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Great Tomatoes!

Tomato growth habits and early blight

By: Sandy Feather ©2009
Penn State Extension

Q. Even though I have been raising tomatoes for many years, my plants are growing tall and lanky -- to six feet tall -- instead of being bushy. Also, the leaves start turning brown as soon as tomatoes start to ripen. This doesn't seem normal. What would you recommend Sandy?

A. Tomatoes can be classified by their growth habits. Those that produce tall vines that continue to grow, blossom and set fruit up until frost are classified as having an indeterminate growth habit. They can easily grow 6 to 10 feet tall through the growing season. These tomatoes are the ones most likely to outgrow all but the tallest stakes and sturdiest cages. It sounds like your tomato plants fall into this category.

Indeterminate varieties of tomatoes

Indeterminate varieties should be staked to keep the fruit off the ground to minimize problems with rot. Staking also allows better air circulation, which can reduce the incidence of disease problems. And staking allows more thorough coverage if fungicide or insecticide sprays are needed through the growing season. Examples of indeterminate varieties include Sweet 100 (cherry tomato), Big Boy, Brandywine and Beefmaster. Indeterminate varieties can be used for fresh eating through the growing season, as well as canning and freezing.


Determinate tomato varieties

Other varieties of tomatoes naturally have a bushier, more compact growth habit. They are classified as having a determinate growth habit. They grow to a certain size -- 3 to 3-1/2 feet tall -- then produce flowers and fruit. Determinate tomatoes tend to ripen together, which makes them a good choice for gardeners who grow tomatoes for canning and freezing. They are also good for fresh eating. Although many varieties are self-supporting, staking can help support a plant under a heavy load of fruit. Once they produce their main crop, production can fall off sharply, and the plants may go downhill quickly. Determinate varieties are much easier to grow in containers than indeterminate ones. Examples of determinate varieties include Roma VF (many paste tomatoes have a determinate growth habit), Better Bush, Bush Early Girl and Mountain Spring.


Semi-Determinate tomatoes

Still other varieties of tomatoes fall somewhere between these two growth habits, and are called semi-determinate. They will grow larger than determinate varieties, but are not as rampant as indeterminate ones.  They typically grow 3 to 5 feet tall. They should be staked, but are less likely to outgrow their stakes than indeterminate types. They will produce a main crop that ripens together, but will also continue to produce up until frost. Examples of semi-determinate tomatoes include Celebrity and Mountain Pride.

You may be happier with varieties that have a determinate or semi-determinate growth habit. Many seed catalogs include the tomato’s growth habit in the description, and most catalogs can be found online these days.

Browning of tomato leaves

The browning on the leaves is probably caused by one of several leaf spot diseases tomatoes are susceptible to. Early blight is one of the most common tomato diseases that matches the description of your problem. The fungus that causes early blight overwinters on plant debris in the garden. Good sanitation - removing all of the dead annual vegetable plants from the garden, cleaning up tomato stakes and ties, etc. - is an important step in controlling early blight. The fungus can survive up to a year without a susceptible host. It can also be introduced to the garden on infected transplants. It is always wise to practice crop rotation, even in small gardens.

If you grow tomatoes in the same place year after year, you increase the likelihood of insect and disease problems becoming established in the soil. Be sure to rotate among plant families rather than just individual plants. For example, tomatoes, potatoes, peppers and eggplant are all in the nightshade (Solanaceae family). A good rotation for tomatoes would be green beans or cucumbers because they are completely unrelated and are less likely to suffer from the same insect and disease problems. A three to four year rotation is recommended to allow diseased plant matter to decompose completely.

Early Blight

Early blight symptoms start close to the ground and work their way up the plant. The oldest leaves - those closest to the ground - are infected first as spring rain splashes up from the ground, carrying spores of the causal fungus that overwintered on bits of debris from last year’s garden. The leaves develop dark brown spots characterized by dark concentric rings. Usually some yellowing develops around the leaf spots, too. Spots range from pinprick-sized to one-half inch on diameter. Early blight develops under a range of weather conditions, but it is favored by heavy dew and/or rainfall, moderately warm weather (75 - 85°F), and high humidity.

Protecting Tomato Plants

Mulching around plants with an organic mulch such as clean oat straw or shredded leaves, or a synthetic mulch such as black or red plastic, reduces the likelihood of spores splashing up from the soil to infect the lower leaves. Use drip irrigation or soaker hoses rather than overhead watering, if possible.  You can also make fungicide applications to protect the plants from infection as they grow. Repeated applications are required through the growing season, at intervals recommended on the label of the product you choose. Organic gardeners can use a copper based fungicide. Daconil 2787 (chlorothalonil) is also labeled to control early blight in the home vegetable garden.


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