I am in the beaches part of Toronto. We have had baltic ivy growing over our front garden wall for over 15 years. It is a very sunny exposure yet lately I am finding many leaves going yellow with dark brown largish blotches on the individual leaves. Other plants seem fine ( yucca, cotoneaster, sedum ).
What could this be? We do not over water.
Due to the rainy cool weather we had this spring, we are noticing an increase in fungal & bacterial diseases. Perhaps this is why you have not noticed it in past years. Fungi and bacteria cause spots on plant leaves, in a variety of colors, shapes and sizes. In some cases the spots may spread to cover entire leaves, stunting plant growth. Generally if the disease is not too extensive then it will not have a major impact on your vine, but if your vine undergoes heavier infestations in several successive years, this can weaken your vine
According to the Missouri Botanical Garden: ” Leaf spots on English ivy are caused by either a bacterium, Xanthomonas campestris, or a fungus, Colletotrichum trichellum. Both can cause defoliation, but the fungal leaf spot is more active in causing stem infection.
Bacterial leaf spot first begins as light green, watersoaked spots that enlarge and become brown or brownish black in the center. On mature leaves the margin of the spot may be red. An infection in the leaf petiole causes the petiole to become black. Infection can move into the stem causing tips to turn black and die.
The fungal leaf spot produces large tan to brown spots on the leaves. They do not have a red margin. Black specks, fungal fruiting bodies, may be visible in the dead tissue, giving the spots a speckled appearance. The fungus can also infect stems, resulting in tip dieback.” The Missouri Botanical Website has a list of Intergrated Pest Management Strategies to combat this disease.
You may also be interested in an article titled Diseases of English Ivy which lists the various diseases as well as their management practices.
Good Luck with your Ivy.