The genus Ilex, holly, plays a significant role in the beliefs and traditions of the winter season. To the Romans, hollies were the trees of the god Saturn and wreaths of holly were gifts during his holiday, Saturnalia. In Celtic legends, evergreen hollies with their beautiful red berries, announced the ascension of the Holly King who ruled the forest with his green leaves in summer. For Christians, the pointed leaves of the holly are associated with the crown of thorns worn by Jesus and the bright red holly berries symbolize drops of his blood.
For arborists and plant health care technicians, hollies are among the most important landscape plants and they require special attention due to the presence of a few egregious scale insect plants.
Soft scales injure hollies in two ways. First, by removing the vital products of photosynthesis, soft scales rob hollies of nutrients. In heavy infestations, leaves become chlorotic and sometimes drop prematurely. Chronic infestations can result in dieback of branches. Second, to obtain adequate nutrients for development and reproduction, these scales imbibe large volumes of sap. Processed sap is excreted in the form of a sugar-laden liquid called honeydew.
As honeydew accumulates on leaves beneath the scale, a black fungus called sooty mold colonizes the sticky liquid and uses the sugars as a substrate for growth. Sooty mold does not harm the holly directly, that is, it is not pathogenic. However, sooty mold’s grimy appearance is disagreeable and one can imagine that enough sooty mold might cut down on the plant’s ability to gather energy from sunlight. Fortunately, once the scales are controlled, sooty mold is easily removed with a vigorous plant wash.
Managing soft scales on holly
As with all pest and abiotic problems, early detection is the key to effective management. During the regular inspection of hollies, make note of discolored leaves or branches with dieback. Carefully inspect the lower surface of leaves for signs of soft scale nymphs or white waxy ovisacs. The presence of honeydew and ants, wasps and bees that forage on honeydew are good indicators of soft scale infestations. Accumulating sooty mold is another dead giveaway of the presence of these pests.
by Michael J. Raupp, Tree Care Industry Magazine, Vol. XXLL, Number 1-January 2011
