As tomato growers, we might consider any ailing tomato to have a disease. That would end up making this blog post really, really long. However, we need to consider diseases separately from damage done by pests (both vertebrate and invertebrate—see blog post from July 18: Tomato Diseases in the Home Garden) or environmental disorders such as blossom end rot (see blog post from July 4: https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=57297). We will cover fungal, viral, and bacterial diseases here.

Fungal
The most common tomato diseases are fungal. Many of these fungal spores are nearly everywhere all the time, and given the right conditions, will find a home on your tomato plants. Some fungi prefer cool conditions while some prefer warm. Most prefer wetness and high humidity. Crowding can prevent proper air circulation and encourage fungal diseases. Nutritional deficiencies and injuries also encourage fungal diseases.

Damping Off Disease typically affects seedlings. It's caused by various soil fungi that grow under damp conditions. The affected tap roots of seedlings in contaminated, overly damp soil are dark and mushy and the seedlings usually die. Prevent this by using fresh clean soil and sanitized containers with good drainage. Use alcohol or a 10% bleach solution to sanitize. https://ipm.ucanr.edu/PMG/PESTNOTES/pn74132.html

Septoria Leaf Spot is favored when plants are exposed to cool, rainy weather or splashing from soil. It's relatively uncommon in Contra Costa County. Prune off infected leaves and twigs and keep plants dry. https://ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISEASES/septorialfspot.html

Septoria leaf spot

Phytophthora Root and Crown Rot is a soil-borne fungus-like organism transmitted under wet conditions by splashing water or contaminated garden debris, pots, or tools. Plants appear drought-stressed since the vascular system is compromised, and often die. It can also cause damping-off. Look for darkening of the crown, roots, and stems. Good drainage, avoiding overwatering, and sanitizing any tools used on the diseased plants are preventive measures. In previously affected soil, avoid planting members of the Solanaceae family (tomatoes, eggplant, peppers, potatoes) in the infected soil and plant a resistant crop instead such as corn. https://ipm.ucanr.edu/PMG/PESTNOTES/pn74133.html

Phytopthora root rot

White Mold, also called Cottony Soft Rot, appears as bleached areas on stems from white mycelia. Fruit can be affected and appears gray. The mold favors hot, moist conditions and often spreads from dying flowers. Bury or dispose of infected tissue; avoid overhead watering, overwatering, and crowding. https://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/tomwhmold.html

Powdery Mildew looks different on artichoke, pepper, and tomato leaves from its appearance on other plants (see reference). It requires warm weather and living tissue to grow but does not require moist conditions. Prevention includes planting resistant varieties in sunny areas and avoiding crowding. Occasionally a fungicide or a biologic is needed. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7406.html

Early Blight's name is somewhat misleading as it occurs on mature tomato plants and can affect fruit. It is uncommon in our Mediterranean climate. See reference for photos, prevention, and treatment: https://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/tomearlyblight.html

Late Blight (Phytopthora infestans) occurs in our coastal areas and is favored by average temperatures and high humidity. It can spread rapidly from other Solanaceae family members or their cullings. Avoid overhead sprinkling and crowding of plants and buy certified blight-free seeds and tubers. Dispose of affected plants and debris in green waste. https://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/lateblight.html

Black Mold typically affects ripe tomato fruit during conditions of warmth and high humidity. It can appear as small dark brown spots or grow into large, sunken areas. Pick fruit as soon as it ripens. https://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/tomblkmold.html

Verticillium and fusarium wilt are fungal diseases that will be discussed in an upcoming blog.

Viral
Tobacco Mosaic Virus is a disease primarily of Solanaceae, of which tobacco is a member. It is transmitted by infected seeds or by tobacco residue on the hands of smokers. The leaves appear mottled and stringy, but the fruit is edible. Herbicide damage can appear similar. Many tomato cultivars have resistance. https://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/tobaccomosvir.html

Curly Top Virus and Spotted Wilt Virus are fairly unusual afflictions. Curly Top Virus is carried by the beet leafhopper and causes curling, puckering, and stunting of leaves. Fruit is usually discolored and small. Spotted Wilt Virus is transmitted by the western flower thrip. It can be difficult to diagnose as it presents differently depending on the stage of plant growth. Fortunately, it's rare in Contra Costa County. Both have wide host ranges. For severe infections in the garden, testing may be warranted since the viruses can mimic other diseases. Affected plants will need to be removed and disposed of. Unfortunately, insecticides do not kill thrips or leafhoppers in time once the damage has been noticed. https://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/curlytop.html
https://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/tomspotwltvir.html

Spotted wilt virus on tomatoes

Bacterial
Bacterial Speck, Bacterial Spot, and Bacterial Canker are all easily confused. They tend to be introduced on infected seeds, and can overwinter on garden debris, flats, and stakes. They all prefer wet conditions. All three cause lesions on fruit. Speck and Spot cause similar leaf lesions and are chiefly distinguished by their appearance on fruit.

Bacterial Speck prefers cooler conditions such as in coastal regions. A Pseudomonas bacterium causes small sunken spots with white halos that can become scabby. The leaf spots are similar and appear greasy, and leaf margins can turn brown in an angular pattern. Stems can also be affected.

Bacterial speck

Bacterial Spot is caused by Xanthomonas bacteria, resulting in large, black, sunken spots on fruit and irregular black spots on leaves. Warm, humid conditions favor its appearance. The fruit may be eaten once the black spots and any underlying maceration are removed. https://u.osu.edu/vegetablediseasefacts/tomato-diseases/bacterial-leaf-spot/basics/

Bacterial spot

Bacterial canker

Bacterial diseases can be managed somewhat with copper sprays and these sprays are acceptable for organic farming.

Prevention
Prevention is the ideal way to manage all these diseases:
• Rotate crops
• Don't overwater or spray the plant
• Don't crowd plants
• Remove lower leaves that can touch the soil
• Use mulch to prevent spread from soil
• Buy resistant varieties
• Control weeds to prevent thrip and leafhopper invasions
• Dispose of infected plant parts and debris, sanitize tools, planting flats, and hands
• Baby heirloom tomatoes because they typically have little resistance

For more information about pests and diseases of tomatoes, see this website: https://ipm.ucanr.edu/home-and-landscape/tomato/index.html

Help Desk of the UC Master Gardeners of Contra Costa County (EAS)

It's July and the tomatoes in your garden are finally starting to ripen. One afternoon you notice the first ripe one is nearly ready to be picked. The next afternoon, you head out to harvest the tomato and find it on the ground looking like this one: 

Photo credit: B.Messenger-Sikes

After you get over groaning about the loss of your first ripe tomato of the season, you may wonder, “What critter ate my tomato? And what can I do to stop it?” Here are some tips to answer those questions.

Many home gardeners love eating garden-fresh tomatoes. Unfortunately, many pests also love to share in the bounty of vine-ripened tomatoes. Known nibblers on home-grown tomatoes include birds, rabbits, squirrels (both ground and tree), rats, hornworms, and even slugs and snails.

Start by doing some detective work to figure out likely suspects. In this case, the half-eaten tomato was on the ground near the plant. That fact narrows the list of possible pests. It's not a hornworm, slug or snail which had no means or incentive to remove the tomato from the plant. Also, it is probably not a bird which would more likely peck on the tomato while it remains attached to the plant. So, we're left with rabbits, squirrels and rats as the leading suspects of interest.

Can you narrow the list further? Unless you live near an open space area where you've seen ground squirrels foraging near their burrows, you may also be able to eliminate that suspect as well. If you have the misfortune of trying to grow a garden close to ground squirrel territory, it would be unlikely that one missing tomato would be your first experience with the critter in your garden. Hopefully, you're already familiar with the University of California's recommendations for managing the pest. If not, you can find UC's recommendations here: https://ipm.ucanr.edu/home-and-landscape/ground-squirrel/pest-notes/?src=302-www&fr=3777 We'll assume for this blog post that we can rule out the ground squirrel.

Likewise, you may be able to rule out rabbits if they don't live anywhere near your garden. If you do live near rabbits, it would also be unlikely that your first encounter with rabbit damage to your garden would be one missing tomato. A rabbit's diet preference is for succulent, green vegetation, with grasses and herbaceous plants making up the bulk of the diet. If rabbits are in your neighborhood, UC has very good suggestions for building a fence to exclude them from your garden: https://ipm.ucanr.edu/home-and-landscape/rabbits/pest-notes/?src=302-www&fr=3783 So, we'll also eliminate rabbits from the suspects list.

Now we're left with tree squirrels and rats as our leading suspects. Both pests love to eat tomatoes—particularly just as they are ripening. Maybe you've never seen a rat in your yard or neighborhood but frequently see squirrels. Don't assume that fact means that the squirrel is the top suspect. People don't often see rats, but most of us with gardens probably have them living nearby.

A good way to know whether a rat or a squirrel caused the damage is to figure out the time of day when tomato raids occur. In this case, you visited your garden on two successive afternoons so there is no way to know for sure what time the tomato was stolen. But the culprit is almost certain to visit your garden again as more tomatoes ripen. Get in the habit of taking a walk in your garden in the evening and again early the next morning. Squirrels are active only during the daytime and rats are mainly active at night. So, if you notice a tomato that looked fine on your evening garden visit is missing or partially eaten when you visit in the morning, you know the culprit and it's time to arrest the rat. And vice versa, when the tomato raid occurs in the daytime, a squirrel is the prime suspect.

If you decide the culprit is a rat, my recommendation is that you start setting some snap traps to kill them. This UC blog post has good instructions for trapping with an easy to set snap trap: https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=39179?src=blog43296. Be sure to take note of the blog's suggestion to bait the traps without setting them until the bait has disappeared a couple of times. Rats are very wary of new objects and will avoid them. If a rat visits an unset trap and safely eats the bait a couple of times, you're more likely to catch the rat once you start arming the trap.

If you trap a rat in your garden, you might want to do some further investigation to find where they are nesting. This UC website warns: “Once rats have invaded your garden or landscaping, unless your house is truly rodent proof, it is only a matter of time before you find evidence of them indoors.” https://ipm.ucanr.edu/home-and-landscape/rats/pest-notes/ The website also provides good directions on steps to take to make your house rat proof.

Finally, we come to the tree squirrel as the culprit—the toughest nut to crack. If you do an internet search for “how to keep squirrels from eating my tomatoes”, you'll find many sites that recommend using plant or chemical repellents with smells that squirrels don't like. The effectiveness of such repellants is questionable. Likewise, while frightening devices may work initially to keep a squirrel away, the squirrel will soon get used to it and start ignoring the device.

Live-kill squirrel traps are available, but they are much more challenging to set up and use successfully than the easily set snap traps used for rats. And some folks who are willing to kill rats may not feel the same way about killing a squirrel. Live trapping squirrels is also possible, but it is illegal to move a trapped squirrel to a new location. Squirrels trapped in a live trap must be humanely euthanized by gassing with carbon dioxide or shooting. Even if you are successful in eliminating a squirrel that was eating your tomatoes, chances are good that another squirrel will soon take over the territory and won't ignore your garden for long.

To protect a tomato plant from squirrels, consider building a cage around the entire plant using hardware cloth or chicken wire topped with plastic bird netting to exclude the squirrels from reaching the tomatoes. It may keep the squirrel out, but it will take some effort to build and will make it difficult to care for the plant and harvest ripe tomatoes.

To read UC's suggestions for managing squirrels, check out this website: https://ipm.ucanr.edu/home-and-landscape/tree-squirrels/pest-notes/?src=302-www&fr=3788

Here are a few more photos of nibbled tomatoes with links to the UC websites that tell you how to manage the culprits:

Hornworm damage to tomatoes

UC website: https://ipm.ucanr.edu/PMG/GARDEN/VEGES/PESTS/hornworm.html 

Snail damage to tomatoes. UC Website:

UC Website: https://ipm.ucanr.edu/PMG/PESTNOTES/pn7427.html 

CC license reference.DebRoby CCPDM1.0

Bird damage to tomato. UC website: https://ipm.ucanr.edu/home-and-landscape/birds/pest-notes/

Help Desk of the UC Master Gardeners of Contra Costa County (TKL)

When I first started growing tomatoes, I was reluctant and nervous about pruning my tomato plants for fear I would be doing it incorrectly. After 9 years of growing, I have learned that it is one of the best practices to include in your plant care. It is easy to do and produces better tasting and bigger tomatoes because you are helping focus the energy of the plant.

Here are a few simple tips for pruning your indeterminate tomato plants (determinate plants do not need to be pruned):

Removing suckers

• Suckers are the stems/leaves that grow out of the “V” junctions on plants. They grow fast and keep growing all season. These are best snipped off when they are small.
• Pinching can work as well but make sure you don't tear the tender stems. Before removing suckers wait until at least 2 leaves develop and pinch/snip just above that point.

Establishing the leader

• The leader is the main stem of the plant which starts near the ground.
• You may choose to allow additional leaders (or stems) to grow as well. There are advantages for each.
• Plants with two or more stems produce more tomatoes and greater/denser foliage which protects the plants from the sun. Tomatoes can sun burn!
• While the denser leaf canopy may reduce the incidence of black mold and cracking, it may also increase the incidence of other fruit molds such as gray mold.
• Plants with only one leader will bear fruit sooner but will ultimately produce a smaller total crop and may increase the incidence of some diseases due to the lighter foliage.

Topping your plants

• Pruning the top of your tomato plants once they have reached a desired height (usually about 5–6 feet) is perfectly acceptable and will push the energy down into the development of the fruit below.
• I find I need to continually do this all summer.

“Good to know” tips

• DO NOT Prune your plants when they are wet as this could spread diseases.
• DO prune off any bottom branches that are touching the ground as they can provide a direct vector for soil borne diseases to move onto the plant.
• DO prune off any yellowed or discolored leaves later in the season to keep the energy focused on the fruit.
• DO keep your nippers sharp and clean to avoid damaging your plants.

Below is a link to more information about growing and pruning tomatoes from the UC Master Gardener site: 

https://ipm.ucanr.edu/home-and-landscape/tomato/cultural-tips/index.html?src=307-pageViewHLS#:~:text=Pruning%20tomato,-Pruning%20is%20not&text=Plants%20with%20two%20or%20more,the%20others%20as%20they%20develop.

Happy Growing!

Help Desk of the UC Master Gardeners of Contra Costa County (PDS)

It is not unusual to find tomato seedlings for sale in local nurseries and big box stores as early as February or March. Don't make the mistake of rushing to plant them in your garden. In our County it is much too early to put tomato seedlings in the garden, but it is the perfect time to make plans for a bumper summer crop of garden-ripened tomatoes.

When should you plan to plant tomato seedlings in the garden? The easiest way to determine when it is time to plant is to check the soil temperature. The soil should be no less than 60º Fahrenheit when you transplant tomato seedlings. When soils will reach that temperature will depend not only on the climate of the garden location but also on soil type. Sandy soils will warm sooner than clay soils, and soil or potting mixes in containers and raised beds will warm more quickly than soils of in-ground garden beds.

To check, use a thermometer—a soil or kitchen type both work--and measure the temperature at a depth of four inches below the soil surface. Check early morning when the soils are at their lowest temperature. The soil temperature will reach and maintain at least 60º F only after daytime highs are reliably in the 60's and overnight temperatures don't fall below 50º. In Contra Costa County those temperatures generally are achieved late April or early May. If you transplant seedlings by the end of May, the plants still have time to produce well.

So, you still have at least two months to get ready to plant tomato seedlings in your garden. Use that time to decide which tomato varieties you'll grow to get the best results. Two important topics to consider are identifying varieties that will grow well in your local climate and choosing varieties with resistance to diseases that may have been a problem in prior years.

If you live in a cool, foggy or windy climate, choose varieties with shorter “days to maturity”. “Days to maturity” is the estimated time the tomato variety will take to start producing harvestable tomatoes after seedling transplant to the garden. Tomatoes requiring 75 or fewer days are more likely to produce crops in cool climates than those with longer maturity. Most cherry tomato varieties need less than 75 days to start producing, and you can also find some “slicer”,” paste” and “beefsteak” tomato varieties that reach maturity in 75 or fewer days.

If you live in the hot, dry climate found in interior areas of our County, look for varieties with good heat tolerance. They may include both varieties with short days to maturity and those with longer maturities. An internet search for “tomatoes for hot, dry climates” will identify sites with lists of tomatoes well adapted to grow and produce in such conditions.

If you have had disease problems when growing tomatoes in your garden in prior years, try to determine which disease was present. These links provide information that you can use to diagnose and manage common tomato diseases and other problems: https://ipm.ucanr.edu/home-and-landscape/tomato/index.html (Managing Pest in Garden) and https://ucanr.edu/sites/ccmg/files/140320.pdf (Tomato Growing Tips).

Often disease pathogens remain in the soil long after diseased plants are removed. If you've had disease problems, grow your tomatoes in a garden bed where you haven't previously grown tomatoes or other members of the Solanaceae (nightshade) plant family such as peppers, eggplants and potatoes. If your garden area is small and you don't have a disease-free planting area, grow your tomatoes in large containers or plan to plant hybrid varieties instead of heirloom varieties.

Heirloom tomatoes are “open pollinated” varieties that are grown from seeds passed down for more than fifty years. Seeds from open pollinated varieties grow plants that are a genetic match to those of the parent plant. A shortcoming of heirloom tomatoes is that they rarely possess resistance to common tomato diseases.

Hybrid tomatoes are varieties that are created by intentionally cross-pollinating two or more tomato varieties to achieve desired characteristics which may include disease resistance. Seeds from hybrids won't produce matching tomato varieties, so don't bother to save their seeds. If you have identified a disease that has caused problems in your garden, choose tomato varieties with resistance to the disease. Seed packages and descriptions of tomatoes in seed catalogs typically include letter codes to indicate any disease and pest resistance. Common codes include:

• V: Verticillium wilt
• F: Fusarium wilt; a code such as FF or FFF indicates resistance to multiple strains
• T: Tobacco mosaic virus
• A: Alternaria
• EB: Early Blight
• LB: Late Blight
• N: Nematodes (not a disease but microscopic worms that feed on plant roots

If you don't know the disease resistance of a tomato variety you want to grow, you can likely find it on this Cornell University website:
https://www.vegetables.cornell.edu/pest-management/disease-factsheets/disease-resistant-vegetable-varieties/disease-resistant-tomato-varieties/ You may not find tomato varieties with disease resistance to all tomato diseases. For those diseases, be sure to check the UC websites referenced above for tips on managing the disease.

Once you have identified tomato varieties you would like to grow, check with your local nursery to see if it plans to carry them. If you plan to shop the Great Tomato Plant Sale (GTPS) sponsored by UC Master Gardeners of Contra Costa County, you will find a list of tomato varieties that will be available at https://ccmg.ucanr.edu/EdibleGardening/GreatTomatoPlantSale/ If you aren't sure your targeted varieties will be available locally, it's not too late to order seeds and start your own plants. It will only take about six weeks from the time you plant seeds to have seedlings ready to transplant to the garden. Stay tuned for our next blog post to get tips for caring for seedlings and transplanting them to the garden. And mark your calendars for the GTPS which will be held “in person” at the Walnut Creek Our Garden location on April 1, 2, and 3 and at the Richmond Library on April 29.

photo credit: Terry Lippert

Help Desk of the UC Master Gardeners of Contra Costa County (TKL)