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Defoliation of pear tree caused by leaf rolling grub

Pear    None Given

This morning in a garden where I work I noticed that all the pear cordons had a number of young leaves that were rolled tightly and sealed shut with silk webbing. When I opened up the leaves I found a single grub about five mm long in each one.

I guess this is some sort of leaf roller insect, probably a moth, but I would like to know which one and also the best way to treat the problem. Spraying the leaves with insecticide doesn't seem practical as all the leaves are tightly rolled and would be impervious to the spray.

Last year I came across the same problem on another pear tree and it completely defoliated the plant in a short space of time - the plant recovered but didn't fruit very well.

I am in Bristol in the south west United Kingdom. I don't have an image at the moment but can take a photo when I visit the garden again next week.


Posted by: James Edwards (1 point) James Edwards
Posted: April 21, 2017




Answers

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Hi James
There are different possible culprits. Moths in the family Totricidae commonly do this. An identification would usually require an adult but some larvae are diagnostic. Irrespective of what the identity of the pest it, it is clear it is a pest. You can clip the leaves are drop them into a bucket of soapy water.

If the problem is very large consider a Bt spray (which is a virus that kills moths and butterfly larvae). This from UC

"The microbial insecticide Bacillus thuringiensis, which is sold as a variety of products, is effective against the larval stages of leafrollers. Bt, as it is commonly known, is a bacterial preparation that causes a disease in many kinds of caterpillars but does not harm beneficial insects, birds, humans, or other organisms. Leafrollers stop eating within hours after feeding on a sprayed leaf and die several days later. Thorough spray coverage of the tree is required for control. Bt is most effective on leafroller larvae when they are small (less than 1/2 inch long) and usually requires more than one application. Caterpillars must ingest the pesticide to be killed. Bt is available for use on ornamental trees, vines, and some fruit and nut trees. Check labels for uses. Spinosad (Monterey Garden Insect Control) is another, organically acceptable insecticide that is effective against leafrollers and widely available."
http://ipm.ucanr.edu/PMG/PESTNOTES/pn...

I look forward to some pictures


Posted by: David Hughes (43 points) David Hughes
Posted: April 26, 2017




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