With the arrival of warm weather comes the arrival of summer’s threats: insects.
While some people may detest insects because they are so buggy, for gardeners every year it can feel like a new battle against the bugs as they determine which pest is ruining their plants and how to protect their crops from complete destruction.
Here are some of the most annoying garden pests in Michigan and how to get rid of them, says David Lowenstein, Integrated Pest Management expert and consumer horticulture lecturer at Michigan State University.
Sawflies
Sawfly larvae, which are especially a problem for roses, feed on leaves with a chewing mouthpart that causes “paning,” an effect that occurs when insects eat the material between the leaf veins, causing the veins and remaining plant tissue to crumble into holes. .
Sawfly larvae look like caterpillars, but Lowenstein says it’s important to note there’s a difference between the two to keep the pests under control. Insecticides that normally kill caterpillars prove to be ineffective on sawflies because the biology of the sawflies tolerates the chemicals.
Lowenstein says pesticides such as insecticidal soap or neem oil can be used to kill sawfly larvae, or they can easily be picked directly from the plants and thrown into a bucket of soapy water.
Boxelder bugs
Boxelder bugs, also called box bugs or maple bugs, are more of a visible pest than a harmful one, Lowenstein says. Boxwood bugs feed only on the seeds and leaves of the boxwood, so they don’t actually cause damage to most plants.
“They show up in large numbers, which leads people to worry when you see 50, 60 insects on a tree or plant,” Lowenstein says. “Usually they are an aggregating insect that doesn’t cause any damage in the garden and I wouldn’t really do anything about it.”
Boxelder bugs can be more of a problem when temperatures drop in the fall because they can swarm outdoors or invade people’s homes. But again, they should not cause structural damage and can easily be sucked up with a vacuum cleaner or sprayed down the side of a house.
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Slugs
Because they have just gone through breeding season, slugs may be more conspicuous around this time throughout Michigan, especially in cool or shady, moist places, where they snack on ornamental plants and sometimes vegetables.
Lowenstein says there are several ways to control the number of slugs in your garden:
- Reduce crowds in areas of your garden that may be overgrown or otherwise busy, giving the snails fewer places to hide.
- Aerate your soil in areas with poor soil drainage, otherwise wet soil is also a favorable place for slugs and snails.
- Sprinkle diatomaceous earth around your plants or other problem areas to destroy slugs’ exoskeletons and kill them if they come into contact.
- Set beer traps by filling a small container or pan with cheap beer. Yeast in the beer attracts the snails, after which they crawl into the trap and drown. However, Lowenstein recommends checking the traps regularly and replacing the traps as necessary in case the container becomes full of dead snails or the amount of beer decreases.
Lily leaf beetle
Unlike some of the other pests mentioned, lily leaf beetles are more of a problem in southeastern and central Michigan, mainly because they are an invasive species that does not have many natural predators.
In addition, the bright red lily-eating beetle covers itself with feces in the larvae stage, making it appear inedible to predators.
Lily pad beetles can be hand-picked from plants or garden owners can try treating an infestation with insecticides, but Lowenstein says if you already have lily pad beetles, they will likely come back.
“Unfortunately, it doesn’t look like these insects are going away in southeastern Michigan,” he said. “It’s been a pretty tough year for lily leaf beetles, so if you have them one year, chances are you’ll have them next year too, so you might want to treat your lilies in May when they hatch.”
However, Lowenstein said he and a professor of entomology at Michigan State University have been working on a project, modeled after an experiment that was successful on the East Coast, to control the number of lily leaf beetles through the manipulation of a parasitic wasp. The wasp lays its eggs in the larvae of lily leaf beetles and kills the larvae. Lowenstein said they hope to release wasps next year in areas with high amounts of lily pad beetle damage.
Four-lined plant bug
Four-lined plant bugs are what Lowenstein calls generalists: they eat ornamental plants, weeds, herbs and virtually any other plant in your garden. However, they will not actually kill the plant.
The insects have a piercing, sucking mouthpart that leaves brown circles as they feed on leaves. Although the damage is only cosmetic, the insects move quickly, making it appear as if the plant has contracted a disease overnight.
Lowenstein said it’s best to leave the insects alone and let the plants grow, but if gardeners really can’t stand the spots, they can use an insecticidal soap to treat the plant. However, he emphasizes that it is better to treat plants that have not yet been exposed to the four-lined plant bugs to prevent them from suffering irreversible damage; Unfortunately, it is too late for plants that are already full of brown circles.
Because the insects feed on weeds, Lowenstein says getting outside and pulling weeds to eradicate their food source can also help.
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Japanese beetles
The Japanese beetle is another generalist species, feeding on vegetables and leaving holes that resemble skeletonized leaves on ornamental plants.
Although the beetles don’t emerge until summer, they spend the spring in the soil as larvae feeding on the lawn plants, which can cause browning no matter how much water is sprayed from your sprinkler system.
“We get a lot of questions about ‘Why isn’t my lawn doing well?’ and often that’s due to grub damage,” says Lowenstein. “Another way people can realize they have grubs is if their lawn has been completely dug up by wildlife that likes to eat grubs. There will be a lot of holes, and if you pull back your lawn and see more than 10-15 grubs per day per square meter, that is an indication that you might want to consider treating the grubs in the lawn, and the best time to do that can be done from August to October with an insecticide.”
Once Japanese beetles mature, Lowenstein says you can hand-pick them from your plants and otherwise put up a mesh or similar barrier to keep the beetles out.
He says insecticides should then only be used in extreme cases and that pheromone traps should not be used, no matter how attractive they are. The traps do a very good job at attracting Japanese beetles, but once too many beetles flow in and fill the trap, you will be left with more beetles in your lawn than you started with. Pheromone traps are better for commercial use or multi-acre sites, Lowenstein warns.
Tomato hornworms
As adults, tomato hornworms turn into five-pointed hawk moths, but while in caterpillar form, the insects can wreak havoc on your tomato plants.
The hornworms can completely defoliate a plant and can chew holes in fruits and other produce.
Fortunately, tomato hornworms can easily be picked from a plant and dropped into soapy water to kill them. Or you can remove the insects from your plants and set them aside to sell; Hornworms can make a good basic diet for pet reptiles and amphibians, normally selling for more than a dollar per worm in pet stores.