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Fruit Tree Diseases

Fruit Tree Diseases


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Fruit Tree Info

I have received many phone calls about fruit trees lately. Many are concerned about recent frost damage, a disease called fire blight, when to starts praying for coddling moth and about blisters or lesions on pear and apple leaves.

Frost Damage: With the recent warm-up, many trees have started blossoming. Unfortunately the warm-up has been interspersed with cold weather. Although, I cannot say for certain whether a particular tree's flowers were damaged without looking at the blossoms, the critical temperature at which damage occurs is around 28°F. This is somewhat variable though. Other weather conditions influence this such as humidity and cloud cover. Within the next few weeks, if the blossoms were not greatly damaged by frost, fruit will be visible on the tree.

Fire Blight: Fire blight is a bacterial disease that affects many apples and pears. The disease spreads through spores that are in ooze produced by cankers in previously infected trees. The ooze is released just before blossoms open and contains nutrients attractive to insects. The insects feed on this ooze and pick up spores. When the insects pollinate newly open flowers, the bacterial spores potentially enter to create new infections. There are preventative sprays available from most garden centers and farm stores. These are only effective when the trees are in blossom. Otherwise, once an infection has occurred, it must be pruned out. For more information about fire blight, download the following USU Fact sheet: http://extension.usu.edu/files/publications/factsheet/fire-blight-08.pdf.

Coddling Moth: The USU pest plant pest diagnostic lab has not released an official date to start spraying for coddling moth. The point at which to start spraying varies greatly from year to year. However, the lab is monitoring and will release the date within the next few weeks. The lab e-mails out regular updates detailing potential pest problems for most areas of the yard including fruit trees, gardens, ornamental plants and turf and how to manage them. To subscribe to the updates, visit the following website: http://utahpests.usu.edu/ipm. In the meantime, a good way to minimize damage from coddling moth is to thin the fruit so that there is one fruit for every 6 to 12 inches of branch. The moth prefers to lay eggs where apples or pears touch.

Blister Mite: I have received several samples of pear and apple leaves that have black or brown blisters on them. The condition looks similar to apple scab, a fungal disease. However, apple scab is extremely uncommon in our dry climate. The culprits are almost always small mites that are only visible with a powerful magnifying glass or a dissecting scope. They start to feed on sap from the leaves in the spring, and, over a short period of time, enter the leaves and the lesions become evident. Initially, the mites cause only cosmetic damage. Later on in the season they can cause the same lesions or blisters on fruit.The mites are usually only problematic in trees that are not properly managed. The only way to control them is with applying dormant oil or sulfur in the fall or early spring.

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Taun Beddes

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