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Evan's Garden
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Garden Pests

Oak Worms
Oak Leaf Rollers
Oak Leaf Rollers
Oak Leaf Rollers Close-up
Oak Leaf Rollers Close-up
Parasitic Wasp
Parasitic Wasp
Click to order Garden Minerals
Garden Minerals

It was hard not to notice those little green "worms" dangling from a thin web strand under the oak trees. If you were plagued with them as I was, you would know what I was talking about. I ended up waving a long PVC pipe in front of me every time I wanted to leave my house, sweeping these critters along with their web down to the ground so I could walk to my car or back into the house without carrying extra tiny passengers with me.

Silkworms? I did an internet research to find out more about them and what I could do to handle them. First of all, these are not silk worms, so making silk thread from them is not a choice. There are several so-called web worms that find their way into our oak trees. These are actually not worms but caterpillars and here are 2 of them:

Oakworms - These caterpillars are charcoal in color with yellow orange stripes. The head is jet black and the segment just behind the head is bright orange-yellow. There are long, black spines just behind the head, but they are only used to scare away predators and cannot sting you. They feed in late summer, usually skeletonizing the leaf surface which has little impact on the tree since most of the photosynthesis is complete by then. Also native predators and parasites usually help keep the insect from being a problem every year.

CONTROL: You can manually destroy clusters of young larvae when you find them on small trees. An application of Bacillus thuringiensis (Thuricide) or horticultural oil will control young larvae. Damage is seldom widespread and chemical control is rarely needed.

Oak Leaf Roller - This caterpillar is milky-white to pale green having a head that is brown or black. The moth lays its eggs in May in the host tree (in our case, the oak tree) where they reside for approximately ten months. They hatch in March and begin to feed on the oak leaves until April. In May, the moths lay their eggs and the cycle repeats.

When disturbed the caterpillars drop to the ground via their web, curl up in a web inside a leaf to prepare to become moths. These are the caterpillars that have currently been pestering us.

When there are a lot of these caterpillars, they tend to defoliate the tree and this stresses the tree. This is because the leaves produce the sugar needed by the tree to grow. No leaves means less sugar and the tree begins instead to use up its valuable stored energy which it would need for its natural defense mechanisms. This brings in the disease and other pests which in turn destroys the tree.

What can you do to help protect your oak tree? Insecticide is not the answer, apparently, and being organic, we wouldn’t want to use this toxin anyways. However, you can spray with biological caterpillar sprays that contain Bacillus thuringiensis var. kurstaki, as this is a bacterium that kills the caterpillar when they ingest the leaves sprayed with the solution. This you can buy at any garden center.

Other natural solutions include encouraging birds to your tree with bird feeders and houses. The mocking bird in particular likes to dine on these caterpillars. Use of parasitic wasps are considered the best control and these you may find at your organic gardening centers, or you can attract to your garden with plantings of sweet alyssum, fennel, yarrow, or a few carrots left to flower in the vegetable garden. Parasitic wasps use garden pests as nurseries for their young, but the adults need rich sources of nectar to feed on. Without a nectar source, the adults emerging from their insect hosts will simply fly away to find food. Just so you know, they are not aggressive as some of the other wasps are and are great as a biological pest control agent.

Another important thing to do to help your oak tree to overcome the added stress of these pests is to give it a lot of minerals and added watering. One interesting thing to note is that at the Hambly residence, the oak tree did not have caterpillars dropping down out of branches. And yet nearby, the rest of us were inundated with them. What is the difference? Jai has been adding lots of minerals to her garden and flower beds whereas the rest of us have not. Another thing is that the oak tree in my back yard does not have the caterpillars as does my front yard tree. And guess what. I have been adding minerals only to my back yard gardens and neglecting the oak tree and flower beds in the front yard. Moral to the story? Get some minerals and add them to your landscaping.