Nursery Notes: Spray ASAP to prevent Ambrosia beetle damage
Sufficient Asian Ambrosia beetles have been trapped at the NCRS to suggest that a spray should be applied as soon as possible.
Astro is thought to be more effective than other permethrin-based insecticides, such as Ambush, Dragnet, Pounce or Tempo. The rate on Astro 36.8 percent by FMC is 5.35 qts per 100 gallon; or 2.7 qts per 50; or 1.7 fl oz per gallon; or 5 fl oz per 3 gallon; or 6.85 fl oz per 4 gallon.
Only two applications may be required, applied 10 to 14 days apart. Researchers do not think it necessary to spray once plants have broken dormancy.
Two researchers in the southeast have observed the beetles backing out of their tunnels within 10 minutes of the application. If the beetle has only been inside the stem for a few days, she will not have had time to deposit the ambrosia fungus and the tree may survive.
Researchers also recommend making the application with a hand gun or back pack sprayer, wetting the bark from two sides. A previous article March 3 gave more information on this pest.
Ambrosia beetle attacks have been sporadic, unpredictable and extremely costly to a few producers over recent years. Weakened or stressed plants are attacked. They have killed cherry, chestnut, hydrangea, lilac, red maple cultivars, especially October Glory, weeping mulberry, and redbud locally.
Adult beetles bore into the wood and form a gallery, which the female inoculates with an ambrosia fungus to feed herself and her larvae. Toothpick-like filaments composed of frass (excrement and sawdust) protrude from the holes several inches. Wind and rain will remove these tell tale signs. Attacked trees usually die. The time to prevent damage is prior to the adult boring into the tree.
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Weed control provided by pre-emergent herbicides applied last fall is still looking very good. Control could last another month. I would plan on re-spraying in April and not gamble, unless you have an Enviromist to clean up the first weeds that germinate indicating that the pre-emergent herbicide has run out.
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Try not to top shade tree liners, especially pears. Try to maintain straight trunks. Any branches created will be removed later by you or the consumer. Low branches left will increase caliper. They can be shortened to not interfere with cultivation, etc. Remove a branch before it becomes half the stem diameter to prevent an enlarged wound.
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Additional tasks include: spray ryegrass with Envoy, Fusilade or Vantage; prune out & burn black knot from plum trees; spot spray thistles with glyphosate (Roundup); finish transplanting and sidedressing quickly; record and post all pesticide applications; replace filters in respirators and tractor cabs (charcoal). Request a task calendar if you lost yours.