Garden Pests: Leaf Miners
July 2, 2014
Have you ever gone out into your yard to tend to your garden only to discover serpentine brown lines on the leaves of your plants? This damage is caused by an extremely common garden pest called a leaf miner.
Leaf miners are usually the larvae of flies, moths, or beetles that feed, or mine, between the upper and lower epidermal leaf surfaces. The larvae tunnel through the leaf creating a mine that may be narrow, whitish, and linear; serpentine or winding; or blotchy. The tunnel is often clear except for a trail of black fecal material left behind as the larvae feed. Many ornamental plants are attacked by leaf miners, but azalea, bougainvillea, citrus, hollies, chrysanthemum, Ixora shrubs, lantana, oak, and certain vegetable plants are some of the preferred hosts.
Leaf miner damage is very obvious, but healthy plants should be able to tolerate considerable injury before losing vigor or yield. However, during heavy infestations, plants appear bleached or faded and their aesthetic value is reduced. In some cases, the leaves turn yellow and drop due in part to the entry of pathogenic fungi and bacteria into old mines.
The following is a list of some common leaf miner pests in Florida:
Blotch Leaf miner: The blotch leaf miner is a pest of chrysanthemums in landscapes. The adult is a small shiny fly and the larvae are yellowish-white. Heavy infestations may kill some leaves, but most damage is just aesthetic.
Azalea Leaf miner: Azalea leaf miner larvae make blister-like blotch mines on azalea leaves. Single, white eggs are laid along a vein on the underside of a leaf. A mine turns brown when the larvae exit the leaf in favor of an intact leaf to roll up and pupate in.
Citrus Leaf miner: The citrus leaf miner can be a serious pest of citrus, kumquat, calamondin, and native citrus. Adults are tiny moths with white, silvery wings and a black spot on each wingtip. Larvae make meandering serpentine mines that can result in leaf curling. In a heavy infestation, larvae may mine through succulent stems and fruit.
To manage a leaf miner infestation, prune off and destroy infested plants or plant parts. Keep plants healthy by properly irrigating, fertilizing, and placing in the appropriate sunshine so they can tolerate and outgrow the damage. Populations are generally prevented from reaching truly damaging levels by parasitic wasps that attack leaf miners. Wasp larvae develop on or in the leaf miner larva or pupa, and pupation occurs in or near host remains. In some species, the wasp stings the host, injects a paralyzing venom, lays an egg, and its larva develops externally.
Leaf miners are difficult to control because they are protected by the leaf tissue. The best time to manage leaf miners is when larvae first hatch inside the leaves and begin to feed, but the damage may be hard to see. Treatment at this time also minimizes plant damage. If many large or long mines are visible, the leaf miner may have completed its development, and control is not useful.
Because leaf miners are difficult to identify early in an infestation, and infestations are generally not lethal to plants, the best line of defense against them is to maintain strong healthy plants. You can keep your ornamental plants healthy by providing proper living conditions, the right tree in the right place, providing proper nutrition with fertilizer, and keeping them healthy from other damaging pests.
< Previous Next >