Tomato Disease Issues in the Garden

As I have posted in the weekly updates we have several tomato issues in the garden.  I have been researching these issues and have come up with the following information.

GROWTH CRACKS

Growth cracks result from extremely rapid fruit growth. This may be brought on by periods of abundant rain and high temperatures, or can occur when water is suddenly available to the plant through rain or irrigation after a period of drought. Cracks may radiate from the stem end of the fruit or may encircle the fruit. Cracks are often invaded by secondary fungi and bacteria that further rot the fruit.

Maintaining even moisture by watering regularly and mulching the soil around the tomato plant can help reduce growth cracks. Varieties differ in susceptibility to cracking, and variety descriptions may be helpful in choosing a plant less likely to crack.  Heirloom tomatoes are most susceptible to growth cracks.  I still like them even though,due to our heavy rains, we have many growth cracks this year.

BLOSSOM END ROT

Among the problems we have seen with our tomatoes is blossom end rot.  This is very common among Roma tomatoes.   Affected fruit have a tan to black flattened spot at the blossom end of the fruit. Secondary fungi and bacteria can enter the blossom end rot area, resulting in further decay of the fruit. Blossom end rot can appear on fruit in any stage of development, but it is most common when fruit are one-third to one-half grown. The first fruit produced by the plant are often most severely affected. Fruit that develop later in the season on the same plant can be unaffected. I generally, in the past, ignored this problem unless it became so rampant that I did not get enough fruit.  I was warned that some people believed there were calcium problems in the soil of the Community Garden and the cause of blossom end rot is calcium deficiency in the tomato plant. Although blossom end rot means that the plant does not have enough calcium within the developing fruit, it does not mean that there is a lack of calcium in the soil. Often blossom end rot occurs as a result of several cultural or environmental factors that affect the plants ability to take up calcium. Fluctuations in soil moisture, heavy applications of nitrogen fertilizer, and injured roots can all predispose tomato plants to blossom end rot.

Blossom end rot, M. Grabowski

The amount of calcium salt available to the plant decreases rapidly in the presence of excessive salts such as potassium, magnesium, ammonium, and sodium. Extreme fluctuation in moisture can also reduce the availability of calcium salts needed by the plant. Heavy applications of nitrogen fertilizers and abundant rain cause rapid and luxuriant plant growth and predispose the fruit to blossom-end rot, especially during periods of dry, hot weather.

Blossom-end rot can be minimized by maintaining a uniform supply of moisture through regular watering and soil mulches, applying fertilizer according to the results of a soil test, and avoiding root injury by not cultivating within 1 foot of the base of the plant.

Although we have blossom end rot on a few plants it is not wide spread and can be linked to the heavy rains we had so is not unexpected.  I just pick the damaged fruit and dispose of it.

VERTICILLIUM WILT

Probably verticillium wilt

However among the plants we have other symptoms such as spotted and dying leaves.  So my first thought was we might have Verticillium wilt.  This is a common fungus and I have seen it before in my herbs and my maple trees. The fungi causing this disease overwinter in the soil as mycelium or on plant debris as microsclerotia. The fungi infect a susceptible host through wounds in the roots caused by cultivation, nematodes (microscopic worms), or the formation of secondary roots. This disease is considered a cool-weather disease, developing between 65° and 83°F.  Since we had a very cool start to the season I thought this was a great disease to start with in my research.

verticillium wilt

Diseased plants often have only a portion of the plant wilting, such as one or two stems rather than the whole plant, but it will be a whole section of a plant, not a few leaves or branches.  The look of my tomato plants is a bit different than what is expected in Verticillium wilt.  However, my search here took we to other fungal diseases that lay dormant in the soil and that was when I discovered early blight.

EARLY BLIGHT

Early blight is a common tomato disease caused by the fungus Alternaria solani. It can affect almost all parts of the tomato plants, including the leaves, stems and fruits. The plants may not die, but they will be weakened and will set fewer tomatoes than normal. Early blight generally attacks older plants, but it can also occur on seedlings. Stressed plants or plants in poor health are especially susceptible. Early blight is also a problem with potatoes.

Symptoms: Dark spots with concentric rings develop on older leaves first. The surrounding leaf area may turn yellow. Affected leaves may die prematurely, exposing the fruits to sun scald.

Early Blight fungus overwinters in plant residue and is soil-borne. It can also come in on transplants. Remove affected plants and thoroughly clean fall garden debris. Wet weather and stressed plants increase likelihood of attack. Copper and/or sulfur sprays can prevent further development of the fungus. 

The best treatment for this is to rotate crops.  It can take 4 to 6 years to work out of the soil.  And it comes from infected plant material not being removed as well as coming in on seedlings and compost materials imported from other locations.  In other words all the ways people grow plants in a community garden increases the potential for this disease to be present.  There are no good ways to treat for this fungus in a home garden so the best treatment is disease resistant plants.  

Here is a list of some resistant plants: 

Aunt Ginny's Purple - Heirloom, indeterminate, beefsteak (16 oz.) 
Big Rainbow - Heirloom, indeterminate, bi-color beefsteak (16 oz.) 
Black Plum - Heirloom, indeterminate, plum (2 in.) 
Juliet - Hybrid, indeterminate, cherry (1 ounce) 
Legend - Open-pollinated, determinate, beefsteak (14-16 ounces) 
Manyel - Heirloom, indeterminate, yellow globe (8-10 ounces) 
Matt’s Wild Cherry - Heirloom, indeterminate, cherry (1/2 inch) 
Mountain Supreme - Hybrid, determinate, globe (6-8 oz.) 
Mountain Fresh Plus - Hybrid, determinate, globe (12 ounces) 
Old Brooks - Heirloom, indeterminate, globe (6-8 ounces) 
Tigerella (aka Mr. Stripey) - Heirloom, indeterminate, globe (4-6 oz.) 
Tommy Toe - Heirloom, indeterminate, cherry (1 inch)

Resources:

        Identifying Diseases of Vegetables, by MacNab, Sherf and Springer, Penn State, 1983 

   University of Minnesota Extension service website 

         http://www.extension.umn.edu/garden/yard-garden/vegetables/#tomatoes

Texas A&M Agrilife Extension website
      http://aggie-horticulture.tamu.edu/vegetable/problem-solvers/tomato-problem-solver/