra Costa Help Desk

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Note: The Contra Costa Master Gardener 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/