Posts tagged diagnostic clinic

Suffocating conifers

The following is by Mark Gleason, plant pathologist at Iowa State University Extension:

 

    The 2008 growing season was a bad time to be a conifer in Iowa. The Iowa State University Plant and Diagnostic Clinic was inundated with suffering conifers from windbreaks, commercial landscapes, and backyards. What happened?

    Rain is what happened: too much of it. The six months from January through June saw record rainfall totals in Iowa – the most since record-keeping began in the 1850s. Late May through mid-June was especially sodden, as much of the state saw damaging floods. The result was wet soils, week after week.

    What’s wrong with lots of water in the soil? After all, trees need plenty of water to stay healthy. But 2008 was a case of too much of a good thing.

During the seemingly endless rains of May and June, soils in much of the state became saturated with water – and stayed that way. Even when trees weren’t engulfed in floods or giant puddles, they were rooted in sodden soil.

   When soil is saturated, the normally air-filled spaces become water-filled instead. This profoundly changes the roots’ environment. Roots get almost all their oxygen by absorbing it from the soil, and the soil oxygen is replenished from the atmosphere.

    Once soil water replaces soil air, the ballgame changes. Water carries only a tiny fraction of the oxygen found in the air. In prolonged periods of saturation, that smidgen of oxygen is further siphoned off by soil microorganisms. Faced with oxygen starvation, roots begin to slow their activity.

    Tree roots, like people, go into distress pretty rapidly when their oxygen is cut off.
    In extreme cases like 2008, the roots can die. The first roots to bite the dust (or mud) are the ones that work the hardest: the tiny roots that do most of the work absorbing water and nutrients from the soil. As a last gasp, some roots start making their own alcohol; this can be a fatal goodbye party, since alcohol also poisons the roots.

    Damage to conifers was extremely varied. Common symptoms included dead branch tips, yellowed needles, top dieback, and dieback of scattered branches. Some fungal diseases were stimulated by all the rain, too, but the vast majority of the conifer problems had a physical cause – root damage due to low-oxygen stress.

    Often, the problems showed up in late July or August, even though the worst of the wet spell was long gone. Why the delay? A tree can tolerate some level of root damage. But in warm, dry spells in mid- to late summer, trees call for water to stay cool. If the roots are damaged, the tree can’t take up water fast enough to avoid overheating, and the foliage overheats. So spring’s root damage became summer’s fried foliage.

    How come conifers got nailed worse than broad-leaved trees? Most conifers hate wet feet, and the longer the soil stays saturated, the worse they do. At the ISU Clinic, we saw hundreds of samples and photographs of damaged blue and Black Hills spruce, white fir, arbor vitae, and other species.

    On the hopeful side, most of these damaged conifers are not at death’s door. For many, the prospects of eventual recovery are good – as long as the weather cooperates a bit. Meanwhile, avoid the temptation to help nature along by fertilizing, since you are likely to harm rather than help the tree’s recovery. Watering should be done only when the soil is dry, and should add only one inch of water (rain included) per week.

    With luck and patience, 2009 will return us to green conifers instead of brown ones.

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Know your bugs

 

 
Sixspotted tiger beetle, a beneficial insect
Sixspotted tiger beetle, a beneficial insect

   The watch continues for the notorious emerald ash borer, a pest that has devastated ash trees in at least seven states, including neighboring Illinois.

   The emerald colored bugs appeared near Detroit six years ago and have been advancing toward Iowa.

   Having seen photos of the emerald ash borer, I quickly reacted when I saw a pretty emerald bug outdoors earlier this summer.

   Iowa State University has an awesome insect identification program that allows Iowans to e-mail a photograph of their bug and have it identified by entomologists.

   I shot a photo of my bug next to a ruler to show its size and sent it to the site.

   Good news: it wasn’t an emerald ash borer. Bad news: I had killed a sixspotted tiger beetle, a beneficial insect that extension entomologist Donald Lewis said is easily mistaken for an emerald ash borer.

   Lewis tells me the beetles are predators that chase other insects across the ground in woodlands.  They hunt food like a tiger.

   Tiger beetles are ecologically beneficial.  They are not a pest.  The beetles do not bite, sting or carry disease.  They do not feed on crops, trees or houses.  They are remarkably fast and difficult to catch.

   I’m bummed that I caught one, but glad it wasn’t an ash borer.

Lewis says the emerald ash borer is much smaller and narrower and does not have the long sharp jaws of a tiger beetle (predatory

hunter.)

 

   For Iowans who have a bug they’d like identified,  specimens can be submitted to the Iowa State University Plant and Insect Diagnostic Clinic for diagnosis at no charge.

   You can e-mail a close-up digital image to  insects@iastate.edu

   Specimens can also be sent to the clinic.

   Bugs should be dead when shipped and mailed in a bottle, box or padded envelope.  Soft-bodied insects such as caterpillars, aphids and ants, and spiders, mites and ticks can be preserved in hand sanitizer gel.  Hard insects such as moths, butterflies and beetles do not need to be preserved, but they should be restrained inside the container so they don’t bounce around during shipment (for example, secure a moth or butterfly inside a box with layers of dry paper toweling.)

    Mail sample to:

Plant and Insect Diagnostic Clinic
327 Bessey Hall
Iowa State University
Ames, IA 50011-3140

 

Include information about where you live, where you found your insect, and how to get in touch with you. 

 For  a photo of the emerald ash borer, go to:  http://www.emeraldashborer.info/files/E2944.pdf

 

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