In this post, we reprise last year’s article along with some articles we wrote this year.

Last year, in April 2017,  we posted the article below for our clients and friends asking them to map the spring melt off and water flow across their field.  By mapping water flow, when water runs across the field, you can avoid the natural drains that form while fields drain water to the nearest creek or river.  If you have concerns about water in certain part of the field, it is probably too wet. Remember, chestnuts want well drain soils–all of the time.

A Reprise of a COS article from April 10-17, 2017

Finding Dry land

Fields are under water this spring (again, this article is from 2017).  You can use this information wisely! Perhaps the single most important aspect of chestnut orchard establishment is finding dry, well-drained land.  Many of the trees that have died in orchard settings after cold winters, even in proximity to trees that survived, had their feet in natural field drains.  You cannot always see these drainage areas, but if your field looks like the the dramatic field flooding in Figures 1, 2, and 3 you know what I am hinting about.  In dry seasons or dry years, you may not know these natural drains are even in the field until the fields are saturated in a wet year, like they are this year—then the drains show themselves.  But these drains are always present.Healthy trees that die from cold winter weather are trees that are somehow compromised.  We have learned over time that “wet roots” is one of the factors that compromise chestnut trees.  What’s more confounding is that these trees can look good in droughty times, when they are the only ones with their roots in water. But once the snow melt runs off, summer showers downpour on the field, or spring rains flood the fields, these roots are in water-saturated soils which weakens the roots and allows pathogens to infect the trees.  When winter temperatures strike, these are often the trees that die first.

Too often in Michigan, we are concerned with irrigation of chestnut a tree that needs irrigation but for a few days a year or during a drought. Chestnut trees are capable of growing in extremely dry locations where the water is added only as needed.   In other words,   if you cannot manage the amount of water the tree gets, don’t plant there.

Chestnuts Prefer it Hot and Dry

Below are European chestnut trees I saw  on my travels to Lebanon last year as a volunteer for USAID, Land of Lakes International Programs. Totally, 85 to 95 F, cloudless skies for more than 4 months, yet the trees flourished as they were only provided water when needed. These trees can withstand dry conditions.

Below, are trees planted on mountains with elevations representing 2000 feet near Aydin, Turkey. Water from small plastic reservoirs was supplied as needed; otherwise these trees are hot and dry and thriving.

Hills, mountains, slopes, drain, and dry.

Finally, below are orchard trees planted in Australia that have survived some of the worse droughts yet yield heavy each year. One year, it was so dry, the grower’s reservoir completely dried up.  In a desperate attempt to reduce water demand by the tree, the grower cut off all of the branches on the trees. The trees survived and flowered the following year.


This year  2018 in Michigan we witnessed another manifestation of wet roots, and that is bubbly bark.  It is thought that because the warm temperatures came on so fast, roots that were in wet soils tried to pump water to grafted scion that was not ready to accept the flow of water so the rootstock tissues became saturated with water. This results in bubbly bark issues where the water appears as it it is trying to exit the tree via the lenticels, natural openings in the bark used for gas and water vapor exchange.  Read below what we wrote about this a couple of weeks ago.

Reprise from June, 2018

Water and Bubbly Bark Issues

The role of water in the soil around chestnut roots has been known for several years.  When in a drought year like 2012, it is easy to see the trees struggle to get enough water to keep the leaves from wilting and the tree from collapsing.  But what about the role of water in non-drought years?  Every orchard will be different in the amount of water held in place by the soil. Some soils will hold water, more or less, based on the chemical and physical aspects of the soil.  Particle size, organic versus inorganic make up, level of the water table, location of the hardpan, and slope of the land all influence the water holding capacity of the soil in the vicinity of the roots. There are times when the soil is more saturated than at other times, such as spring snow melt, spring rains, increasing summer temperatures, summer rains (or lack of them) and added water from irrigation.

This all spells a system where orchards and the trees in the orchards deal with water differently.  This difference provides a different scenario for each grower.  In the other article I sent you, you can see where natural drains channeling water across a field may actually affect tree survival.  In drought years, it may help, but in rainy years if may inhibit tree growth.  The orchard in that article had a year where 25 inches of rain were recorded one summer and then it was exposed to one of the coldest winters in history (2013-14).  Many trees died.  While the temperatures were exceedingly cold, trees in other orchards survived these temperatures. In fact, most of the trees in the orchard did survive.  Why do some die while others live?  If we look at the role of water and the natural drains, there appears to be a role of wetter areas versus drier areas.

The first hint that water is detrimental— mountain trees: Chestnut trees are mountain trees that grew/grow in the Appalachians or in the mountains of Europe and even Asia.  I saw them successfully planted and growing in the mountains of Turkey and Lebanon. Mountains are important for chestnuts and especially Mediterranean mountains for the European trees.  Water in the mountains moves away from the trees rapidly.  The trees do not sit long in saturated soils.  Root rot caused by Phytophthora (a water mold) and wet soils normally occurs in the mountains along points of natural drainage.

Water and tree death in Michigan: flat land trees die where water is left on the orchard floor. Trees have died in orchards with drains running through them and where naatural springs are found.  It doesn’t have to be flooded, just damp, wet soil.  Chestnut trees cannot grow in damp, wet soil.  Christmas tree growers learned that their favorite tree, Fraser fir, can’t grow in damp, wet soils; it is not out of the ordinary to find trees that require soils to dry between rain and irrigation events.  Chestnut trees require well drained soils. We have been saying that for decades now.  Wet soils bring on root rot diseases and it has been implicated in seasonal start up issues (see below).

Here is some evidence suggesting that water in orchards is problematic.  

1) Grafting—After several years of successful grafting at MSU and at a local Michigan nursery, failures began appearing and the stems of those trees that failed were water soaked and damp.  We discovered, by accident that if the pots were watered heavily before grafting, the rootstock would pump water up the stem, and when the rootstock is cut (as in grafting), the water will push out at the cut end of the rootstock. This water will prevent a successful union of the scion wood to the rootstock.  Water is the enemy of grafting.  Sure it can seep into the graft from external rains, but it can also be pushed up through the rootstock as the rootstock tries to eliminate the water in the soil of the pot.

2) Hills—Trees in the lowest rows on a hillside in an orchard are usually where it is most difficult to keep the trees alive.  We used to think it was where the cold air was located, but now I am sure it is due to the wetter soils found at the bottom of the hill, and probably a little of both.

3) Leaving the water on:  For some reason, over the years, we have had a few instances where growers have left the water on their trees.  When this happens, trees die. Young trees, old trees, a few or many, but when the trees are overwatered, they have the tendency to die off.

4) Orchards—After reading and hearing reports about bubbly bark disease, Chris Foster, a Portland, Oregon chestnut grower came to MSU to report on bubbly bark disease.  Chris has figured this out on his own and has reported it previously. Basically, it is when chestnut trees in wet areas of an orchard try to eliminate water from the area surrounding the roots. The trees pump it up the stems faster than the tree can eliminate it.  The lenticels, the air exchange organs (white dots on the bark) cannot eliminate the water fast enough, and the bark begins to become saturated.  It swells and lifts off the cambium layer of the trees.  This usually leads to the death of the trees. He has found it to be more common with grafted trees than seedling trees.

Here is Chris’ explanation in his own words:  “My postulate as why this is largely a problem in grafted trees is due to a type of mismatch between seedling rootstock and the cultivar above. The mismatch is the timing of emergence – perhaps by just a few days. Hybrid seedlings will, to a very high degree produce seedlings that emerge earlier than their parent tree. What happens in spring and especially aggravated by a quick transition to warm weather is a root system that pushes sap up before the cultivar above can properly manage it. Wet soils of course are a key ingredient too. A tree with only buds and no leaf stoma, can only rely on lenticels for respiration and that’s simply not adequate.  The excess sap stagnates and eventually damages bark tissues. The lenticels become hypertrophied or swollen in response to the overload. Sun exposed bark becomes extremely sensitive to heating and dies (often mistaken after the fact as winter freeze damage).

While Bubbly Bark is typically a problem in young trees (say ages 4 to 8), we had the same quick transition to summer temps that Michigan experienced. For the first time ever, I had a few limbs from older trees affected.

If I am correct, the remedies are obvious. Stay off wet sites, promote better drainage, pray for a slow transition into summer, and for the ultimate solution, either stay away from seedling rootstock or somehow select roots for later emergence than the cultivar above.”

A young healthy tree and its bark

Chestnut trees with bubbly bark problems

Chestnut trees with bubbly bark problems–close up

Should we take Chris’ advice and stay away from seedling rootstock?  Using clonal rootstock?  Currently, this is impossible. Plant seedlings and your yields will suffer dramatically.   Grafted trees are grafted to seedlings.  However, as Chris suggests in his last paragraph about getting away from seedling rootstock, well, that may be happening right now as MSU has rooted cuttings of 5 or 6 cultivars.  The choice could be a cloned rootstock that does not push water faster than the cultivar can take it up or just a cultivar on its own roots. So maybe the answer is, find that one clonal rootstock, that will agree, water wise, with the scion wood grafted on top.

MSU rooted cuttings of chestnut

Why don’t we see large numbers of trees die every year?  Fortunately, we don’t.  Even this year, we have orchards in Michigan that simply did not experience any tree death, yet they planted the same cultivars from the same nursery.  Orchard water maybe one of the culprits.  Flat orchards are usually the most problematic and always have been (remember, chestnut trees like slopes), from the first 1997 plantings.

Has bubbly bark been an issue in Michigan before?Here is an orchard map that shows the death of trees (open areas on the map) on a farm in the western part of the state. There was this particular area where tree death occurred and it was worse years ago than it is now.  It seems to have stabilized.  The part of the orchard with the highest percentage of tree death was down hill from a perched woodlot that drained into the chestnut orchard. Snow melt and rain drained from the forest into the field.  The water is draining from the perched woodlot to a large river meaning the orchard is part of the river’s water shed.  The trees closest to the wood lot experienced more water than the trees distant from the wood lot.  I can tell you, because I was called the farm to check it out, that the trees that died had bubbly bark disease.

Below, we see the map of an orchard where trees at the north end of the field were subjected to a continuous draining of water which saturated the soils as water drained from the woodlot down through the orchard. Water was moving to a river and the orchard functions as a water shed for the river. The woodlot is perched above the orchard floor by a few feet.

And that was before we knew it as bubbly bark or knew what was causing it.  Why didn’t all the trees die?  Not sure, but if you use Chris Foster’s explanation, some the rootstock were good matches for the scion wood and perhaps other weren’t.  When we say match here, I am not necessarily saying there is a genetic miss-match (which has not been seen), but a physiological mismatch where particular seedling rootstocks push water to the scion portion of the graft before the scion can eliminate the water. It might look like a graft incompatibility as the damage will take place at the graft union, but it is really water being blocked by the un-activated cultivar at a time that it needs to be moving water.

If you look at some of the dead 2017 young trees, you may see some of the bumps or what one grower called pimples.  This is just bubbly bark, but in miniature.  The water was pumped up by the roots of the rootstock, it could not escape as the cultivar had not activated quickly enough, the tissues swelled in the rootstock, and the water disruption of the plant tissues killed the scion and sometimes the rootstock.

Above, a planted tree with rootstock showing signs of water logging and swelling. Perhaps this is the equivalent of bubbly bark in young grafted trees.

Water In the Orchards and Its Effects on Chestnut Trees

A grower showed me this when I was out looking at mature tree die off. We walked the wet areas of his farm and it coincided almost perfectly with his tree death. These wet areas were not really noticeable until he took me to his property line and showed me how his neighbor’s property drained across his field. These natural drains would not be seen in the summer unless a lot of rain fell. They are more obvious in the spring, after snow melt and heavy spring rains. It was amazing. As the water crossed his orchard, the Colossal bordering this natural drain were dead whereas the other Colossal trees were hardly damaged. I became a believer that wet roots and cold winters are complicit in chestnut tree death. Since then, I have been saying, do not plant in areas that are wet. Chestnut is a Mediterranean tree and survives best in the hills and mountains where the water drains fast. They will struggle during droughts, but die in wet soil.

Below are two maps of a farm (not the one I just wrote about, above) and if you look at the unmarked orchard map first, you will see there are areas where trees are missing or smaller than the rest. If you use imagination, you can see the natural water ways or drains that move from the bottom (neighbors field) and run downhill to the top where a big pond can normally be found in spring.

In the second map, I have marked some, but not all, of these natural drains. They were ground verified. In fact, there is a natural spring below the line of wild trees that bisects the orchard. I am a believer in water, wet roots and low winter temperatures as strong factors determining why chestnuts die in orchards.


Something to Keep in Mind

In 2016, we visited 3 orchards, all with the same problem. They were all non-grafted Chinese chestnut trees.  Our goal in visiting their orchards was to determine, to the best of our ability, the cause of the tree deaths.  After visiting the orchard and looking at the trees, we believe all the tree deaths were due to Phytophthora root rot.

1)  In these orchards, the wet/damp sandy soil was  conducive to Phytophthora root rot a fungus-like pathogen, called a water mold, which thrives and reproduces in wet soil. Depending on the species of Phytophthora present, it can attack and kill chestnut trees.

Phytophthora Root Rot

We have seen much more root rot in the past three years than if the previous 20 years.  I think it may be due to the tremendous amounts of wet springs we have encountered for the past 7 years.  There are several ways to check the presumptive diagnosis of root rot.  These methods can be more or less time consuming or expensive.  I first use one of the cheap methods in orchards which meant cutting away bark on the trunk at the soil line.  I look for darkened areas on the trunk where the root rot may have killed or begun to kill the root collar.

Most of the trees dying from root rot were either in southeast Michigan or west Michigan.  The trees were relatively large 20 to 30-year old Chinese chestnut trees and they were collapsing.   Almost all of my experiences with root rot in Michigan orchards has come from Chinese chestnut trees.  This is somewhat surprising as Chinese chestnut trees are supposed to be resistant to root rot, but other than a few examples, most root rot in Michigan has been on Chinese chestnut.

Water drainage from soils in Michigan is diverse and as we move toward the center of the state the soils are heavier with more clay and hardpans.  But as we move toward shorelines, rivers, ponds and watersheds, soils may retain water longer. Wet periods like our recent springs, saturated soil for several weeks.  A non-aggressive Phytophthora root rot organism can begin to infect the roots and it may take years to finally kill the tree.

Root rot is primarily the cause of death of large old chestnut trees in Italy and elsewhere in Europe and Turkey.  Again those are European chestnut trees which are known to be very susceptible. Chinese are supposed to be root rot resistant, but we have found root rot on Chinese in Michigan before and we know we have a species of Phytophthora in Michigan that can kill Chinese chestnut trees.  At the August 11 meeting, we will discover there may be an answer to this problem.

Root rot dying Chinese chestnut in Michigan

In the figure above, you will see root rot symptoms  on Chinese chestnut trees in Newaygo from 2016.  The black on the root collar is called the flame.  The is the diagnostic symptom of root rot.


We have a tendency to overwater chestnut. If it doesn’t get enough water it will die, but it can survive better than you think under dry conditions.  Water can be detrimental to the chestnut tree and it needs slopes or well drained soils to help it thrive.  If you are looking for orchard land, find land without water issues where adjacent land at a higher elevation doesn’t drain through your land.  Look for higher elevations and well drained soils for the best land. One of the best chestnut orchards in Michigan is nested about 800 feet while the land around it is more like 600 feet.






























Figure 2. Better photo of the trunk and how you have to cut away at the bark from trees at Newaygo.  Yes, we did isolate Phytophthora from this tree.