During the past couple of weeks a few individuals have come into the office to express concern about damage to euonymus with little white spots. These little white spots are actually the protective coverings of scale insects.
Scale insects are very common on Indiana trees and shrubs and there are more than 60 known to exist in the state. The most common scale problems reported locally are euonymus and tulip tree scales.
Scale insects cause damage to its host plant by sucking juices from the plant. Furthermore, scales may or may not produce honeydew. Scales that produce honeydew like the tulip tree scale provide additional nuisances and hurt plant health. The honeydew makes a sticky mess that attacks ant, fly and wasp insects; provides an environment for black sooty mold; fungal problems; and makes the shrub or tree unsightly. Also benches, tables, cars and walkways under such problem trees become a sticky mess.
In fact some see black sooty mold on tulip trees and mistaken the sight for fire or burn injury as the twigs have a charcoal appearance.
Since scales don't travel very well, they tend to spend most of their life feeding on the same area of a plant. After eggs hatch, the young are called "crawlers" as they are able to walk in this phase of the life cycle. Crawlers are very tiny at <1/32 of an inch. Most never see crawlers as they are flattened and appear as dust on the plant surface.
Infestations occur when crawlers walk or are blown by the wind to nearby plants. This is the time that scales are most vulnerable to insecticides. The problem is that this is a relatively short period of time and the critters are so small that they remain unseen.
Besides being classified as either honeydew producing or non-honeydew producing, scales are also segregated as either armored or soft scales.
As scales mature, the armored scales become flattened and covered with a waxy material that protects the scale. Soft scales are not covered with the waxy protective coating.
Most contacts in the office with euonymus scale have already sprayed an insecticide and commented that the problem seemed to get worse or at least not be helped by the application. Euonymus and tulip scales are armored scales that are protected and as such the insecticide never reaches the target. Interestingly, there are a number of wasps and other insects that feed on scales. Therefore spraying an insecticide now may actually help the scale insects as one knocks out the predators.
Purdue publication E-29 entitled "Scale Insects on Shade Trees and Shrubs" is a good pictorial and informal publication. Horticultural oils will not harm the beneficial predator insects and can kill the scale insects by smothering them under the protective cover. This pub has a number of recommendations for control and the important keys to proper timing application specific to various scales that one may find.
You can contact the local Purdue Extension Office by calling 829-5020 x14 in Owen County or 448-9041 in Clay County for more information or publication copies regarding this week's column topic or to RSVP for upcoming events. It is always best to call first to assure items are ready when you arrive and to RSVP for programs. While most publications are free, some do have a fee. All times listed are Eastern Time.
Sept. 26 Pen Space Request Due for IBEP winter evaluation
Sept. 27 Indiana Goat Assoc. Member Meeting, Quincy, 10 a.m.
Oct. 8-9 Indiana Flower Growers Assoc. Annual Conference
Oct. 11 Adventures in Gardening, Danville 8:30 a.m.
Oct. 14 Ribeye Blood Drive, Spencer, 3-6 p.m.
Oct. 18 IBEP Bull & Bred Heifer Sale, Springville, 2 p.m.