Category Archives: Trees

Emerald Ash Borer

emerald ash borer

Bagworms in Evergreens

I’ve been receiving questions regarding when to spray for bagworms. Bagworms overwinter as eggs in these up to 2″ bags which are formed throughout the summer with silk and evergreen needles by larvae. Larvae feed until late August or early September. Males then emerge and mate with females through the bag opening in September. 500-1000 eggs are deposited by female moths within their own bags.  After depositing eggs, the females drop to the soil and die.  Bagworms overwinter as eggs within bags fastened to twigs such as these shown in this photo.

Bagworms

Eggs hatch in mid-May to early June. Some caterpillar larvae remain on the same trees containing the bags from which they hatched.  Others are blown by the wind to area trees allowing for new infestations to occur.  This photo shows new bags (1/8-1/4″) being formed on trees as they create these bags around themselves.  Look closely for these tiny bags on trees right now.  The video below shows how to look for bagworms on evergreen trees right now.  Study your trees and look for small movements on small bags being formed.  If you are seeing this, consider treating your trees for bagworms.  Products containing bifenthrin or permethrin irritate caterpillar larvae causing them to come out of the bags and be exposed to the pesticide.  There are a number of other management options available.  Please see the following publication for more information.   

Nebraska Extension Publication:  Bagworms

Treating Iron Chlorosis in Trees

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Throughout the County, iron chlorosis is appearing in trees and landscapes. It can especially be seen in the silver maples (shown in this photo) and pin oaks. Iron chlorosis symptoms appear as yellowing of leaves while the leaf veins remain a dark green color. Eventually the leaves become so chlorotic that leaf tissue begins to turn brown/black and die. Severely affected leaves often drop from the tree and new leaves emerge in 7-14 days. Alkaline soils (pH above 7) reduce the availability of iron and manganese; two important nutrients found in tree leaves. It’s not necessarily that these nutrients are deficient in the soil. The high pH just makes these nutrients less soluble and unavailable to the trees. Adding iron to the trees or the landscape around the trees won’t correct the problem as the pH ultimately needs to be corrected.

Early in my Extension career, I inherited the job of injecting trees with a solution of iron sulfate. There would often be a waiting list of people to help, particularly in Sutton, when they’d see the jugs hanging from trees. As a plant pathologist, I was concerned about how much damage we were doing to the trees with repeated injections every five years or so…if secondary pathogens would affect these areas we were drilling in the trees. I was also concerned about providing a free service that took a great deal of time and if we were competing with industry by doing so. Eventually we stopped providing the service but we do rent out the equipment and can provide the recommendations on how much iron sulfate to add based on tree diameter if you are interested. But you may be interested in another less invasive method instead.

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I learned of another potential method to consider from John Fech, Extension Educator in Douglass/Sarpy Counties, and we tried it at the Sutton Cemetery for two years and at the Clay County Courthouse last year with decent results. The first step is to double aerate the area from the trunk to the dripline of the trees showing iron chlorosis symptoms. The dripline is the outer leaves of tree. Do so several days after irrigation/rainfall to avoid tearing up the grass in your lawn. Often people aerate their lawn in the spring and/or fall, so if you have a problem with iron chlorosis, you could include the following treatment into your routine.

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The second step is to broadcast spread granular sulfur on the soil surface. Then broadcast spread iron sulfate on the soil surface. What was recommended to us by Omaha Master Gardeners was using 3 lbs of sulfur + 3 lbs of iron sulfate for “small” or newly established trees; 4 lbs of sulfur + 4 lbs of iron sulfate for “medium” sized trees; and 5 lbs of sulfur + 5 lbs of iron sulfate for “large” established trees. I realize that’s not very scientific based on sizes so do the best estimation of tree size that you have. We used 5 lbs for everything at the cemetery and courthouse. Here Mike, Clay County Courthouse Custodian, is spreading the product close to the trunk first.

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He continued applying around the tree in a circle gradually moving out towards the drip line.  The final step is to then water the lawn.

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We have numerous silver maples at the courthouse. This is a photo of one of the trees and a close up of these leaves was shown in the first photo. You can see the yellow cast to this tree in this photo and how severely affected many of the leaves were from the first photo.

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This is the same tree a year later from the opposite side. The photo doesn’t do it justice as it truly is greener than last year and the leaves are hailed damaged. It didn’t really change during the season last year but all the courthouse trees are greener this year. They could use another application though as they still show symptoms of iron chlorosis. This method may take several years before the soil pH changes enough for symptoms to disappear.

You most likely will not see any changes the first year, although the grass under the tree may appear greener.  The goal is to change the soil pH to make the iron more available to the tree in the future.  This may be a process that needs repeated for several years in a row and while it doesn’t show instantaneous results, it will most likely aid in the longevity of your trees by reducing the symptoms without additional harm to the tree through injections.

Proper Tree Pruning

Special thanks to Dr. Scott Dewald for the wonderful evening of information he provided at our tree care workshop last week!

Scott Dewald explaining what to look for when considering pruning a tree.

Scott Dewald explaining what to look for when considering pruning a tree.  Scott shared that one should never prune more than 1/3 the height of a tree in one season.  Pruning should also be done to obtain a main leader and overall structure.  It’s also best not to prune limbs more than 2″ in diameter.  If the limb needs to be pruned but it encompasses more than 1/3 of the limit of what should be removed in a season, one could “head” the limb by removing a portion of it one year and then complete the cut the following year.  This will slow the growth of that limb.  

Scott Dewald showing workshop attendees where the bark collar ridge occurs on this branch.

Pruning cuts should always be made at the “bark collar ridge” which produces a round cut and allows the tree to naturally heal.  Scott shows attendees where the bark collar ridge is on this branch. 

Pruning Fact Sheet ENH847 from University of Florida Extension written by Edward Gilman.

Pruning Fact Sheet ENH847 from University of Florida Extension written by Edward Gilman with good visuals of where proper pruning cuts should occur.

Workshop attendee demonstrating "heading" of a branch.

We learned that on large branches, it’s good to make a cut farther out to remove the weight first, and then go back and make the proper cut at the bark collar ridge.  Improper pruning can result in further damage to the tree.  Here we were trying to correct this tree for not having a main leader.  Typically one would leave the southern-most branch according to Scott, but in this case, the northern-most branch was stronger.  Scott said there was no need to stake the tree or try to get the northern-most branch to straighten out as it would naturally do this in time on its own.

This attendee is now making the proper cut at the bark collar ridge.

After a large part of the branch weight has been removed, this attendee is now making the proper cut at the bark collar ridge.  

Additional Problem-Planting too shallow.

We also walked from tree to tree in the park looking at additional problems.  I noticed how high the mulch was piled on some of the trees.  Mulch should never be placed against the base of the tree as it can cause rot.  But in this case, it was observed that the person who planted the tree did not dig a deep enough hole.  What appeared to be a pile of mulch was the actual root ball and soil mounded up above ground.  

Additional problem with this tree.

This situation also most likely was a result of improper planting.  In this case, the tree roots began wrapping around the base of the tree girdling it (like choking it).  

Weed wacking

This is the most common problem I see with tree calls.  A huge enemy to trees are weed whackers!  In this case, you can see extensive damage to the bark  and the base of this tree.  Depending on the damage and how well the tree can seal the wound will depend on if the tree will survive or not.  Often, as in the case of this tree, the tree will be weakened with few leaves appearing on branches.  It’s best to place mulch around trees in order to avoid having to use weed whackers on them-but again, don’t place the mulch up against the base of the tree!

This was a fun workshop for me with the right size of group and great hands-on demonstration where we also learned from pruning mistakes and how best to correct them.  Thanks again Scott!

Tree Care Workshop

TreeCareWorkshop

The Memorial Day and August 1st storms of 2013 did significant damage to our trees in Clay County. This workshop is designed to provide demonstrations on pruning techniques, what to look for, and learning how care for your storm damaged trees in future years. There is no charge and all are invited to attend. Please spread the word as many trees were damaged last year!

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