Lemon trees are favourite citrus plants for those living in southern regions that experience subtropical and tropical weather. Lemon trees also are the favourite meal and home of citrus tree pests. These pests can take up residence on a lemon tree and cause a host of problems. In addition, other environmental factors may be contributing to your lemon tree's leaves curling. It's crucial to know what is causing the leaf curl to provide the proper treatment.
Citrus leaf miners are pests that lay their eggs on leaves. When the larvae is hatched, the insect tunnels through the leaves. Generally, new growth or the newest flush of foliage is the host to the larvae. In addition to curling leaves, a decrease in lemon production may occur. These pests are difficult to control because the leaf provides protection from pesticides. Apply a pesticide spray to the entire lemon tree to eradicate the leaf miners. A second application may be necessary to complete the job.
Aphids suck the nutrients out of lemon tree's leaves and cause leaf curling, yellowing, disfigurement and stunted growth, The pests leave behind a sticky secretion called honeydew, which picks up fungal spores such as sooty mould and inhibits photosynthesis. Lemon trees should be monitored for aphids when temperatures are between 18.3 to 29.4 degrees Celsius. Sooty mould can be removed with a spray from a garden hose. An insecticidal soap safe for food crops also can be used to treat aphids.
Citrus mealybugs start infesting lemon trees in March. When mealybugs feed on leaves, they inject a toxic substance that causes leaf curling, fruit splitting, fruit drop and defoliation. According to the University of Arizona, a heavily infested lemon tree can loose as much as 100 per cent of its fruit. Prune back foliage to allow for better pesticide penetration and more air circulation. Pesticides formulated to kill mealybugs can be applied to the entire tree or to one area.
Wind burn is caused when windy conditions absorb moisture from the leaves and cause dehydration. Dehydration is what causes the leaves to curl. It is important when planting to avoid placing lemon trees in windy locations. Citrus trees do not make great wind breaks. Also, provide additional water to the tree during times of wind. Spreading a 3- to 4-inch layer of mulch 1 foot from the tree out to its drip line will conserve soil moisture.