Shoestringing

Shoestrings are no surprise on your sneakers. Finding them in the garden is something else.

Leaves and stems grow in predictable ways, except sometimes they don’t. Sometimes stems grow strangely flattened in a behavior known as fasciation. If you see leaves or other growths that look like a Halloween hag's broomstick, then it's witches broom. But when leaves grow oddly thin and leathery, it is called shoestringing. There are several types of shoestringing, and they have different causes and cures.

Fasciation of milkweed (Kate Russell)

Birch tree infected with witches broom (Ann Harrison) CC BY-SA 2.0

Temperature-based shoestringing

Temperature-based shoestringing is a disorder commonly seen on eggplant leaves. At first, you would see holes in the middle and on the edges of leaves and think it was insect feeding. As the condition worsens, you might suspect it was a viral disease or chemical overspray. In severe cases, you may see chlorosis or stunting. This type of shoestringing occurs when high temperatures occur as plants are in specific growth stages. In other words, there is nothing you can do. You should still probably monitor for insect pests, just in case.

Chemical-induced shoestringing

Chemical overspray can also cause shoestringing. A neighbor (or you) may spray herbicide on a breezy day. Chemicals soar over the fence (or across the yard) and land on your tomatoes or other crops, causing leaves to become thin and stringy. The same symptoms may also indicate viral disease.

Symptoms of blueberry shoestring disease (Dr. Mark Longstroth, MSU Extension) CC BY-SA 3.0

Viral shoestringing

Cucumber mosaic virus (CMV) can cause shoestringing in tomato plants. Are the leaves mottled? Take a closer look at the stems. If you see a zigzag pattern, it is CMV.

Blueberry plants are susceptible to a virus that causes shoestringing. Symptoms are not visible at first. This disease lays dormant for up to 4 years before long red streaks appear on stems. Those streaks are more frequent on the side of the plant that gets the most sunlight. Leaves take on a reddish or purple straplike or cupped shape. Rather than deep purple, infected fruit has more of a reddish tinge. Healthy white flowers develop a pink tint. Spread by blueberry aphids, this disease is highly contagious. Remove infected stems and monitor the plant closely.

Armillaria rhizomorphs, or “shoestrings” seen on exposed roots (USDA) Public Domain

Armillaria root rot is another viral shoestringing disease. Also known as shoestring rot, this disease affects several fruit and nut trees. Rather than growing normally, infected leaves cup downward and start yellowing. If you were to dig up the roots of a tree infected with Armillaria root rot, you would see blackened rhizomorphs, or shoestrings, growing on the surface of otherwise healthy-looking roots. In some cases, those shoestrings may grow up under the bark. And sometimes, they glow! Sadly, trees infected with Armillaria root rot must be removed.

If you see shoestringing in your garden, look again. See if you can figure out what's causing it.​