Spindle Galls

Spindle galls on maple leaves are abnormal growths caused by tiny insects called mites. Spindle galls on maple leaves are formed when mites lay their eggs on the leaves. The plant reacts by growing the gall around the eggs. They're generally harmless to the tree and won't cause significant damage.

When mites bite the leaf, it triggers the tree to immediately produce chemicals in response. These chemicals help create the gall structure around the mite eggs. The specific chemical exchanged in the sugar maple (Acer saccharum) is a plant hormone called abscisic acid. This chemical helps regulate various plant processes such as seed and bud dormancy, the control of organ size, stomatal closure and other stress responses. The production of abscisic acid (ABA) is part of the plant's defense mechanism against the mite infestation. These changes help the plant defend itself and minimize the impact of the mite infestation.

In more general terms - The production of abscisic acid helps shut down access routes in the vascular system of the leaf, indirectly preventing disease and other pathogens from entering the xylem and cambium layers. The production of abscisic acid doesn't render the leaf useless or cause it to drop from the tree. Instead, it helps regulate the leaf's physiological processes, including the closure of stomata to reduce water loss which causes the breakdown of chlorophyll that can contribute to the leaf's eventual color change and senescence (leaf drop.)

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SUMMARY – When a mite bites and lays eggs on a maple leaf, the leaf produces a hormone that causes a weird growth to incapsulate it. The red spots in the leaf are a symptom of the hormone causing the stomata (leaf pores) to close, because the hormone is limiting the water supply to the chloroplast cells (the cells that absorb sunlight). This can lead to the death of the chloroplasts and a decrease in chlorophyll production, resulting in the change of leaf color and preventing photosynthesis. The spindles serve as a physical barrier that prevents the mite from causing further damage to the leaf. Additionally, the spindle provides protection for the mite, making it more difficult for other insects to prey on it. It's a mutually beneficial arrangement for both the leaf and the mite!

THE BIG QUESTION! – Spindle galls are normally harmless to the tree but if the tree is already stressed, could the leaf damage cause the tree to remain in decline?

Yes, if a tree is already stressed or in a weakened state, the damage caused by the leaf infestation can contribute to its continued decline. The tree's ability to photosynthesize and produce energy may be compromised, which can further weaken its overall health. It's important to address any underlying stress factors and provide proper care to support the tree's recovery.

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RECCOMDATION - Using neem oil or other insecticide/miticide in early April can be an effective preventive measure against infestations. Neem oil has natural insecticidal properties that can deter pests, including mites. Applying it to the buds before bud break or the leaves during the early stages of growth can help protect the tree from potential infestations.

In Western North Carolina, zone 7b, mite infestations on sugar maples typically occur during the warmer months, from late spring to early fall. Keeping an eye out for signs of mite activity and taking preventive measures, can help protect the trees. I recommend in November, after maples have dropped their leaves and set their new buds. These mites are small enough that they can wedge into the buds and other almost microscopic places, so the treatment will have to be immense and thorough for good control.

For a professional opinion on any tree-related issues, contact Dalton Tree Consulting at DaltonTreeConsulting@gmail.com or send me a PM through facebook to schedule a consultation.

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Sources

Maple Bladdergall Mite | NC State Extension Publications (ncsu.edu) | J.R Baker

https://content.ces.ncsu.edu/maple-bladdergall-mite

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