It’s time to check evergreens for bagworms – but is it time to treat?

The bagworm hatch began in early June across much of northeast Kansas. Began is the key word in that sentence, however, since treatment too early could miss those that are still to emerge. Treating too early can result in additional feeding damage from later emerging larvae, potentially requiring a second insecticide application as a ‘clean up’. With that in mind, approach bagworm treatment using a three tiered sort of approach.

First, make sure you even have bagworms! Infestation in the past doesn’t guarantee bagworm pressure now. Natural predators and parasites can provide good levels of control, resulting in no need for an insecticide application. What you are actually looking for is a miniature version of the mature bagworm. The pencil lead sized bags will typically be difficult to find without close inspection of the tree’s foliage. Their small size is one problem, but they will also likely be the same color as the foliage as well. Look for the small wiggling bags to make sure that feeding larvae are present.

Second, determine the level of infestation and stress being caused by newly hatched larvae. If levels are light and the tree is healthy, waiting until later in June might allow you to get by with a single insecticide application. If levels are high or the trees are under stress, go ahead and pull the trigger on an insecticide application. Just be prepared to continue to watch the tree to determine if later hatches are causing damage as well.

Third, apply insecticides appropriately. Insecticide active ingredients commonly used for controlling bagworms include spinosad, Bacillus thuringiensis, acephate, cyfluthrin, and permethrin. Spinosad and Bacillus thuringiensis (BT) are organic products. BT is only effective when used against small bagworm larvae. Spinosad is a more effective product, especially on larger larvae. The product label is the law, so make sure you are getting a product labeled for the pest you are after (bagworms!) and the species of tree you will be spraying! For a list of some common products, feel free to contact your District Extension Office.

The difference in control between most products is typically very small. A bigger difference in control is typically due to the level of insecticide coverage. Most control failures are due to the insecticide not penetrating deep enough in the tree rather than the insecticide not working. Make sure that you are getting trees covered with plenty of your insecticide mix from top to bottom and inside to outside as well.