Garden Plot: Why bagworms should be taken seriously and how to improve your lawn

Greg in Loudoun County, Virginia, writes:

We have a tamarisk tree that is covered with bagworms. In a normal year there might be a half dozen, but this year the tree is covered. I pick the ones I can, but most of them are out of reach. Short of chopping the tree down, is there anything I can do to get rid of them?

Bagworms are a tough pest, Greg. The small caterpillars (“worms” is a misnomer) that will hatch next spring from eggs being laid right now spin cocoons around themselves that incorporate material from the tree they’re infesting, so that the finished cocoon looks exactly like it belongs on that specific tree.

Keep removing as many bags as you can reach and destroy the bags. The females inside can produce an enormous number of eggs, so careful use of a ladder may be warranted. Every bag removed is a lot of future trouble prevented.

The males are trying to mate right now, so get pheromone traps specific to bagworms and use them to capture the males (that look like odd flies) before they can successfully couple up and cause even bigger problems next year. That’s if you can find the traps. Call around; larger independent garden centers may have them in stock or be able to order them. Be sure to specify that you need them for bagworms, not pantry moths.

Be ready to bust bagworms next spring

Greg said his tree is covered with the little cocoons and they each hold a single caterpillar and each look like they’re part of the tree.

It’s kind of late in the game to effectively control these pests this season other than by physically pruning off as many “bags” as possible.

Next spring, keep an eye out for the first new nests. And when they appear, spray them with the organic caterpillar control — the old original form of Bt. Available under brand names like Dipel, Thuracide and Green Step, Bt. kills any caterpillars that eat the parts of the plant you’ve sprayed. But Bt. harms nothing else — not you, your pets, frogs, toads, birds, bees or even butterflies.

Keep spraying through the summer, and you’ll break the cycle of bagworms. (Bt is available at virtually every decent garden center and by mail.)

Improve your lawn by taking chunks out of it!

Mike in Front Royal, Virginia, tersely writes, “Is it about time to core aerate and overseed the lawn?”

Yes, Mike, it is. In fact, this is the perfect time to do just about anything and everything to improve — or even start — a cool-season lawn of fescue and/or bluegrass.

Let’s start with core aeration: Using a machine to pull plugs of sod and soil out of a lawn to reduce soil compaction. Core aeration is one of the best ways to improve a lawn that was planted in heavy clay or that gets a lot of foot or vehicle traffic.

But cores must be pulled! It is not enough to just poke holes in the soil. You have to actually remove plugs to allow the remaining earth to breathe more easily. (Those plugs can be left in place to decompose or added to other raw ingredients in a compost pile.)

Need a new lawn? Now’s the perfect time to seed it!

This is also the perfect time to start a new cool-season lawn of bluegrass and/or fescue from seed. It’s much better than trying to start from seed in the spring, when the soil is too cold for good germination.

Between now and the middle of September, the soil is the perfect temp for speedy germination. And then the cool season grass (a very important designation) emerges into the kind of weather it loves: warm (not blisteringly hot) days and progressively cooler nights.

Our turf grass expert, Nick Christians of Iowa State University, has long stressed that a cool-season lawn seeded in late summer/early fall will always look better than a cool-season lawn sown in the spring.

Overseeding 101

It is absolutely that time to core aerate and overseed the lawn if you’re talking about a cool-season lawn composed of fescue and/or bluegrass.

To overseed properly, scalp the grass you have down to a little over an inch, immediately spread an inch of compost or composted manure over the area (be sure to have this bulk material on hand before you give the lawn that crew cut) and then scatter fresh seed that matches the turf you already have into the compost.

Gently rake the new seed into the compost until its mostly covered. No straw, no mats or other nonsense.

Water gently every morning until the new grass sprouts, which should occur in a week or less. Then back off to a more normal watering schedule (twice a week if we don’t get an inch of rain a week for the first month after seeding, and then back to normal — 1 inch a week).

The scalped grass will quickly grow back up through the compost and join the newly emerging turf to make a nice carpet of green — which you’ve already fed for the season with that inch of compost!

Note: Delay this chore if a hurricane or heavy thunderstorms are predicted in the next 10 days. I did not check the long-range forecast one fall and a gentleman named “Ivan” moved my new lawn into somebody’s basement a mile downstream. …

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