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Maple trees can be vulnerable to root rot

Posted: June 27, 2015 - 11:03pm

This area has had a lot of rain, and with it, perfect conditions for root rot and fungal leaf spot on all types of plants. Maples have been the main concern in the area according to homeowners.

Maple trees are popular in home landscapes all over Georgia. You can find several varieties that do well in our area, including red maple, sugar maple, silver maple, and Japanese maple, but this season the weather has been optimal for fungal diseases.

Phytophthora root rot is favored by high soil moisture and warm soil temperatures. Root rot is by far the most damaging disease in Georgia’s landscapes. It occurs in wet soils with limited drainage or in areas that are overwatered or remain wet due to gutters and downspouts, air conditioning units and slopes. All landscape plants (trees, shrubs and flowers) are susceptible to root rot. Fungicidal applications are rarely effective on controlling Phytophthora root rot after above-ground symptoms are seen. The best way to fight root rot is prevention. Be sure to inspect the landscape site for collection spots of excess water. If soils consist of heavy clay, consider raised beds. Raised beds are created by using triple-screened topsoil with a height of 1 to 3 feet. The topsoil will support the roots of plants and also provide a well-drained soil. The material should be incorporated to a depth of 8 inches into the existing soil to ensure drainage. In extreme cases some areas my need additional drains constructed of gravel placed 6-12 inches below the surface. Never plant any deeper than the soil level in the container. Firm the soil beneath the soil ball so that the plant will not settle into the bed.

Most leaf spots need high temperatures, high humidity and extended periods of leaf wetness to infect their host. There are a few leaf spots known to affect maple trees.

Phyllosticta, or purple eye. On the leaves of maples the fungal spots can be round or irregular, and are about ¼ inch in diameter. They have purple margins with yellow or tan centers. A small, black fruiting body will appear in the middle of the diseased area, somewhat resembling an eye. The good news is that Phyllosticta leaf spots rarely pose any long term damage to maples. Phyllosticta leaf spot is the most common disease I have seen on the leaves of Japanese maples, especially on the darker varieties, such as “Bloodgood.” The disease appears as small, round, bleached spots, easily contrasting the dark red of the leaves. Another common leaf spot on maples is tar spot. We normally see this disease in spring and early summer. Tar spot first appear as light-green or yellow round areas. These spots then develop a black, shiny, tar-like dot on the upper side of the leaves. In many cases, leaves with several spots will prematurely drop to the ground.

Your best defense against these fungal leaf spots will be proper management. Rake all of the leaves from around the maples in the fall and remove them from the property. Pruning may also help control these diseases by allowing more air flow to dry out the leaves.

Chemical control is rarely needed, and is most often not feasible due to the size of most maple trees. However, some homeowners choose to treat their Japanese maples because they are small enough to easily spray and are expensive enough to justify the cost. Propiconazole, a systemic fungicide, can be found in the brand names Bonide Infuse and Fertilome Liquid Systemic. Chlorothalonil, a contact fungicide, can also be used against Phyllosticta leaf spot. It can be found under the brand name Daconil, which is the name used by several companies.

Always read and follow all label instructions when applying pesticides.

Tripp Williams, Columbia County’s agriculture and natural resource extension agent, can be reached at (706) 541-4011, or trippj@uga.edu.

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