Leaf Roll

What happened? Yesterday, your plants looked lovely. Today, several leaves look more like green cigars. Why did this happen? Is it a problem? And what can you do?

Lemon leaf beginning to roll

Leaf roll (or leafroll) is not the newest thing in Burmese take-out. Instead, it is a symptom that can give you clues about what is going on in your garden. Leaf roll can be in response to chemical overspray, environmental stresses, disease, and pests.

Fully rolled and dried citrus leaf

If you notice leaves starting to roll on any of your plants, start by asking yourself the following questions:

• Are the leaves rolling upward or downward?
• Which leaves are rolling? Are they new or old? On the top or bottom of the plant?
• Is it only on one side of the plant that leaves are rolling or all over?
• Are other parts of the plant showing symptoms?

Physiological or environmental causes of leafroll

Environmental or physiological damage is usually visible near the base of a plant first, as leaves cup upward, toward the leaf vein. Affected leaves tend to thicken and become leathery while remaining green. Environmental damage is a common problem when growing plants in the nightshade family, such as tomatoes, peppers, and eggplant. Interestingly, bush (determinate) varieties are less likely to exhibit leaf roll than vine (indeterminate) varieties. Symptoms of environmental damage can indicate any of these problems:

• Heavy pruning
• Root damage
• Sunburn
• Transplant shock
• Temperature extremes
• Too much nitrogen
• Water stress from drought or flooding

Viral infections

Viral diseases affect newer leaves first. Leaves cup upwards and then turn pale green. They may also have yellow edges and mottling. Veins may look purplish. This color change is due to damage to the phloem. Infected fruit may start rotting from the inside out.

Viruses often enter plant tissue as insect carriers, such as aphids, mealybugs, and soft scale insects, feed. Leaf roll viruses can also spread through infected scion wood. Once infected, vascular bundles become clogged as the viruses reproduce in the nutrient-rich phloem, reducing water and nutrient flow within the plant. Stunting, delayed maturity, reduced crop size,  chlorosis, and necrosis may also occur.

Three major types of viral leafroll warrant concern:

• Bean leafroll (BLRV) occurs in peas, beans, alfalfa, and lentils; and is spread by aphids.
• Grapevine leafroll (GLRaV) infects grapevines through mealybug and soft scale feeding.
• Potato leafroll (PLRV) enters plants through aphid feeding and can reduce your crop by 50%.

Because these viruses can spread rapidly and over relatively great distances, close monitoring and control are in everyone’s best interest. Once infected with one of the leafroll viruses, plants should be removed and destroyed. There is no cure or treatment. When shopping for plants, choose resistant varieties and put them in quarantine when you bring them home. Controlling carrier pests will also help reduce the likelihood of leafroll affecting your garden.

Nectarine tree infected with peach leaf curl

Fungal diseases

Leaf curl caused by fungal infections can be particularly destructive since the virus responsible is inside ubiquitous whiteflies. Peach leaf curl, bacterial blast, and botrytis are common examples. Symptoms of a fungal disease include the following:

• Red blisters
• Twisted, rubbery leaves
• Early leaf drop

Pests

As aphids, leaf miners, mealybugs, mites, scale insects, and thrips feed on sap, they can cause leaves to curl. Occasionally, a spider may curl a leaf to create a cocoon, but spiders are Good Guys in the garden, so we leave them alone. The larvae of moths are frequent pests when it comes to leaf rolling. For example, the tortricid family lays eggs in almond, apple, apricot, citrus, pear, plum, quince, raspberries, blackberries, walnut, plus most ornamentals. Ragged edges on nearby leaves and tightly rolled nesting leaves indicate light brown apple moths. Inspect fruit and nut trees regularly in spring for signs of these pests.

Herbicide damage

Advertisements make herbicides look so safe and helpful, but they are not. Leaching, overspray, rain splash, a sudden breeze, and the failure to break down in the soil, as advertised, can put many other plants at risk. Symptoms of chemical overspray and herbicide damage include the following:

• Deformed fruit
• Downward cupping leaves
• Stems that twist or turn white
• Twisted leaves

Tomato plant affected by chemical overspray. Photo courtesy of Les Rosenthal.

If you notice leaf rolling on your garden or landscape plants, take a closer look to see if you can figure out what is causing this change. Knowing the cause helps you find a solution that helps your plants stay healthy and productive.