Back to Cues Walkabout
a collaborative project with The
Bell Museum of Natural History and The Minnesota Landscape Arboretum)
Welcome to the
Integrated Pest Management Tour
at the Minnesota Landscape Arboretum
Integrated Pest Management (IPM) is a program for managing insects and diseases
incorporating the principles of plant health care and the limited use of pesticides.
IPM is different from traditional approaches that use preventative cover sprays
regardless of the presence or potential for insect and disease problems.
IPM is a decision-making process for determining if treatments are necessary,
when the best time is for their application, where the treatments are needed,
and what treatment methods will be used. The components of an IPM program are:
- Threshold determination
- Treatment options
When control measures need to be taken, IPM uses a combination of cultural, biological,
and chemical controls. Cultural controls try to increase or maintain plant
health, since many insect and disease attacks are facilitated by poor plant health.
Examples of cultural control are reducing plant stress, or choosing a plant species
or cultivar that is suited to the sun, soil, and other environmental conditions
at the site.
IPM encourages the conservation of naturally occurring biological control
organisms (predators, parasites, and pathogens) to control pests. An example
of biological control is ladybird beetles killing and eating the aphids feeding
The wise use of chemical controls is one of the most important ways
of conserving natural enemies. Chemical controls are used only when needed,
and are applied at the point in the pest's life cycle when it is most vulnerable.
Soft pesticides, such as horticultural oils, insecticidal soaps, and
microbial insecticides are recommended since they have lower toxicity and fewer
effects on organisms other than the pest (non-target effects). The use of these
biologically rational pesticides - instead of hard pesticides, in conjunction
with the practices of targeting pesticide applications to only the areas where
pests are active, and applying pesticides only at the time which pests are most
vulnerable, allows more of the natural biological control agents to survive.
The first step in IPM is being able to recognize some of the organisms that
damage plants. This is intended as a brief, self-guided walking tour to familiarize
yourself with some of the insects and diseases found on plants in Minnesota.
spruce gall (Adelges cooleyi) on Black Hills spruce (Picea glauca
var. densata). This adelgid (an aphid-like insect) causes galls
to form on the branch tips of various spruce species. Initially, the branch
tips appear swollen, with the final stage having the appearance of a dry,
brown pine-cone with needles. Control is normally not needed for this pest,
but if they are unsightly, the galls can be pruned off by hand. After a gall
is formed, the adults emerge and fly to Douglas fir (Pseudotsuga menziesii)
to continue their life cycle. Pesticides such as carbaryl are used to control
these adelgids in the summer when infesting Douglas fir.
- Leaf galls on broadleaf trees. Leaf galls occur on many species of
trees, shrubs, and herbaceous plants. They can be caused by many groups of
insects, including wasps, sawflies, flies, mites, aphids, and their relatives.
The galls on river birch (Betula nigra) are caused by an eriophyid
mite, and causes small bumps to form on the leaves as they expand in the spring.
Maple trees (Acer spp.) also have galls caused by eriophyid mites.
These galls look like small patches of red velvet and are called maple velvet
gall. Additionally, basswood trees (Tilia americana) have galls caused
by eriophyid mites, but these look like small, tan, hairy patches. Though
unsightly, these pests are minor enough to not require treatment.
leaf miner (Fenusa pusilla) on river birch (Betula nigra).
Leaf miners are larvae of sawflies (a non-stinging wasp) that develop between
the upper and lower layers of a leaf. They begin feeding in the spring and
cause irregularly-shaped, dry, tan patches on the leaves. Proper timing is
essential for effective treatment. Controls should be implemented at the time
of egg laying, which is in spring after the leaves have expanded fully. Use
a systemic pesticide, such as acephate.
plant bug (Poecilocapsus lineatus) on mums (Dendranthemum sp.)
and ligularia (Ligularia sp.). These easily recognizable insects
feed on more than 250 species of trees, shrubs, and herbs. They suck plant
juices and leave small darkened circles where they inserted their mouthparts.
They are best controlled with horticultural oil sprayed in May when the insects
- Aphids (many species) on viburnum (Viburnum sp.) and herbaceous
perennials. These tiny pear-shaped insects are common pests in the landscape,
feeding on many species of trees, shrubs and herbaceous plants. They feed
by sucking fluids from buds and leaves, which can result in stunting, deformation,
discoloration, and/or death of tissues. Aphids can excrete large amounts of
a sticky waste product called honeydew. Ants often feed on the honeydew deposited
on the plant leaves. The honeydew is also associated with sooty mold fungus
that can blacken the leaves. Aphids have abundant natural predators and parasites,
but if they are disfiguring the plant, aphids can be controlled with insecticidal
browse damage on arborvitae (Thuja occidentalis). This damage is
caused by feeding deer, and can be differentiated from other types of damage
by the ragged ends of the chewed branches. Deer repellents have some effect,
though fencing is a preferable approach.
- Dutch elm disease (Ophistostoma [Ceratocystis] ulmi) on
elm (Ulmus spp.). Elm bark beetles spread this fungus as they look
for sites to feed and lay eggs. The fungus causes rapid discoloration and
wilting of leaves on branches in the crown. The spread of Dutch elm disease
can be slowed by removing diseased trees and by not pruning between April
15 and September 1 in Minnesota. Trees prized by homeowners can be protected
with a fungicide injection (like the large Elms at this arboretum). This is
done by professionals, and is a costly procedure.
- Anthracnose (Discula quercina) on white oak (Quercus alba).
This fungus is mostly innocuous but can cause significant damage if it repeatedly
infects a plant. Damage symptoms are the irregularly shaped lesions on leaves,
as well as browning and shriveling of leaves. Anthracnose is generally controlled
by removing fallen leaves, but for severe cases it can be treated with a fungicide
early in the season. A much more severe fungus that infects and kills oak
trees is oak wilt (Ceratocystis fagacearum). Both diseases cause browning
of the leaves, but oak wilt affects the outer portions of leaves on tips of
branches, while anthracnose affects the center of leaves on the lower and
inner portions of the tree.
- Nectria canker (Nectria cinnebarina) on Pagoda dogwood (Cornus
alternifolia). This fungus attacks the outer parts of stems that have
already been weakened by damage or disease in many species trees and shrubs.
Symptoms include no leaf production, sudden wilting, and branch girdling.
It is treated by pruning out the infected area. No chemical controls are available.
mildew (many species) on Beebalm (Monarda fistulosa). Powdery mildew
is a fungus that occurs on many plant species. The grey-white fungus is found
on leaves and sometimes stems, and can cause leaf distortion. Control by pruning
to increase sun penetration and air movement. Rake out and destroy infected
leaves in the fall. If heavily infested, spray with oil or an anti-transpirant.
- Apple scab (Venturia inaequalis) on crabapple (Malus sp).
Symptoms are lesions on leaves that turn black or brown, followed by yellowing
and leafdrop. Control by selecting resistant varieties, pruning to increase
air movement, and raking away infected leaves.
If you wish to learn more about the pests that attack landscape plants and
how to control them, see the CUES display in the Andersen Library at the Minnesota
For Further Information
The University of Minnesota Extension Service
has the following bulletins on IPM of landscape plant pests:
Spring and Fall Cankerworms
Insect and Mite Galls in the Landscape
Leaf Beetles in Urban Landscapes
Sawflies of Landscape Trees and Shrubs
Scale Insects of Trees and Shrubs
Insecticide Suggestions to Manage Landscape Insects
Sustainability in urban ecosystems
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