Elm Trees

Elm trees and the weather are typically the most common topics at trade shows and meetings where growers congregate.  When attending trade shows I somehow end up in the booth as I am a grower, not a salesman.  I am always happy to see my friends and associates throughout the industry and to listen to our sales team answer some of the usual questions about availability, shipping, etc.  I’ve heard some potential customers say, “I stopped growing elms because I always get a bark canker and I’m tired of losing money,” or “I got freeze damage that split the bark,” or “the tops all died out this year.”  All of these comments get me stirred up.  It’s not that difficult so please don’t give up on elms!  There are a few simple rules for growing an elm.  When I speak of elms, I’m only talking about Ulmus Parvifolia, the trees that Abby Farms currently grows; Allee and Bosque.  Let’s discuss two major diseases that affect elms and how to prevent them from occurring.

Bark Canker is actually Fusarium stem canker and there is no chemical control if you get it.  The telltale signs are orangish-colored spore masses on the trunk about the size of a pencil eraser and you may see bark peeling or a wound that looks like a bull’s eye leaking sap.   The large wounds will not heal and will continue to leak sap periodically.  There are several causes of these wounds; the most common being mechanical injury.  Wounds provide an entry point for Fusarium to infect the tree.  Mechanical or physical injury can come from shipping.  If one or three gallon trees are stacked like cordwood in very hard, rigid pots, bouncing down the road may cause it.  If your planting crew is in a big rush, they can drop or slam trees around.  Mowers throwing sticks or rocks, bump sprayers and a whole host of other factors like hail, can cause injury.  Herbicide damage from repeated chemical weed control applications is another possibility and one that is hard to detect.  Are the entry points at the same height?  Are they on the same side of the tree?  A little detective work can eliminate many possibilities.  I almost forgot to mention that stress from inconsistent moisture, and water-logged or too dry a specimen can amplify the problem.  Get a good book or read up on Fusarium online.  This one is easy to prevent.

Coral Spot Nectria shows up in the spring and early summer.  As with Fusarium, there is no chemical control.  You will know when you have it as the tree will usually flush from the bottom in the spring with no flush occurring at the top.  It may flush separately, and will soon turn brown, usually dying in four to eight weeks.  After careful examination, you will see pink pustules.  You may also see discolored bark or dead, sunken areas.  The cause is simple; it is usually a stress condition.  Untimely late summer or fall pruning leaving fresh pruning cuts exposed, provides entry points for this fungus.  Other causes for points of entry are root pruning at the wrong time and freeze damage.  Freeze damage is the most common cause, resulting in injured bark or buds during the first or second cold snap in the fall when the trees have not yet hardened off.  Coral Spot Nectria mainly affects younger trees.  I have not observed this to any major degree after they have reached about a 2” caliper.

What steps can the grower take to lower the risk of getting either of these diseases?  The first step is to gain knowledge such as what I’ve outlined here, a quick overview, based on my personal experience as a grower.  There are several things you can do to set yourself up for a successful elm crop.  The prevention of man-made injury and bruising, timely pruning and not getting herbicide on the trunk are all under your control.  Don’t blame the tree.  Train your crew to be careful with them.  The weather is a factor that is completely out of your control, but you can minimize your risk by preparing the tree for the cold.  Forget the old wives tale of shutting elms down in the fall.  Reducing the fertilizer and shutting the water off are the two most detrimental things you can do.  Adjust your water to match the weather.  Inconsistent fall moisture, mainly being too dry, is also a major factor in container production.  Also, change your fertilizer.  Nitrogen is essential going into the winter months, especially if you plan on digging.  When doing this with elms, drop the sodium level in the soil down to no more than 3%.  Personally, I aim for 1-2% sodium.  Remember, potassium and sodium have the same positive charge; the plant will absorb sodium because it’s more mobile and move it into the cell walls.  As long as the weather is cool, you’ll have no problem.  But when it gets hot and humid, the sodium will expand and break the cell walls allowing an entry point for Fusarium or Nectria, occurring in the summer.  This is the beginning of the problem.  You will most likely see the damage in the following spring.  I lower the sodium and raise the potassium to try to keep this from happening.  It is actually very simple; just get a base saturation soil sample.  This is usually a free service provided by your fertilizer sales person.  Read your test and make sure you have good potassium levels.  Potassium also helps with your cold hardiness by regulating pressure in the cellular tissues.  The next step is to make sure you have adequate sulfur levels.  I like to be in the mid-20 ppm minimum, which helps the plant deal with stress.  With all of this being said and done, I think these simple steps help lower my risk of loss due to Mother Nature.

In conclusion, I am a grower and these suggestions, again, are based on my personal experience.  In 2002 I lost over 4,000 three gallon elms to Coral Spot Nectria.  Since then using these methods, I have not lost a single tree to the disease, so these methods are working.