Web worms in trees

Fall Webworms Are Back! Here’s How to Control Them

While visiting growers in mid-June, I started noticing quite a bit of fall webworm infestation in native pecan groves as well as in backyard pecan and fruit trees. If early populations are any indication, we can expect a lot of defoliation heading into the fall.

The range of trees attacked by this pest is impressive. Worldwide, more than 600 kinds of deciduous trees have been attacked. Favorites in Oklahoma include pecan, hickory, walnut crabapple and persimmon.

The Webworm Cycle

Entomologists tell us that webworm outbreaks run in cycles. Some years outbreaks are severe, while in other years they are barely noticed. Weather, birds and the predatory insect population contribute to the circular nature of these outbreaks. Heavy, driving rains can flush the worms from the foliage early in the season, reducing the level of damage.

Two generations of fall webworm caterpillars can occur in the Southern Great Plains. The first generation usually appears from June through August. If a second generation is produced, it can extend into October.

This pest overwinters as a pupa in a cocoon concealed in ground litter, cracks and crevices, or in the soil. Following mating, female moths usually deposit their egg masses on the undersurface of the leaves. Larvae hatch in approximately seven days. They immediately begin to spin a small silken web over the foliage on which they feed. In the initial stages, the small, hairy, yellow-brown worms feed only on the leaf’s upper surface; but as the size of the caterpillar increases, the whole leaf is eaten. As they grow, the web grows to enclose more and more foliage.

For the first half of the 4- to 6-week period during which the caterpillars feed, all feeding occurs in the web. As caterpillars near maturity at 1 3/4-inch long, they leave the web at night to feed.

During the final development stage, caterpillars leave the web and crawl to a convenient hiding place, such as a thick patch of bark or the leaf litter at the tree base, where they pupate.

How to Control Webworms

During most years, a fall webworm infestation can be ignored, especially if it is in a large, mature tree in good condition. When small trees are attacked, they can be severely defoliated and can even be completely encased by webs. In most cases, complete defoliation will not kill the trees. However, if small trees are not well established or are experiencing any type of severe stress, defoliation can result in death, especially if it happens twice in one season. On pecan trees, nut production and quality can be reduced if severe infestations are not controlled.

Removal of webworms in small yard trees can be accomplished using a rake or a long pole equipped with a hook to pull down the webs. If within reach, a web located at the tip of a branch can easily be pruned out and destroyed. Do not attempt to burn the webs out as you may cause additional damage to the tree and possible personal injury.

Insecticide applications are most effective when the caterpillars first hatch and the webbing is still small. Because the webbing is not very noticeable early in the life cycle, you must be intentional in your scouting efforts during this time.

Several classes of insecticides are labeled for control of fall webworms. However, many of these spray materials, including pyrethroids, are harmful to predatory insects that aid in webworm control.

Bacillus thuringiensis (Bt) sprays are a safer alternative and ideal for use in home situations. Bt is most effective when applied to small caterpillars. Unless the webbing is widespread, it is not necessary to treat the entire canopy. When treating isolated webs, spray the leaves next to webs. As these leaves are incorporated into the webs and eaten, the Bt will be ingested. The molting disrupter class of insecticides, including the brand name products Confirm and Intrepid, are recommended for control of fall webworms in commercial pecan plantings for the same reason; they target caterpillars and will not harm beneficials. Orchards sprayed to control pecan nut casebearer using molting disrupters in May to early-June seldom experience significant fall webworm infestation.

Fall webworm populations vary from year to year. Several strategies and techniques are available to control this pest. Early detection is important when controlling heavy infestations of webworms.

Fall Webworms Noticeable In Pecans As Summer Wains

Fall Webworm beginning to get started on a branch tip. Image credit: Matthew Orwat

Bare limb tips and clusters of webbing in pecan trees are often the first sign that fall is right around the corner.

This webbing is caused by clusters of the larvae of the Fall Webworm (Hyphantria cunea (Drury)) which is often also called Pecan Webworm. “Fall Webworm” is a bit of a misnomer in our region since they are able to strike in spring and summer thanks to our long growing season. They are most noticeable in the fall thanks to cumulative effects of earlier feeding.

The adult form of the fall webworm is a solid white or white and brown spotted moth that emerges in late March through August in southern climates. After mating they lay orderly clusters of green eggs, usually May through August. Soon after emergence, the larvae begin creating silk webs to protect themselves as they voraciously feed on their various host plants, of which Pecan is of primary agricultural importance in this region.

Although they are capable of defoliating complete trees, especially smaller ones, most seasons they are kept in check by beneficial insects such as the paper wasp. It is beneficial for small orchards or home growers to scout their trees from June through August. If small webs are observed in young trees, it is best to prune them out with a pole saw or pole pruner and dispose of the branch. Pruning of small branches does not harm the tree, but it may be of no benefit to remove small webs in larger trees, if they are being controlled by natural enemies.

Active feeding by webworm on pecan branch tip. Image credit: Matthew Orwat

Most large pecan orchards have a routine insecticide program, so fall webworm rarely creates problems. For smaller orchards or homeowners it is difficult to spray for control, due to the cost of the equipment required to get the spray into the tree canopy. If spraying is an option, many insecticides containing spinosad or Bacillus thuringiensis (Bt) exist. Both of these products target caterpillars while not harming beneficial insect predators that feed on these worm populations. Several more toxic insecticide products exist that will control fall webworm, but they often exacerbate insect problems by killing off beneficial insects that might be controlling other insect pests.

Fall webworm is not usually a serious problem for pecan production. Fortunately, when control is warranted, there are plenty of options available.

Learn more about the fall webworm’s life cycle at the UF/IFAS Entomology Department’s Featured Creature website.

Leaves stripped by Fall Webworm. Image Credit: Matthew Orwat

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Matthew Orwat

Matthew J. Orwat started his career with UF / IFAS in 2011 and is the Horticulture Extension Agentfor Washington County Florida.His goal is to provide educational programming to meet the diverse needs of and provide solutions for homeowners and small farmers with ornamental, turf, fruit and vegetable gardening objectives. Please feel free to contact him with any questions you may have.

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  • Fall Webworms Noticeable In Pecans As Summer Wains – August 24, 2018

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Keep more pecans for yourself by trapping troublesome squirrels or preventing them from climbing your pecan tree.

(Brett Duke / The Times-Picayune archive)

QUESTION: We have two pecan trees that stand about 30 feet tall. Every year, I’ve tried to control the webworms, but either I don’t spray early enough or use the wrong pest control. When is the best time of year to spray, and what is the best insecticide to use? — Paul LeBoeuf

ANSWER: There are numerous generations of fall webworms that attack pecan trees over the summer. There is no way to precisely time when the generations will emerge, other than to say they can show up as early as May and appear periodically through the summer and into the fall. Heaviest infestations tend to be in the late summer.

If you want to do a preventive spraying, you could spray once a month beginning this month and continuing to October. Or you could wait for the first signs, spray, and then wait for the next group to show up and spray then.

Light populations don’t generally affect the trees that much. Populations can vary from year to year. Some years, they are very bad, and some years they hardly show up.

Your spray equipment must be able to reach the top of the trees, and the entire canopy needs to be thoroughly sprayed for the treatment to be effective. For lower web nests, you can hit them with a long pole and tear open the nests to allow the insecticide to penetrate.

Insecticides to control webworms include BT (various brands, but this is the least toxic organic option), Malathion and carbaryl (Sevin and other brands).

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Q: We have two large pecan trees that are too large to spray. Every year the pecans have a small hole with a white worm in them. What can be done to prevent this?

A: You have pecan weevils in your pecans. The adult female weevil is a beetle-like insect that emerges from the ground in early August each year. She crawls or flies up into the tree and drills a hole through the shuck and into the nut, where she lays eggs.

The grubs that hatch afterwards feed on the nut interior. Some escape through a hole they bore in the shell while others remain inside.

It’s impossible for a homeowner to spray insecticide over an entire tree but there are some strategies that might help control the weevils.

First, pick up and destroy all damaged nuts each year.

Second, apply in late July a foot-wide band of sticky material like around the trunk six feet above ground. This will catch weevils that crawl up the trunk into the tree. To keep the material from staining the bark, wrap wide masking tape around the trunk before spreading it.

Third, spray as high as you can reach in the tree beginning the first week of August and repeating every 10 – 14 days until shucks begin to open.

Also see Pecan Weevil Control

pecan weevil

pecan weevil

Tags For This Article: pecan, weevil

Why are there so many creepy webs on the tree branches over your head? | The State

In this file photo, webworms ensnare a portion of tree. The Wichita Eagle

You’ve seen them.

Tree branches, covered in webs. And unless they’re very small, entire trees are not covered, it’s just a limb or two are coated with the creepy webbing.

But what is causing the specifically placed webs? And should you be scared of what’s inside of them?

Unless you are a tree being infested by the fall webworms, you’re safe from what a North Carolina State professor in entomology, Dr. Steven Frank, calls “a perennial nuisance and in some cases a destructive pest.”

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The webs are cocoons spun by fall webworms, where the females lay their eggs on “undersurface of the leaves,” and feed off the branch the web covers, according to the Penn State College of Agricultural Sciences research.

In spite of the shocking image of a tree branch being smothered in a web, fall webworms pose no threat to people or most trees.

In this file photo, a fall webworm web drapes a tree. Centre Daily Times

The webs are “a big, showy bag … over the end of a branch on a shade, fruit or ornamental tree,” according to Michigan State University, which said fall webworms can be lumped into a group of insects that it calls “much ado about nothing.”

HGTV called the damage caused by webs “strictly cosmetic.”

A Clemson University publication echoed that sentiment, saying “true damage to the tree is minimal,” as the fall webworms’ eggs will hatch in about a week, and proceed to feed off the living leaves for about six weeks before departing the tree.

“Fall webworms upset people because they are ugly not because they damage trees that much,” Frank wrote.

This file photo shows a fall webworm crawling across a dried up leaf. Kansas City Star

The prime season for fall webworms is late summer through early fall, according to Penn State. That is one of the ways to differentiate fall webworms from similar insects — Eastern Tent Caterpillar and Gypsy Moths.

Fall webworms and tent caterpillars are less destructive to the trees they infest than Gypsy Moths, according to the Washington State Department of Agriculture.

And in spite of many similarities, there are subtle differences between fall webworms and tent caterpillars.

Tent caterpillars spin their webs in the spring, compared to summer for fall webworms; and tent caterpillars’ webs are found in “in crotches of branches,” as opposed to the end of the branches where fall webworms cocoons are located, Clemson University reported. Additionally, fall webworms can produce four generations a year, so their webs will be active longer, opposed to tent caterpillars single generations.

In tis file photo a fall webworm moth rests at Lee State Natural Area. [email protected]

Perhaps the biggest threat posed by fall webworms is the overreactions people have in attempts to remove the webs.

Michigan State reported that fires have been set in attempts to get rid of the webs, and pesticides are more likely to harm the person spraying them since the webbing is so strong it will repel the spray.

Tearing the web down with a pole, or puncturing it to allow natural predators access to the fall webworms is the best approach to getting rid of the webs, HGTV reported.

On their own, the webs will likely dissipate by the winter, according to Penn State.

By that point, some other white, clingy substance could be coating a tree, with snow creating a much greater nuisance.

What is growing in these cocoon-looking structures found on a mountain in Massachusetts, USA?

We went back today and spoke with the naturalist, Cindy, who’s part of a team that cares for that property which includes hundreds of acres.

These are webbed nests filled with hundreds of caterpillars of the fall webworm moth, (Hyphantria cunea). The caterpillars are tiny and hairy, and at the early stage can be any dark color. There’s an outer fur that gets longer and more fluffy as the caterpillars grow.

The life cycle begins when adult moths emerge from cocoons which have been in wet ground for the winter. They come out usually in June and July.

The adult fall webworm is a nocturnal moth. The wings are bright white (usually with dark spots) and the wingspan is 3 to 4 cm. The body is hairy and the bases of the front legs are orange or bright yellow.
Source

They then lay hundreds of eggs on the underside of the leaves of their chosen tree.

The egg mass of Hyphantria cunea is almost iridescent green in color. The egg batch contains 400-1000 eggs. The eggs are usually deposited on the undersides of leaves in the spring. The egg mass is lightly covered with scales from the female’s abdomen. Source

The eggs hatch in about a week, and the caterpillars start to eat the leaves and create webs to enclose their feeding area. They like hundreds of different tree varieties, including fruit trees when available. The tree in the picture in the question is a black cherry tree, and, as you can see, the webworms have made sure to enclose the berries into their webs. As the caterpillars (larvae) get bigger, they extend their nests.

In mid-July the eggs hatch and the caterpillars begin to spin out an extensive silken web. The webworm encloses whole clusters of leaves at the ends of branches and feeds on the leaves within their tent, expanding the web downward toward the trunk and capturing more leaves as the colony expands. Source

When the caterpillars are full grown, they drop out of those webs and pupate through the winter in small cocoons located in dead leaves or dark moist areas around the tree base, and emerge as new moths the following spring!

Because they’re woven around the foliage rather than the bark, webworm nests do not usually damage the tree branches. The foliage will regenerate as the season goes on. The tree in the picture is proof of that. Cindy said last year’s nests were on the side of the tree which looks perfectly fine now.

Conservation organizations, and many local arborists, do not recommend pesticides or any chemical management. The moths are important in controlling pests that are bad for other flora and fauna, and the webworms are food for many natural enemies of other pests. If you have mature webs in your yard, and don’t mind the way they look, wait until they’re empty and knock them down. Try not to do that until you know the caterpillars are all out. If stressed, they do a dance which indicates danger, and this may interfere with their growth or ability to survive.

If you really don’t like them, as many homeowners don’t, try to watch for early signs of the web in the spring and knock them down while they’re still small. Pick off any leaves that have started to deteriorate. That stops the spread in the tree and eliminates the worms while they’re still very young.

has excellent information of all the life stages of this moth including great pictures.

How to Identify Cocoons on Trees

Brand X Pictures/Brand X Pictures/Getty Images

Caterpillars which turn into moths make cocoons using a thick material they produce in two rear glands. The caterpillars of each moth species make a slightly different type of cocoon. Some cocoons are large, some are tightly woven, and some have multiple layers. Caterpillars add protection to their cocoons by shedding their larval hairs and weaving them into the cocoon’s silk. This helps keep predators from eating the cocoon while the caterpillar is undergoing its transformation. The best time of year to find cocoons is early fall.

Find a book which depicts a variety of common moths and shows pictures of their caterpillars and cocoons. A book specific to where you live is helpful, since different species of moths occur in different parts of the United States.

Identify the tree the cocoon is hanging from. Chances are good that the caterpillar spun its cocoon from a branch of its main food source. Look over the tree to see if you can locate any caterpillars. Identifying the caterpillar is a little easier than identifying the cocoon, and more than likely, the same species is inhabiting the tree.

Read the descriptions given in the book for each caterpillar which eats that specific food. Some of these caterpillar species may make their cocoons underground, which means they would not be a match for the cocoon hanging from the tree.

Hold a ruler or tape measure next to the cocoon to measure its length and width, and check the measurements against those in the book.The cocoon’s size should help narrow down possible candidates.

Hold the pictures of the remaining candidates next to the cocoon you encountered. Pay attention to the way the cocoon is hanging from the tree and how tightly woven the thread is.

What Spider Builds Webs in Trees? And How to Get Rid of Them

When you see a tree, words like majestic, serene and awe-inspiring spring to your mind.

Creepy and scary are two words that rarely describe trees. But, that’s likely what you think when you see large, silky nests in your tree.

Now, you’re wondering what kind of spider builds webs in trees. Surprisingly, it isn’t a spider. It’s another tree pest –either fall webworms or Eastern tent caterpillars. Learn what they are, why they make webs and how to get rid of those “spider webs” in your tree.

Helping Trees Covered in Spider Webs

Why does my tree have huge, giant “spider webs” on tree branches?

Spiders actually don’t make those webs in trees. Instead, you can thank fall webworms or Eastern tent caterpillars, depending on the time of year.

Fall webworms are caterpillars that weave a thick web as they feed on trees. Fruit trees are usually their first pick, but they feed on more than 100 different kinds of trees.

If you see tree webs in spring, that’s likely tent caterpillars. These caterpillars feed on these types of trees but are only a serious problem for black cherry trees.

What’s the lifecycle of fall webworms? When are they around? What about tent caterpillars?

As their name suggests, you’ll spot fall webworms most often in fall.

But, they’re there all year. In winter, they lay eggs, which hatch in spring. Come summer, those caterpillars eat your tree leaves and begin spinning webs in time for fall.

On the flip side, tent caterpillars hatch in early March and build webs for shelter in late April. They feed on leaves as caterpillars for about a month before spinning a cocoon and emerging as moths a few weeks later. Then, they lay their eggs in May.

Do fall webworms or tent caterpillars damage our trees? Are webworms poisonous?

Though fall webworms and tent caterpillars are eyesores, that’s about their only threat. These caterpillars aren’t poisonous and don’t damage established trees. Phew.

It’s a different story for younger trees, though. As webworms and caterpillars feed on young trees, they can cause complete leaf loss before the tree has a chance to thrive. In this case, your trees are counting on you to step in and stop the pest.

How to get rid of “spider webs” in trees

First, use a broom to remove webs from branches and improve the look of your trees.

But, fall webworms live in cocoons in winter rather than their webs. So, even if you remove their webs, they can still return next summer.

To get rid of fall webworms for good, prune webbed branches or apply an insecticide to tree leaves, not the webs.

To rid your tree of Eastern tent caterpillars, remove their eggs, which look like black bumps on your tree’s branches, in winter. If they still hatch in early spring, you can apply an insecticide.

“Oh, gross!” wailed Donna, my sister-in-law, as we drove along the highway in West Virginia last week. “Look at all those giant spider webs in the trees! We have them at our house too!” I could sympathize with her concern. Many people are afraid of spiders, especially giant ones that eat people.

© JimVallee/Getty Images

Fortunately, her fears were unfounded. These webs were the work of fall webworms. Fall webworms rarely eat people.

Fall webworms are caterpillars that hatch from eggs laid in the branches of hardwood trees by a nondescript, whitish moth. The caterpillars proceed to enshroud the ends of branches with silky webs, so they can feed on the leaves inside while hidden from predators. They range in color from pale yellow to dark gray, have yellow spots and long, bristly hairs, and grow an inch or so long.

People often confuse fall webworms with Eastern tent caterpillars that also build webs in trees and eat leaves. The two are easy to distinguish, though. Eastern tent caterpillars appear in spring and construct webs in the crotches of branches. Fall webworms show up in late summer and fall and confine their webs to the ends of branches.

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Fall webworms aren’t picky eaters and feed on many different tree species. However, pecan, hickory, mulberry, sycamore, birch, sourwood, fruit trees, and willows seem to be favorites. I’ve seen big pecan tree with 25 or more webs in it and all its leaves devoured. The good news is that fall webworms do no serious damage. This is because the leaves they’re eating would naturally fall off in a few weeks anyway, so it’s no big loss to the tree.

What you should do if you find webs in your trees this fall? Well, if the web is close enough to reach from the ground, you could cut off the branch and throw it away. Or you could tear open the web and let birds and wasps eat the caterpillars. If webs are high up, though, just ignore them. Consider them another miracle of nature.

Do run, however, when confronted by a 100-foot, marauding tarantula. Run very fast and scream!

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