Sugarbush Diseases and Insects

The following information has been taken from: Sugarbush Management: A Guide to Maintaining Tree Health


Major Early-Season Defloliators
Members of this group usually overwinter as eggs on tree boles or branches. Caterpillars begin to feed at budbreak or shortly thereafter, and feeding usually is completed by late June.
Forest Tent Caterpillar (Malacosoma disstria)
Fall Cankerworm (Alsophila pometaria)
Bruce Spanworm (Operophtera bruceata)

Major Late-Season Defoliators
Defoliators that feed late in the growing season usually over winter as pupae in the soil or in leaf litter. The pupa is an inactive, nonfeeding stage. During pupation, the caterpillar transforms into a moth. Eggs usually are deposited on maple foliage during late June or early July. After hatching, larvae may continue feeding into early fall. Many of these caterpillars are “window feeders” at first, later becoming whole-leaf feeders.
Saddled Prominent (Heterocampa guttivitta)
Greenstriped Mapleworm (Dryocampa rubicunda)
Orangehumped Mapleworm (Symmerista leucitys)
Maple Leafcutter (Paraclemensia acerifoliella)

Other Defoliators
Some defoliators cause damage only occasionally. Yet, due to their prevalence in sugar maple stands, their unique feeding behaviors, or their distinctive appearance, these insects are often noticed by sugarbush operators. Infestations usually are limited to several trees or to relatively small areas.
Maple Trumpet Skeletonizer (Epinotia aceriella)
Meaple Leafblotch Miner (Cameraria aceriella)
Maple Petiole Borer (Caulocampus aceicaulis)

Maple leafrollers
Linden Looper (Erannis tiliaria)
Gypsy Moth (Lymantria dispar)

Management Recommendations for Defoliators

Other Insect Pests
Pear Thirps (Taeniothrips inconsequens)

Wood Borers
The insects in this group succeed only in stressed or weakened sugar maples, or in damaged portions of otherwise healthy trees. These secondary insects initiate the decomposition process that eventually leads to nutrient recycling. In economic terms, however, wood borers may cause significant losses because of the lumber degrade or reduced crown size that results from their activities.
Sugar Maple Borer

Ambrosia Beetles

Conspicuous Insects of Little Consequence
A number of innocuous organisms feed on sugar maple foliage and cause visible damage, but the resulting discoloration or distortion of the leaves rarely affects maple growth or sap quality.

Some insects and mites alter plant growth when they stimulate the host to produce strange-looking growths called galls. These tumor-like abnormalities are derived from cells that grow excessively large or numerous. This unusual development is triggered by growth stimulants introduced into the plant in the saliva of insects and mites. The location, shape, and color of a gall, which provides a source of nutritious and readily available food and shelter for the pest, usually is distinctive enough to identify the gall maker.
Gall Mites
Ocellate Gall Midge (Acericecis ocellaris)
Gouty Vein Midge (Dasineura communis)
Snout Beetles (Weevils)


A tree disease can be caused by abiotic factors such as air pollution, mineral imbalances, and climatic extremes; by biotic agents such as tiny viruses, bacteria, mycoplasma-like organisms, and fungi; by nematodes; or by larger parasitic plants such as mistletoe and broomrape. Nearly all diseases of sugar maple incited by biotic agents are caused by fungi. Like insects, fungi can be classed as primary (able to successfully infect and invade healthy vigorous trees altered by stress). Collectively, diseases probably cause more losses to sugar maple than all other destructive agents.

Diseases of sugar maple range from conspicuous, but rarely significant, leaf diseases to inconspicuous, but often lethal, diseases of internal stem wood and roots. The presence of many diseases often goes unnoticed until the damage is significant. And since little can be done to halt their progress, it is important to prevent or reduce the conditions that lead to tree diseases. Nearly all biotically incited diseases of major consequence other than dieback/declines are facilitated by wounds. Wound prevention, especially to roots and lower stems, must be central to an IPM program for sugarbushes.

Dieback/decline diseases epitomize the complex nature of tree diseases for they reflect the interactions of fungal pathogens and various stresses, including defoliating insects, as well as adverse abiotic factors. Their complex etiology also serves to emphasize the need for a holistic approach to managing the sugarbush.

Leaf Diseases
Sugar maple has many leaf diseases, most of which are caused by fungi. Symptoms range from minute dead spots to the death of the entire leaf. Leaf diseases occur throughout the growing season but are more common and important in late spring during wet and cool periods. Defoliation by leaf diseases generally does not cause significant damage. It seldom lowers a tree’s ability to produce food energy by more than 25 to 30 percent. However, growth may slow and dieback can occur following serious episodes. Air pollutants also may cause discolored or dead areas on leaves. With the exception of anthracnose, leaf diseases do not cause significant damage.
Phloeospora Leaf Spot (Phloeospora aceris)
Phyllosticta Leaf Spot (Phyllosticta minima)
Tar Spots

Cankers and Canker Rots
Stem cankers are localized dead areas in the outer and inner bark. They often extend into the wood. They are caused by fungi that infect trees through bark injuries. Some of these fungi repeatedly invade and kill the inner living bark and cambium and cause perennial cankers. In perennial cankers, callus tissues develop around the affected area, producing a steam distortion that may become excessive with time.

Stem cankers are conspicuous tree diseases in that they generally deform the lower tree bole and often render it unsuitable for tapping. Cankers themselves often are points of entry for decay fungi, and create weak points where trees often break. Affected trees should be removed so long as doing so would not create a large opening in the canopy that, as mentioned earlier, would encourage unwanted vegetation or promote excessive soil drying.
Eutypella canker
Nectria canker
Coral spot canker
Steganosporuim ovatum
Maple canker

Canker Rots
Canker rots are perennial, canker-like distortions of tree stems. They are caused by certain wood-decay fungi that also can kill the inner bark (phloem) and cambium. Most canker-rot fungi enter stems through wounds and produce cankers by killing overlying bark tissues and decaying the wood underneath. After decaying the wood at the original wound, some canker rots form a mass of fungus tissue that spreads slowly through the bark and eventually kills the adjacent cambium and reinfects the wood underneath. These cankers enlarge as this process is repeated.
Inonotus glomeratus

Decays of Stems and Roots
Stem Decay
Stem-decay fungi infect trees through dead branches, branch stubs, cankers, and other wounds that expose the wood. Spores of decay fungi are common and abundant in the forest. Once a decay fungus has successfully invaded a tree stem, its progress cannot be controlled. However, unless the fungus also attacks the roots, the growth rate of the tree will not be reduced noticeably. Only after the decay becomes extensive within the tree is the damage easily detected.
Some Common Decay Fungi
Root and Butt Rots

Vascular Diseases
Verticillium Wilt (Verticillium albo-atrum)
Sapstreak Disease (Ceratocystis coerulescens (C. virescens)

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Additional Information may be found at:

Cornell Tree and Shrub Guidelines