Friday, April 27, 2012

Plant Galls: Where Do They Come From?

Creosote gall.
This morning while hiking I came across a few odd masses of leaves growing on Creosote Bush.  These masses of leaves are technically galls caused by the Creosote Gall Midge.  This insect lays an egg or eggs along with fungal spores in part of a Creosote Bush.  There are 15 species of the Creosote Gall Midge, each specializes in laying their eggs in a specific location on the bush.  Some specialize in laying the egg and forming galls in the leaves, others on stems, others buds or flowers and so on.  Each species also does this only at specific times of the year.  When the fungus begins to grow it forms a gall on the Creosote.  Later, the midge eggs hatch and the larva begin eating the fungus inside of the gall.  Once mature, the larva eat their way out of the gall and morph into adult insects.  Once adults, the whole process is of laying eggs with fungal spores in the Creosote begins again. 

Galls are not unique to Creosote.  In-fact they are quite common, especially among oak species.  Gall wasps actually specialize in forming galls, most often on oak leaves.  Gall formation almost always is part of the reproductive life cycle of these wasps.  There are well over 1000 species of Gall Wasps, each individual species specializing in forming galls on one specific plant species.  These galls are often quite unusual looking, sometimes looking even Christmas ornament like.  Below are a few pictures of galls.



7 comments:

  1. I have a young creosote plant that has recently developed 5 different galls due to the creosote gall midge. Is there a simple way to get rid of this problem and will it kill the creosote plant? Can the plant be treated with a common pesticide?

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    1. Spraying your plant with a pesticide will kill the gall midges, preventing galls from forming. Just about any common pesticide should work. Typically though, once a gall is formed it won't go away, it will need to be cut off.

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    2. Thank you for the reply. If I don't do anything, will the health of the plant be an issue. It appears healthy enough at this point. I'll treat the plant with Demand CS, a microencapsulated pyrethroid made by Syngenta.

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    3. Doing nothing won't hurt the plant at all. I have never run across a creosote killed by or even stunted by galls. That pesticide should work. The problem is figuring out when to apply and how often.

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  2. I removed the galls and will start treating the plant when I do my own house and yard. I usually do some of my yard plants with Demand CS, as it is a great pesticide to use for mosquito control as well as other critters found around the house, i.e. roaches, crickets, silverfish, and scorpions plus many more. I used to be licensed by the state of Arizona as a pesticide applicator. Thanks for your comments.

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  3. I have no intention of removing mine. I think if it is not harming the plant, nature should be left alone but thanks for the info.

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  4. I have no intention of removing mine. I think if it is not harming the plant, nature should be left alone but thanks for the info.

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