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Welcome to the Good Going podcast. I am Ken Johnson, horticulture educator with University of Illinois Extension, coming to today from Jacksonville, Illinois, with a Gardenbite. And on this week's Gardenbite we're going to talk about the dreaded bagworm.
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So if you’ve had
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problems with bag worms in the past. Have no fear. We still have plenty of time to do something about them before they start emerging.
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So before we get into to management of bagworms, talk a little bit about their lifecycle. So bagworms are going to overwinter as eggs in the bags
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of the females
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and a lot of times is going to be laid within the pupal casing
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those female
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moths.
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Eventually those caterpillars will hatch
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and some of those caterpillars are going to spin silk strands,
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which is going to catch the wind and it's going to carry caterpillars
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to other plants.
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And this is known as ballooning. That's something that spiders will do as well. You may have heard of it
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in reference to spiders.
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Other
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bagworms will stick on the same plant and we'll just hang around and feed there. So some will move off,
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some might stay if it's a really good plant and there's plenty of food.
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Regardless of they stay or leave, eventually they're going to settle down
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and they'll start feeding.
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And it's commonly believed that bagworms only feed on evergreens. However,
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they've been found to feed on over 125 species of plants, both evergreen and deciduous,
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and 45 different plant families. So there's a lot of different types of plants. They feed on. That being said,
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we most commonly see them
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on spruce, Eastern redcedar and other junipers, arborvitae, white pines, some of
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those almost evergreens. You can also find them on crabapple
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pin oak. I've seen them on maple trees
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and other
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types of trees and shrubs as well.
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So when bagworms start feeding. They'll feed on the edges of broadleaf foliage. And sometimes, especially as they get bigger, they may make it down into the mid vein
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and then the leaves of needled evergreens
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are eaten back
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to the base of the plant until nothing remains. A lot and will start to tip and work their way down
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that needle.
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When we have early bagworm feeding, damage often appears kind of light green at first and then whitish to brownish as those cells that have been damaged start to die, the foliage will start to turn brown.
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And like everything else, as bagworms get bigger and older,
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they start eating more and more. And a lot of times the entire leaves
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for the entire needle of the plant
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will be eaten.
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One of the problems with
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needled evergreens, is that when they start feeding on that foliage, those needles
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that can kill a branch
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and if an infestation is really bad,
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entire trees could die, which doesn't happen all that often.
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But it is a possibility. Oftentimes
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bag worms are starting off at the top of the tree and they kind of work their way
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down. So it's not uncommon to see like the top third of an evergreen
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that is dead or has been completely defoliated.
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Fortunately, with deciduous trees, they can refoliate, send out new leaves, and that damage is going to primarily be aesthetic.
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It's not as big of a concern
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with deciduous trees as it is
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with evergreens and bagworms are going to feed
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throughout the summer.
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And the reason we call them bagworms
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is that they spin these individual silk kind of tents to cover up their bodies and they will attach foliage or frass or their poop
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to those bags.
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That's going to help camouflage them, which can make it kind of difficult to find them, especially
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when they're small.
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When they're
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constructing these bags, only the head and the thorax or the
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part of the insect of that caterpillar
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is going to stick out of the bag,
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and that is going to allow it to move around and feed while still being primarily inside
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of the bag
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it's constricting.
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Now, if you were to open up the bag
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now like we have in this picture and take out this caterpillar,
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the back end of that caterpillar is going to be kind of brownish
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or dark brown in color,
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whereas the kind of a head in the thorax area
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is going to have yellow and dark brown patterns
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on it.
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And as they as the caterpillars grow, they will increase the size of the bag and a lot times they're kind of spindle shaped
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and they can be an inch and a half long when they're fully grown, when the caterpillars are fully grown.
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And as long as those caterpillars are feeding,
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they're going to keep adding
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pieces of the foliage that they're feeding on
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onto that bag.
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So, one kind of trick to know if bagworms are still feeding is the presence of green foliage on those bags.
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If that bag is completely brown, there's a good chance that
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insects have stopped feeding
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or is dead or something like that. If it still has green foliage,
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it's still feeding.
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Eventually the caterpillars
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will finish developing.
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They'll go through seven inch Stars. Eventually they will then pupa within their bags. So they will
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they'll attach their bags to a branch with some more silk. And this is a pretty strong strand of silk.
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And they will pupate inside the bag. They'll seal off the tip
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and they'll pupate over a week to ten days.
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And then eventually the adults will emerge from those pupa.
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And adult bagworms
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usually go unnoticed, especially the females. The females do not leave the bags. She spends her entire life
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in the bag
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and they're kind of the females are kind of caterpillar like they don't really look like a moth, that you would typically think of. The wings are reduced,
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the legs are reduced, all of that.
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And males on the other hand, they will emerge
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in their bags and they're capable of flying and they're kind of hairy and charcoal black in appearance.
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So once we have the adults they are going to be emerging in the fall, the females are going to release a pheromone that's going to attract the male moths to their bags.
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The males will then mate with the females while she's still inside of that bag.
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And once the female mates will stop releasing that pheromone
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and will no longer be attractive to males and the males will no longer come
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to those bags.
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The females will then start to lay eggs and again they're laying these eggs inside of that bag often inside of that pupal casing
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that's left behind.
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And either the female will then die within that bag or may fall out right before she dies.
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Neither the male
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or the female feeds.
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So basically, once they emerge, they're mating,
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females are laying eggs and that's it.
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Females can live for a couple of weeks.
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Males usually only live a couple of days. Basically, they mate and then they die.
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That's kind of the life cycle. So then the eggs are going to be overwintering and then they will emerge in the spring.
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So one of the easiest ways to manage bag worms in our landscapes is to handpick the bags off of plants,
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and we still have
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plenty of time to do this.
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And when you're picking those,
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you
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want to make sure you either discard those bags or crush them, because if you just throw them on the ground,
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those eggs can still hatch in those caterpillars, can still get on to your trees and start feeding on them.
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So bagworms I mentioned we still have a lot, still have a good amount of time before they hatch. Bagworms hatch
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at 600 growing degree days with a base 50.
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And that starts at March 1st,
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Which if you're not familiar with growing degree days and how that works, that probably makes no sense whatsoever.
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But in Illinois, it's usually maybe mid to late May and southern Illinois.
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And then going into June
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when we get up into northern Illinois. So still plenty of time. If you want to learn more about the growing degree days, you can check out the National Phenology Network
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at usanpn.org.
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You got a link to that here on the screen. And we'll also put it in the show notes if you really want to check that out.
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And they have maps where you can track the growing degree day accumulation and how close we are getting to
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bagworm emergence. And they also have this for a lot of other insect pests as well.
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So once we kind of get close to that time where they're going to be start emerging, we want to start scouting for bagworms. So start looking for early damage on the leaves. So they may have some kind of scarifying. They may just be scraping off the surface of the leaves, start looking for that, start looking for caterpillars walking around.
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You can open up bags if you still have bags on the trees and look to see if there's eggs in there
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that have hatched or not.
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And then once you start noticing that feeding damage, you start noticing caterpillars on your plants
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one thing you can do is pray for them. So sprays of Bacillus thuringiensis kurstaki or Btk
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or Spinosad can be used.
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These are pretty selective insecticides,
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so they don't really harm non pest insects all that much. And they're also organic if you're interested in organic products. But a word of caution here, these products, like a lot of other things, become less effective as the caterpillars get bigger. So they're much easier to control with these little more specific organic type insecticides when they're younger.
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As they get bigger, you may have to look at things like some of the pyrethroids
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and things like that, but even then they're going to have their limitations once they get really big, they get more difficult to control. So
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like many other things, the sooner you can manage them, the more successful
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you'll be.
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And there are also a lot of different natural enemies that will also help manage bagworms.
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So there's a lot of different types of parasitoid wasps, there have been over 11 species of parasitoid wasps that have been found to feed on bag worms.
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There's predators,
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mice will feed on them.
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Larger wasps. Wasps like baldfaced hornets have been noted as feeding on them. So a lot of things will eat
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bagworms even birds
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will eat them as well.
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So another thing we can do can have a little more long term, maybe, sustainable approach to managing bagworms is planting flowers. So, like I mentioned,
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parasitoid wasps will feed on them,
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other wasps will feed on them.
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And these these wasps, both parasitoid and predatory wasps,
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they are using, in this case, the caterpillars of bagworms as food for their offspring.
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So the parasitoid wasps are laying their eggs in the bagworms and the larvae are feeding on them.
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Something like a baldfaced hornet will cut open that bag, pull out that bagworm, chew it up, and then feed it to its offspring.
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But the adults, they feed primarily on pollen and nectar. So they are pollinators. So these insects are acting as pollinators and predators.
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So
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if we have a lot of floral resources, a lot of flowers for them
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that's going to provide food sources for these adults, which will attract them to your landscape and keep them around long term.
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So there is a study in 2005 that kind of shows how beneficial it can be to have flowering plants near plants that are going to be attacked by bagworms. Maybe if you have a lot of problems with bagworms on your evergreens,
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maybe plants a flowerbed by
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or a flowerbed nearby.
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So in this study, they found
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70% of the bagworms
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that were on plants that had a flowerbed nearby were parasitized by these parasitoid wasps. On the other hand, bagworms that were on trees and stuff that weren't near flowerbeds, they only had 40% parsitized. They had
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30% more
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bag worms are parasitized when you had
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flowerbeds nearby.
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So, if
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consistently have issues with bagworms, maybe consider
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putting a flowerbed in nearby your plants.
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That's all I got for you for this week's Gardenbite.
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Thank you for doing what you do best. And that is listening. Or if you're watching us on YouTube watching.
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And as always, keep on growing.
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