2017-07-15 / Outdoors


June’s rain was mixed blessing

Our rainy June was a mixed blessing.

It has extended good trout fishing, made our forests and gardens grow well, and has favored certain beneficial fungi, including those that prey upon forest pests like gypsy moth caterpillars.

However, lots of rain in the spring and early summer also provides ideal conditions for the spread of fire blight, a bacterium that causes branches to die on apple trees, crab apple trees, pear trees, and related species.

Infected branches and their foliage show a browning and die-back of new growth. The branches appear to have been scorched by fire, hence the name. This die-back migrates down the branches until controlled by the tree.

Fire blight is believed to be native to North America, but has been spread to other parts of the world where it is a concern in apple and pear orchards.

These bacteria over-winter in cankers on the blight-infected wood of trees. In the spring. they begin multiplying and ooze to the surface, where they are spread through the tree by rain or from tree to tree by insects.

Fire blight bacteria are often spread to the flowers from infected branches by rainwater. Once in the flowers, pollinating insects such as bees easily spread the bacteria from tree to tree as they fly around pollinating apple blossoms.

Blossoms will then wilt and die as bacteria multiply. Rain or insects also spread the bacteria to the tree’s new growth, causing the die-back that is evident on many trees in our area.

Most apple trees can ride out the infection without any serious long-term problems. For the most part, it only affects the new growth.

However, several types of domestic dwarf apple trees are highly susceptible. Bacteria can easily spread from the infected branches to the rootstock, killing the whole tree.

Removing infected branches is one effective remedy. They should be cut 10 inches below the infected area. It is important to disinfect cutting tools after each cut. Pruning should be done on dry, sunny days to prevent other infections.

On older, slower growing trees, the tree’s immune system will block the bacteria before they spread very far down larger limbs. Fire blight can often be left to run its course without damaging the tree.

Fire blight infections seem to be cyclic, based on weather conditions.

This year we are experiencing one of the best apple crops that we have seen in a long time. The fire blight, although significant, is not as pervasive as it is some years. In most areas, it should run its course without affecting the apple crop or causing widespread damage.

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