What Is Causing My Tomato Leaves to Curl?

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The majority of homeowner calls this month have been related to tomato issues. If you have grown tomatoes before, there is a good chance you have experienced some of these issues discussed below. Here is what you could be experiencing with your tomatoes at this time:

Physiological Leaf Roll

This falls under the abiotic disorders of tomatoes. Meaning, caused by environmental or cultural conditions.

Leaf roll is when you notice your tomato leaves starting to curl inward. This can be caused by excess nitrogen, heat stress, pruning, harsh winds, and other climatic factors. Some cultivars are more susceptible than others. It does not cause growth or yield reductions.

To combat leaf roll, provide consistent moisture and proper fertilization. Avoid high nitrogen fertilizers.

Herbicide Injury

Tomatoes are very sensitive to broadleaf herbicides. Herbicide injury usually occurs when weed control spray drifts onto nearby plants. In some cases, herbicides can drift many feet from the site of application.

How to ID:

Damage looks like twisted and bent shoots and petioles, leaves become twisted and tightly curled. The plant may not show symptoms until 7-10 days after being exposed.

Symptoms of herbicide injury include: tightly twisted and bent shoots and petioles.

Symptoms of herbicide injury include: tightly twisted and bent shoots and petioles.

Other issues you could be seeing with your tomato leaves could be due to these certain pathogens.

Early Blight (Alternaria linariae)

Most home gardeners are familiar with blight related to tomatoes. There are two different types of blight that tomatoes can get. Early blight is a fungus that shows up when temperatures are >80F with moderate to heavy rainfall.

Spores of Alternaria linariae are primarily spread by wind, air currents, and water splash. Pruning lower leaves and avoiding leaves while watering your tomato plant can help with management. You can also look for a fungicide that contains the active ingredient, chlorothalonil.

How to ID:

Lesions first develop on lower leaves as small, brownish-black spots which can expand to about 1⁄4 – 1⁄2-inch in diameter with characteristic concentric rings in the darkened area, similar to leaf spot. Lesions can also be found on fruit and are typically sunken, leathery, and dark brown to black with concentric rings.

photo credit: Inga Meadows Caption- Symptoms of early blight can be seen with Lesions developing on lower leaves as small, brownish-black spots.

photo credit: Inga Meadows
Caption- Symptoms of early blight can be seen with Lesions developing on lower leaves as small, brownish-black spots.

Southern Bacterial Wilt (Ralstonia solanacearum)

I have seen this tomato disease present every year. This bacterial disease develops in high temperatures (over 85°F) and moist soils and is very persistent if introduced. The bacterium clogs the vascular tissue within the stem and prevents water and nutrients from moving through the plant, causing the wilted appearance.

How to ID:

Beginning stages of the disease include a wilted appearance of the youngest leaves. The base of the plant may show brown cankers. Plants may appear wilted in the afternoon, seem to “recover” overnight only to wilt again in the afternoon.

If you suspect bacterial wilt, cut the plant at the base, place it in water and if you see a stream of a white slimy substance, then that is a strong indicator of the bacterium present. The inside of the stem will be a light brown color in the pith area.

photo credit: Jason Brock, University of Georgia, Bugwood.org Caption: The white slimy substance observed here is a strong indicator of the southern wilt bacterium is present.

photo credit: Jason Brock, University of Georgia, Bugwood
The white slimy substance observed here is a strong indicator of the southern wilt bacterium is present.

Management of this disease includes: crop rotation and planting cover crops of non-susceptible plants (i.e. corn, rye, beans, cabbage) to help reduce soil-borne pathogens.

Be vigilant in your garden. Scout for disease and pest problems often. Crop rotation should be a part of your garden plans! Next year consider looking for cultivars that are tolerant or resistant to certain tomato diseases. You can identify these tolerant or resistant cultivars with abbreviations beside their names like EB for early blight or V for verticillium wilt.

If you have questions about your tomatoes, contact the N.C. Cooperative Extension, Caldwell County Center at 828-757-1290 or visit us anytime online.