Mature Boston ivy climbing up a wood fence in shade develops brown spots and leaves dry up starting now. Narrow bed is probably poor soil.
Has occurred for last 3 yrs. Also there could be tiny white insects.
There are three issues at hand: the easiest to tackle first is the soil. Although Boston Ivy (Parthenocissus tricuspidata) is very hardy and grows well, amending the soil with compost and adding mulch at the base will enable moisture to be absorbed by the roots to keep the vine healthy.
You don’t say whether or not the white insects are on the plant now, or you saw them last year. One whitish insect, the mealy bug usually shows up during warm, dry spells. They suck the sap of the plant, and are often difficult to control when in large numbers. Picking them off the plant for a small number, or treating with insecticidal soap may keep the numbers in check.
The spots could be the fungus, Boston Ivy Leaf Spot (Guignardia bidwellii). It shows as irregular rusty spots on leaves, the black fruiting bodies come later, and show up in the central portion of the spot. It can cause the leaves to brown and curl, then fall off. This fungus overwinters, and will infect the plant if water is on the leaves longer than an hour. With the wet spring we have had, it will likely cause it to spread rapidly.
Control is difficult. Everything I have found mentions chemicals that are not allowed in Toronto. A Bordeaux mixture or a liquid mixture of copper sulphate can be used to control the spread, but not actually remove the existing fungal spots. If possible, remove all affected leaves. In the fall, a very thorough clean-up is required, and do not compost the leaves.
For more information about the disease and other pests on Ivy, check out the following: