Bacterial blight of lilac

About

Bacterial blight blackens young lilac shoots, leaves and flower clusters in cool, wet springs, often right after a frost. It can blacken a whole season's flower clusters.

Also called bacterial blight of lilac, lilac bacterial blight, lilac blight, Bacterial blight, Pseudomonas blight, shoot blight of lilac

How to recognize it

Symptoms

In early spring, brown spots, sometimes with a yellow halo, appear on young leaves and shoots and quickly turn black in rainy weather. Young shoots bend over at a black lesion and wither above it, young leaves blacken in a wedge from the edge, and flower clusters and buds turn black and die.

Often confused with

Blackened buds can look like winter injury; bacterial blight keeps spreading on new shoots and leaves in wet weather.

Worse when

Cool, wet spring weather, frost injury, wounds, and soft growth from too much or late fertilizer.

How it spreads

The bacteria live through winter in old cankers and on buds, bark and leaves, and spread by rain, wind, insects, tools and infected nursery plants.

When

Early spring through late spring, during rainy weather.

What to do, gentlest first

Prevention works best; most sprays only protect healthy leaves and can't cure infected ones. Always read and follow the product label.

1. Choose resistant lilacs Prevent

   Most common lilac cultivars are susceptible. Species such as Syringa josikaea, S. komarowii, S. pekinensis and S. reflexa resist it, and common lilac cultivars such as 'Edith Cavell', 'Glory' and 'Pink Elizabeth' have shown less disease in gardens.

2. Air, spacing and careful feeding Prevent

   Space lilacs and thin them so air moves through. Do not fertilize late in the season or overfeed young plants.

3. Prune out blighted shoots By hand

   Cut out blackened shoots and flower clusters well into healthy wood as soon as you see them, in dry weather, and destroy them.

   Clean pruners between cuts so you do not spread the bacteria.

4. Copper (such as Bordeaux mixture) Organic spray

   Spray before fall rains and again before buds break in spring. Bordeaux mixture can still work on bacteria that resist other copper products.

   Copper can injure lilac leaves early in the season, and overuse breeds copper-resistant bacteria. WSU's bee guide rates Bordeaux highly toxic to bees and copper hydroxide toxic, so do not spray when bees are around. Follow the label.

Plants it affects

Lilac