Shoestringing

Shoestrings are to be expected on your sneakers. Finding them in the garden is something else.

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Leaves and stems grow in predictable ways, except that sometimes they don’t. Sometimes, stems grow strangely flattened. This is called fasciation. If you see leaves or other growths that look like a Halloween hag's broomstick, it's called witches broom. 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. You might think it’s some sort of an insect, chewing on your eggplants. As the condition persists, you might suspect a viral disease, or maybe chemical overspray. In severe cases, you may see chlorosis or stunting. This type of shoestringing occurs most often when very warm temperatures happen at the same time plants are in very specific growth stages. In other words, there isn’t much you can do about it. You should still probably monitor for insect pests, just in case.
 
Chemical-induced shoestringing
 
Chemical overspray can also cause shoestringing. This is most commonly seen when a neighbor sprays herbicide on a breezy day. Chemicals soar over the fence 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
 
If it wasn’t chemical overspray that caused shoestringing in your tomato plants, it might be cucumber mosaic virus (CMV). Are the leaves mottled? Take a closer look at the stems. If you see a zigzag pattern, it’s CMV.
 
Blueberry plants are susceptible to a virus that causes shoestringing. You won’t see any symptoms, at first. This disease lays dormant for up to 4 years before anything visible happens. Those symptoms include long red streaks on stems, most often 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. Normally white flowers have a pink tint. This disease is spread by blueberry aphids. Infected stems should be removed and the plant should be monitored 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 normal roots. In some cases, those shoestrings may grow upward, under the bark. And sometimes, they glow! Sadly, trees infected with Armillaria root rot need to be removed.

If you see shoestringing in your garden, look again. See if you can figure what's causing it. If you need help, just let me know! ​