Master Tips from a Master Gardener (7/20/17)

Bill Koellner · Tuesday, July 18, 2017
As a master gardener, we often get questions about specific plants. There are three questions that I often get regarding tomatoes.

1. Why are my tomatoes leaves curling?

2. Why do I have blossom end rot?

3. Why are my tomatoes splitting?

Why are my tomatoes leaves curling?

There can be several causes for tomato leaves to roll or curl. Some of the main causes for these symptoms to occur are 1) physiological issues, 2) herbicide exposure, 3) viral infection, or 4) less common problems such as nutritional issues or insect infestation.

To determine which factor is the culprit, it pays to take a close look at the plant. Which leaves are rolling – old leaves, new leaves, all leaves? What direction do the leaves roll – upward or downward? Are any other parts of the plant, including fruit, exhibiting symptoms?

Physiological Leaf Roll:  Excessive moisture and nitrogen, heat, drought, severe pruning, root damage and transplant shock are some of the environmental factors that can cause physiological leaf roll in tomatoes.

Initial symptoms are usually apparent in the lower leaves with an upward cupping of leaflets followed by an inward lengthwise rolling of the leaflets toward the mid-vein. The affected leaves tend to become thickened and have a leathery texture, but retain a normal, healthy green color. Over time all of the leaves on the plant may be affected.

Interestingly, vine tomato varieties tend to exhibit physiological leaf roll more often than bush tomato varieties. While this condition can occur at any time of the growing season, it usually occurs at season changes. The condition has minimal impact on tomato fruit production and plant growth. Maintain consistent moisture level in the soil, and avoid over fertilization, excessive pruning and root damage during cultivation.

Viral Infections:  Some viral infections also cause leaf rolling in tomatoes. When tomato plants are infected with tomato yellow leaf curl virus, new leaves become cupped and pale green in color. Note yellowing leaf edges, purplish veins on the undersides of leaves and decline of fruit production.

A second virus, tomato mosaic virus, causes rolling of leaves, but other symptoms, including mottled-coloring of leaves, small leaflets and internal browning of infected fruit, distinguish it from physiological or herbicide-induced leaf roll.

Herbicide Damage:  When tomato plants are exposed to the herbicide, typical symptoms include downward rolling of leaves and twisted growth. In addition, stems may turn white and split; fruit may be deformed. Depending on the level of exposure, the plant may or may not survive. Herbicide injury cannot be reversed, but if the plant is not killed, new growth may be normal. Always be very careful when spraying an herbicide as it may drift much further than anticipated.

Why do I have blossom end rot?

Blossom end rot is a common problem that gardeners encounter when growing tomatoes. This problem is not caused by a disease organism, but is rather a physiological disorder that results when there is an inadequate supply of calcium available to the developing fruit.

Initial symptoms of blossom end rot generally appear as water-soaked areas on the blossom end of the fruit. Over time the damage becomes a sunken, dark-colored rot.

While the occurrence of blossom end rot may indicate calcium deficiency, in reality, the soil may have adequate calcium. However, for various reasons the plant may not be able to take up enough calcium to supply the rapidly developing fruit. How do we manage this problem?

Prior to planting, the main preventative measure is to have a soil test done to determine if adequate calcium is present in the soil. Limestone should be applied if soil test results recommend it.

After tomatoes are planted, gardeners can minimize the potential for blossom end rot by doing the following:

a. Once transplants become established, encourage the production of a large root system by keeping plants a little on the dry side for a few weeks. A large root system is better able to take up the calcium needed for the healthy development of the tomato fruit.

b. After fruit set begins, keep soil evenly moist.

c. Apply a layer of mulch, such as grass clippings, to help maintain even moisture and keep soil cooler.

d. Do not overfertilize.

e. Do not cultivate closer than 1 foot to plants to avoid damaging roots.

f. Remove fruit with symptoms.

Why are my tomatoes splitting?

Splitting or cracking can be quite common and is brought about by fluctuations in watering. This can be due to heavy watering after a long period of no water. It can also be caused by having a period of dry weather, then getting a heavy rain that suddenly over-waters the tomatoes. Splitting and cracking is most prevalent in the later stages of growth when it is beginning to ripen.

When it begins to ripen during a spell without water, the outer skin will thicken and toughen up. A sudden influx of water will cause the tomato to swell on the inside. This inner swelling will then cause the thickened outer skin to rupture resulting in a split or crack.
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