Botany - (ebook) - Holly Leaf Miners

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Educating People To Help Themselves

There are over twenty species of holly native to the United

States. Most of these species are limited to the Southeast

Coastal Plain and many are grown in Maryland. Leaf

miners attack several kinds of holly and the value of these

plants has in some cases has been greatly reduced.

In Maryland there are several species of leaf miners which

feed on holly. The most important is the native holly leaf

miner, Phytomyza ilicicola, which feeds mainly on Ameri-

can holly. The holly leaf miner, Phytomyza ilicis, is a

European species often reported from the Eastern United

States, but research indicates it is confined to the Pacific

Northwest. Damage

Severe injury by the native holly leaf miner has appar-

ently never been reported in natural stands of American

holly, although these insects are found throughout the range

of its host. Parrasites and other beneficial insects are

usually effective under natural conditions. Unfortunately,

cultivated trees may be subject to heavy infestations.

Damage is due mainly to the feeding of the minute yellow

fly maggots (or larvae) which feed by mining between the

top and bottom surfaces of the leaves. In early summer

these mines are narrow, oval, inconspicuous tunnels, but

in early fall the maggots lengthen the mines until they

look like irregular, dark streaks. If only one mine is present

in a leaf, it may look unsightly, but it will remain on the

plant for its normal period (about two years). However, if

a leaf has several mines, it will fall in the spring or fall

after the first year.

Injury is also caused by adult females which insert their

ovipositors into leaves. Males and females then feed on

the juices which appear. If a leaf receives too many punc-

tures, it will become stunted and twisted.

Home & Garden Mimeo #HG 22 Holly Leaf Miners

In Central Maryland, most of the tiny, 1/10 inch long,

blackish flies emerge, mate, and lay eggs from early to

Native Holly Leafminer

mid May. (Egg laying may be delayed in cold wet

springs.) The eggs are inserted into the leaf by the

female. The young maggots begin mining in June but

the mines are not obvious until late summer. ( The

tiny, new mines are oval with reddish halos.) The

winter is spent in the leaf mine. Some over-winter as

mature maggots and others as pupae. There is only

one generation a year.

Control

When possible American hollies should be grown in

partial shade. Trees in full sun are usually more

heavily damaged by this pest. The simplest way to

control the holly leaf miner is to pick off and de-

stroy all infested leaves before May. This will elimi-

nate the overwintering maggots in the mines. Where

the size and/or number of plants makes this method

impractical, this pest can be controlled by timing an

insecticide spray with the emergence of the adult flies.

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Botany - (ebook) - Holly Leaf Miners

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