Pests, Invasive Plants, & Diseases

Pests and invasive plants can do irreparable harm to your landscape, so it's best to stay ahead of any potential threat. Click on any of these potential invaders to learn more about their behavior and treatments. This list is not comprehensive, but represents the most common pests, invasive plants, and diseases our Bachman's Landscaping Customer Service Representative experiences while assisting customers in the Twin Cities metro area.

Apple Scab

Level of Harm: Minimal (mostly aesthetic)

Apple scab is a very common disease, and one of the most aesthetically damaging diseases of several ornamental trees and shrubs in Minnesota. The main symptoms of the disease are leaf and fruit spots. Very susceptible trees become defoliated by mid-summer, which weakens the trees over time.



Older infections turn black, leaves turn yellow and fall off

  • Velvety, mostly round, olive-green spots up to 1/2 inch across, with feathery-looking borders.

  • With age, spots turn dark brown to black, enlarge, and grow together, generally along leaf veins.

  • Infection on newly forming leaves causes curling and puckering.

  • Severely affected leaves yellow and drop by mid-summer.

  • Infected fruit have olive-green spots that turn brown and corky with time.

  • Severely infected fruit may be deformed and cracked.


You can treat this with a spray. In time, if left untreated, apple scab could weaken the tree.


Click here for more information from University of Minnesota Extension.



Level of Harm: Severe

Buckthorn Removal Guide

The first step in removing buckthorn is understanding the invasiveness of this plant. Buckthorn is easily controlled in mowed areas, but in natural areas it is devastating. Experts say that "if we don't do anything, 10 to 20 years from now we won't see any fall colors; it will all be green." That is why buckthorn is on the state's noxious weed list. Learn more about Buckthorn Eradication at the Minnesota DNR website.


Remove Seedlings and Small Shrubs by Hand

The roots are not deep but rather stretched out horizontally, so small seedlings can be gently pulled out by hand using a hoe or by mowing. Gather the loose seedlings so they don't re-root.


Cut Large Stems and Prevent Their Return

  1. Use pruners or a hand saw to remove the upper portion of any larger buckthorn. (Please note: Do not cut buckthorn within 4 hours of raining. The following spray method will not have time to be effective.)

  2. Areas should be cleared of buckthorn brush when cut to remove any berries that may be on the brush and to make the spraying easier.

  3. Use the stronger formulation of Roundup (25% concentration). Spray this undiluted concentrate directly onto cut stumps making sure to spray all sides of the bark area on the stump as well. This stump treatment must be applied within 24 hours after cutting and when temperatures are above freezing between June 1 and March 15. 


Note: This method of removal may also be used to remove other woody invasive species such as Tartarian Honeysuckle or Mulberry. 

The last step in removal of buckthorn is to prevent its return to avoid the process again. Reasonably high success can be accomplished with the above methods, but we need to be diligent about checking the area for new seedlings and removing them as done previously. Each buckthorn berry contains 3-4 seeds. Seedlings may appear in the area where a stump was removed or treated for several years after. However, the battle can be won if we persist with our efforts.


Box Elder Bugs

Level of Harm: Minimal

In the fall, hordes of box elder bugs descend on homes and outdoor living areas trying to find dry, protected locations to hibernate for the winter. These brownish-black bugs are about 1/2" long with red stripes on their wings. Occasionally, box elder bugs will bite and may feed on houseplants, but are otherwise harmless. Mostly, they’re just a nuisance and an eyesore. 



Level of Harm: Severe

Chlorosis is a serious condition where a tree’s ability to manufacture chlorophyll has been compromised. This weakens the tree and will shorten its life expectancy. Mineral deficiencies and poor root system health are the most significant causes of chlorosis. Other causes may include severe soil compaction, overwatering, lawn herbicides, deicing salts, severed roots, repeated drought, and root rot.


There are several products available to improve the health of the tree. By adding iron and other minerals, chlorophyll production will be stimulated and will improve the health of the root system. Healthy roots make healthy leaves which make more food to feed the roots to make them even healthier.


Dutch Elm Disease

Level of Harm: Moderate to Severe

Dutch elm disease is a fungal disease that will infect all native Minnesota elm trees; however, the disease does not always kill the tree. The success and rate of movement within the tree depends on tree size, time, the location of infection in the tree, climate conditions, and defensive response of the tree.


Dutch elm is a fungal disease spread through root grafts or carried by three different varieties of beetles. Adult females lay their eggs under the bark of recently dead or dying trees or in firewood or logs with firmly attached bark. The spores carried by the beetles or through the root grafts are introduced into the vascular tissue of the healthy tree and infection occurs. A combination of severing the root grafts and injections of preventative fungicides have been used to manage the disease and keep trees alive. To keep the trees living, a treatment cycle must be established and maintained.


Emerald Ash Borer (EAB)

Level of Harm: Severe

Emerald Ash Borer (EAB) is an exotic beetle that attacks and kills Green, White, Black and Blue Ash trees. It was introduced from Asia into the Great Lakes region and has devastated native and planted ash throughout the Midwestern and Eastern United States. In May 2009, EAB was discovered in the Twin Cities by Rainbow Treecare and confirmed by the Minnesota Department of Agriculture.

EAB will kill the affected tree if left untreated; treatment of EAB can also be quite expensive.


Download EAB PDFs:
How to Identify Emerald Ash Borer
Insecticide Controls for Emerald Ash Borer 
Treating Emerald Ash Borer & Protecting Bees 
Recommended Replacement Trees


Gypsy Moths

Level of Harm: Moderate

Gypsy moths are one of America’s most devastating forest pests. Brought to America in 1869 to help kickstart the silkworm industry, they soon escaped and we’ve been battling them ever since. Tree damage is caused by caterpillars (larva stage). They feed on a tree’s leaves from early spring through mid-June or early July. They moult multiple times during the summer with their appetite growing with each moult. Then they enter the pupal stage and emerge as a moth. Next, they mate, lay eggs, and die.


Gypsy moths prefer oaks and aspens, but have been known to eat the leaves of many deciduous hardwood along with some evergreens. The best time to combat gypsy moths is during the egg or larval stage. Egg masses can be burned or, better yet, soaked in water or kerosene. Horticultural oil insect spray can be used when the eggs are unreachable. Spray in the fall and a few times in early spring before the leaves begin to form.


Japanese Beetles

Level of Harm: Moderate

In Minnesota, Japanese beetles (Popillia japonica) are primarily found in the Minneapolis-St. Paul Metro area, and in some areas in southeast Minnesota. Japanese beetles have an exceptionally large host range, feeding on the leaves of over 300 species of plants, including apples, grapes, blueberries, raspberries, roses, and plums.



Japanese beetles are 3/8" long and oval. Their head and prothorax (the area behind the head) are metallic green, while the wing covers are a shiny bronze. Look for five white patches of hair along each side of their body and two white patches on the tip of their abdomen to verify that they are Japanese beetles.

These pests can defoliate plants and leave them weak. This causes difficulty in making food for their roots. Luckily, plants affected by Japanese beetles can be sprayed to solve this issue.


Click here for more information from University of Minnesota Extension.



Level of Harm: Moderate

The feeding on leaves, especially seedlings in moist and shady gardens, qualifies the slug as a damaging pest. Slugs are best described as snails without shells. Slug bodies are mostly made of water and their soft tissues are prone to desiccation. In the garden, baits are the method used most to control these pests. Iron phosphate baits are preferred because they are safer to other animals. Cultural management practices include keeping the planting area clear of debris large enough for the slugs to hide under. Do not have mulch any thicker than 3’ deep, to deprive the slugs another place to hide. Irrigate in the morning so that the plants are dry by evening. Water only when necessary.


Spider Mites

Level of Harm: Moderate


The two-spotted spider mite, Tetranychus urticae (Family: Tetranychidae), has been reported infesting over 200 species of plants. This mite can be found on deciduous trees, evergreens, bedding plants, and annual garden plants. Some of the more common ornamental plants that can become infested include arborvitae, azalea, spruce, and rose. Common bedding plants that are hosts include lantana, marigolds, New Guinea impatiens, salvia, and, viola. Garden vegetables at risk include cucumbers, snap beans, peas, tomatoes, and lettuce. They can also be found on blackberry, blueberry, and strawberry. Spider mite infestations are particularly common during hot, dry summer weather.



Mites are not insects but are arachnids, a related group of arthropods. Other types of arachnids include spiders, ticks, daddy longlegs, and scorpions. All arachnids, including mites, have two main body parts and eight legs.

Two-spotted spider mites are minute (1/50" long), yellow-orange in color, and have two dark spots, one on each side of the body. They are difficult to see without the aid of a 10x hand lens. When a heavy infestation occurs webbing will also be present.

Spider mites suck the moisture out of plants, which causes leave to dry up and fall off. Plants affected by spider mites can be sprayed, and it's best to do so when it's hot outside (the spider mites' feeding season).


Click here for more information from University of Minnesota Extension.



Oak Wilt

Level of Harm: Severe

Oak wilt is a very serious, aggressive disease that affects all species of oaks found in Minnesota. It is caused by a nonnative fungus (Ceratocystis fagacearum) that invades the water vessels of oak trees and eventually kills most infected trees. In Minnesota, oak wilt is typically found in the southern half of the state.


There are two ways the disease spreads, below and above the ground. Below ground spreading happens when oak roots from different trees grow together and become fused and grafted with one another. The fungus can then move from tree to tree through the root grafts. Above ground spreading happens when sap feeding beetles pick up the spores on an affected tree and spreads them to a freshly wounded tree.


Infected trees wilt from the top down, a few branches at a time. Leaves begin to drop at a rapid rate. Root graft disruption and fungicidal treatments aid in preventing the spread of oak wilt. Removal of all dead red oaks will help sanitize the area. The spore mats produced only on members of the red oak family are the fungal source for all new infection centers created by beetles. Several universities and the US forest service have shown that macroinfusion with fungicide can be used as an effective tool for managing oak wilt.


Winter Burn


Level of Harm: Severe

Winter burn only affects evergreens and is not always a severe problem, but can be if damage has overtaken your plant. You'll know your evergreen has succumbed to winter burn easily, since the needles and foliage on evergreens turns a golden brown. Evergreen browning during the winter is caused by dehydrated plant tissues. As evergreens photosynthesize, they release stored water or take it in from the ground. During frigid temperatures when ground water is inaccessible and when that stored water runs out, they become dehydrated, effectively killing parts, if not all, of their foliage.

There's not much you can do to treat an evergreen once it has been affected by winter burn. If the damage is not severe, there is hope that the plant can recover on its own after trimming out the parts affected by winter burn. In severe cases, the affected plant will have to be removed and replaced.

Since there's not a great treatment for winter burn, it's best to take steps ahead of winter to prevent this from happening to your evergreens. Water these evergreens well as they establish themselves in your yard. Ensure you're watering your plants right up until the ground freezes (this is perhaps the most important time to be watering your evergreens to prevent winter burn). Before winter, you can also wrap your evergreens in burlap to insulate them and protect them from harsh winter sun.