European Elm Scale

Gossyparia spuria

European elm scale, Gossyparia spuria, is a soft scale insect that attacks a variety of elm trees as well as hackberry species. Heavy infestations may kill weakened trees and cause branch dieback in healthy trees. Large amounts of honeydew are produced which eventually cause the leaves to be covered with grayish/black colored sooty mold. The sooty mold reduces the aesthetic appearance of trees and honeydew can become a nuisance as it coats patios, decks, and vehicles. European elm scale is difficult to see as it usually infests the smaller limbs that are higher in the tree. Often a thin crown in an elm is a symptom of heavy feeding.

Download European Elm Scale Fact Sheet

Treatment Strategy

European elm scale is easily treated with soil applied products such as Xytect and Transtect. These are systemic products applied to the soil at the base of the tree and are taken up by the root system, working from the inside of the plant. A contact insecticide such as Up-Star® Gold can be sprayed on the scales, but this is rarely used as getting good coverage is difficult on large trees, and the timing must coincide with crawler emergence to be effective.

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European Elm Scale Treatment Option 1

Transtect is applied to the soil in late May through June and will provide a quick knockdown (within 2 weeks). It has a residual of at least 90 days, so one application in early summer will provide season long control.

Application Type - Soil drench

DIY Product/Equipment Needed:

• Transtect

• Soil drench kit

• Measuring or diameter tape

• Bucket or watering can

• Gloves

European Elm Scale Treatment Option 2

Xytect is applied to the soil and has a long residual (1 year). However, it usually takes 30 – 60 days for the product to reach the leaves. Professional arborists will often apply Xytect™ in the fall of the year for control next season. Early spring application is also effective; apply in May for current season control.

Application Type - Soil drench

DIY Product/Equipment Needed:

• Xytect

• Soil drench kit

• Measuring or diameter tape

• Bucket or watering can

• Gloves

European Elm Scale Treatment Option 3

Spray products such as Up-Star® Gold are not used very often anymore for larger trees due to wind drift and contact with beneficial insects. However, they’re still used on smaller plants that are easily treated with a hand sprayer. These products typically have a residual of 10 – 14 days, so applications should begin in mid-June; a second application may be necessary in July to control crawlers that hatched later in the season.

Application Type - Foliar spray

DIY Product/Equipment Needed:

• Up-Star® Gold</a>

• Hand pump sprayer with wand

• Gloves

• Safety glasses

European Elm Scale DIY Kit

Option 1

Application Type - Soil drench

DIY Product/Equipment Needed:

• Transtect

• Soil drench kit

• Measuring or diameter tape

• Bucket or watering can

• Gloves

Option 2

Application Type - Soil drench

DIY Product/Equipment Needed:

• Xytect™

• Soil drench kit

• Measuring or diameter tape

• Bucket or watering can

• Gloves

Option 3

Application Type - Foliar spray

DIY Product/Equipment Needed:

• Up-Star® Gold

• Hand pump sprayer with wand

• Gloves

• Safety glasses

How Is It Spread?

European elm scale has one generation per year. Females mature in late May, mate and begin laying eggs. Crawlers begin hatching in late June through July. Once hatched, crawlers migrate toward the leaves where they feed until fall. At this time, they return to twigs and branches to overwinter in bark crevices.

Susceptible Trees

Elms and hackberry

Symptoms

• Black lumps with white fuzz along the edges of the insect attached to the twigs and branches.

• Stunted, yellowing leaves leading to premature leaf drop and dieback.

• Honeydew secretions on the top of branches with black sooty mold growth on the honeydew.

Lookalikes

Dutch elm disease, Elm leaf miner

Related/Similar Problems

Dutch elm disease, Elm leaf miner

Timing

Spring

Urgency

Low

Risk of Spreading

Moderate

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