Minnesota Tree Care Advisors

Characteristics
Disease Management

Norway Maple is an introduced species that has become naturalized in some areas and is considered "invasive" in some regards. Since its introduction, Norway Maple cultivars have become popular for lawns, parks and boulevards.

Large tree height:		40-60'

Canopy spreads:		30-50', Rounded, symmetrical crown.

Drought Tolerance:		intermediate

Shade Tolerance:		Intolerant

Soil pH Tolerance:		Tolerant to high pH

Poor Soil Drainage:		Intermediate to flooding

Salt Tolerance:		Tolerant to salt spray and Tolerant to soil salts.

Oppositely branched tree with smooth gray bark when young and maturing to a rough, dark colored bark. The foliage is quite variable in the cultivars - the deep purple of 'Crimson King' to the dark greens of 'Emerald Queen' and 'Emerald Lustre'. The fall colors are just as variable with some becoming brilliant yellow, while others remain red in the fall.

The leaves tend to have 5 strong lobes. The fruit is a double samara with almost a 180 degree spread, unlike the "U" and "V" shapes of the other maples common to Minnesota. The twigs tend to be brownish in color with visible lenticels and the buds tend to be rather large, imbricate (overlapping scales) and often waxy or rather sticky.

This tree is readily available in the nursery trade. Norway maple and its cultivars are highly sought after from the 'Crimson King' cultivar to the 'Emerald Queen' variety. Dirr's "Manual of Woody Landscape Plants" lists 36 cultivars.

Did you know
Look for white milky sap when you pull a Norway maple leaf off of a tree. The sap looks very much like what you would see in a milk weed.

DISEASE		SYMPTOMS	MANAGEMENT
Anthracnose, Discula species and others	Fungi	Tan/brown/black spots and blotches develop on leaves during wet periods. Spring infections result in leaf distortion. Necrosis may follow the veins.	Rake up and destroy or compost fallen leaves. Promote tree vigor. Not seriously damaging to healthy established trees. CHEMICAL: Preventative fungicides should be applied beginning at bud break when deemed necessary. Bordeaux, chlorothalonil, fixed coppers, mancozeb, thiophanate-methyl or zyban.
Leaf spot, Phyllosticta minima	Fungi	Well-defined lesion on the leaf surface with a light-colored center and dark margin at maturity. Tiny black dots (fruiting bodies of the fungus) are often visible.	Rake up and destroy fallen leaves. Avoid wetting the tree foliage during irrigation. Promote tree vigor. Seldom damaging to healthy, established trees. CHEMICAL: Treat preventatively with Bordeaux 8-8-100, fixed coppers or mancozeb.
Target-shaped canker, Nectria galligena, Eutypella parasitica	Fungi	Perennial cankers develop around wounds on immature trees, usually within 10 feet of the ground. The trunk is swollen around the canker, which often has a ãtarget-likeä appearance.	Plant on good sites in proper zone. Prevent damage to trunk and limbs. Promote tree vigor. Remove branches with cankers. May become a hazard tree and should be evaluated as such. CHEMICAL: None.
Tar spot, Rhytisma acerinum	Fungi	Roughly circular, raised black spots on the leaf surface which resemble spots of tar. Seldom a problem.	Maintain tree vigor. Infected leaves can be raked up and destroyed or composted. CHEMICAL: None necessary.
Wilt, Verticillium dahliae	Fungi	Slow growth, dwarfed foliage and/or wilting. Leaves with scorched margins. Defoliation. Often occurs on only one part of the tree. Green to black vascular discoloration may be present in the sapwood of larger branches and the trunk. REFERENCE: Verticillium Wilt of Trees and Shrubs, AG-FO-1164 (MN), Deciduous Tree Diseases, PP-697 (ND).	Fertilize to promote growth; keep nitrogen to a minimum. Prevent moisture stress. Remove dead limbs. Do not plant susceptible tree species where Verticillium is present in the soil. CHEMICAL: None. NURSERY: Preplant fumigation.