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Tomato fruit disorders
Clark MacCallister

Tomato season is in full swing and many local gardeners have been seeing several different issues arise. Much of what I am seeing on tomatoes is non-pathogenic disorders, meaning they are not caused by a disease and are not infectious. The main tomato fruit disorders I have encountered are blossom-end rot, cat-facing, cracking, zippering and sunscald.

Several of the common tomato disorders are just the plant responding to unsuitable weather conditions. Many of them can be corrected by adjusting water and environment.

I wrote about blossom-end rot in a column a few months ago. This disorder leaves dark, sunken lesions on the bottom end of a tomato fruit. It is caused by a calcium deficiency, usually brought on by irregular or insufficient watering. Increased irrigation will help alleviate this issue.

Cat-facing is the next most common tomato disorder I see routinely. This is characterized by fruit with deep, scar-like indentations that distort the fruit on the blossom end. The indentations can run the length of the tomato. Cat-facing is caused by low temperatures during flowering, which causes the female part of the flower to develop abnormally. Long periods of cool daytime and nighttime temperatures can lead to cat-facing. Using row covers can help avoid this disorder during cooler periods.

Cracking is another disorder often seen on tomato fruit. The cracks can be either radial or concentric. Radial cracks looks like the spokes of a wheel coming from the stem end of the fruit. They are the result of excessive watering after an extended dry period. Even watering will help prevent these cracks.

Concentric cracks form on the shoulders of the fruit and appear as rings of brown scar tissue. These are often caused by droplets of water being exposed to heavy sun. Maintaining healthy foliage cover on the tomato plants should keep the fruit from cracking.

Zippering is a disorder that shows up as thin lines of brown tissue running from the stem end to the blossom end, resembling a zipper. This is the result of part of the tomato flower remaining stuck to the new fruit during development. Choosing varieties not prone to this disorder is the only known method to avoid zippering.

Sunscald is a disorder caused by heavy exposure to sunlight. Fruit will appear bleached and blistered on the surface. Maintaining healthy foliage on the plant, avoiding excessive pruning and planting vines closer together can help avoid sunscald.

Most of these disorders are very common this time of year. Luckily, most can be prevented by a slight change in cultural practices. Simply adjusting things like irrigation frequency, plant spacing and changing varieties can often make big difference in dealing with these annoying issues.