Hello Jenifer,

Frass in amber-colored sap on your plum tree likely indicates insect activity—most commonly peach tree borers or other wood-boring pests. Non-chemical treatment focuses on physical removal, tree health, and natural deterrents.

What Causes Frass in Gummosis?

Gummosis itself is a symptom, not a disease. It’s the tree’s response to stress, injury, or infection. When frass (insect excrement mixed with wood shavings) is present in the gum, it strongly suggests boring insects, especially:

Peach Tree Borer (Synanthedon exitiosa): A major pest of stone fruits in Michigan. Larvae tunnel into the lower trunk or roots, causing sap to ooze and frass to accumulate.

Lesser Peach Tree Borer (Synanthedon pictipes): Targets upper branches and trunk wounds.

Other borers or canker-causing pathogens may also be involved, but frass is a hallmark of insect activity. More information at these links:

Gummosis of Stone Fruits – IPM Pest Advisories

Pest Alert – Gummosis in Cherries, Peaches and Plums | N.C. Cooperative Extension

Non-Chemical Treatment Strategies

To manage gummosis and borers without chemicals, focus on tree health, physical control, and natural deterrents:

1. Inspect and Remove Larvae

Use a sharp knife or wire to probe the sap area and remove any visible larvae.

Gently scrape away dead bark to expose tunnels and frass.

Avoid damaging healthy tissue.

2. Improve Tree Vigor

Water deeply during dry spells, especially in summer.

Apply organic mulch around the base (but not touching the trunk) to retain moisture and regulate temperature.

Prune dead or damaged branches in late winter to reduce entry points.

3. Use Physical Barriers

Wrap the lower trunk with cardboard or burlap in late spring to trap emerging adult borers. Remove and destroy weekly.

Consider tree guards to prevent mechanical injury and pest access.

4. Encourage Natural Predators

Maintain a biodiverse garden with flowering plants to attract parasitic wasps and birds that feed on borers.

Avoid broad-spectrum insecticides that harm beneficial insects.

5. Sanitation

Remove and destroy any heavily infested branches or trees.

Clean pruning tools with alcohol to prevent disease spread. More information at this link:

Gummosis of Stone Fruits – IPM Pest Advisories

Diagnostic Tip

To confirm whether the gummosis is pest-related:

Scrape under the gum: If the inner bark is brown or dead, pests are likely involved. If it’s cream-colored, the cause may be environmental (e.g., frost, sunscald, or mechanical injury).

Timing in Michigan

Borers are most active late spring through summer. Begin monitoring in May, especially around bloom time.

Fall is ideal for tree health assessments and pruning.

If the infestation is severe or persists despite these methods, you may need to consider targeted, low-toxicity options like beneficial nematodes or pheromone traps—but these are still considered organic-friendly. More information at these links:

Gummosis of Stone Fruits – IPM Pest Advisories

Pest Alert – Gummosis in Cherries, Peaches and Plums | N.C. Cooperative Extension

I recommend you send your image by email to the MSU Plant & Pest Diagnostics Lab to get a confirmed and precise diagnosis and identification.

Their email is <personal data hidden> - Please include your first and last name.

The experts there can also provide you with the best treatment options.

The lab will let you know if they need a sample sent.

The lab may also ask for additional images. So be prepared.

Their website is at this link:

Plant & Pest Diagnostics (msu.edu)

Their Contact Information is at this link:

Contact Us - Plant & Pest Diagnostics (msu.edu)

This link will explain the details on submitting a sample to the MSU Plant & Pest Diagnostics Lab:

Submit Samples - Plant & Pest Diagnostics (msu.edu)

I hope this helps!