Numerous factors can cause pear tree leaf curl. There’s an entire checklist of things to run through before reaching for insecticides or digging down to inspect the roots.
At the most basic level, leaf curl on any plant is caused by stress. The mystery surrounding why your pear tree has leaves curling is identifying the stressor.
Stressors for plants include bacterial and fungal diseases, pest problems, accidental herbicide damage, and the environment, such as drought, humidity, and temperatures.
A more complex problem is rootstock issues; however, these are rare as it’s a commercial problem originating from the nursery you bought your pear tree from.
Explore the Simplest Causes of Leaf Curl on Pear Trees First
Do you know how much water a pear tree needs? Estimates are 1 gallon of water every 7 to 10 days. The hotter the weather, the more water it needs.
Low temperatures will stress a variety of plants. Leaf curl is a symptom of stress. When it happens after a cold chill, such as a late spring frost, check for buds swelling and leaf discoloration.
Frost damage stresses plants, leaves curl to preserve energy, then the lack of photosynthesis results in leaf discoloration.
The fix: Prune back the damaged leaves above a leaf node and new healthy leaves will soon grow back without leaf curl.
Insects that Cause Pear Tree Leaf Curl
Aphids are the bane of gardeners. They were gifted with mouths with needle-like stylets that they use to pierce the leaves of plants to suck the juices right out of them. Great for them, terrible for growers. Aphids cause plants to display symptoms of drought.
And they’re sly about it. They feed on the main veins at the center on the underside of plant leaves. You have to go looking for them.
A few will not harm a pear tree. An infestation will. The more they feed, the more honeydew they excrete.
Honeydew is aphid poo. Ants feed on the stuff. Then you have more than one symptom.
Leaf curl caused by the drought symptoms, and honeydew causing sooty mold to appear on the leaves resulting in hindered photosynthesis. It stresses the plant and that’s what causes leaf curl.
The more honeydew is present, the bigger the attraction is for ants. They come along, protect the aphids as those are the food source for ants.
Not even nature’s helpers like ladybirds can help. Ants will fight them off to protect the aphids.
The Green Apple Aphid is a Common Pest on Pear Trees
The green apple aphid (aphis pomi) is a common culprit (worldwide) for pear tree leaves curling.
They get the nickname (green apple aphid) because it is mostly apple trees they will infest. They will colonize on pear trees too.
Apple trees are just the primary host. Like most insects in the wild, they feed on what they find.
The green apple aphid is more active in warmer weather. Early spring through summer is when to be extra cautious with fruit trees.
Adults lay eggs in the soil, those survive over the winter, emerging as nymphs that feed on pear tree leaves. It’s the feeding stage of nymphs that causes leaf curl.
Eggs are only about the size of a grain of rice. You will not see it in soil. The nymph stage is when they become noticeable, feeding on the underside of plant leaves. Newly hatched, it is dark green.
As it matures into a wingless aphid, the green coloring becomes brighter. By the winged stage, adult green apple aphids have a yellow-green body, black head, and is around 3 mm in length. Still hard to spot.
Pear trees have an average lifespan of 15 to 20 years. They will always be an attraction to aphids. For that reason, insecticides should only be used as a last resort on fruit trees to prevent pest populations developing a resistance.
In a garden, the best technique to naturally get rid of aphids is manual removal with a jet stream from a garden hose, hand-picking them, releasing predatory nematodes, or if using chemicals, use neem oil as that is organic.
In an orchard with multiple fruit trees, disrupting their mating habits using pheromones is a preferred method to keep pest populations under control, rather than spraying everything with an insecticide.
Apple and Pear Leaf Curling Midge
While aphids will cause an entire leaf to curl, the midge is even more sly. This causes only the edges of leaves to curl.
The leaf edge rolls inward essentially turning the edge of the leaf into a tube. A tube the larvae can then use to live, feed, and hide in safety from insecticides since the larvae are inside the tube. Spraying won’t get rid of them.
The midge is a gall making aphid. The resulting damage is tight rolling along the leaf edges, then the galls take on a reddish color with a brittle texture.
They don’t cause entire leaves to curl, but they do cause a tight rolling over of the leaf edges. Leaf curling right on the margins of leaves of pear trees is a sign of a midge larvae presence.
Fruit Tree Leafroller
The fruit tree leafroller is a caterpillar. It emerges from the eggs laid by the tortricid moth. A firm favorite for feeding and laying eggs is hardwood. Pear wood is a hardwood.
The moth lays eggs to overwinter on branches and twigs. By spring, the eggs hatch, then the larvae start feeding. That’s when you see leaf curling emerge.
Leafrollers are caterpillars around 2.5 cm in length. They use the leaves to build nests, and they tie leaves together with silk for added protection from predators.
A few leafrollers won’t do much damage, and they don’t all hatch all at once. They only affect appearance. In high droves of them though, damage can be severe.
When treatment is needed, often recommended is to treat the leaves with Bacillus thuringiensis (Bt), however, once the leaves are rolled up, spraying won’t work. Bt is only effective if you treat the plant before the eggs hatch.
Once the larvae get to work, the alternative is to either release beneficial bugs such as parasitic wasps or the larvae of green lacewings. For a heavy infestation, Spinosad is an insecticide that poisons leafroller caterpillars.
Other Possible Stressors that Cause the Leaves on Pear Trees to Curl
Leaf Blight (Fire Blight)
Fire blight is the most destructive bacterial disease to infect the pear tree. It’s incurable. Leaf curl is only one symptom, and the first to show. It is quickly followed by leaf discoloration.
Within two weeks, leaves take on a scorched/burned appearance. It spreads from the leaves, and stems, then into the branches.
Just because fire blight is incurable, doesn’t mean it’ll kill an infected fruit tree. Apple and pear trees are the most susceptible.
As leaf curl is the first symptom, keep a close eye on the color of leaves. As soon as the leaves start turning brown or black, get pruning.
Fire blight becomes a tree killer when it spreads. It is contagious. To control the spread of leaf blight on fruiting trees, make pruning cuts above the closest growth bud to the trunk.
Cutting above a growth bud doesn’t stop growth. Cutting below a growth bud will stop new growth.
The point of pruning to control disease spread is to prevent the disease reaching the trunk. Once it reaches that point, it can spread to every branch and leaf on the tree. That’s when the pear tree will die.
To limit the damage, pruning is a necessity.
Couples don’t always garden in harmony. While one person may find that a quick way to get rid of henbit on lawns is to spot-treat with glyphosate, which is not a selective herbicide. 2, 4-D is and will not kill everything else around the garden.
Spraying glyphosate can easily cause herbicide drift, which is when the chemical is spread by the slightest of a breeze. Glyphosate, being non-selective, will damage the leaves of pear trees and every other plant the herbicide drifts onto.
Commercially grown pear tree rootstocks are not all the same. They can be grafted onto a different type of rootstock.
If it is an incompatible genus, the entire crop will be affected. Customers will only notice the problem after transplanting in the garden.
In the United States, two common rootstocks are Bartlett, and Quince. Bartlett produces bigger fruit; Quince rootstock is more suitable for dwarf pear trees. Grafting the two rootstocks together produces medium sized fruits.
Over in Europe, Hawthorne rootstocks are more common, however, in the US, it isn’t compatible for the climate.
The rootstock used for grafting affects the hardiness of the tree. In the US, pear tree rootstock needs to be resistant to fire blight.
The standard rootstock worldwide is from the Bartlett seedling. Within this genus are OH (Old Home), and Farmingdale. Combining the two is expressed as OHxF, meaning it is a cross graft of Old Home and Farmingdale, followed by a number such as OHxF 333, or OHxF 97.
Incompatible grafting (in some climates) is combining a Quince rootstock with a Bartlett rootstock. When that happens, the resistance to fire blight and cold-hardiness is weakened.
The pear tree will be more susceptible to disease. Sometimes, to the extent that the leaf curl happens really early, quickly followed by black leaf spots on pear tree leaves.
When that happens, it will be evident in the nursery you bought the pear tree from as all pear trees with the same rootstock used will all show the same leaf curling, and possibly, the early signs of fire blight.
Rootstock issues are evident in the first season the tree is planted. They don’t all of a sudden develop leaf curl sporadically.
When the leaf curling happens soon after transplanting, and there are no other possible explanations, contact the nursery you purchased the pear tree from.
Most reputable suppliers will offer an exchange or refund when it’s their fault that your pear tree won’t grow properly.