Grow Your Tomatoes
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Tomato diseases and disordersThese are some diseases I have documented myself, as well as a link to additional disease info and photos.
Late blight is encouraged by cool, wet weather conditions and severe cases of it can kill crops of tomatoes. Common symptoms are brown areas on fruit, brown areas on the stem, and gray-brown lesions on the leaves.
The brown rot on the fruit is not the same as blossom-end rot and may appear similar to buckeye rot. Blossom-end rot affects only the blossom end of the fruit, while late blight can cause rot on any part of the fruit. Buckeye rot is caused by soil contacting the fruit, and won't be found higher on the plant.
Late blight is also found on other plants in the same family as tomatoes. It can infect and devastate crops of potatoes, and it can also affect peppers, eggplant, and wild plants such as nightshade, ground cherry, etc. Tomatoes and potatoes seem to be affected the most by late blight.
In the spring of 2009, shipments of Bonnie® tomato plants infected with late blight were sent across the US to thousands of stores. Favorable conditions for the blight, especially in the Northeast, promoted rapid growth and spread of the disease.
Late blight spores may be killed in the ground overwinter, if the ground freezes. Airborne spores do not last long, especially in dry or hot weather. The airborne spores can travel with the wind and can be transmitted to other plants by wind and sometimes by rain. Any infected tomato plants must be pulled, and sealed in an airtight trash bag and disposed of in the trash. Do not compost any infected tomato plants!
The disease can be soil-borne and may be transmitted by watering the plants if water splashes up onto the stem. It is also more prominent in cooler weather. To help prevent this disease, use sterilized soil-less seed starting mix, and water the mix carefully and don't splash the stems. (Bottom watering is preferred by some as a better way to water seedlings.)
Some people like to give seedlings "cold treatment," a period of a couple weeks long with lowered temperatures, which helps develop stronger plants. The period of colder temperatures increases risk of damping off, but if other preventative measures are taken, you can grow seedlings in cooler temps without much worry.
Blossom-end rot (BER)
Blossom end rot is not a true disease; it happens when tomatoes are do not receive enough water. While overwatering can cause excessive cracks in tomatoes, underwatering can cause blossom-end rot.
The rotten patch starts from the blossom end (bottom) of the tomato. If it gets bad enough, it can consume half of the tomato. I have only had mild cases of BER because I frequently water.
Some varieties are more prone to BER than others. Cherry tomatoes, for example, rarely get BER if at all. Plum tomatoes, such as Roma, on the other hand, are much more suceptible to BER.
If you have tomatoes with blossom-end rot, you can eat the undamaged portion of the fruit. BER does not render the fruit inedible unless it has consumed a substantial portion of the fruit. BER like that in the photo above is mild and can be sliced off.
Also not a disease, catfacing is common when temperatures are cool. It happens as the bud is just forming. Catfacing is not noticeable till a fruit is set. The fruit is often misshapen at the blossom end, with creases or folds and tough, brown scarring. The above picture is of some severe catfacing that happened to one of my White Wonder heirloom tomatoes.
Unlike the tomato in the picture above, catfacing is usually less severe and may appear as creases and/or indentations in the blossom end surrounded by thin brown scarring.
Like blossom-end rot, catfacing is more likely in some varieties than in others. To avoid catfacing, pick off flowers during cool weather and/or select varieties that aren't as suceptible to catfacing. Tomatoes that are not severely catfaced may be eaten; catfacing does not effect edibility of tomatoes.
Not a disease. It can happen to green or ripe tomatoes. When the fruit are exposed to direct, strong sun for extended periods of time, they will develop sun scald. It can take days for the scald to appear, but continuous sun exposure will eventually create yellow or white, bleached areas on the fruit that may be slightly shriveled. Sun scald happens when there isn't enough leaf cover to shade the fruit. Heavily pruned plants, or diseases that kill the leaves, can result in sun scald because of loss of leaves. Artificial shade (paper plates, fabric, etc) can be used to protect tomatoes from the sun.
This disorer is caused by stink bugs. The immature and adult bugs pierce the fruit much like a mosquito would do to a person. The result is often yellow or otherwise pale-colored irregular spots under the skin of the fruit. I have found tomatoes with mild to moderate cases of cloudy spot to be fine for eating. The damage is usually just below the surface of the skin, and from my experience, the fruit can be eaten.
If you ever see stink bugs on your tomato plants, kill them right away. Don't use insecticide spray on or near your tomatoes - pick the bugs off by hand or crush them with pliers.
Dodder is an orange or yellow, parasitic vine that does not photosynthesize. Instead, it steals the nutrients it needs from host plants, by winding around and attaching to the stems. When dodder sprouts from seed, it must find a hostplant within a few days or it will die. When it finds and attaches to a host, it detaches from its roots and continues to grow on its host plant without roots.
Dodder is an annual plant that will die out during the winter, but the seeds can survive a few years in the soil. The leaves are almost nonexistent - they are merely bumps at the stem nodes. Dodder flowers mid to late summer. It can only feed on plants that are dicotyledons, which includes tomatoes. Grasses are monocotyledons and are not host to dodder.
If you ever were to see a yellow or orange, string-like plant sprout in your garden, you would need to pull it up immediately before it could reach your tomatoes. Even if you detach dodder from its host plant, it can re-grow from haustoria that are left inside the stem. Dodder haustoria are basically parasitic roots that grow inside the host plant's vascular systems and suck nutrietns from the host. They cannot be removed simply by pulling, and will re-grow if the main dodder stems are removed.
If you ever find yourself in or around a patch of dodder during late summer, you should change clothes before going near your tomatoes to prevent stray dodder seed from spreading to your garden.
In California, Dodder has caused some problems for commercial tomato growers. But like I said, it usually doesn't invade home gardens.
Other diseases and disordersClick here for a Web page with plenty of photos to help diagnose many common tomato diseases and disorders.
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