Fire blight

We are noticing a lot of Callery pears (some people call them Bradford pears) with brown and black wilted foliage and stems, an indication that they are infected with fire blight. That’s good news for those of you who don’t like Callery pears, but it could mean trouble for edible pears, quince and apples!

Wilted stems and foliage with scorched appearance characteristic of infection by fire blight.

 

Fire blight is caused by the bacteria Erwinia amylovora and is especially common in warm, wet springs. It attacks a variety of plants in the rose family, particularly pears and quince, though apples, hawthorns, cotoneasters and pyracantha can also be infected. Oddly enough, the Callery pear is supposed to be resistant to fire blight, but it isn’t this year!

The bacteria most often enters through blossoms, transmitted by pollinators, including honey bees, and splashing by rain. It can also enter through wounds. The infected blooms and stems wilt and turn brown, reducing fruit production. The bacteria can be transported through the vascular system. If the disease becomes systemic and reaches the roots the tree can die.

Infected branches can be pruned and destroyed to prevent the bacteria from reaching the vascular tissue in the trunk. However, pruning can stimulate growth of tender tissues which are more susceptible to fire blight. The addition of nitrogen fertilizers should be avoided for the same reason.

If you do decide to prune, cut at least one foot below where the symptoms are visible and make sure your pruning implement is cleaned before/after each pruning cut to avoid transmitting the bacteria to new branches. Pruned material should be removed from the area and destroyed to reduce the risk of re-infection.

To avoid loss of production fruit growers sometimes apply antibiotics, but this must be done PRIOR to infections. In some locations fire blight has shown resistance to commonly used antibiotics and they are no longer effective. Some work has shown that innocuous bacteria or yeasts can outcompete the fire blight bacteria and protect blossoms and stems if applied PRIOR to infection.