Update on Thousand Cankers Disease

The following is an excerpt from an email sent to several listservs by Whitney Cranshaw regarding a new confirmation of Thousand Cankers Disease in Tennessee.
"Thousand cankers disease of walnut has been confirmed from Tennessee.  This was first identified about 10 days ago with a sample we received from Knoxville, but a formal announcement has been pending per the Tennessee Department of Agriculture's wish to delay announcement for further confirmations.  As this has been done, and I see an AP report on the internet, I think that we can now let it be generally known. 

The known infestation is in and around Knoxville.  As this is a fairly recent find, the extent of the infestation has not been delimited.  But the extent of the infestation suggests that this disease (i.e., the walnut twig beetle and its associated fungus, Geosmithia morbida) has been there for a decade or more.

This is a disaster of tremendous proportion.  It had been my deepest hope - clearly a naive hope - that this problem would stay bottled up in the western states where black walnut, Juglans nigra, is planted but not native.  I had long ago given up that black walnut would survive in the West and that is a sad situation, but not tragic.  Now that it is irrevocably established in the center of the native distribution of Juglans nigra, there are no geographic/ecological barriers to prevent its ultimate spread throughout the US.  Furthermore, the fact that the disease appears to be progressing as a lethal tree killer in Tennessee as it has been doing for 10-20 years in the Rocky Mountain States answers the question as to whether this is a regional problem.

It also suggests that there may well be many other infestations in the Midwest that have gone undetected.  This is a very difficult disease to detect in early stages.  Apparently in Tennessee, as in our area, what attracted attention were plantings that showed symptoms of apparent drought stress.  But it is not drought stress nor related to drought.  For some help with this situation we have a web site:  http://www.colostate.edu/Depts/bspm/extension%20and%20outreach/thousand%20cankers.html.  There are sheets on diagnosis, Q & A, and a fact sheet (that needs a bit of updating).  Also available are links to pictures and powerpoint talks, including the version of "Nightmare on Walnut Street" that I presented at the ISA meeting last week in Chicago.

I am assuming that there will now be a scramble to have state quarantines become a reality.  As I understand it, following Missouri's lead, that Nebraska, Kansas, Michigan and Indiana have or are in the process of enacting state quarantines that restrict movement of certain Juglans material that originates from TCD-affected states.  And this disease is a deal breaker.  It is relatively slow to develop, at least compared to DED or EAB, but its progress will be inexorable.  My guesstimate from watching it in urban settings is that about 30 years after this is introduced into a city, all the black walnuts will be dead.  That is based on the disease taking 10-20 years to show symptoms after the initial point infestation and 10-15 years for it to progress across a city once the first symptomatic tree is detected.  How this disease will progress where there are native stands affecting the epidemiology will undoubtably change things in ways we will all have the unfortunate chance to see in the upcoming years. 

However, containment/slow the spread is still something we need to throw ourselves into.  The longer you can delay the introduction of the disease (by movement of fungus contaminated walnut twig beetles), the longer your black walnuts can survive.  Perhaps with dedicated effort we can push back the ultimate effects of this disaster for a generation or two in many areas, giving us valuable time to develop means of managing it and finding resistant cultivars."

Posted by Whitney Cranshaw, 8.2.2010

Some Insect-Issue Thoughts and Predictions

Whitney Cranshaw, CSU Entomologist/Extension Specialist is providing his thoughts on insect issues that we may or may not see this summer: 

"This part of the state has had quite a spell of unusual weather.  Last fall we had a severe cold snap on October 13 and a very cool winter, often with some snow cover.  It has been above average with moisture, continuing the trend of last summer, and this spring has been very cool, with everything delayed.  Based on those conditions and some other things, I am going to guess on a couple of insect related events."

Yellowjackets:  Down.  The cold, wet spring is going to have the colonies get off to a slow start.  Furthermore last year wasn't great for them and the winter may have knocked out some queens.

Honey Bees.  Very rough start.  Late summer/early fall conditions were poor for setting up winter stores that allow colonies to survive winter.  Then this spring was late with bloom.  We now have abundant blooming, but weather is usually too cool for foraging.  Altogether this has to be very stressful for colonies and I suspect many starved out.

European mantids (aka 'praying mantid').  Down.  At least around here this is a marginally adapted insect.  It tends to be abundant in seasons when the previous winter was mild.  Last winter was not and I suspect that many of the eggs were killed.

Tobacco budworm.  Down.  Another marginally adapted insect that will freeze out if the overwintering pupae freeze.  Last winter there was a lot of deep soil freezing, which should have dinged the populations.

Squash bugs, Striped cucumber beetles.  Down.  At least around here these also are marginally adapted insects.  They tend to be abundant in seasons when the previous winter was mild.  Last winter was not and I suspect that the overwintering adult stages of both of these had above average mortality.

Mites on lawns.  Way down.  Good winter moisture in many places made clover mites a minor issue this year.

Miller moths.  Down.  Low numbers were present last year and few eggs likely were laid in fall.  There have been no reports of cutworms active in crops yet, further suggesting that the insect numbers are low.  Plus, with all the moisture there will be abundant flowering of native plants which will provide an abundance of nectar sources for the moths; they will not aggregate around landscape plantings as occurs in drought years.  Flights will be later than normal, below normal in total number of  moths, and will be dispersed so people will not notice them as serious nuisance pests.

Aphids on trees and shrubs.  Up.  Cool, wet springs usually signal prolonged, heavier activity of many aphids at least until the end of June when natural enemies (e.g. lady beetles) come roaring back.

Slugs.  Up.  Last season was a building year.  They should be in great shape heading into the 2010 season.