Arborvitae Green giant
There are 9 green giant Arbs planted 20ft apart on center installed approximately 2yrs ago. 3 are slightly yellowed and stunted. They are on the bay end of the planting. All plants exhibit a 'canker ' on the leaves. Please see the attached photo. I need an accurate diagnosis in order to treat the problem properly. Thanks, Nathan Ullrich
It is challenging to ascertain the cause of the leaf symptoms in the photo, but the cause could be from over-arching environmental stresses. The weather was so wet the first half of the growing season and so dry afterwards that many plant roots suffered damage and dieback. Since a compromised root system cannot supply all the foliage with water and nutrients as well as it should, leaf death can occur.
If the whole plant were visible, we might be able to evaluate the plant's health as a whole from the pattern and extent of the yellowing. Western Arborvitae such as this do have good moisture tolerance compared to other Arborvitae and other screening evergreens, but it is possible that they received too much this spring and summer, in addition to perhaps some salt exposure from their proximity to the Bay, as you mention. Stunting is concerning, as 'Green Giant' Arbs are known for rapid growth, and establishing trees commonly put out at least a foot of vertical growth per year, especially on the terminal (leader). Stunting could be a sign of compromised roots, especially from poor drainage (leading to infection and rot) or obstacles in the soil or heavily compacted soil. Most likely in this case would be improper planting depth, buying the surface roots too deeply and creating conditions favorable for opportunistic rot to set in. Check the base of the trunk at the soil line and see if the "root flare" is visible. This is the natural widening (flare) of the trunk as it transitions into root tissue, and it is a very common occurrence for nursery-grown plants and installed garden plants to be planted too deeply, burying the root flare. You could try to dig up and re-plant one of the stunted plants to check the root system, as its stunting is a sign the root system is already stressed or reduced; spring would be a good time to try this. While a nutrient deficiency is unlikely, you could also check your soil conditions with a soil test. Area labs offering this service and basic information about soil testing can be found here: https://extension.umd.edu/hgic/topics/soil-testing.