Spring Diseases

By Ashley Harbaugh, LC/dbm

Sooty Mold

The melting snow and warmer temperatures of spring make landscapes prime areas for disease and fungi. Here's a list of common turfgrass and tree diseases that come out in the spring, and how they can be prevented.

Sooty Mold

Sooty mold is a charcoal black fungus that appears as a black coating on the surface of leaves, fruits, twigs and branches of many deciduous and evergreen shrubs and trees. This fungus is not pathogenic to plants but obtains its nourishment from insect honeydew, which is a clear, sweet, sticky substance secreted by insects that feed on sap. Wind-blown sooty mold spores stick to the honeydew, and when the spores germinate, they send out black fungal strands (mycelial threads) that cover the plant tissue and cause the discoloration. The mold can build up on twigs, needles, and leaves, and if the coat of mold on the leaves is heavy enough, it screens out light and reduces the plant's capacity to produce food. To prevent sooty mold, you need to manage the insects that make the honeydew. The systemic insecticide imidacloprid is available to control the pests.

Net Blotch

Net Blotch

Net blotch is a disease that occurs on tall fescue during cool, wet and cloudy periods in the spring or early summer. Net blotch is a Helminthosporium disease, which is a complex of diseases caused by fungi that produce large, cigar-shaped spores. Symptoms of net blotch appear as tiny, brown spots on the leaves, and as the lesions expand, they become oval or square and coalesce to form a net-like pattern on the leaf. From a distance, net blotch appears as a general thinning of the turf stand that is yellow or brown in color. Watering deeply but infrequently, ensuring good surface and soil drainage, and removing excessive thatch reduce the potential of this disease. Fungicides containing azoxystrobin should be applied in the early stages of disease development.

Yellow Patch

Yellow Patch

Yellow patch is a common disease of cool-season turfgrasses (bentgrasses, bluegrass, fescues) during the fall, winter, and spring. Symptoms appear as irregular patches or rings up to three feet in diameter that are yellow in color, and multiple rings or patches may coalesce to form large, irregularly-shaped areas. Individual plants exhibit a yellow dieback of leaves or blighting of entire plants. No distinct lesions are evident on the affected plants, and the pathogen does not produce mycelium or other signs. Recovery from yellow patch can be very slow because it occurs at a time of the year when the turf is growing slowly. Avoid high rates of nitrogen during the late fall and early spring, ensure adequate surface and subsurface drainage, and aerify and topdress to reduce thatch accumulations.

Dollar Spot

Dollar Spot

Dollar spot appears on turf as small bleached-white or light tan spots approximately the size of a dollar coin, and it occurs on bluegrasses, bentgrasses, fescues and zoysia. On turf mowed at heights greater than half an inch, the spots may expand in size up to six inches or more in diameter. The affected leaves typically remain upright and are characterized by having white or light-tan lesions with light reddish-brown margins. The lesions first occur randomly on the leaf blade and then frequently extend across the entire blade. The grass in the spots may be killed to the soil surface if the disease continues to develop, and many spots may merge to produce large blighted areas. Mowing grasses at the recommended maximum height and maintaining adequate soil moisture and nitrogen fertilization help avoid dollar spot. Fungicides with the chemicals metconazole and myclobutanil are also available for dollar spot management.

Pythium Root Dysfunction

Pythium Root Dysfunction

Pythium root dysfunction is a disease of creeping bentgrass putting greens, and is most damaging to greens that were constructed within the last 10 years. The pathogen infects bentgrass roots during the fall and spring and reduces their ability to absorb water and nutrients from the soil. Symptoms may appear at any time of year, but are most severe during periods of hot and/or dry weather. Pythium root dysfunction appears in circles or irregular patches up to two feet in diameter that initially show signs of wilt or nutrient deficiency. As the disease progresses, affected areas turn orange and decline, eventually collapsing to the ground. Good surface and subsurface soil drainage, as well as aerification, are important for prevention. If necessary, commercial fungicides containing pyraclostrobin or cyazofamid are among the most effective for this disease.

Anthracnose

Anthracnose

Anthracnose diseases are caused by fungi that are capable of infecting stems, leaves, branches, and fruits of a wide variety of deciduous trees and shrubs. These diseases can be found throughout the eastern United States, and the symptoms of these diseases are more severe in years of extended cool, wet spring weather. Anthracnose pathogens overwinter in leaf debris and produce spores in the spring that are carried by air currents to young buds on the plant. Leaf infections cause necrotic spots, irregular dead blotches or necrotic lesions, and buds are often invaded and killed. Twig lesions often expand and may girdle the twig entirely, causing death of the parts beyond the lesion, and cankers form on the branches, which in turn girdle and kill the branches. Anthracnose diseases can be controlled by destroying plant materials and debris in which these plants overwinter, and trees that are severely affected can be sprayed with fungicide containing chlorothalonil or propiconazole in the spring before bud break.

Eastern Filbert Blight

Eastern Filbert Blight

Eastern filbert blight is indigenous to the Northeast United States and is a lethal disease of the European hazelnut. In spring, spores are released in a sticky, white ooze in wet weather and spread to young, developing shoots. The first symptoms to appear on infected trees are elliptical black stromata, which erupt from branches 12-18 months after the initial infection. The infected area is known as a canker, and these cankers are perennial, adding more stromata to existing rows each year. Infected branches become girdled, and leaves on the branches die. If no action is taken, in 5-12 years time the tree will be dead. Infected branches should be pruned .6 to .9 meters below the edge of a canker, as the fungus grows ahead of the area in which it produces reproductive structures. The cut branches should then be burned or chipped since the fungus can continue to sporulate in the branch. Fungicides with chlorothalonil may also be applied in the spring to protect emerging shoots.

Bacterial Wetwood (Slime Flux)

Bacterial Wetwood (Slime Flux)

Bacterial wetwood, also known as slime flux, is a common disease that affects the core of many shade and forest trees. Symptoms of this disorder include a water-soaked, yellow-brown discoloration of the wood, generally confined to the central core of the tree. Bacteria enter through open wounds from boring insects, mechanical damage, or poor pruning, and the build-up of bacterial populations within the tree causes fermentation of tissues, thus resulting in internal gas pressure. The gas pressure and high moisture content cause a foul-smelling, slimy oozing or bleeding of slime through bark cracks. Wetwood slime is toxic to the tree's cambium, and foliage, young shoots, and grass die if slime flux drips on them. No effective methods exist to eliminate wetwood disease, but preventing damage and stress to a tree's roots and stem is the best way to avoid a serious problem.