{"id":1228,"date":"2015-03-12T15:08:47","date_gmt":"2015-03-12T22:08:47","guid":{"rendered":"http:\/\/blogs.oregonstate.edu\/treetopics\/?p=1228"},"modified":"2015-03-12T20:36:40","modified_gmt":"2015-03-13T03:36:40","slug":"use-caution-spring-tree-release","status":"publish","type":"post","link":"https:\/\/dev.blogs.oregonstate.edu\/treetopics\/2015\/03\/12\/use-caution-spring-tree-release\/","title":{"rendered":"Use caution with spring tree release"},"content":{"rendered":"

By Amy Grotta, OSU Forestry & Natural Resources Extension – Columbia, Washington & Yamhill Counties<\/em><\/p>\n

\n \"Dead<\/a>\n
Dead tips (upper branch) and stunted growth (lower branch). Photo taken in January 2015, eight months after herbicide was applied.<\/figcaption>\n <\/figure>\n

A local landowner contacted me this winter, concerned about his ten acres of young trees and whether they had been damaged by herbicides.\u00a0 In May 2014, a year after the trees were planted, grass was coming in thick, so he hired a contractor to do a release spray.\u00a0 We don\u2019t know what the exact spray mixture was, but the landowner thought it may have been a formulation of glyphosate such as Accord.\u00a0 Glyphosate is known to damage Douglas-fir seedlings (and many other conifers) during the active growing season \u2013 the time from when buds begin to swell in spring until resting buds are formed and hardened off in fall.<\/p>\n

Affected trees showed several symptoms characteristic of herbicide damage. The least affected trees simply had stunted growth. On many others, the leader and branch tips were droopy and dead. Some seedlings were completely dead.<\/p>\n

But the contractor knew the risks, and had attempted to protect the trees.\u00a0 According to the landowner, he had covered each seedling with a section of PVC pipe before spraying around it.\u00a0 This is a common practice which many people assume is sufficient to protect desired plants from spray.\u00a0 Unfortunately, it doesn\u2019t always work.\u00a0 The outside of the pipe (or bucket, or whatever barrier is used) ends up getting drenched in herbicide as the applicator sprays around it.\u00a0 Then, when the pipe is lifted off, the solution drips off all over the plant it was supposed to protect.\u00a0 There seemed to be a pattern where the lower branch tips on many seedlings were the most affected, so it looks like this could be what happened.<\/p>\n

So the symptoms are consistent with damage from herbicides, but can we pinpoint them as the culprit?\u00a0 Many months had passed since the spray occurred, making it impossible to detect any residual chemical.\u00a0 We\u2019d have to rule out other possibilities.<\/p>\n

Could it be freeze damage?\u00a0 Tender new growth in spring is sensitive to freezing temperatures, and the symptoms from frost damage and herbicide exposure look very similar<\/a>.\u00a0 But the planting site was not one that would be typically considered frost prone, such as a low-lying area.\u00a0 Instead, the site was mid-slope.\u00a0 Did we have any unusually cold weather last spring?\u00a0 We didn\u2019t remember any, but just to be certain we looked back at temperature records<\/a> from the closest weather stations.\u00a0 There were no records anywhere close to freezing in May 2014.\u00a0 So, we ruled out frost damage and concluded that unintended herbicide contact was the most likely cause.<\/p>\n

\n \"herbicide<\/a>\n
Lower branches were killed, while upper branches and leader exhibit poor growth in previous season. Note the grass regrowing around the seedling.<\/figcaption>\n <\/figure>\n
\n \"herbicide<\/a>\n
Confirmed herbicide damage from a different site, for comparison. Photo: Dave Shaw<\/figcaption>\n <\/figure>\n

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This unfortunate situation leaves the landowner with several challenges. First, it\u2019s not clear whether the residual stocking is adequate to meet the landowner\u2019s goals, or to meet Forest Practice standards for that matter. The trees that were not killed should recover, but they lost a crucial year of growth in their race against competing vegetation. And, as the photo shows, the grass is growing back around the seedlings. The landowner may need to consider a repeat herbicide application, this time selecting a chemical that is safe around growing conifers, or that effectively controls weeds in early spring (before bud break).<\/p>\n

So what are the lessons learned here?<\/p>\n