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Emerald Ash Borer

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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

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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!

The Season for #ag & #horticulture Questions!

This past week was a blur of calls, questions, and visits to homes and fields but it was a great week and flew by staying very busy!  I’ll touch on a few of the common questions I’ve received this week.

Trees:  Some trees such as willows, hackberries, tops of maple trees, ash, and black walnut are just taking time leafing out.  Some trees leafed out once already and dropped leaves.  Things that may have caused this were the sudden flux of temperatures from very warm to cool and the strong winds we received.  Some trees have also unfortunately had herbicide drift damage that caused leaves to drop.  On those trees, watch for new buds as nearly every situation I’ve looked at thus far have new buds forming after about a week-10 days.  With all these situations, give the trees a few weeks to leaf out again and if they’re still not doing it, feel free to give me a call.  Trees are interesting plants as sometimes environmental impacts that happened 3-5 years ago will show up that much later-and sometimes environmental impacts show up right away!

Disease/Insect issues:  This year has been a strange year all around but with our warm winter, I was concerned about an increase in diseases and insects.  Thus far, we’re experiencing increases in both-so hang on-it may be a long growing season!  Our high humidity, warm temps, and heavy dews have created perfect conditions for fungal diseases on our trees, ornamental plants, lawns (I’m currently fighting a bad case of powdery mildew-as a plant pathologist it is kind of pretty but I don’t like what it’s doing to my lawn!), and in our wheat and alfalfa crops and some pasture grasses.  Fungicides may help in some of these situations, increasing airflow can also help as can more resistant varieties or hoping the weather will change.  In the case of most ornamentals, we don’t usually recommend doing anything.  The same goes for insects as insecticides can help in some situations.  I’ve received several calls this past week of people afraid they had herbicide drift damage.  While there were a few cases of that, many of the cases were actually fungal leaf spots on leaves.  There are various fungicides and insecticide products available from home/garden centers, etc.  Be sure to read and follow all label directions and only apply the product on places the label specifies it can be applied.

Crops Update: Later this week we may have a better idea on the extent of storm damage and if some fields will need to be replanted after the storms from last week.  Dr. Bob Nielsen from Purdue University reported that most agronomists believe young corn can survive up to about four days of ponding if temperatures are relatively cool (mid-60’s F or cooler); fewer days if temperatures are warm (mid-70’s F or warmer).  Soil oxygen is depleted within about 48 hours of saturation and we know soil oxygen is important for the root system and all the plant’s life functions.   So we’ll have to wait and see what happens.

Have also had a few calls regarding rye cover crops.  When rye is killed out and decomposing, it releases toxins that can affect the germination of other cereal crops such as corn if it’s going to be planted into that rye cover crop.  Thus we recommend at UNL that the producer kill the rye and then wait at least two weeks to prevent any major damage to the crop.  I realize at this point with the rains to get in and kill that crop on top of waiting an additional two weeks, we’re getting close to the end of the month and will most likely be looking at reduced yields…and depending on maturity, you may need to consider different seed if you end up having to plant in June.  If you have specific questions about this, please let me know and we can talk through some situations.

Stripe rust and powdery mildew have been obliterating mid-lower canopies of many wheat fields.  I’ve received several calls on why wheat canopies are yellow-that’s the main reason but other factors such as the dry spell prior to these rains and/or deficiencies in nitrogen/sulfur or some viruses may also have been factors.  Wheat in Nuckolls County last week was beginning to flower.  Fungicides such as Prosaro, Folicur, or Proline are labeled for up to 50% flowering and cannot be applied after that.  Remember the wheat head begins pollination in the middle-so if you’re seeing little yellow anthers at the top or bottom of that head, you’re towards the end of flowering.  All those products have a 30 day pre-harvest interval-which has been the other main question-are we going to be harvesting in a month?  I do believe we’ll be harvesting a month earlier than normal just because pretty much everything in wheat development is about a month ahead of schedule.  I still feel the 30 day window for the fungicide application is worth it with the large amount of disease pressure we’ve seen. Wheat in Clay Co.  and north still may have time for a fungicide application; those products mentioned above will help prevent Fusarium Head Blight (scab) as well as kill the fungi causing disease already present on your leaves.  A list of all fungicide products, pre-harvest restrictions, and rates can be found here. Also check out my previous blog post with video on scouting for wheat diseases.  

The other major disease appearing in wheat is barley yellow dwarf virus.  This is a virus vectored by bird cherry oat aphids which we were seeing earlier this year.  Unfortunately, this disease causes the flag leaves to turn bright yellow-purple causing yield loss (at least 80% of the yield comes from the flag leaf) as there’s nothing you can do once the virus manifests itself in those leaves.  If you have a large incidence of barley yellow dwarf in your fields, you may wish to reconsider spraying a fungicide as the fungicide won’t kill the virus; however, it will help kill the fungi on the remainder of your leaves and potentially help protect some yield from the two leaves below the flag leaf.

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