Bagging Bag Worms

I saw on the news yesterday that this is the hottest summer in the Tulsa area in three years. I so believe that!! But unfortunately, the heat hasn’t detoured the pests that are very active this year. Today I’m going to touch on bag worms.

These horrible little worms can defoliate and kill evergreens very quickly. They may also feed on deciduous trees and shrubs, fruit trees, and sometimes, even perennial flowers. The only good thing about bag worms infesting deciduous trees or shrubs is that they grow new leaves each year so the defoliation that the bag worms cause usually doesn’t kill the tree.

The key to bag worm control is to understand their life cycle in the Oklahoma area. The most effective treatment will depend on what stage of life they are in.

Since I’m writing this in August, that’s where I’ll start on their life cycle. In most cases, the mature larva stops feeding in late July and August and attach themselves to a branch. They close their bag and remain there for about 4 weeks as pupae, a non-feeding, metamorphosis stage between the larva and adult.

Once the larva quit feeding, spraying with insecticides is useless because they must ingest it to kill them. The only control method that will now work is to literally pick off the bags and destroy them. If the bag worms are discarded on the ground, they will very likely return to your trees and shrubs after hatching in the spring. It is best to put the bags in a container of gas or burn them.

During September and early October, the female emits a pheromone to attract the male. The adult males then emerge from their bags, find a female, mate and then die.  The female will then lay 300-1000 eggs within the bag and then dies, becoming mummified around the egg mass.

The bag is now insulated and the eggs will over-winter. The eggs will begin to hatch in late April to early May.  They will be only 1/8 inch long and can be difficult to see. After hatching, the baby larva emerges from a hole at the base of the bag and spin down a strand of silk. The tiny insect is often caught by the wind and carried to nearby branches, trees or shrubs. Once a host tree or shrub is found, the young larva will start feeding immediately and constructing a bag around its hind part with silk and plant material. This is when you can see the first sign of infestation. It will appear as a small bag, about 1/4  inch long, standing almost on end.

In Oklahoma, the most effective time to kill bag worms with insecticide is May, June and early July. This is the when they are feeding, maturing and completing construction of their bags. A bacterial insecticide containing Bacillus thuringiensis (Bt) is reported to provide good control or other products containing spinosad, acephate (Orthene), carbaryl (Sevin), bifenthrin, cyfluthrin and/or lambda-cyhalothrin can be used. These insecticides must be ingested by the larva in order for them to die, so realize it may take some time. You should also be prepared to retreat in a few weeks to be sure none were missed due to late hatching or insufficient coverage of the insecticide.

So basically, what I’m telling you is…..its August….wait until the weather cools off and then pick the bags off the trees so you don’t have a new infestation in the spring. Sorry I didn’t start this blog sooner so I could have helped you treat them for this year. For more helpful hints for pest control and other subjects, check out our website at http://peppysdevelopments.com

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