Hello fourni49,

It looks like your parents are dealing with a very common Euonymus pest: Euonymus scale (Unaspis euonymi). The insects in the photo — tiny white specks clustered along stems and leaf undersides, paired with browning, yellowing, and leaf drop — closely match this pest. More information at these links:

Euonymus scale - Integrated Pest Management

Euonymus Scale

Euonymus Scale | University of Maryland Extension

Below is a clear breakdown to confirm the ID and choose the best treatment strategy for Michigan conditions.

What the pest likely is: Euonymus Scale

Key identifiers that match your photo:

Small, white, elongated, oyster‑shell–shaped insects (females) stuck to stems and leaf undersides

Tiny brown/gray specks (males) on leaf surfaces

Leaf yellowing, browning, and premature drop

Heavy infestations often start on older wood and spread outward

Very common on Euonymus in the Midwest, especially Euonymus fortunei and E. japonicus

This is one of the most destructive ornamental shrub pests in Michigan landscapes.

Why it’s happening

Euonymus scale thrives when:

Plants are stressed (heat, drought, winter injury)

Shrubs are planted against a wall or in low‑airflow areas

Natural predators (lady beetles, parasitic wasps) are low

The plant is sheared frequently, creating dense, shaded interiors

Michigan’s warm summers and cold winters don’t kill them — they overwinter under their shells.

How to treat Euonymus scale (Michigan‑appropriate options)

1. Prune out the worst‑infested branches

This is the fastest way to reduce the population.

Remove stems that are heavily encrusted with white scale

Bag and dispose of them (don’t compost)

This alone can dramatically improve control.

2. Apply horticultural oil (most effective + safe)

Timing matters more than the product.

Early spring (April–May): Apply a dormant or early‑season horticultural oil to smother overwintering scales.

Summer (June–July): Apply summer-weight horticultural oil when crawlers (the mobile young stage) are active.

Michigan State University Extension specifically recommends oil sprays for Euonymus scale because they’re effective and low‑toxicity.

Important: Thorough coverage of stems and leaf undersides is essential.

3. Use systemic insecticides (if infestation is severe)

For heavy infestations, a systemic can help the plant recover.

Common homeowner options:

Imidacloprid (soil drench; applied in spring)

Dinotefuran (faster-acting; applied as soil drench or bark spray)

These move through the plant and kill feeding scales.

Caution:

Avoid applying when Euonymus is flowering to protect pollinators.

Follow all label instructions carefully.

4. Encourage natural predators

Lady beetles, lacewings, and parasitic wasps help keep scale in check.

You can support them by:

Avoiding broad-spectrum insecticides

Planting flowering plants nearby

Leaving some leaf litter or habitat for overwintering beneficials

How to prevent future outbreaks

Annual horticultural oil spray in early spring

Avoid heavy shearing, which creates dense growth scale loves

Improve airflow by thinning interior branches

Water during drought to reduce plant stress

Inspect Euonymus twice per year (spring and mid-summer)

Should the plant be replaced?

Euonymus scale is persistent. If the shrub is:

losing most of its foliage

Heavily encrusted on stems

Repeatedly infested year after year

…many Michigan gardeners choose to replace Euonymus with less pest-prone shrubs (e.g., boxwood, inkberry holly, dwarf viburnum).

I hope this helps!