Discussion on an interesting pest popped up on the Chestnut (TACF) Growers List this past week. We're fortunate not to have seen this pest (yet) here in Connecticut. Hill Craddock of Hamilton County Tennessee describes it as "by far the most damaging pest in (his) orchard." Hill goes on to say
Although we have only two years of observations, it appears that there may be varietal differences. The cultivar 'Mossbarger' was nearly destroyed in 2005, while the other cultivars in the 20-cultivar trial were significantly less damaged (fewer trees attacked). In our experience, the attack was always fatal; infested trees never recovered.Chris Foster of Cascadia Chestnuts suggests an interesting analysis of the problem and a creative (and slightly lower impact) solution ...
Endosulfan (Thiodan, Phaser) or chlorpyrifos (Lorsban) are some of the recommended chemical controls, but timely application (before infestation) and thorough application may be critical for success. I do not know if these chemicals are labeled for chestnut production as a food crop.
In the Pacific Northwest, we have a similar beetle Xyliborus Dispar which is a European ambrosia beetle a.k.a. "sholehole borer". For what its worth, here's an educated guess or theory as to what the underlying problem which usually provokes the attack by ambrosia beetles in chestnuts. I should qualify this by saying this applies to the Pacific Northwest and may or may not apply to your area. Very little is written on this subject. With great brevity:
The magnet bringing the pest to your trees unusally high ethylene gas production. The pores or lenticels of your trees are expelling this gas. In large the majority of cases, high ethylene production is associated with excessively wet soil conditions at a particular time of year; spring, when the trees are just beginning to bud or leaf out. Poorly aerated roots at this time are not able to keep up with a the usually young tree's oxygen demand and the ethlene production soars as a reaction. Wet spots or compacted areas in an an orchard or already weak trees may be deciding factors on which trees are going to have problems with beetles. These same trees will frequently have hypertrophic or swollen lenticels. The twigs or branches will have a pimply or bubbly character. There are other causes (sometimes winter injury like sunburn), but I think timely wet soil conditions are usually the cause in the Northwest. Tree emergence and wet soil occurring at the time of the beetle flight (the first few days of 65 to 70F degree weather) can be a deadly mix.
The long term remedies are either praying for reasonably dry spring weather, and/or improving drainage and lessening soil compaction. One short term remedy (though debatable as to whether or not it will actually keep them off your trees) is mass trapping. Homemade sticky traps, usually a perforated plastic bottle, fueled with a bit of vodka to mimic the ethylene are the "standard", but there are many variations. Hang these at the perimeter of your orchard. Timing is everything; the beetles flight cycle may only last for a few days if it stays warm; it may already be too late for this year in your area. You can also try to intercept them and physically crush them or root them out before they get to far in.
Hill Craddock also provided these links for additional research.
http://www.bugwood.org/factsheets/99-010.html http://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/note111/note111.html http://www.ces.ncsu.edu/depts/ent/notes/Fruits/NoteP-3.html http://creatures.ifas.ufl.edu/trees/asian_ambrosia_beetle.htm http://www.walterreeves.com/insects_animals/article.phtml?cat=21&id=336
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