Soluble aspirin is known to help, because a traditional method of keeping blight at bay, is to layer willow chippings around the stems.
Salycylic acid is a known deterrent for blight, but it may not always work! I've used it many times in the past but sprayed it on the whole plant before blight descends, not during or after an attack.
Use one standard tablet per 3.5 litres of water, but that's just a calculation I got from the net, you could use more - or less!