Phytomyza species The damage caused by these leaf miners is unsightly and ruins the value of those types of holly used as winter holiday decorations. Both the larva and the adult cause damage. The insect spends the winter as a larva, or pupa, inside a fallen leaf or a leaf still attached to the plant. Adults-tiny black flies-appear during May, when new plant growth is 1/2 to 1 inch long. The female deposits eggs inside the leaf by making a slit in the lower surfaces of the leaf. The flies (only the females in some species) feed on the sap by stabbing through the leaf surface. This feeding causes the puncture marks and distortion. The eggs deposited inside the leaves hatch into maggots that feed on the inner leaf tissue, producing the mines, or trails. In a heavy infestation, especially during a dry season, the plant may drop almost all its leaves and will remain bare until the following spring.
Control leaf miners with an insecticide labeled for this pest, following label directions. Rake up and destroy fallen leaves.
This is a common problem with acid-loving plants such as holly. The plant prefers soil with a pH between 6.0 and 6.5. The yellowing is due to a deficiency of iron and other minor nutrients in the plant. The soil is seldom deficient in iron, but iron is often found in an insoluble form that is not available to the plant, especially in soil with a pH above 7.0. A high soil pH can result from overliming or from lime leached from cement or brick. Regions where soil is derived from limestone or where rainfall is low also have high-pH soils. Plants use iron in the formation of chlorophyll in the leaves. When iron is lacking, new leaves are yellow.
Fertilize with a plant food formulated for acid-loving plants. If your soil drainage is poor, add enough peat moss at a 50:50 ratio to native soil when planting holly. Never lime the soil around this plant.
Several different fungi cause leaf spots on holly. These spots are unsightly but rarely harmful to the plant. The fungi are spread by splashing water and wind. Spots develop where the fungi enter the tissue. If wet or humid weather persists, the fungi spread through the tissue, and blotches form. The fungi survive the winter on the leaves and twigs. Most leaf spot organisms do their greatest damage in mild to warm weather (between 50° and 85°F).
Where practical, remove and destroy infected leaves. On valuable specimens, spray with Ortho Garden Disease Control or a fungicide containing ferbam. Repeat at intervals of 2 weeks for as long as the weather remains favorable for infection.
Many different species of scales infest holly. They lay their eggs on the leaves or bark in the spring, and in midsummer the young scales, called crawlers, settle on various parts of the tree or shrub. The small (1/10 inch), soft-bodied young feed by sucking sap from the plant. The legs usually atrophy, and a hard crusty or waxy shell develops over the body. Mature female scales lay their eggs underneath their shells. Some species of scales infesting holly are unable to digest fully all the sugar in the plant sap, and they excrete the excess in a fluid called honeydew. A black sooty mold fungus may develop on the honeydew. An uncontrolled infestation of scales may kill the plant after 2 or 3 seasons.
Spray with an insecticide labeled for this pest, following label instructions. In spring, before new growth begins, spray the trunk and branches with a horticultural oil.
Oligonychus ilicis The southern red mite, also known as red spider, is a major pest of many broadleaf evergreen plants in the eastern half of the country. The mites cause damage by sucking sap from both the top and the undersides of leaves. As a result of feeding, the green leaf pigment disappears, producing the stippled appearance. These mites are most prolific in cooler weather. They feed and reproduce primarily during spring and, in some cases, fall. At the onset of hot weather (70°F and up), the mites have already caused their maximum damage.
When you first notice stippling in the spring, appl an insecticide labeled for this pest, following label directions. Injured leaves remain on the plant for more than 1 growing season. Hose down plants frequently to knock off webs and mites.
Metaphalaria ilicis This insect feeds exclusively on yaupon. It secretes a substance that stimulates abnormal leaf growth, producing galls that enclose the insects. Immature psyllids feed during the spring and summer, sucking the juices from the succulent tissues within the gall. In the fall they develop into winged adults. The female adults lay eggs in the late fall; the eggs hatch the following spring. Psyllid infestations do not kill yaupon but can greatly slow its growth. Severe, repeated infestations over several years give the plant a bushy, pruned appearance.
If galling has already occurred, cut out deformed plant parts and compost or dispose of them.