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?

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.

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.

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

Any word that ends with ‘-cide’ means death to something. In the case of herbicides, it means death to some or all plants that it contacts.


Non-selective herbicides kill everything, while selective herbicides are slightly more choosy. Until the 20th century, weed management included cultural controls and old-fashioned elbow grease.

Chemical warfare

Chemical warfare research from WWII discovered how synthetic plant hormones and other chemicals could kill many broadleaf plants. Several chemical reactions are going on when these chemicals are applied. Some herbicides work by halting cell production in the meristems (growth tips). Other chemicals starve plants by interfering with the production of amino acids or by halting photosynthesis.

Using herbicides can lead to several problems, including:

• Overspray can kill nearby plants.
• An area may become unsuitable for planting for several years.
• Weeds become resistant (and we do not).
• Chemicals may enter groundwater, causing algae blooms and other environmental problems.
• Some herbicides may increase the risk of cancer. (Union of Concerned Scientists)
• Groundwater can become contaminated by herbicides.
• Forage grown for livestock may release herbicide residue through manure. (NC Cooperative Extension)

Loss of biodiversity is a serious problem when it comes to herbicides. Nature’s balancing act is delicate. The effects of this chemical use are not fully understood. For example, Roundup (glyphosate) has decimated global Monarch butterfly populations. Other herbicides, like Paraquat, are so dangerous that only licensed professionals are supposed to have access. Long-term exposure to paraquat can kill you. You can read more about the health effects of paraquat here.


Safer alternatives

While chemical herbicides offer short-term convenience, there are many safer, sustainable options, including the following:

• Hand weeding
• Maintain healthy plants
• Mulching
• Good garden design
• Proper irrigation methods
• Install porous grout in hard surface cracks or apply clove or lemongrass oil.

If you must apply chemicals in the garden, follow the package directions exactly. Confirm it is the correct herbicide for the site and the specific weeds. Apply too much, and the excess enters our water supply. You will also want to ensure that the weeds are in the correct life stage for the herbicide to be effective. If a chemical claims to be pre-emergent, it will attack germinating seeds. Post-emergent herbicides attack growing plants, and they work better on young plants. Post-emergent herbicides can be foliar (leaf absorption), root, contact, or systemic. Systemic herbicides are absorbed and spread throughout the plant.


Be sure to read and follow product labels carefully. And dispose of the container properly. Better yet, practice sustainable, organic gardening.

Over-watering container plants is a surprisingly common mistake. According to the University of California, improper irrigation is the #1 cause of plant problems.


Unfortunately, the signs of too much and not enough look almost identical: yellowing, wilted leaves, stunted growth, and leaf drop are symptoms of both problems.


Rather than drowning your plants, allow the soil to dry out between waterings. Don't guess. As critical as water is for good plant health, this is not a time to assume your plants are getting the water you give them. Soil structure can redirect water away from roots in surprising ways. When plants show water stress symptoms, gently dig down next to the root system to ensure the water goes where needed.


An inexpensive moisture meter is an excellent investment in your plants' health.

The damage caused by too little (or too much) water is called water stress.


Water-stressed plants exhibit these symptoms:

• Wilting or drooping leaves do not return to normal by evening.
• Curled or chlorotic (yellow) leaves that may fold or drop.
• Foliage becomes grayish and loses its green luster.
• New leaves are small.

Water stress can be due to extended drought, long, hot summers, and irrigation failures. On the other side of the same coin, flooding, urban drool, and heavy rains can create a different type of water stress. When soil is waterlogged, plants cannot breathe.


Water-stressed trees and plants are more susceptible to pests and diseases. As trees die, erosion increases, causing more drying out. It's a tough cycle. Rather than letting household water go down the drain, collect it in a tub or bucket and give it to your local trees. You'll be happy about the shade this summer!