Hello,

The gummy substance oozing from your nectarine fruit is likely due to a condition known as gummosis. Gummosis is not a disease itself but a symptom of stress or injury in stone fruit trees, including nectarines.

Gummosis is a condition that affects stone fruits like nectarines, and it’s characterized by the oozing of sap from the fruit, twigs, or branches. In Michigan, particularly with reference to Michigan State University (MSU) resources, gummosis can be caused by bacterial or fungal pathogens.

The bacterial spot, caused by Xanthomonas campestris pv. pruni, is one of the diseases that can lead to gummosis in nectarines. Symptoms include fruit spots, leaf spots, and twig cankers. The fruit may show pitting, cracking, and gumming, which makes them more susceptible to other infections1. Management of this disease includes a comprehensive disease management program and may involve cultural practices like removal of gummy tissue during spring pruning to reduce inoculum levels.

Fungal pathogens like Leucostoma persoonii and L. cincta, formerly known as Cytospora spp., are also known to cause gummosis. The condition is influenced by the overall health of the tree, environmental factors, and growing conditions.

It can be caused by various factors such as:

Borers: Insect damage can cause the tree to exude gum as a response to the injury.

Diseases: Fungal infections like Coryneum blight can lead to gumming on the fruit and other parts of the tree.

Environmental stress: Poor growing conditions, such as compacted soil, can also lead to gummosis.

The gum can be clear, milky, or amber-colored, depending on the cause. If the gum is clear, it’s usually due to abiotic (non-living) factors. If it’s milky or dark-colored, it could be due to an insect or disease.

To manage this issue, it’s recommended to:

Prune and destroy all infected plant tissue to prevent the spread of disease.

Avoid wetting the leaves with irrigation water as this can spread spores.

More information is at these links:

The Backyard Orchard - Peach and Nectarine Pests | USU

Gummosis of Stone Fruits – IPM Pest Advisories (usu.edu)

Because of the many problems this tree might have, I recommend the below options:

OPTION 1:

For a confirm and precise identification of the problem, I recommend you send all your images by e-mail to the MSU Plant & Pest Diagnostics Lab. The experts there can also provide you with the best treatment options. Their email is <personal data hidden> - Please include your name – The lab will let you know if they need a sample sent. FYI – The lab may also ask for additional images too.

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 MSU Plant & Pest Diagnostics Lab:

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

OPTION 2:

You can consult with a local arborist for a more detailed onsite assessment and personalized advice. To find an arborist in your Zip Code go to this link:

Find an Arborist (treesaregood.org) 

I hope this helps!