Leaves falling from Monterrey Oak
I have 2 Monterrey Oak trees about 25' tall (planted in 2003). They lost leaves in the fall and sprouted new leaves about 6-8 weeks later - normal process. During the last month, one of the trees has been losing a lot of leaves - about 1/4 leaves have fallen off. I'll send a pic of some leaves (still attached to the tree). The other tree is now losing leaves. I sprayed Triazicide on both trees a couple days ago. A few years ago both trees had bore worms and I used a product with permethrin to resolve. No signs of bore worms right now. Any idea what is causing the leaves to fall off?
Tree damage (the tip and margin burn) like this is sometimes a water or herbicide issue or tree is planted too deep.
Your posting does not say where you are located. Every county has a County Extension office you can call for advice.
Trees are damaged by salt in water if groundwater is used from the many aquifers in Texas that have too much salt both Calcium and sodium. The picture shows no salt damage on the other plants so this may not be the situation. Switch to city water if this is the case.
Poor drainage will cause these symptoms, but the rosemary in the planted bed is not tolerant of poor draining soil so this may not be the problem. If the soil was amended in the planted are but not in the tree area, then drainage or compacted soils may be the issue. Poor drainage causes the irrigation and Stormwater to saturate the soil too long and the roots rot and the water displaces oxygen away from the roots. Use a long screw driver or piece of rebar to stick into the soil. These objects will easily go into wet soil but not into dry. When you pull the screw driver or rebar out, look and smell the soil along the side. If the soil has stayed too wet due to poor drainage, the soil will smell. Poor drainage is improved by installing a sump by inserting a perforated drain pipe filled with gravel into the tree hole.
If the screw driver or rebar come our dry or the soil is so dry the tools cannot be pushed into the soil, than the soil is too dry. I see drip tubing in the planted bed. Is this how you are irrigating these trees?
Certain herbicides (weed killers) in fertilizer called ‘weed and feed’ (particularly Atrazine) may damage tree roots particularly in clay soils.
Only other situation I see causing these symptoms is planting tree too low or tree sinking below soil as the compost the tree was planted in decomposes. The clay soil expands around the tree to take the place of the decomposed soil. The tree could always be lifted and reset or you can remove the heavy soil over the roots with an air spade or water pressure device. When looking at a properly planted tree, you should see a flaring at the base. If the trunk is the same width all the way, then the tree is too deep.