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Tomato Problems: Walnuts & Soil Borne Diseases

Help for the Home Gardener from the
Contra Costa Master Gardeners' Help Desk

Client's Question:

Tomato with Fusarium Wilt... impact of walnut trees is similar

The client bought 8 different tomato plants from the CCMGs' "Great Tomato Plant Sale". They are withering and dying. The client had previously purchased tomato plants from Navlet's Nursery; she reported that those plants did pretty well. The client observed that the growing season last year and this year were quite different. Each plant was a different variety but each died in a similar way. The plants are in two raised beds, 4' x 8' x 12”. The plants were transplanted from the original containers into gallon pots for two weeks while the bed was being prepared. Each plant was mounded and a base formed around the plants. The tomatoes were watered twice per week, in addition the tomatoes were fed once. The plants did well at first and then one by one they withered and died. The client had recently read about black walnut trees affecting tomatoes adversely, and they wondered if Master Gardeners had more information on that issue. The client has two black walnut trees in close proximity to the raised beds. These trees are in the neighboring yard.

Master Gardener's Response:
The proximity of the black walnut trees to your yard could certainly be contributing to the distress of the tomatoes. However, if the black walnuts are the sole problem, it's hard to understand why you had better success with your tomatoes last year than you've experienced this year.  So there may be some other factors at work. We'll first give you some information about how black walnuts affect tomatoes (and certain other plants) and then desccribe some other possible causes for the decline of your tomatoes.

Black Walnuts and Tomatoes: As you noted in your email, black walnut trees produce a substance (called juglone) that is toxic to some plants, including tomatoes.  Most of the toxic chemicals accumulate within the drip line of the tree (the area measured from the trunk to the outer reaches of its branches), but so
me effects of the chemical can extend beyond the drip line to a distance of 50 to 80 feet from the tree.  If your tomatoes were planted within the drip line of the walnut trees, the toxic effect of the juglone may be the cause of the decline of the tomatoes (or at least a contributing factor). If the trees are more distant from the tomatoes, it is less likely that juglone is the problem, unless the toxic substance has been introduced into your garden area in some other manner—for example, from the debris from the trees blowing into the garden area or composting tree debris and spreading it in the garden.

If the tomatoes were within drip line of the tree, or if you are aware of other means by which the trees could have contaminated your garden areas, here is a description of the symptoms you would have seen if the problem is juglone toxicity:

"Plants sensitive to juglone may be stunted, have yellow or brown, twisted leaves, exhibit wilting of some or all plant parts, and die over time. Often, the vascular (i.e., water-conducting) tissue of affected plants will be discolored. Symptoms may occur rapidly, even within a few days after sensitive species are transplanted into a walnut tree's root zone. Alternatively, some plants may survive for years near a young walnut tree, but will wilt and die as the tree increases in size."

You can find more information about black walnuts and how they affect tomatoes and other sensitive plants at the Wisconsin Cooperative Extension website cited above and in the Washington State University fact sheet at

Other Possible Causes: If your tomatoes are outside the drip zone of the trees, and you aren't aware of other ways that the trees may have contaminated your garden area, you might want to consider other possible causes.

Given that you had better success last year with the tomatoes you purchased at Navlet's, the problem this year may be connected with the varieties of tomatoes you tried to grow. Most of the tomatoes sold at the CCMG tomato sale are heirloom variety tomatoes.  The ones you purchased last year were likely hybrid varieties which are common in commercial nurseries. If successfully grown, heirloom tomatoes often give you a better flavor than many hybrid tomatoes.  Also, if you save seeds from a heirloom variety, the seeds will produce the same variety of tomato plant while seeds saved from a hybrid will not reliably grow the same plant variety in future years. The downside is that many heirlooms have less disease resistance than hybrid tomatoes.

Some common plant diseases that affect non-resistant tomato varieties are caused by soil borne pathogens that build up over the years in the soil.  To minimize the chances that such pathogens will be present, crop rotation is a must.  If you planted your tomatoes in the same spot as last year, then such problems are more likely to occur.  It is best to use at least a three-year crop rotation cycle and not plant tomatoes (or other members of the same plant family such as peppers, potatoes, and eggplant) more than two years consecutively in the same garden bed and not plant other solanaceae plants (egg plant, peppers, potatoes, etc.) in the other years.

If you plan to try growing tomatoes again in the same garden area, and you are unable to practice crop rotation, be sure you buy or grow tomatoes that have some disease resistance.  As mentioned above, you are most likely to find disease resistance in hybrid varieties.  The plant label or seed package of disease resistant varieties will be labeled with codes for the diseases for which some resistance exists. Here's a list of the Codes and the tomato disease represented by each of the code letters:

Tomato disease resistance codes:

Disease Resistance
V Verticillium Wilt A Alternaria
F Fusarium Wilt T Tobacco Mosaic Virus
FF Fusarium, races 1 and 2 St Stemphylium
(Gray Leaf Spot)
FFF Fusarium,
races 1, 2, and 3
TSWV Tomato Spotted
Wilt Virus
N Nematodes    

Most varieties will only be resistant to some of these diseases.  Look particularly for resistance to verticillium and fusarium wilt which are common in our county. Nematodes can be a problem also. The UC publication at may possibly help you identify what disease could be affecting your tomatoes. Providing us with a sample and/or pictures would help us assist you.

If you suspect that soil borne diseases could have been the problem, perhaps next year you might try growing an heirloom tomato variety in a container, using a purchased soil mix which is unlikely to contain soil borne diseases.  The purchased soil mixture in the container would also be unlikely to be contaminated with juglone, particularly if you position the container as far as possible away from the black walnut trees and keep any debris from the trees from falling into the container.  If you decide to try growing a tomato in a container, use a container that is at least 16 inches deep.  Cherry tomatoes or other varieties that produce smaller sized tomatoes usually do well in containers.  “Determinate” varieties also do better than “indeterminate” varieties in containers.  Look on the plant labels or seed packages to find determinate varieties.  (We sell many determinate varieties at our annual tomato plant sale.)

Here's hoping that next year's varieties will prove fruitful and tasty tomatoes.

Contra Costa Master Gardeners' Help Desk

Editor's Note: The CCMG Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA  94523.  (map) We can also be reached via telephone:  (925) 646-6586, email:, and we are on the web at "Ask a Master Gardener" help tables are also present at many Farmers Markets as well as at the CCMG's "Our Garden" programs (map). See the CCMG web page for details/locations.

Posted on Monday, September 1, 2014 at 7:00 AM

Edible Landscaping


Edible Landscaping 

By Lee Oliphant   Master Gardener


Want to grow something edible in the coming seasons without increasing your landscape water requirements? There is an edible crop you can grow right in your perennial beds that you can count on to produce, sweet, delectable produce without straining your water conservation efforts.


Planting alliums like bulb or globe onions (Allium cepa) and garlic (A. sativum) in the fall will allow them to grow through the winter and spring when soil is normally moist. They should mature by June and July when water supplies may be limited.


Growing globe onions and garlic requires nothing more than good, rich soil. If your soil is clay or sand, enrich it with compost for nutrients and improved drainage. Plant seeds directly in the soil from October to December and sets (small immature onions) in January or February. Plant them pointy end up just below the soil surface, leaving 3 to 4 inches between sets.


Onions need a specific number of daylight hours to set bulbs; the requirement varies depending on the variety. Fortunately, we live in an area of California that grows both long-day and short-day onions. Choosing which varieties to grow may depend on whether you prefer sweet onions for salads and sandwiches or strong onions for cooking.


Garlic is planted and cared for in a manner similar to onions. A few feet of planting will provide an ample supply for most families. Plant bulbs between mid-October and mid-February. Purchase garlic bulbs from a nursery and plant each clove blunt end down with the top about one inch below the surface. Harvest both garlic and onions when leaves turn brown.


These easy to grow bulbs fit nicely into any garden bed. Once you're confident in growing traditional onions and garlic among your flowers, you may want to extend your planting to include bunching onions, scallions, shallots, and leeks; all part of the big, happy family of alliums.


Save the Date!!!  Saturday September 6, 2014, 10:00 to 2:00, is the UCCE Master Gardeners 8th Annual Tomato Extravaganza. Tomato and basil tasting, guest speakers and lots of fun in the garden! See you there!!!



Posted on Sunday, August 31, 2014 at 5:28 PM

A Lady Beetle and Gulf Fritillary Caterpillars

What's this?


A lady beetle, aka ladybug, sharing stories with Gulf Fritillary caterpillars?


Well, not likely.


The lady beetle (family Coccinellidae) preys mainly on aphids--it can eat about 50 aphids a day or some 5000 aphids in its lifetime. But it will devour other soft-bodied insects, including mites, scales, mealybugs, leafhoppers, and butterfly eggs and larvae (caterpillars). Butterfly caterpillars move quite slowly; they are not Indy 500 speedsters.


We spotted a lady beetle early this morning on one of our passionflower (Passiflora) seed pods, surrounded by hungry Gulf Fritillary (Agraulis vanillae) caterpillars. It was  somewhat like a two-peas-in-a-pod scene, but without the peas.  Here were two insect species ON a pod, and both sharing the same warning color: red.


The Gulf Fritillary caterpillars are hungry.  Very hungry. They've stripped the passionflower vine of all its leaves and are now eating the stems and seed pods. Actually, we planted the passionflower vine for them.  But are they THAT hungry? They are. They're famished. And there are literally hundreds of them.


Sometimes we think that all of the Gulf Frit butterflies west of Mississippi are gravitating toward the plant to lay their eggs. The vine cannot support that many hungry caterpillars,  despite predation by scrub jays and European paper wasps.


The lady beetle, we assume is not only eating the tiny yellow eggs of the Gulf Frit, but the tiniest of the tiny larvae.  It's an exquisite buffet of tasty treats with high nutritional value.


And easy pickings. 

Lady beetle, aka ladybug, with its new
Lady beetle, aka ladybug, with its new "friends"--Gulf Fritillary caterpillars. (Photo by Kathy Keatley Garvey)

Lady beetle, aka ladybug, with its new "friends"--Gulf Fritillary caterpillars. (Photo by Kathy Keatley Garvey)

Gulf Fritillary caterpillars move around the lady beetle, aka ladybug. (Photo by Kathy Keatley Garvey)
Gulf Fritillary caterpillars move around the lady beetle, aka ladybug. (Photo by Kathy Keatley Garvey)

Gulf Fritillary caterpillars move around the lady beetle, aka ladybug. (Photo by Kathy Keatley Garvey)

A touching moment. (Photo by Kathy Keatley Garvey)
A touching moment. (Photo by Kathy Keatley Garvey)

A touching moment. (Photo by Kathy Keatley Garvey)

Gulf Fritillary caterpillars will grow up to look like this. (Photo by Kathy Keatley Garvey)
Gulf Fritillary caterpillars will grow up to look like this. (Photo by Kathy Keatley Garvey)

Gulf Fritillary caterpillars will grow up to look like this. (Photo by Kathy Keatley Garvey)

Posted on Friday, August 29, 2014 at 4:29 PM

Lighter crop of wine grapes blamed on drought

Sangiovese grapes.
Wine grape growers are expecting a lighter than normal crop in 2014 due to the drought, reported Jeremy Thomas in the Contra Costa Times.

"The drought is impacting everybody," said Kevin Zollinger, a Livermore vintner. "Everybody's cutting back. Are our vines more stressed this year? Yeah, probably, because you don't have the charge in the soil that you normally have."

The winegrape grower said he and other farmers are holding back water as much as possible without stressing the vines.

Janet Capriele, UC Cooperative Extension advisor in Contra Costa County, said winemakers typically withhold water to limit vine growth and intensify berry flavor and color. However, excessive underwatering could be harmful.

"We're already cutting back, so the plants are already a bit stressed," Caprile said. "With these additional cutbacks, we may be stressing the grapes beyond the quality you'd want. We'd expect to have smaller crops and smaller berries."




Posted on Friday, August 29, 2014 at 4:28 PM

143-year-old Washington navel mother tree gets special care

The mother of millions of navel orange trees around the world, a 143-year-old Washington navel orange tree in Riverside, is carefully protected by UC scientists and the Riverside parks department, reported Suzanne Hurt in the Riverside Press-Enterprise.

Georgios Vidalakis vows to protect the Washington navel 'mother tree.'
"We're not going to let this tree die," said Georgios Vidalakis, UC Cooperative Extension specialist in the Department of Plant Pathology at UC Riverside. Vidalakis is the director of the UC Citrus Clonal Protection Program.

Scientists protect the tree using special tools, insecticides and disease monitoring.

According to legend, the seedless and sweet Washington navel was an accidental mutant that appeared on the grounds of a Brazil monastery in the early 1800s. Tree clones were sent to USDA in Washington, D.C., and from there acquired by Eliza Tibbets, who tended the trees at her home in Riverside.

"Producing budding stock to make other saplings, Tibbets' trees birthed a citrus industry dubbed California's second gold rush," the Press-Enterprise story said.

John Bash, a UC Riverside staff researcher who worked with the Washington navel for 32 years, called the mother tree "one of the world's agricultural icons."

"There are literally millions and millions of trees that can trace their ancestry back to that single tree," Bash said.

Posted on Friday, August 29, 2014 at 9:17 AM

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