Grow Healthy Tomatoes
Tips for spotting diseases and problems
If your tomatoes aren't at their prime this season (or haven't been in the past), any number of culprits could be to blame. Below is a brief description of the most common tomato problems, along with some suggestions for avoiding them next year.
This fungal disease is perhaps best known for killing thousands of dogwood trees around the country. It causes sunken spots on tomatoes that look water-soaked and that often form concentric circles that look like a bulls-eye. If you suspect an anthracnose attack, remove any infected plant parts from your tomato and throw them away; the plant may survive. To prevent further infections, pick fruits promptly, promote good air circulation, and keep the foliage dry. Never compost infected plants or fruit.
If you cut open a tomato and find a dark rotten part inside, the culprit is blackheart. This is a problem, but not a disease. It's caused by a lack of calcium. Your plant might have been "hungry" for calcium for any number of reasons, including drought, a variation in the amounts of soil moisture when the fruits were forming, root damage, or heavy soils.
This disease was the cause of the dreaded Irish potato famine. Late blight also affects tomatoes. The diseases shows up as spots on leaves and stems that appear water-soaked. These spots can grow into large, dark lesions. A white, fuzzy mold may appear on the bottom of the leaf as the disease progresses. Remove and destroy any affected parts promptly. Spots may also form on green fruits and expand, causing malformed fruit with dark lesions. To help avoid this disease, don't plant tomatoes and potatoes together.
If all or some of the blossoms fell off your tomato plants, stress was the cause. Stress occurs when your garden suffers from sustained high temperatures (above 90 degrees F daytime; above 75 degrees F nighttime), large temperature swings, cold weather (below 55 degrees F), drought, soil that was too dry, or excessive moisture fluctuations.
This common problem shows up as a dark, sunken area at the bottom of fruits. The rot enlarges and can cover a good portion of the fruit as it grows. As with blackheart, the cause is a lack of calcium.
Botrytis (gray mold)
This disease causes spots on tomato leaves that look water-soaked, while the fruits show pale halos that can be up to 3 inches across. The halos start out white and turn yellowish as the fruits mature. A gray, fuzzy mold may appear on the affected parts of the plant, too. Botrytis is spread by spores in the soil, so avoid splashing leaves when watering. A thick layer of mulch (3 inches or more) will help.
A common pest in hot arid climates is the bronze mite (also called tomato russet mite). Thousands of these minute critters can turn a tomato's main stem bronze and its leaves brown. Spray plants with sulfur every few weeks to control.
Ugly, gnarled fruits with scars near the blossom end are caused by cold temperatures or uneven moisture while fruit is developing, or by viruses, fungi, or insect damage. Remove catfaced fruits to encourage later crops.
Fruit that cracks at the stems or shoulders is caused by too much moisture while fruit is developing. Don't overwater at this time. Some tomato varieties are prone to cracking, and some are more resistant. Seed catalogs and packets should offer this information.
A frost-damaged plant has wilted leaves that look water-soaked, and damaged leaves and stems often turn black. (Because tomatoes are tropical plants, they can't tolerate cold temperatures. When they do get cold, the plant cells freeze and the cell contents leak out.)
The first symptom of this common soil-dwelling fungus is wilt. Bottom leaves will turn yellow and fall off first, and you might also notice that the insides of the affected stems are discolored. Eventually fusarium will kill the whole plant. The fungus loves warm soil--above 82 degrees F--so if you garden where it's hot, lay down a cooling mulch early (a layer about 3 inches or more is best). Once fusarium attacks your plant, destroy it. Don't compost the plant, though, because it may spread the disease to your compost, and then on to your other plants.) Resistant varieties are marked "F" or "FF."
Root knot nematodes are tiny, worm-like creatures that attack plant roots and kill affected plants. Nematode-affected plants may have yellow leaves, become stunted, and wilt. If you suspect nematodes, dig out the affected plants and inspect their roots. If nematodes are your problem, the roots will generally look stunted and knobby. Destroy any infected plants. To prevent this problem in the future, try planting resistant varieties (designated with a "N" on the packaging) and rotate your tomato-family crops each year.
Although you may be familiar with the type of powdery mildew that affects garden plants such as phlox and lilacs, a different strain of this disease can also attack your tomatoes. The main symptom of this fungus is white or gray spots that form a powder which eventually covers the leaves and fruits. Affected plant parts discolor and drop. Powdery mildew likes still air and lower light conditions. Keep lots of space between your plants to help your tomatoes stay safe from this disease.
Septoria leaf spot
This fungus attacks older plant leaves first, covering them with yellow spots that darken to brown or black and often become rings. The affected leaves eventually fall off. Remove and destroy infected leaves at first sign of infestation. If the problem continues, destroy the plants.
Just like people, plants can get sunburned. Sun-damaged fruits first show blisters, which dry out into pale, bleached areas. Leaves become shriveled and dry. Sunburn is generally only a problem when there is extra light reflected off of a surface onto the plant--such as if you plant your tomatoes next to a white building.
Tobacco mosaic virus (TMV)
Viruses are the worst diseases in the plant world. They cause abnormal, distorted growth, mottled leaves, blotchy fruits, and stunt entire plants. TMV, one of the worst viruses, is spread in many ways, including by human contact with tobacco products. Destroy all infected plants the moment you suspect this disease. To prevent infection, wash hands after handling tobacco. Resistant varieties are marked "T."
This shows up as a wilt, much like fusarium, except that verticillium thrives in cooler conditions. This disease causes leaves to become yellow or mottled, and like fusarium, it causes the bottom leaves of a plant to wilt first. Later, the whole plant dies. Remove and destroy affected plants as soon as wilt strikes. Resistant varieties are marked "V."
Prevention is the best care
Planting tomatoes that are resistant to the diseases most common in your area is the best way to prevent problems. Resistant varieties are labeled V, F (or FF), N, T, and A after the name of the plant to designate which diseases or problems they resist.
Thursday, August 26, 2010 12:42 PM
This year we are finding that the center of tomatoes are very hard and white inside. After this is removed only a small ring of the tomato is left, the skin and small amount of fruit. What is causing this?
Thursday, August 26, 2010 7:02 PM
What causes the white hard spots under the skin of tomatoes
Sunday, August 29, 2010 7:14 PM
This would have been a very helpful article if it had included some good photos.
Friday, February 25, 2011 2:36 PM
It sounds like your tomatoes may have been infected by stink bugs. Have you seen any around your plants. They inject a substance into the tomatoes that prevent the tomatoes from ripening in that area resulting in a very hard white area.
ralph and beth
Sunday, May 22, 2011 5:40 PM
what is the blossum end of a tomatoe? ( thank's) rdandbeth@WINDSTREAM.NET
Saturday, June 25, 2011 10:38 PM
My tomatoes are blood red inside, its kinda creapy. What causes this and are they ok?
Thursday, February 09, 2012 9:49 AM
Would be nice to have an article on the dreaded hornworm and its prevention. I got them for the 1st time last summer. Nasty things!
Wednesday, June 20, 2012 8:38 PM
My tomato blooms won't set.. Is there anything I can do to help them.. Beautiful plants, just no tomatos
Thursday, July 19, 2012 8:13 PM
it depends on what kind of tomato it is, i have cherokee black tomatoes that are lack inside. so your tomatoes should be fine @bulldogmama
Tuesday, January 15, 2013 6:10 PM
last year i had a tremendous bounty of sweet 100 cherry tomatoes (got about 600 from 2 plants), at what appeared to be the end of the plants life i got 60 to 100 tomatoes each day for about 4 days then not much after that. my question is; the plant got yellow leaves starting at the bottom moving up very slowly through the season eventually turning brown after the tomatoes were harvested starting from the bottom up. the producing stems higher were very healthy looking and the fruit was awesome. is this the normal progression of the tomato plant as it gets hotter and later in to summer or a sign of some kind of problem. i am a rookie gardener in Oklahoma city
Tuesday, September 10, 2013 11:37 AM
Could really use some help on preventing Tomato/horned worms. I see that Mboley asked for help back in February...we are being overrun by these horrible creatures. Thanks
Tuesday, September 10, 2013 12:18 PM
So sorry to hear about the tomato hornworms! This University of Minnesota article has lots of information, not a lot you can do, but at least you know what you're up against.
One of the most interesting tips is that if you see them with the white wasp larve on their backs, to leave those ones be because those wasps are natural predators. It says:
"Tomato hornworm larvae are also parasitized by a number of insects. One of the most common is a small braconid wasp, Cotesia congregatus. Larvae that hatch from wasp eggs laid on the hornworm feed on the inside of the hornworm until the wasp is ready to pupate. The cocoons appear as white projections protruding from the hornworms body (see photo, left). If such projections are observed, the hornworms should be left in the garden to conserve the beneficial parasitoids. The wasps will kill the hornworms when they emerge from the cocoons and will seek out other hornworms to parasitize."
Also: Tilling after harvest helps kill them: "Tillage has shown to cause up to 90% mortality."