Sunday, August 3, 2008

Nursery and Landscape - Cracking of Nursery Trees

The following is a great article on cracking in nursery trees (which may also apply to landscapes) related potentially to herbicide use from the University of Maryland.

Cracking of Nursery Trees – Interesting Mystery

We (Stanton Gill, Karen Rane and Andrew Ristvey, UM) visited a nursery 3 weeks ago that was having problems with several species of nursery trees showing bark cracking including deciduous magnolia and Thuja ‘Green Giant’. I examined the trees for borers but found none associated with the cracking. Karen Rane examined the cracking for pathogens but could find no disease culprits. Andrew looked at the plants from a water management and nutritional standpoint and though that maybe the plants were being pushed too quickly resulting in bark cracking.

While I was speaking at the Perennial Plant Growers Association meeting in Philadelphia I spoke with some of the Ohio State Extension specialists and mentioned the problem with bark splitting in nurseries. They mentioned that work by a researcher, Hannah Mathers, at Ohio State University indicates that cracking in the bark of nursery trees appears to be on the rise. There are questions being raised as to whether glyphosate with many of the new surfactants is being absorbed into thin barked trees and helping to create some of the cracking.

Hannah Mathers published an article ‘Take Care When Using Glyphosate Around Trees – Glyphosate Can Damage Trees and Affect Hardiness’ in the July, 2008 issue of Nursery Management and Production magazine (NMPRO). Since glyphosate went off of patent in the year 2000 over 40+ generic glyphosate products, all with different surfactants and amounts have been registered by EPA. Ohio State University researchers have received funding from HRI to investigate glyphosate’s role in bark disruption for certain woody plant species by looking at the number of times applied per season and the surfactant mixed with the glyphosate. They are finding that some surfactant formulations are decreasing cold hardiness. Some formulations of glyphosate are using up to 3 different surfactants. Some of the manufacturers are using surfactants that improve cuticle breakdown so they act fast on weeds. This might be impacting the plant material when it hits the bark of some species.

No doubt about it, but glyphosate has become the workhorse of weed control in many nurseries, but many people are over-using this product with some applying it once a month during the growing season. Nursery growers should be making pre-emergent applications at this time of year to try to control annual grasses and broadleaf weeds instead of relying on repeated applications of glyphosate. Several growers are using a combination of Gallery and Barricade at this time of year and have had good success with weed control.

The message from Dr. Mathers is to hold onto the glyphosate application for when weeds get out of control in the spring or early summer. In late summer and early fall be very careful not to hit the trunks of thin barked trees. Using shields and domes may help prevent hitting trunks of trees. We asked Steve Black to comment on the use of spray domes in nurseries. Here are his comments: Hannah Mathers suggest trying to avoid glyphosate right after sucker shoot removal because the greater chance of absorption. Keep in mind that you should be very careful with late summer and fall applications of glyphosate since plants store food reserves and have a greater chance of accumulating the chemical application of glyphosate. If you prune off sucker shoots you usually just get more since the plant responds to wounds with initiation of more shoots. If you have sucker shoots try using Hannah’s suggested Tre-Hold Sprout Inhibitor. This product contains naphthaleneacetic acid to inhibit the sucker shoots. I did a Google search on Tre-hold and found it was test on Bradford pears in a 1999 research study by Gary Keever et al. on using Tre-hold applied to Bradford pears in March to prevent sucker shots and it worked very well. On a web-search we could not find suppliers of this product. Steve Black mentioned he found a company called Monterrey Chemical in California that sells “Sucker Stopper” with NAA in it. He got his product through A.M. Leonard Company. Steve said that the concentrated form was labeled for use in nurseries. Glyphosate is a good product, but you need to use it wisely to prevent damage your nursery and landscape plant material.

Reprinted from the August 1, 2008 edition of the TPM/IPM Weekly Report for Arborists, Landscape Managers & Nursery Managers from the University of Maryland Cooperative Extension.

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