Maple Tree Leaf Issue - Ask Extension
We have three different varieties of Maple tree that are all planted at 16ft spacing from one another and are suffering from leaf discoloration for th...
Knowledgebase
Maple Tree Leaf Issue #878385
Asked July 23, 2024, 9:53 AM EDT
We have three different varieties of Maple tree that are all planted at 16ft spacing from one another and are suffering from leaf discoloration for the second year (see attached photos). The trees were planted 3years ago and are Bowhall, October Glory, and Brandywine varieties with 3-5" diameter trunks. All three have similar discoloration on some of the leaves. I tested the soil last summer and the pH was 6.53 and most macronutrients and micronutrients were within the ideal range with the exception of very low nitrogen (1.61). I don't believe it is chlorosis because the soil test indicated an exceptionally high (45.81) iron content. What could be causing this?
Calvert County Maryland
Expert Response
Chlorosis can be influenced by soil acidity, not just iron (or manganese, magnesium, or zinc) levels, but we agree that the soil is acidic enough that it's unlikely this is a type of nutrient deficiency chlorosis. If you used a soil testing lab for the measurements, it's surprising that they analyzed nitrogen content, since usually this is not something that is measured since it fluctuates too frequently for testing to be of much value. (Therefore, the low levels reported are probably not accurate, at least not all of the time, and the trees are not shedding yellowing older leaves that would support the idea that nitrogen is deficient.)
There may be more than one issue present. Some of the leaf symptoms look like spider mite feeding damage (called stippling), and there is a mite species specific to Red Maples, which are the varieties you listed. Some leaf symptoms look like herbicide exposure damage. Were any weed-killer products used in the past few weeks (or months) this year, as well as last year? (Or at least this year, since last year's maple leaf symptoms might have been only due to mites.) If you didn't apply any type of herbicide, could a neighbor have on the other side of the fence, or is there a nearby farm upwind? Some herbicide chemicals evaporate and drift on air currents more readily than others, especially if applied in warm, breezy weather, or may seep into the root zone and be absorbed by roots.
For herbicide injury, nothing can be done, and either the plant will outgrow the damage or won't; it's a matter of time and waiting to see how it fares, assuming no further exposures occur in the meantime. It's normal for most trees to not produce any more new foliage growth this late into the summer, so recovery, if possible, may need to wait until spring.
For mite damage, you could dislodge a number of mites by spraying the canopy (mainly the leaf undersides, if possible) with a strong spray of plain water from a garden hose. (Of course, let the hot water out of it first so it doesn't scald the tree.) Use of a pesticide like horticultural oil or insecticidal soap won't accomplish much at this level of damage and in this weather, since neither should be applied while temperatures are above 85 degrees. Leaf "burn" may occur if either is sprayed on foliage that has already sustained heavy mite feeding damage, though they may help to protect younger leaves from getting as badly damaged. Even so, thorough coverage of the entire canopy of each tree would be needed for such sprays to work well, and re-application would likely be needed for a few weeks. (Check the interval and other application details on the product label.)
You could also have a certified arborist come out to assess the trees. They can look for environmental sources of tree stress, such as girdling roots from being planted too deeply, a factor that can contribute to leaf stunting. Otherwise, for now, just continue to monitor the trees for watering needs so the root system stress is eased. (Not all of Calvert County is currently in drought status, but many areas are, and it could worsen again if rains do not keep up with plant needs later this summer.)
Miri
There may be more than one issue present. Some of the leaf symptoms look like spider mite feeding damage (called stippling), and there is a mite species specific to Red Maples, which are the varieties you listed. Some leaf symptoms look like herbicide exposure damage. Were any weed-killer products used in the past few weeks (or months) this year, as well as last year? (Or at least this year, since last year's maple leaf symptoms might have been only due to mites.) If you didn't apply any type of herbicide, could a neighbor have on the other side of the fence, or is there a nearby farm upwind? Some herbicide chemicals evaporate and drift on air currents more readily than others, especially if applied in warm, breezy weather, or may seep into the root zone and be absorbed by roots.
For herbicide injury, nothing can be done, and either the plant will outgrow the damage or won't; it's a matter of time and waiting to see how it fares, assuming no further exposures occur in the meantime. It's normal for most trees to not produce any more new foliage growth this late into the summer, so recovery, if possible, may need to wait until spring.
For mite damage, you could dislodge a number of mites by spraying the canopy (mainly the leaf undersides, if possible) with a strong spray of plain water from a garden hose. (Of course, let the hot water out of it first so it doesn't scald the tree.) Use of a pesticide like horticultural oil or insecticidal soap won't accomplish much at this level of damage and in this weather, since neither should be applied while temperatures are above 85 degrees. Leaf "burn" may occur if either is sprayed on foliage that has already sustained heavy mite feeding damage, though they may help to protect younger leaves from getting as badly damaged. Even so, thorough coverage of the entire canopy of each tree would be needed for such sprays to work well, and re-application would likely be needed for a few weeks. (Check the interval and other application details on the product label.)
You could also have a certified arborist come out to assess the trees. They can look for environmental sources of tree stress, such as girdling roots from being planted too deeply, a factor that can contribute to leaf stunting. Otherwise, for now, just continue to monitor the trees for watering needs so the root system stress is eased. (Not all of Calvert County is currently in drought status, but many areas are, and it could worsen again if rains do not keep up with plant needs later this summer.)
Miri
