by Edith Isidoro-Mills — I’ve noticed a lot of deciduous trees in our area still have their leaves hanging on the branches even though they have turned brown and brittle. This is called marcescence. There are number of reasons marcescence occurs and we currently have had those conditions this fall.
Fall conditions that are ideal for leaves to turn various shades of yellow, red, and orange are gradually shorter daylength, gradually cooler temperatures with occasional light frost. Conditions like this allow the for natural degradation of chlorophyll in the leaves and the unmasking of other pigments such as carotenoidsto be unmasked. These no longer hidden pigments are that give leaves on deciduous trees and shrubs their fall color. While chlorophyll is disappearing, a layer of cells is forming at the base of the leaf petioles that blocks the flow of water and nutrients between the leaves and their tree or shrubs vascular system. This layer of cells is an abscission layer that when completely formed allows the tree to shed leaves. Marcescence is the condition where this abscission layer is either not completely formed or doesn't form at all.
Two of conditions the conditions that can cause leaf tissues to die before an abscission layer forms occurred here in Churchill County during both our late summer season and fall.The two conditions I observed were insect infestations that attack the leaves and sudden severely cold weather.
The insect infestation we had specifically attacked the local poplars and cottonwoods. You most likely noticed the trees turning dull green or in severe cases, the tree just turned brown. There were very thin strands with little white worms hanging from the trees everywhere. One friend even suggested she didn’t need to purchase Halloween decorations that looked like cobwebs because there were enough of these fine strands hanging from the trees that had gotten tangled together that they actually looked just like the decorations you purchase in the store. These little white worms had already killed the leaf tissues of the leaves they fed on before making their way to the ground on these very fine strands. The leaf tissues died before the chlorophyll could degrade and a layer of abscission cell form to allow the leave to fall of the tree. Some mechanical force such as a strong wind or something beating on the leaves will eventual break the dead leaf petioles thus allowing the trees to eventually shed their leaves..
If the leaf miners weren’t enough to cause leaves to die before chlorophyll could degrade and an abscission layer form, we then experienced at least two weather incidents that caused temperatures to dive suddenly and severely to destroy plant tissues. Extreme sudden freezes while plants are still actively photosynthesizing can cause cell membranes to break as the water in the cell freezes and expands. This kills the cells in the leaf tissue before any abscission layer can form.
The good news is that if the tree or shrub is otherwise healthy, is should recover to produce leaves next growing season. In the case of the leaf miner infestation, our poplars and cottonwoods will most like survive but unless we get a hard enough and long enough winter to kill most of the leaf miners we will most likely witness the same brown leaves and sticky strands with white worms again next year.Sign up to receive updates and the Friday File email notices.Support local, independent news – contribute to The Fallon Post, your non-profit (501c3) online news source for all things Fallon.
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