With the arrival of warm weather also comes the arrival of summer’s menaces: bugs.
While some people might detest insects just for being so buggy, for gardeners, each year might feel like another new battle against the bugs in determining what pest is ruining their plants and how to defend their crops from complete destruction.
Here are some of Michigan’s peskiest garden pests as well as how to get rid of them, said David Lowenstein, Integrated Pest Management expert and consumer horticulture educator at Michigan State University.
Sawflies
Sawfly larvae, which are particularly a problem for roses, feed on leaves with a chewing mouthpart that causes “window-paning,” an effect that happens when insects eat the material between leaf veins, leaving the veins and remaining plant tissue to crumble into holes.
Sawfly larvae look like caterpillars, but Lowenstein says it’s important to note there is a difference between the two in order to manage the pests. Insecticides that normally kill caterpillars prove to be ineffective on sawflies because sawflies’ biology tolerates the chemicals.
Lowenstein says pesticides like insecticidal soap or Neem oil can be used to kill sawfly larvae, or they can be easily picked off the plants directly 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. Boxelder bugs only feed on box elder seeds and leaves, so they don’t actually cause damage to most plants.
“They appear in high numbers which leads people to get concerned when you see 50, 60 insects on a tree or plant,” said Lowenstein. “Most of the time they’re an aggregating insect that doesn’t cause damage in the garden and I wouldn’t actually do anything about them.”
Boxelder bugs may be more of a concern when temperatures drop in the fall because they can swarm the outside or get into people’s homes. But once again, they shouldn’t cause structural damage, and can easily be sucked up with a shop-vac or sprayed off the side of a home.
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Slugs
Having just gone through hatching season, slugs might more noticeable around this time throughout Michigan, particularly in cool or shaded, damp spots, snacking on ornamental plants and sometimes vegetables.
Lowenstein says there are several ways to control the number of slugs in your yard:
- Reduce crowding in areas of your garden that might be overgrown or otherwise crowded, which will give the slugs less places to hide in.
- Aerate your soil in areas with poor soil drainage, otherwise wet ground will also be a favorable place for slugs.
- Sprinkle diatomaceous earth around your plants or other problem areas to destroy slugs’ exoskeletons and kill them when they come into contact.
- Set beer traps by filling a small container or pan with cheap beer. Yeast in the beer attracts the slugs, then they crawl into the trap and drown. However, Lowenstein recommends checking the traps regularly and replacing the traps when needed in case the container fills with dead slugs or amount of beer becomes reduced.
Lily leaf beetle
Unlike some of the other pests listed, lily leaf beetles are more of a problem in southeast and mid-Michigan, particularly because they are an invasive species that don’t have many natural predators.
Additionally, when in larvae stage, the bright red lily-eating beetle covers itself in feces to appear inedible to predators.
Lily leaf beetles can be hand picked off of plants or garden-owners can try to treat an infestation with insecticides, but Lowenstein says that if you already have lily leaf beetles, they’re likely to make a return.
“Unfortunately, these insects don’t look like they’re going to go away in southeast Michigan,” he said “It’s been a pretty rough year for lily leaf beetles so if you have them one year, there’s a good chance that you’ll also have them the next year, so you might want to treat your lilies in May, that’s when they start to come out.”
However, Lowenstein shared that 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 numbers of lily leaf beetles through the manipulation of a parasitic wasp. The wasp lays its eggs inside the larvae of lily leaf beetles, killing the larvae. Lowenstein said they’re hoping to release wasps next year in areas with high amounts of lily leaf beetle damage.
Four-lined plant bug
Four-lined plant bugs are what Lowenstein calls generalists: they’ll eat ornamental plants, weeds, herbs, and just about any other plant in your garden. However, they won’t actually kill the plant.
The bugs have a piercing, sucking mouthpart that leaves behind brown circles as they feed on leaves, and while the damage is just cosmetic, the bugs move fast so it can seemingly look like the plant contracted a disease overnight.
Lowenstein said it’s best to leave the bugs 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’s better to treat plants that haven’t been exposed to the four-lined plant bugs yet to prevent them from irreversible damage; for plants that are already filled with brown circles, it’s unfortunately too late.
Because the bugs feed on weeds, Lowenstein says it might also help by going out and pulling weeds to eradicate their food source.
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Japanese beetles
The Japanese beetle is another generalist species, feeding on vegetables and leaving behind holes that look like skeletonized leaves on ornamental plants.
While the beetles don’t emerge until the summer, they spend the spring living in soil as grubs and feeding on the lawn plants, which can cause browning no matter how much water is spritzed out of your sprinkler system.
“We get a lot of questions about ‘Why isn’t my lawn doing well?’ and a lot of times that’s because of grub damage,” said Lowenstein. “Another way that people might realize they have grubs is if their lawn is al dug up from wildlife that like to eat grubs. There’ll be lots of holes, and if you pull back your turf and see more than 10-15 grubs per square foot, that’s an indication that you might want to consider treating the grubs in the lawn, and the best time to do that is August through October with an insecticide.”
Once Japanese beetles are full-grown adults, Lowenstein says you can hand-pick them off your plants and otherwise put up netting or another similar barrier to keep the beetles out.
He says that insecticides should then only be used in extreme cases, and pheromone traps should not be used no matter how appealing they may be. The traps do their job very well in attracting Japanese beetles, but as soon as too many pour in and fill up the trap, you’re left with more beetles in your lawn than you started off with. Pheromone traps are better for commercial use or multi-acre properties, Lowenstein warns.
Tomato hornworms
As adults, tomato hornworms turn into five-spotted hawk moths, but while in caterpillar form, the bugs can wreak havoc on your tomato plants.
The hornworms can completely defoliate a plant, and they can chew holes through fruit and other produce.
Fortunately, tomato hornworms can be easily plucked off a plant and dropped into soapy water to kill them. Or, alternatively, you can remove the bugs from your plants and set them aside to be sold; hornworms can make for a good live diet staple for pet reptiles and amphibians, which are normally sold at pet stores for more than a dollar a worm.
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