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Organic Approaches to Spongy Moths in the Orchard & Garden

Named for their soft and ‘spongy’ egg cases, Spongy Moth, Lymantria dispar, is also known as LDD moth and formerly known as ‘gypsy’ moth. 

Brought to Medford, Massachusetts from Europe in the mid 1850s, Spongy Moths were bred with other silkworms to create a new variety to spur a silk industry in the US. Though that industry never materialized, a few moths escaped in 1868 and they’ve spread wide ever since.

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The common name of ‘Spongy moth’ eludes to the texture of their egg cases. There may be 100 to 1000 eggs in each one!

Here are two offerings, a quote and a poem, that fit well for late spring, Spongy moths and sitting with the depth of our decisions before we act:

Look closely at nature. Every species is a masterpiece, exquisitely adapted to the particular environment in which it has survived. Who are we to destroy or even diminish biodiversity? 

~ E O Wilson

Instructions on Not Giving Up

More than the fuchsia funnels breaking out

of the crabapple tree, more than the neighbor’s

almost obscene display of cherry limbs shoving

their cotton candy-colored blossoms to the slate

sky of Spring rains, it’s the greening of the trees

that really gets to me. When all the shock of white

and taffy, the world’s baubles and trinkets, leave

the pavement strewn with the confetti of aftermath,

the leaves come. Patient, plodding, a green skin

growing over whatever winter did to us, a return

to the strange idea of continuous living despite

the mess of us, the hurt, the empty. Fine then,

I’ll take it, the tree seems to say, a new slick leaf

unfurling like a fist to an open palm, I’ll take it all.

Ada Limón 1976-

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The best way to reduce Spongy moth populations are in their egg stage. If they’ve already emerged, the younger you can remove them the better.

Spongy moths, now present in our ecosystem, can significantly defoliate our forests and orchards every few years. Young apple trees are especially prone to their munchings. We’ve thankfully found them largely disinterested in our garden vegetables, though in 2021 we had ravaging populations defoliating forests around us and spongy moth caterpillars took a liking to our pole beans, which we squished daily. In addition to ravenous munching, the hairs of Spongy moth can irritate skin for some people.

Spongy Moth Damage

Known for their cyclical 10-15 year boom/bust episodes, Spongy moths are more often in our orchards munching, compared to our gardens. They eat hundreds of species of trees and shrubs, preferential to oak, maple, birch, willow and many trees in the rosaceae family, including apples, pears and plums.

Their munchings are only truly damaging when their populations are at such high levels that severe/complete defoliation occurs, especially multiple years in a row. Around our farm, most trees recover and produce new leaves in July once Spongy moths have entered their pupal stage. Conifers are more significantly affected, since their needles don’t re-grow in the same way deciduous trees do.

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Once Spongy moths are this large, it’s rare to see them on top of leaves; they prefer to hide from predators beneath the leaves.

Spongy Moth Life Cycle

Like many insects, Spongy moths have four distinct life stages: egg, larva (caterpillar), pupa, and adult (moth). In August, adult females lay eggs in masses of 100-1000 eggs in beige, velvet/spongy material, inspiring their common name. We’ll find egg masses on an impressive diversity of surfaces both well-hidden and not, from tree trunks to buildings, mail boxes to rocks.

Tiny gray caterpillars with characteristic hairs emerge in spring just as leaves are expanding. Here in the Finger Lakes, we often see them in mid to late May. If the first tree the caterpillar climbs is not delicious, they ‘balloon’ on the wind, like a kite from a single, strong thread of silk. They feed for five to six weeks once they find their buffet. 

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If you’re not sure if a tiny caterpillar is a Spongy moth, look for it’s characteristic hairs.

As they grow, Spongy moth caterpillars pass through 5 or 6 substages known as ‘instars.’ The first three instars feed during the day and cause little damage. By the fourth instar, they feed at night and hide on rough bark by day. Approximately 90% of the feeding damage caused by larvae is done by the last two instars: one caterpillar can consume up to 1 square meter of foliage each day.

Caterpillars pupate in brown structures the size of a peanut. By late July, the emerging adult moths emerge. Creamy with toffee splotches, they do not even have mouth parts, since they live only long enough to mate and lay eggs. Females are slightly more pale as well as more large, up to 1.5 inches long. 

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Spongy moth pupae are often well hidden and vary in size, though their shape is consistent.

Approaching Spongy Moths Organically

Scrape & Spray Spongy Moth Eggs 

Spongy moths spend ~75% of their life cycle as eggs. We destroy egg masses August through April! You can scrape off the eggs mass into a container of soapy water, leaving them there several days to be sure they don’t survive. Alternatively, egg masses can be sprayed with a dormant horticultural oil to effectively suffocate them. This is by far the most efficient method and effective method.

Pros: eggs are easiest life stage to control; affect is species specific 

Cons: if you’re scraping a lot, wear a mask: the little fibers making the egg mass ‘spongy’ are very sharp and can irritate skin as well as our respiratory tract. If you’re scraping, you’re inhaling, sigh ~ 

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A female Spongy moth may lay 100 to 1000 eggs in her egg case! The males are smaller and more dark.

Squish & Scrape Spongy Moth Larvae

The smaller the caterpillars, the easier they are to squish! If you’re not into the squish method, scrape or pluck them off and toss them into soapy water to drown.

Pros: affect is species specific 

Cons: as caterpillars get larger, squishing can become more revolting (lol!)

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If you’ve missed their egg stage, younger caterpillars are easier to manage than older.

Physical Barriers for Spongy Moth Larvae

Sticky Tree Barrier Bands

are best engaged as an early season preventative measure for larger trees. Several weeks before we expect emergence (late April here in the Finger Lakes), we place sticky bands around the tree’s trunk to catch caterpillars as they hatch and crawl. These bands can be bought or made at home using common household materials. On a dry day, we create a 4 to 6-inch band of duct or packing tape with the adhesive touching the bark 4 feet high, preventing them from crawling under the trap, smearing a sticky material like Tanglefoot or petroleum jelly in a 2-inch band on top of the tape to catch the caterpillars. For more detailed instructions, hop on University of Wisconsin’s site. As rains fall, check in a replace the sticky substance as needed.

Pros: Tall trees that are challenging to spray benefit from sticky barriers. Additionally, there is less risk to other caterpillar species as it takes advantage of spongy moth behavior.

Cons: This method can be dangerous to birds as they can get stuck in the band, though you can top with chicken wire to prevent them getting stuck. Frequent monitoring is needed to prevent the sticky band from getting too gummed up (or too washed out) to be effective. Also, this method works best with larger caterpillars as the younger caterpillars don’t exhibit the climbing up and down behavior.

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Thanks to Tanglefoot for this photo! Diverse tapes can be used and petroleum jelly is effective as well as products like Tanglefoot.

Non-Sticky Barrier Bands 

As caterpillars grow about an inch long in mid-June, they travel down the trunk to hide from predators during the day.  Similar to sticky traps, burlap barrier band traps take advantage of this behavior.  Their construction is simple: cut a strip of burlap 12 to 18 inches, long enough to reach around the tree with several inches overlap. With a string tied around the center of the band, the top six inches flop over, making a convenient place for caterpillars to hide. Check your burlap band daily in the late afternoon, plucking all caterpillars into soapy water to drown. If you’re sensitive to their often irritating hairs, wear gloves. For more detailed instructions, University of Wisconsin will not disappoint!

Pros: Burlap bands often look nicer than the sticky bands —- with less potential risk to birds.

Cons: Daily caterpillar removal can be a hassle! This strategy works best with larger caterpillars as the younger caterpillars don’t exhibit the climbing up and down behavior.

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Thanks to University of Wisconsin for this photo! People often use both sticky and burlap barriers in concert together.

Organic Sprays for Spongy Moth

Bacillus thuringiensis kurstaki also known as Bt or Btk

 Widely available and OMRI (Organic Materials Resource Index) listed, this bacterium, when ingested by caterpillars, has the approximate effect of melting their digestive tract. Bt is by far most effective on young caterpillars. Not specific to spongy moth, you may end up killing a lot more types of caterpillars with Bt than you’d hope. On large trees this is a very real concern; on young apple trees where you can easily reach all leaves, this is a much smaller concern.

Pros: Bt only harms caterpillars actively feeding on leaves treated. Bt is very safe for people, invertebrates and other pollinators.

Cons: Bt is not specific to spongy moth, so you may end up killing a lot more types of caterpillars than you’d hope. 

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Bt and spinosad are not species-specific, so they kill every caterpillar that ingests (Bt) or touches (spinosad) them, including Luna moth caterpillars.

Spinosad

More effective for larger caterpillars than Bt, Spinosad is available in several OMRI listed products and once dry it will not harm beneficial insects. It’s a contact pesticide so it must come in contact with the caterpillars to control them.

Pros: If you have larger spongy moths and you’re very concerned about defoliation — and squishing/drowning is not an option, this is one to consider.

Cons: Since spinosad is not a species-specific pesticide, all the cons of Bt apply here as well. We recommend only using it to protect a super loved ornamental or fruit tree if you’ve missed the window for Bt. We try to never apply when pollinators are active. 

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Bt and spinosad are not species-specific, so they kill every caterpillar that ingests (Bt) or touches (spinosad) them. These wide-spectrum pesticides, though organic, should be applied with great care and only as a last resort.

If you’re struggling with Spongy moths, you’re not alone and we’re right there with you, Friends.

As we’re grappling with our options, we often return to these words from E O Wilson:

Look closely at nature. Every species is a masterpiece, exquisitely adapted to the particular environment in which it has survived. Who are we to destroy or even diminish biodiversity? 

~ E O Wilson

Sow Seeds & Sing Songs,

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& the whole Fruition crew

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Despite our heartache, aren’t Spongy moths beautiful? We can see this is a male from it’s darker wings as well as massive antennae adept to sense female pheromones.
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