Webworms (...and bagworms)

Webworms or bagworms...which do you really have?  Many people have been asking me about "bagworms" as of late, but after asking a few questions I discover that they have webworms.  So, what's the difference?

Bagworms:

· Form small cases that hold larvae, pupae, or female adults and eggs

· Cases are often found on evergreen trees & shrubs such as cedar, juniper, cypress, or pine

· Cases are made from silk and plant material laid down similar to shingles on a house, overlapping in layers

· Newly hatched larvae spin a silken thread & either are carried to a new plant by wind or attach themselves to the plant they are on and begin to build their own silken bag

· Bags remain on plants even if bagworms are dead

· Bags are transportable; larvae carry them along as they move about the plant

 · To manage bagworms, handpick bags off the plant and dispose of them

Webworms:

· Spin webbing over branches of host tree to enclose foliage they feed upon

· Attack over 88 species of plants, including fruit, nut, and ornamental trees and shrubs

· Use web as a protective covering; spin webbing immediately after hatching out of egg

· Webbing remains on tree even if caterpillars are dead/ no longer there

· Webs can be pruned out of the tree or opened with a stick/ spray of water to allow predators to eat caterpillars

· When using a pesticide, webbing still needs to be opened

Spider mites

Do you have webbing covering plants in your landscape? Or maybe, you have webbing covering some of the leaves on your plants? Check the underside of the leaves for spider mites.

Spiders mites are not insects, but arachnids more closely related to spiders. They are very small, often looking like little dots running around on the leaf surface. If you look with a hand lens, you'll see that adults have eight legs and oval shaped bodies. Immatures resemble adults (except for the first stage out of the egg which only has six legs), but will be smaller in size.

Spider mites thrive and reproduce rapidly in hot weather, so conditions have been great for them lately. A generation can be completed within a week when conditions are favorable. Plants under water stress can become infested with spider mites.

Spider mites cause leaves to get a speckled appearance, called stippling, where the mites suck juices from the plant. Leaves may also turn a yellow or bronze color and eventually drop off. Leaves and other parts of the plant may also become covered with webbing.

So, what to do about spider mites?

• First off, check that you have an active infestation. Many times people see spider mite damage, but the mites are long gone.
• Ask yourself if you need to do anything or are beneficials doing the job for you.
• Avoid spider mites by reducing stress to your plants with planting in the proper location, watering and fertilizing properly.
• Try knocking spider mites off the plant using high pressure water spray.
• Be aware that sometimes pesticides may cause spider mites to become more of a problem after they are used.
• If you choose to use a pesticide, treat the underside of the leaves where spider mites like to hang out.

It's not fall yet, so why do I have fall webworms?

While I haven't been getting many questions on them, I thought I would address fall webworms since I've been seen tons of webbing in trees all over town. Webworms can attack over 88 species of plants, but are often seen on pecan trees in Texas. We have 2-4 generations each year that start in the spring and continue into the fall. Fall populations are often the most damaging, giving the name fall webworms.

Caterpillars, the immature state, are very pretty in my opinion. They are about an inch long when fully mature and are pale greenish-yellow with long tufts of hair projecting from their body. Adult moths are somewhat drab with whitish coloring and small, dark spots on the front wings.

When caterpillars emerge from the egg, they immediately begin to spin the webbing that is expanded to cover the tree's foliage. The caterpillars use the webbing to protect them from predators. They enclose the foliage that they feed on and will expand the web size when they run out of foliage to eat.

So, options for managing webworms really depends on how annoyed you may be with the webbing, how large the tree is and what kind of effort you want to give to manage the caterpillars. Egg masses can be pruned or picked off the tree (egg masses are on the underside of leaves and typically covered with hairs). Pruning webs out of the tree or opening the webbing with a stick or stream of water can also help to manage populations. Pruned webbing should be disposed of in a sealed, plastic bag or dunked in a bucket of soapy water to kill the insects. Opening the webbing can allow predators to enter the web and help manage the pests. You do not want to burn the webbing out of the tree as this can often cause damage to the tree as well as being dangerous.

Of course, there are also chemical options. Less-toxic options include using active ingredients such as Bacillus thuringiensis variety kurstaki, also known as Bt. This variety of Bt specifically targets caterpillars, but will not differentiate between "good" and "bad" caterpillars, so avoid drift. Spinosad which comes from a soil microorganism is another option. Both of these chemicals must be consumed for them to work properly, so good coverage of the foliage is key (hence, you must open the webbing to get the chemical to where the caterpillars are feeding!). These options work best on smaller caterpillars (less than 1/3 inch).

For management of larger caterpillars, contact kill chemicals work best. Some active ingredients to look for include permethrin, cyfluthrin, carbaryl or acephate. Again, the chemicals have to get into the webbing where the caterpillars are located or they will not work very well.

Of course, you can always choose to let the caterpillars do their thing. The trees and caterpillars have been here living together for many, many years and nature always seems to find a balance of things on it's own.

Also, don't expect webbing to disappear from the tree once the caterpillars are gone. You will either have to wait for a heavy rain or use a high pressure water stream to knock the web out.