White Powdery Mildew on Red Oak

611 Views | 0 Replies | Last: 2 yr ago by sleepybeagle
adamsbq06
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AG
Howdy AGS,
I am in San Antonio. We have a red oak that is having issues since the freeze. It took a while to get leaves and now we are noticing white powdery mildew. any recommendations on how to treat this?


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sleepybeagle
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Quote:

Powdery Mildew on Oaks

A fungus can cause odd (abnormal) branch tip growth and velvet-like growth on the leaves. The fungus is a species of powdery mildew. In the case of the velvet leaves, the fungus invades the surface cells on the maturing leaf, and the interaction of host and fungus cause the velvet growth, and may also cause a bronzing or reddening of the leaf tissues. The abnormal branch tip growth occurs when the powdery mildew fungus invades the terminal bud of the branch. The fungus becomes systemic in this bud, and the subsequent growth is multi-branched with stunted, deformed, grayish-white leaf and stem tissues.

Control of powdery mildew in oaks, both the coastal and valley species, centers on water management. All coastal and valley oaks evolved in a Mediterranean climate, i.e., winter-spring rains and summer-fall drought. Watering these trees in the summer causes them to continue to grow. This tender summer growth is extremely susceptible to attack by oak powdery mildew fungi. By the way, there are actually several species of powdery mildew fungi that can infect oaks. Therefore, reduce or eliminate summer watering of oaks, if possible. Let the spring growth harden off. Mature, fully expanded leaves are very resistant to powdery mildew attack. In trees that have developed "witches brooms," that is what the abnormal tip growth is called, wait until fall or winter and then prune all the "witches brooms" out of the trees. As for the leaf infections, a spray when trees are dormant in December or January will help reduce the incidence of powdery mildew in coastal and valley oaks, but probably will not eliminate the problem. Remember, summer drought is the best control.
Quote:

Powdery Mildew (Fungus Phyllactinia corylea and others)

All species of oaks are susceptible, but some are more prone to extensive damage than others. Powdery mildew on live oaks is first visible as faint yellow spots on the upper and lower surfaces of the leaves during the latter part of summer. Spots are normally round and approximately to inch in diameter. Premature defoliation occurs with severe infection. Usually, however, leaves are retained until normal leaf shed. In the case of other oaks, powdery mildew may cover the entire leaf surface giving the appearance of a fine white to gray powder. The fungus overwinters on infected leaves in a spore stage which is resistant to adverse weather conditions. In the spring and summer fungal spores are carried by air currents to infect leaves of healthy trees. Fungal structures develop only in and on the outer layer of leaf cells. Sanitation is important in controlling powdery mildew since initial inoculum comes from leaves infected the previous year. Rake and discard fallen leaves in a compost pile where they can undergo complete decay. Applying a benomyl-containing fungicide keeps high-value trees free of the fungus. Use a wetting agent with the fungicide to improve coverage of the waxy leaf surface.
Hope this helps - I had this happen to one of my red oaks last year. I didn't do anything and it fully recovered with new leaves. But - it wasn't stressed by the freeze we had this winter.
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