A New Protector Against Burrowing Animals

This spring I found that a burrowing animal was eating plants, roots and tops, in my small front garden. I know it was not a mole, because moles don't eat plants, just insects and earthworms. Could have been a gopher, but by the amount it ate in a night, I thought maybe something smaller, maybe a RAT! (The rats that burrow are called sewer rats; the ones that don't, roof rats. Rats have burrowed in my backyard before so this seemed a good guess.)

Whatever it was, my Chinese forget-me-nots, the ones I grew lovingly from seed and transplanted into the garden, were disappearing night by night. Then whatever it was started in on the primroses I just bought and set out, and the large 'Moonglow' yellow yarrow was losing branches, then roots. Then it ate most of the tops off of two x kellereri yarrows!  These were divisions of my original plant-which is one of my favorites. Something had to happen.

I dug out all of the yarrow, both 'Moonglow' and  Kellereri, and what was left of the primroses and put them all in pots on the back porch. Then I cleared away and found the place the varmint had blocked up the opening of its burrow. I dug it out, exposing the hole. The varmint had replugged it the next morning. I repeated. It repeated. I repeated. After many repeats, over several days, I decided I had to escalate. I have heard that water down the burrow can discourage a burrowing pest, but doubted it in a large garden, but in my 10 x 12 foot front garden, maybe it would work. I wanted to tell the varmint that this was not a good place for a home, before it ate everything left there. At this point about a quarter of the tiny space was a wreck. My husband was beginning to ask whether maybe I should be looking for a trap. I said hold on, let's see if this works.

So, the next day, I dug the plug out again, got the hose, attached a jet nozzle, and put it down the hole. Turned on the water. Most of it stayed in the hole. But the next say, the plug was back.

Over the course of a week or so, I dug out the burrow plug 8 or 10 times, used the hose 3 times. And then the varmint stopped replugging the hole. 

During the battle, I decided to replant a couple of plants in gopher baskets. And here is where my problem led to a discovery that will be useful to other gardeners. When I went over to San Francisco's Flowercraft nursery, they offered me a new kind of basket, made of a soft stainless steel wire mesh. So this is what I have used, and have written about it in my May 8th, 2016 SF Chronicle column.They are called Grow Master Baskets. To learn more about them and see who sells them, see westernplantingsolutions.com or call 530-751-3366.

These baskets are less expensive than the old kind, easier to handle, and come in many sizes.  The company suggests fitting a basket over the rootball like a glove, but I have used baskets that are a bit larger than present rootballs, spreading the baskets in a wider planting hole, and putting some soil in them, then setting the plants in the soil.That way the plant has room to grow more roots and still be protected.

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'Moonglow' yarrow plant in a Grow Master anti-gopher basket

When I first used the basket, the varmint was still active. Because I had used a somewhat larger basket than the rootball, there was enough of it to roll up over the plant and secure with some plant-tie that I ran through some of the openings in the mesh. This protected the top of the plant as well as the roots while it got re-established, and while I figured out what to do next.

But now I have uncovered all of the protected plants. The 'Moonglow' yarrow is about to bloom. The x kellereri yarrows are still recovering in pots, but they shall return. And one Chinese forget-me-not survived to bloom beautifully!

 

 


Bay Area Citrus in Great Danger

If you have citrus trees in your garden, or know someone who does, listen up. A pest insect that has wiped out half of the citrus crop in Florida is spreading in California and has reached the Bay Area. Last year, a new quarantine area was created in the San Jose region, because the pest was found in trees there. Now the most recent quarantine area covers the northern peninsula and a swath of the southern part of San Francisco.

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Lemons on a Healthy Lemon Tree in San Francisco

The insect itself will not kill the tree, but it often carries a deadly disease, and if a particular individual insect is carrying that disease, it will infect the tree while it is feeding. And then there is no cure. Other Asian citrus psyllids will pick up the disease from that infected tree, and will spread it.

So far, none of the insects found in our region have been carrying the disease, but it seems like only a matter of time till one does. Scientists are looking for a cure, or a way to breed resistance to the disease into citrus trees, and would like to buy as much time as they can by keeping the problem in as small an area as possible.

What to do? Inspect your trees. Spring is a good time to do it, since it is a time when there is much active growth on citrus. Look carefully at as many of the growing tips, with their small, new leaves, as you can. The insect, which is called the Asian Citrus Psyllid, or ACP, lays very small yellow-orange eggs in new growth. They will be easier to see with a magnifying glass. The eggs hatch into yellow nymphs that average sesame seed-sized. They are also distinctive in having long, white "tubules" with bulbous ends that extend from their bodies. The adults are aphid-like, mottled browns, and stand with their rear in the air, heads down, sucking sap.

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Asian Citrus Psyllid Nymphs

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Asian Citrus Psyllid Adult Feeding on Citrus Leaf

If you find the insect on your tree, and are not in an area already quarantined, you should call the California Food & Agriculture (CDFA) Exotic Pest Hotline at 800-491-1899. If you are within  the quarantine area already, you should try to kill the pest.

To see an interactive map of the quarantined areas and more photos and learn the best ways to control the pest, see the following UC  website: http://ucanr.edu/sites/ACP/Homeowner_Options/

Also, be sure to buy citrus only from responsible sources. (Major citrus tree growers are now growing trees for the market only in covered production areas that the pest can't get into.) Don't accept plants, cuttings, or grafting material from other gardeners.

And if you are in a quarantined area, don't take any leafy branches outside of it. (You can share your fruit outside of the quarantined area if it doesn't have any stems or leaves attached.)

The insect can also infest some plants that are related to edible citrus, like calamondin (xCitrofortunella microcarpa), box orange (Severinia buxifolia), orange jessamine or orange jasmine (Murraya paniculata), and Indian curry leaf (Murraya koenigii). They should also be inspected and are subject to the same quarantine rules.

The disease we are trying to avoid, and that I hope we never see, is Huanglongbing, or HLB. It is also known as yellow shoot or yellow dragon disease. The leaves of infected trees have yellow blotches, usually starting in one section of the tree. The blotches don't look like most nutritional deficiencies in that they cross the leaf veins, and are often arranged asymmetrically on the leaf. Fruit develops unevenly, asymmetrically, ripens poorly, with little juice and a bitter flavor. The disease will kill the tree. If it appears, the only recourse at this time is to remove the infected tree before the disease spreads to other ones.

So let's get out there and look now, before it's too late!

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Yellow-blotched Leaves of a Citrus Tree Infected with HLB Disease.


Roly-Poly Problems

I got the following question through my web site. I'll answer it below. I was trying to wait until I had a good photo of these little critters, but I don't seem to have very many of them these days, so there's no photo for this post.

The Question:
My veggie garden has been besieged by roly polies.  When I check gardening blogs, most answer that roly polies do not eat live plant tissue but they are definitely eating the base of my cucumber and squash plants. I caught most of them early and taped the base of the stems so they couldn't continue to gnaw away...but they have!!!  They continue to move up the stem even though the stem is tougher than when they were small seedlings.  I have lost a few plants to them. My vegies are mulched with my homemade compost which is a cold one and probably supports the rolly pollies.  How do I rid my soil of them?  They are everywhere!!  BTW I live in San Rafael, Marin County.  Should I solarize the soil?

The answer:Too many garden how-to books and other guides are researched by reading what others have written, so we get the same information over and over. And wrong information over and over is frustrating.

Roly Polies will generally eat any living or dead plant matter that is soft enough, inlcuding much dead, decaying plant matter. If there are only a few of them, they may not damage crops much, but when their populations build up, they do significant damage. While I've never seen sow and pill bugs eat squash stems, I have watched them chew up the blossom ends of summer squash fruit and eat into ripe tomatoes.

"Roly Polies" is a general common name for both sow bugs and pill bugs, which often occur together in gardens. These are two different species of animal, both more closely related to shrimp than to insects. We call the species that can't roll up sow bugs, the ones that form a tight ball when disturbed, pill bugs, but their habits and management are about the same.

Your goal is to make conditions unpleasant for them and to reduce their numbers if they get so numerous that they are becoming pests. Start by pulling the mulch back from your squash plants, leaving a bare area a few inches wide around them. Try to keep this surface, especially, but all of your garden soil or mulch surface, as dry as possible, since these creatures need to stay moist to survive.

I doubt that solarizing the soil will help with sow and pill bugs. They would tend to run out of the hot area under the plastic. You might get eggs, but the adults are very mobile.

Sow and pill bugs tend to congregate in moist dark places in the day time. You have to move fast, but if you know where they are hiding, and see a lot of them in one place, you can scoop them into a plastic bag, seal it, freeze it, and compost them. Or you can leave out traps, in the form of anchored opaque plastic sheeting or cardboard, remove it fast, and start scooping. Try using a kitchen scoop or a deep trowel.

If you have many sow and pill bugs in an area you are about to clear and replant, try to reduce the population before you plant seeds or set out new seedlings there. Waiting a couple of weeks may be enough, but if you have many of the creatures, you may want to use mechanical means, as just described, or chemical means, as follows, to reduce the population.

I never use chemical means as a first resort, but you may want to supplement your cultural and mechanical methods by using a product called SluggoPlus. In addition to the iron phosphate that kills snails and slugs, it contains Spinosad, an extract from a soil microorganism, that is toxic to sow and pill bugs, earwigs, and cutworms. Use it according to directions, including not spreading it any more thickly than the directions indicate, as it is toxic to pets. (If spread according to directions, very thinly, it is less likely that a dog might eat enough of it to harm it, but do read the directions.)

Good luck reducing your roly poly problem!

 

 


More on Early Blight of Potatoes & Tomatoes

(See photos in the previous post)

In my last post, I reported having seen some potato plants in San Francisco with what looked like early blight, a disease caused by the fungus Alternaria solani. I remembered from my research for the book Controlling Vegetable Pests, which I wrote in the early '90s, that this disease is not common here in California, but much more so elsewhere in the US. I wrote then that it is "less common in arid regions of the West, although overhead irrigation and frequent heavy dew promote disease in these areas." It showed up the week after we had an unusual June rain, and in a garden that has frequent fog. But the question is: Where did the spores come from?

My first thought was that someone had planted potatoes from the grocery store. These could carry the spores, even without symptoms, or could have had dark lesions with underlying brown or blacky corky rot from spores that grew on their surfaces. However, the gardener assured me that these were purchased at a nursery as certified disease-free.

So the spores must have blown in from a nearby garden or were carried in the rain. Then they landed on potato leaves that had some injury, at a time when the temperature and amount of hunidity were right for them to start growing, and the rest is history. The ideal temperature for early blight spore growth is 75-80 degrees F, but the symptoms develop fastest at 70 degrees. 

This disease can also infect tomato, and, occasionally, eggplant or pepper. Wild relatives of these plants are also susceptible. On tomato, the leafe symptoms, the bull's eye spots, are the same as on potato, and there may be sunken lesions on older stems. In additon, there may be excessive blossom drop (common here anyway due to cold nights) and leathery, sunken, dark brown lesions on the stem end of the fruits.

If this disease shows up in your garden, take the plants out of the garden. (In San Francisco, they can go in the Green Bin, since the municipal composting system will heat up enough to kill the spores.) If potato plants have formed tubers, eat them up soon, as they may decay in storage. Don't store them where you will kep other, healthy, potatoes later.

The spores can germinate in plant material from infected plants as long as it has not completely decayed, so pick up every bit of the plant and dig up most of its root. Do not save seeds from tomatoes that ripened on infected plants, as the spores can hide in the seeds.

Remove any solanum weeds that are growing in your garden, as they can harbor the disease. (They have flowers similar to those of tomato, but usually with white or pale lavender petals, and have clusters of small, inedible berries that turn black when ripe.)

Plan not to grow tomatoes or potatoes in the place where infected plants grew for two to three years.

When you do plant potatoes or tomatoes, provide your plants with adequate water and fertilizer and avoid getting water on the leaves of tomato'potato family plants. Start examining them when they are about a foot tall to be sure they do not have symptoms. Prevention is more successful than cure when it comes to plant diseases, but if you have had the disease, or if you see the first lesions it is causing, you might try the fungicide Serenade, which is based on a soil bacterium. Follow directions on the label, including repeated sprayings as it directs. (If you are spraying after seeing lesions on a leaf or two, pick off those first infected leaves before you spray.)

May early blight of tomato or potato not darken your door, or the leaves of any plants you are growing to produce food!


Early Blight Appears on Local Potatoes

When I saw these symptoms on some potatoes in a local garden, I thought they looked like early blght of potato and tomato, a disease caused by the fungus Alternaria solani. But I thought it unlikely, because this is not a common disease in our region. I tried to return to get good photos of the diseased plants, but when I arrived, the plants had been pulled, so my photos show leaves I selected to show the symptoms.

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The most diagnostic symptom is those dark brown lesions on the leaves with concentric rings visible in them. Those are from repeated growth of the fungus and release of spores. Symptoms are similar on tomato. Also susceptible are a number of wild potato/tomato relatives and other members of this plant family.

Eventually, the brown spots coalesce so that the entire leaves become brown and die.

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(This is an entirely different disease from Late Blight, which is Phytophthora infestans. Search this blog for more on that disease, with photos of its symptoms.)

Potato/tomato early blight is spread by spores, as are most fungi. I sent a sample of the diseased leaves, through the Cooperative Extension, to Brenna Aegarter, a UC potato expert in Stockton to ask for help identifying the disease. She lifted spores from the leaves with Scotch tape and put them under the microscope. Here is what she saw, followed by her reply:

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"There is clearly Ulocladium and Cladosporium (which are common “molds” on senescing/decaying leaves) as well as some Alternaria spores. However, the challenge is that there are two types of Alternarias in the world. One type is a common mold and would often be found on dying leaves. The other type are pathogens of plants and infect tissue that is living (and includes Alternaria solani cause of early blight). The ones that are not pathogens have short “beaks” while the pathogenic ones have long beaks (the narrow section of the spore that extends out).  Under the microscope I saw Alternaria spores with beaks, but the beaks were not so long as to entirely convince me that they are spores of Alternaria solani. But I have sent my photo to a colleague to see what he thinks. Stay tuned!"

Later, I heard from her to the effect that her colleague had confirmed that the beaked spores are Alternaria solani. If you look at the slide, you will see the ones with a long point on one end. There are the other, decay bacteria spores also, and I think the large, long objects are probably plant hairs.

I will, in my next post, explain this disease and what to do about it.


Email as an Aphid Managment Tactic

I planted broccoli in my community garden last fall, and this spring, as it neared bearing age, it was overrun with aphids. The worst was the largest plant, which tipped over in a winter storm. (It is often the case that a plant with damaged roots becomes most attractive to aphids.) What to do?

I began by crushing as many aphids on leaves as I could find, and washing the leaves with the hose as I went. I looked over the plants carefully, checking the undersides of leaves and in curled over leaves.

When a leaf was heavily infested, I sometimes broke it off and took it away to a green bin (our municipal composting container here in San Francisco). As it began to bear heads, I removed them too, as they were so full of aphids I didn't want to try to get them clean.

I also noted that there were many lady beetles (ladybugs) on my African blue basil plant (a perennial that was coming back from winter), so I assume some of them were eating aphids on the broccoli, though I never saw one there. And, some of the aphids were turning brown and puffy, since they had been parasitized by the miniwasp that preys on aphids.

But after 2 weeks, with the problem not going away, I used a different pest management tactic, the email. I sent an email to a gardener in an adjacent plot to say that there were so many aphids on the Russian kale in that plot that it was certainly inedible, and so many that they were surely flying over to my broccoli in search of more to eat.

I think this tactic turned the tide. The next time I looked, the infested kale was gone (thank you!) and within a week, the infestation of my broccoli was much lower. I still searched and found pockets of aphids on inner leaves, but it was so much better.

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Then, in a couple of weeks, presto, clean broccoli heads! I have been enjoying them ever since. I like to steam a few lightly and refirgerate them to cut up and put on a salad!

 


Healthy Schools Information

I am giving some classes about pest management for some school garden coordinators in San Francisco. Because of this, I have been researching the legalities of pest management in California schools. Below are some links to information that explains the Healthy Schools Act, including lists of pest management chemicals that can be used in schools without posting, and explanations of how to post use of a chemical that isn't on the list.

Note that the rules were set up mainly for inside and landscape usage, rather than for food gardens. The active ingredients that are exempted from the Healthy Schools Act are all basically food products, so are permitted in food gardens, but there are inert ingredients that aren't, so to find out which these are, see the EPA list of inert chemicals that can be used in "food use sites". (Pesticide labels also indicate whether the product is legal to use in food gardens.)

http://apps.cdpr.ca.gov/schoolipm/   This is the main page of the CDPR School IPM Program. It provides overall info on regulations that  apply to schools, and allows you to link to the next two useful pages: 

http://apps.cdpr.ca.gov/schoolipm/overview/hsa_faq_color.pdf  This document provides FAQs on the Healthy Schools Act.

http://apps.cdpr.ca.gov/schoolipm/school_ipm_law/exempt_products.pdf   Here you can read about Pesticides & Inert Ingredients that are exempted from the Healthy Schools Act (The actual lists start on page 3--scroll down) (This document also includes links to the EPA minimal risk pesticide list and to the list of CDPR exempted products) 

http://www.epa.gov/opprd001/inerts/section25b_inerts.pdf  This is the list of inert ingredients permitted for use on food crops.

www.cdpr.ca.gov   To see if a pesticide is registered (legal) in California (Click on: Look up pesticide products.)

www.npic.orst.edu. Use this site to research a pesticide ingredient through the National Pesticide Information Center, sponsored by the EPA, go to  Look for Active Ingredient Fact Sheets.There are technical or general Information Sheets, depending on your interest and technical background. There are also sheets on inerts and much other useful information on this site. You can also call them to ask for information in person.

www.ipm.ucdavis.edu  Click on Home and Garden Turf and Landscape, then on Pesticide Information, then on "Home & Landscape Active Ingredients Database." Also, within the pest management writeups, there are comparison charts for various pesticides, telling you what parts of the environement they might harm and other health and environmental factors you might consider when choosing among alternatives. 

See also my book, Golden Gate Gardening. The chapter on IPM includes much information about choosing and using pesticides. In addition, the book's Appendix IV, pages 390-397,  explains pesticides in greater detail, including how to read a label and detailed analyses of common active ingredients you may be thinking of using in your garden, so you can make informed choices among your options.


Late Blight Sample Sent for Analysis

I sent my first specimen of tomato/potato late blight off for analysis this week. I found symptoms on a purple potato that grows in the City College of SF garden. I sent it to a lab in Oregon, as I described in my March 2nd post, to become a part of the usablight.org project. They want to know which "clonal lines" of this disease organism are causing the disease in various parts of the country. For my part, I want to know which ones we have here in the Bay Area. Once we find that out, we will be better able to predict which tomato or potato varieties might resist the disease in our region.

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This is the photo of the specimen I sent to the usablight.org lab. They want us to send leaves that are still partly green, like these, but clearly infected. The whitish stuff on the surfaces is, I hope, spores of late blght.

If you want to take part in this survey and find out more about your particular strain, or, more correctly, clonal line, of late blight, go to usablight.org and learn how to submit samples. The first step is to have them send you a copy of the permit that will let you ship your disease samples across state lines to be tested in a lab in Oregon. Do this soon, so you will have the permit in hand when late blight rears its ugly head in your garden.

If you have overwintering potatoes, you might see late blight soon. In last year's tomato trial, the disease showed up at the end of July. Gardens with cool, damp, foggy weather are more likely to be affected by this disease. Spores fly through the air from other infected plants, land on your plants, and begin to grow. Please see the March 11, 2012 post for more details.


April 14th Plant Sale will Have Late Blight Resistant Tomatoes

I just learned that the San Mateo/San Francisco Master Gardeners will offer three late blight resistant tomato varieties at their spring tomato and pepper plant sale on Saturday April 14th, 9:00am-1:00pm, rain or shine.

The sale will be held at the Elks Lodge, 229 West 20th Avenue, San Mateo. They will have 'Defiant PhR', 'Mountain Magic', and 'Golden Sweet' and will also have lots of other tomato and pepper varieties, starts of popular herbs, and gently used gardening books.Go early for the best selection of blight resistant tomatoes.

I know if you live in SF, it's a slog. If you don't ordinarily drive, it may be worth carpooling down or renting a carshare for a chance at some tomatoes that stand a chance against late blight.Parking for the sale is free.

For more information about the sale, call 650-726-9059 Ext. 107, Mon & Thurs, 9:30am-4:30pm or go towww.ucanr.org/sites/MGsSMSF/Special_events/Tomato_Sale.


Battling Tomato Late Blight

 Note to readers: I wrote this to add to information in the SF Chronicle Article that will appear in the print version of the paper on March 4, 2012. The article will not be availabe on sfgate.com until Monday, March 5th, so if you are here on Saturday or Sunday, and want to find out what is in the original Chronicle article, check back on sfgate.com on or after Monday.

Are you losing tomato plants to tomato late blight? This disease has been killing tomato and potato plants in the Bay Area for several years, and I have been trying to find tomato varieties that will resist it. I reported last year’s trial in the SF Chronicle and on sfgate.com. (If you haven't seen that articlet yet, you can find it at http://www.sfgate.com/columns/goldengategardener/archive/ .) In that article, I promised more details here, in my blog, so here they are. (Note: If you are an expert reading this post, and have corrections or more information to offer, please comment or send me an email through my website at pampeirce.com.)

            This is a long post, so I will tell you what is in it here at the beginning. The first section explains what late blight is, with photos of symptoms. The second section is a brief explanation of ways to try to reduce late blight damage in your garden. Section 3 tells you how to set up a tomato variety trial yourself, with photos to show you how we did it. The fourth section includes some details about genetic resistance to late blight among available tomato varieties, with photos of the fruits of the ones that succeeded in the 2011 trial. The fifth section tells you how to send samples of your blight to the website www.usablight.org in order to identify the clonal line(s) of the blight present in your garden. Then, finally, at the end of this post, is the list of varieties that also appears in the sfgate.com column, showing you which I trialed in 2009 and 2011, plus a few new varieties that I haven't yet trialed.

What is tomato late blight?

            Tomato late blight is caused by the oomycete Phytophthora infestans. (Oomycetes are organisms that used to be called “water molds.”) The disease-causing organism is in the same genus as the one that causes sudden oak death, Phytophthora ramorum, though the two diseases infect different groups of plants.

            “Tomato late blight” is a common name. Because the same organism also infects potato plants, it is sometimes called “potato late blight” or even “tomato and potato late blight.” It can also infect petunias, which are in the same plant family; though I have never heard it called “petunia late blight.”

            The words “late blight” are found in the common names of other plant diseases that are caused by different disease organisms. For example there is “celery late blight,” which is caused by the fungus Septoria apii. (Just one more example of why it is important to know the scientific name of a living creature, even if you commonly use the common name.)

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The first symptoms are darkened areas, briefly topped with white fuzz. This lesion is on a potato leaf.

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If a plant is sucseptible, lesions start to appear all over and spread, killing leaflets, whole leaves, and stems. If fruit has formed, it soon has greasy, brown "shoulders." If it ripens at all it wil have poor flavor.

            The tomato disease that causes our grief is known as a “late” blight because the symptoms typically show up only when the plant is mature, the fruit has set, maybe even some has begun to ripen. (By the time it shows up, we have usually had a couple of months to tend the plants and eagerly monitor the progress of setting fruit, so our disappointment is even deeper than had the disease struck early, before we had developing fruits to mourn.) The late onset happens because the mild temperature and moist air that encourages the spores to grow is likely to occur later in the summer, and also because as infections start to occur, there are more spores to blow about in the air and spread the disease.

            It’s important to know that the spores are not in the soil, but are blown in the wind from plant to plant, from as far as several miles away. They also are not carried in seed.

            It seems that we are fortunate, if that is possible, considering the damage this disease causes if it strikes, because so far, we have only asexual zoospores in our part of the world. These zoospores do not survive in soil, only in living or recently living susceptible plants. Because of this, we can get most of the spores out of our gardens by making sure we have no living plants that can get the blight in our gardens for four months in the winter. In our community garden, we remove all living and dead material from tomato, potato, petunia, and wild solanums (nightshades) from the garden in November through March. (If you do this, you also have to watch for and remove volunteer potatoes that can come up in winter and sometimes get late blight during a warm spell in winter and early spring.) While removing susceptible plants in winter can reduce the number of spores around in summer, it can’t, of course prevent new spores from blowing in, so you still may find the disease in your garden, but at least it isn’t a certainty.

            (If the form of the organism necessary for sexual reproduction were to find its way here, we could have sexually produced oospores here that would survive in soil and live longer than the asexual zoospores. Fortunately, there is no sign of this having happened or immediate expectation that it will.)

 Protecting Tomato Plants from Late Blight

            To protect plants from this disease, gardeners try to keep leaves dry, shelter plants from spore-bearing breezes, or spray them with a protective substance. In the Northwest, tomatoes are often grown under row cover (polyester fabric that lets most light through) or plastic hoop houses to keep rain off. In the Bay Area, we aren’t likely to have rain in summer. Our high humidity can provide enough moisture for the spores to germinate, but you may as well avoid wetting the leaves when you water, and you can try putting plants under cover if you like.

            Fungicides based on copper compounds and the fungicide Serenade are both registered to prevent tomato late blight and are permitted to organic farmers. Either kind of fungicide needs to be sprayed starting from the time you set out your transplants, and continued all season following label instructions, which are to spray more or less weekly. If they are used heavily, copper compounds can increase the copper content of soil so much that plants grow less well, so perhaps they aren’t the best idea. I did try spraying a copper fungicide one year. I found it a lot of work to spray my small planting so many times—and the plants still got late blight.

            I haven’t tried Serenade for late blight yet. It is based on the harmless soil bacterium Bacillus subtilis, and it is worth a try if you don’t mind the spraying. (I was able to prevent onion downy mildew from overtaking my perennial “walking onions” by spraying them with Serenade, so I do know that it works against that disease--another one listed on its label.)

 Looking for Resistance to Tomato Late Blight

            In addition to the winter clean up, which is basic to prevention, I have been trialing varieties that might stand up to this disease. I would very much like to grow my favorites, such as ‘Cherokee Purple’ or ‘Old German’ heirloom varieties, but they get late blight. I am looking for varieties that are resistant to late blight because I’d rather have some tomatoes for sure than spend all my time spraying or covering my plants and likely still losing them to the disease.

            The history of my tomato variety trials is in my sfgate article, (http://www.sfgate.com/columns/goldengategardener/archive/ ) along with a summary of how to do such a trial. Here are more detailed instructions for those who might want to carry out a trial.

            To do a trial, you need one or more experimental varieties (ones you have some reason to believe will resist the blight) and one control variety (one you know will get the blight). The control variety is there to prove that the disease was present in your garden, because if it wasn’t, you didn’t prove the experimental ones would resist it. I have been using ‘Celebrity’ as a control plant. It is an early hybrid that has short plants and resistance to quite a few diseases, though not to tomato late blight. You could choose another control, or could duplicate my choice to stay as close as possible to experiments that have been done already.

            The more plants of each variety you can use, the better, since you don’t want an accident, such as a broken stem or a virus attack to wipe out your one plant of a particular variety, and you want to know that your result is true in more than one plant (though because hybrids are more or less identical, what is true of one plant is more likely to be true of another than if you are groiwn heirlooms). I try to have at least 2 plants of each variety; use more if you have lots of space.

            Now you will have two goals. The first is to give all of the varieties in your trial as close as possible to the same conditions, so that resistance or susceptibility to late blight is the only difference. If you can’t treat them exactly the same (for example, you can’t grow them in exactly the same spot in the same year) you will randomize that aspect of their conditions. Your second goal is to keep track of what happened and record it. This you will do by making sure you know which plant is which and by recording whether the blight struck each plant over the course of the growing season.

            Start seeds for all of the varieties in your experiment on the same day, to ensure that they will be at the same age. Label each kind with a tag that gives the date you planted the seed and the name of the variety. When they have a couple of true leaves, pot them all into individual 4” pots on the same day. Make sure each 4” pot has a label with the date of planting, (date of potting up is optional) and the name of the variety. Don’t lose track of your varieties!

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On planting day, all of the plants are the same age and have been treated the same as they grew. Each pot includes a label.

            Choose a place to plant your experiment. Give the plants adequate space. We had 3 rows of 4 plants each in 2012. The plants were about 18” apart, the rows 3’ apart. Prepare the soil of the entire area in the same way. That is, spread any organic amendment or fertilizer evenly and then dig it in. If you plan to set up a drip system, set it up over the entire bed so that all the plants will be evenly watered by it. We used a half-inch tubing down the long side of the bed and quarter inch drip line with emitters every 6 inches. We ran two of the emitter lines along each planted row, one on each side of the plants.

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Spread organic soil amendment and any fertilizers you plan to use evenly on the bed and turn soil once to dig them in. Shown digging is David Elhami.

            Wait until mid-April or early May to plant out your seedlings, so the air and soil have warmed nicely. On the day you plant, have handy a hole-punch, twist-tie, paper and pencil. Before you plant, randomize your planting, as follows:

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Essential for setting up a tomato variety trial are hand-operated single-hole punches and twist-tie, for attaching labels to individual plants.

            Choose the seedlings you are going to plant and write the name of each on a small piece of paper. If you have two of each variety, make two paper names for that variety. Fold all of the papers up to conceal the names and draw names at random. (I like to draw them from a garden hat as a sort of joke, but you can draw them from whatever container strikes your fancy.)

            Make a map on a note pad. Start at one corner and make x’s to mark where the plants will be. Start in one corner, and as you draw names, write them on the map—progressing across the row and starting on the next row until you reach the end. With your randomized planting, you will reduce the chance that differences from one side of a bed to another, such as shade or wind patterns will throw off your results.

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This photo shows the making of the randomly arranged map. I draw variety names from an actual hat, just for fun, but you could use any container. Shown, left to right, are Donna Mandel, Pam Peirce, and Ken Jacobs.

            Now plant the tomatoes in the arrangement described on your map. As you plant each one, use the hole-punch to punch a hole in the label and use a piece of twist-tie to fasten the label to the main stem of the plant. be careful not to make it too tight. You want room for the stem to get a little thicker without being strangled.

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A labeled plant, with the label attached to the main stem. Make sure the twist tie is loose, so the stem can thicken a bit before you move the label higher on the growing plant. Note driplines on either side of the row.

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Here is the entire planting on the first day, April 16, 2011.

            Water well when all of the plants are in the ground, and water as you would tomatoes normally from then on. Probably best not to sprinkle water on the plants after the first day, but on that day it can reduce the chance of wilting.

            As the summer progresses, you will have three goals: 1. Keeping track of which variety is which, 2. Supporting your plants, and 3. Recording what happens vis a vis late blight.

            In order to keep track of the varieties, every 2 or 3 weeks we removed the hole-punched labels and moved them higher on the plant. We were careful that they were on a main branch, so it would remain clear which plant each was on, and so that we didn’t lose track of them when a small branch or leaf died. Of course we did have the map we made as a backup, but is nice to be able to see which plant is which at a glance.

            In last year’s trial, we supported the plants using the chainlink fence that was at one side of the bed, tall bamboo stakes and jute twine. We tied the twine to the fence, then wrapped it around stakes along each tomato row, then tied it to a stake at the end away from the fence. We used two pieces of twine per row, one on each side of the plants. As the plants grew, we used more twine at higher levels.

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A section of a row showing how two lengths of twine are used, one on each side, and how it is wrapped aroung stakes at intervals along the row to support the plants. This was shot on May 18th, 2011.

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Here is the planting on July 13, 2011. Nice tall green plants, but two weeks later, the damage had begun.

            Periodically, we observed to see whether late blight had appeared. We didn’t stick to a strictly regular schedule, since we weren’t interested in the exact progression of the disease, but did check every 3-4 weeks, and were able to tell which plants died first and which had fruit set, etc.

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Here I am, on August 11, 2011, recording relative damage to the plants. Note the plant label, which has been moved higher on the plant twice to make identification fast. The plant with the label is 'Golden Sweet'. The still-green plant behind me is 'Defiant PhR'.

            Need I say that, other than watering at ground level to keep leaves dry, an ordinary precaution I would always take when growing tomatoes, I didn’t take any measures to prevent or avoid late blight? I didn’t put them under cover or spray them with anything. In fact, I grew the trials in locations where late blight was definitely a problem in the previous year, just to be sure my experimental varieties had something to resist.

The Genetics of Tomato Late Blight Resistance

            There are two aspects of genetics that affect resistance. I am not going to be able to explain them in great detail here, but here are a few facts. The first aspect is the genes that provide the tomato variety with resistance.

            In last year’s trial, I grew 4 varieties I obtained from Johnny’s Selected Seeds. Rob Johnston, the founder of that seed company, told me that two, ‘Golden Sweet’ and ‘Plum Regal’ had one gene that provided resistance to late blight, and they were heterozygous for that gene. That is, it was on only one chromosome of a pair. The other two varieties, ‘Mountain Magic’ and ‘Defiant PhR’ had two genes that provide resistance. They are heterozygous for these genes, meaning that each of them appears on only one chromosome of a pair.

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'Golden Sweet' died in my USF planting, but I did get fruit in my community garden, in a warmer microclimate, and where we have been taking out susceptible plants in winter to reduce the number of spores in the garden. The fruits are small, but were indeed sweet.

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'Mountain Magic' was alive, with some damage, at the end of my USF planting. It set some fruit there, but only ripened a few of the fruits it set. In my community garden, it ripened plentiful fruit. The fruit is about 1 1/2 inches in diameter and has an average flavor.If you look carefully, you will see a couple of brown stems, lost to late blight damage.

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'Defiant PhR' had only minor damage at the USF plantng, but didn't set fruit. However, in my community garden, the one plant had 9 pounds of fruit. Size varied, but the biggest was over 3 inches across. This is a beefsteak-type, meaty fruit, with good, though not excellent flavor.

            In my trial, the ones that were heterozygous for two resistance-endowing genes fared better than the ones that had only one of them. Johnston says when varieties have been bred that are homozygous for these genes, that is, have them on both copies of a chromosome pair, resistance should be even better.

            I don’t have details about the genetic reasons for resistance of other varieties, such as ‘Juliet’ or ‘Legend’. The only other fact I can relay is that some wild tomato types have resistance through different mechanisms than the above. Examples are some cherry tomatoes and currant tomato, which is a different species than most tomatoes.

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In 2011, 'Juliet' died at USF, but in 2009 and 2010, it produced fruit in trials in my community garden. This fruit is smaller than an average past tomato, but larger than a plum tomato. Flavor is good, not great, but production is very good.

            The second genetic aspect, the other end of the resistance equation, is that the late blight organism is not genetically uniform. The correct term for the variations are “clonal lines.” They are clonal because they reproduce asexually, thus they are identical to their parent organisms. Why are there different ones? Presumably due to mutations that appear from time to time. There have been 24 clonal lineages in the US, but some may have died out. In any given year, there may be 4 or 5 active ones.

            I have made slow progress on tying tomato variety resistance to clonal lines of the late blight organism. I do know that ‘Legend’ resists US3 and US11. And I know these aren’t the clonal lines we have, because ‘Legend’, touted as a breakthrough in late blight resistance, dies first in my trials.

 What Clonal Lines do We Have?

            When I realized that resistant varieties may have resistance to specific clonal lines of late blight, I saw the importance of finding out which clonal lines we have in the Bay Area. Until recently, I was having difficulty finding this out. The breakthrough this year is locating the website www.usablight.org . This USDA-funded project is a national consortium of late blight researchers. They don’t know what clonal lines we have, but they want to know!

            You can help find out by submitting samples of your infected plants. Do this by going to the website and clicking on “reporting outbreaks,” then on “first time registration.” Register now so you will be sent a copy of the APHIS permit you will need in order to submit samples, since they will be shipped across state lines, to a lab in Oregon. Once you have the permit, you will be able to print copies of it to include with your samples. They prefer leaflets that have blackened lesions, but which have not yet wilted, and would like at least five examples in a sample. You register your sample online, so you will get a sample number to write on the sample bag before you send it, and can then use that number to track your results. You also print out a sample submission form to include with your sample, and write the sample number on that too.

            Full directions are on the website. I encourage you to look and register now, so you will be ready when the disease shows up.

A List of Tomato Varieties You Might Like to Try

            Here is a list of varieties I have trialed, plus a few I haven’t yet, as reported in my Chronicle/SFGate column, follows. (See that article at http://www.sfgate.com/columns/goldengategardener/archive/ for full trial results.) My best results so far have been with ‘Juliet’, ‘Defiant PhR’, ‘Mountain Magic’ and, in a warmer SF microclimate, with ‘Golden Sweet’. As seed sources for varieties listed below, start with Johnny’s Selected Seeds and Totally Tomatoes.

Note: Numbers (i.e. “70-75) indicate days from transplanting to first ripe fruit under normal conditions, though San Francisco plants may be slower. Det=Determinate or short plant. Ind=Indeterminate, or tall plant. These varieties are listed in order of fruit size—smaller to larger. For more information, such as flavor and other disease resistance, see seed catalogs.

*in my 2009 trial, **in my 2011 trial, ***in both trials

*Currant tomato—70-75, Ind, fruits under ½”, avail in red, yellow, and white. This is Solanum pimpinellifolium, a different tomato species that has some resistance.

*Matt’s Wild Cherry—60, Det, fruits marble-sized, red, some resistance.

*Tommy Toe—70, Ind, ½ -1” round red, fruit, some resistance

*Koralik—61, Det, 1” fruit, round red, some resistance

Red Pearl—58, Ind, 1 oz. oval fruit, said to have intermediate resistance

**Golden Sweet F1—60, Ind, oval, grape-sized yellow fruit, moderate resistance

**Plum Regal F1—68, Det, 4 oz., oval, red fruit, moderate resistance

***Juliet F1—60, Ind, 1½-2 oz. oval, red fruit, in clusters, moderate to good resistance

**Mountain Magic F1—66, Ind, 2 oz., red fruit in large trusses, good resistance

**Defiant PhR F1—70, Det, 5-7 oz. round, red fruit, good resistance

***Legend—70, Det, 4-5 inch, round, red fruit, poor resistance in my trials.

Ferline F1— Ind, 5 oz., round, red fruit, listed as “tolerant” of late blight.

Old Brooks--70, Ind, large fruited, said to have “superior” resistance

Please do write me if you have questions or any results to report. You can send me email at home@sfchronicle.com or write a comment into this blog.