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Winning the Battles of Phytophthora in Your Chestnut Orchard

When someone we care about gets gravely sick, we are taken with sadness and an inner wish we could do something to help them out in their time of need. When there is a sudden onset of sickness that is beyond what we are able to handle ourselves, we turn to the 911 services for help. Chestnut trees can suddenly become ill too. The problem is there is no chestnut tree 911 service.

Chestnut tree infected with phytophthora
Chestnut tree infected with Phytophthora cinnamomi

One of the most devastating sicknesses for a chestnut tree is phytophthora. In a single growing season, a health chestnut tree can contract phytophthora, slide into poor health and die. Usually, phytophthora is a death sentence for a chestnut tree, but not always. As with humans, we look at the signs and symptoms being presented in the affected chestnut tree. We look at the bark, leaves, growth, and visually the overall presenting health. If you have just one chestnut tree, this visual evaluation is very difficult because you have nothing else to compare against. If you have a chestnut orchard, then you would have many other chestnut trees to compare with.

Before we get into the details of diagnosing and treating phytophthora, we have to make a differention between the two different phytophthora sicknesses in chestnuts. Phytophthora cinnamomi is also referred to as .ink disease. or .root rot.. The pathogen phytophthora cinnamomi (PC) is found just about everywhere in the USA. PC prefers heavier and wetter soils. The key word is .prefers., PC can be found in dryer sandy or even rocky soils, waiting for the right conditions, such as an extended wet period in the growing season, often occurring in early spring.

The second form of phytophthora is phytophthora ramorum (PR), also referred to as .sudden oak death.. Chestnut trees are part of the oak family so chestnut trees are highly susceptible to PR. The US Dept of Ag has a quarantine on chestnut trees to prevent the spread of the PR pathogen. PR is found in Northern California and Southern Oregon. Like PC, PR likes the cooler wetter conditions found it the coastal areas. Both PC and PR are soil based pathogens. Walking through an area where these pathogens are present is enough for them to be transported to new areas on footwear and even tires.

If your chestnut tree is suffering from an infection of PR, the outcome does not look good at this time because there is no known treatment for PR in chestnut trees. If it.s PC on the other hand, the tree might have a chance of surviving if the tree is cared for properly. Both PR and PC present in the affected trees have a similar presentation. There are early signs and late signs. If your chestnut tree is presenting the late signs, there may not be much hope for the tree. The early signs are often confused with other issues such as nutrient deficiencies. If there is an available history of the tree.s health and the growing conditions that lead up to the point the tree starts looking sick, then differentiation between a nutrient deficiency and PC or PR becomes much easier. Take a look at other chestnut trees within 100 feet of the tree under stress. Nutrient deficiencies are likely to be present in the rest of the orchard, where as phytophthora infections usually do not infect the entire orchard in a single season.

Late sign of PC infection
Late sign of PC infection

Here are some signs and symptoms of a PC infection: Leaves are smaller than normal, as much as 50% smaller (early sign) Leaves lack the deep green of a health tree, presenting a yellowing in the entire leaf (both early and late sign) Little or no new growth (both early and late sign) Very small buds or no buds at all develop on new growth (late sign) Bark at the base of the tree cracks and exposes the cambium layer (late sign) Tree experiences die back (late sign)

As you have just read there are just a few early signs and several more late signs of PC infections. Aside of the signs and symptoms, the recent history is very helpful and so is examining neighboring trees. PC can infect one tree and all the neighboring trees can remain unaffected. So the examining the neighbors may result in a failure to properly diagnose the problem. It does provide a basis for ruling out a nutrient problem, because a nutrient problem would very likely affect neighboring trees.

Chestnut tree infected with phytophthora
Phytophthora cinnamomi killed chestnut tree

Early and late signs and symptoms are like early and late to a party. If your early, helping out can help make the party even better. Arriving late to the party, well you know, might bring on the stares. So it is with PC, getting there early can help with bringing the tree back to full health. Get there late, well you might as well as put the tree down before the neighbors see your tree dying. No matter if it.s late or early in the infection, doing nothing might be a good thing because adding nitrogen to the soil will make things much worse. Putting nitrogen on a tree suffering from PC feeds the PC infection not the tree.

Now let.s turn to strategies to battle PC. Just like real battles there are three strategies available to the orchardist, offensive, defensive, and the wait and hide strategy, hoping the battle will pass you by. Here are some defensive strategies:

Don.t plant trees in soils conducive to PC infections (deep sandy loam well drained soils at least 2 feet deep are best) Don.t fertilize a tree presenting PC symptoms Drain and tile water prone parts of the orchard

And now some offensive strategies: Prune 50% of the tree back, allowing the reduced root capacity to feed a much smaller tree Only apply fertilizers to the orchard once the soil temp is above 60F at 8. deep Apply phosphite to the leaves and the soil at the base of the tree

Not a lot of weapons to chose from in battling PC. If there is one weapon one must chose, then the first one presented above is the choice .Don.t plant trees in soils conducive to PC infections.. But, if you have a tree with a PC infection, then it.s far too late for that choice. Next on our list are the fertilizer options. These are brought to us from the raspberry producers. There is one other not discussed yet. This new option is to make a raised bed or mound 18. high above the surrounding soils at least 4 feet across. This even works with getting a chestnut tree to grow in heavy soils. The bad part of this option is the chestnut tree will always do poorly even in the best of years. For the commercial chestnut producer, it.s better to just avoid using heavy and or wet soils.

Chestnut tree with burrs
Normal healthy chestnut tree

This article will not discuss draining and placing tiles in a field because local laws would likely limit this option. The phosphite option is still available but lacks good scientific evidence of controlling PC infections and is not well understood of how the phosphite helps to control PC.

Now that cutting the tree back is the last option in this list, it should be considered the last option. Does cutting a tree back that much or even more really help? Yes, it does help, and often results in the tree coming back to full health over the next two growing seasons. The problem is, the tree is already suffering and cutting it back may just kill it. Cutting a tree back this much presenting signs of a PC infection should only be done before the chestnut trees start blooming in early summer, because the trees still has stored reserves to recover. Sounds a little dangerous, doesn.t it? Consider it the same as a major surgery. Doing a major surgery on a very sick person carries much greater risks than on a healthy person.

Let.s get to the bottom line. If a chestnut tree gets infected with PC, is it a likely death sentence? From observations in many chestnut orchards, the chances of a tree surviving a PC infection if nothing is done, is less than 25%. If all the options are utilized, except for the phosphite option, the chances of survival can be as much as 80%. There is just not enough understanding of the phosphite option to provide a probable outcome.

Before closing, we need to discuss secondary infections. What is a secondary infection? This is when the host is infected with one pathogen and weakens the host and then a second infection from a different pathogen enters the host. For chestnut trees we can take the example of a PC infection and the intrusion of the shot hole bore. The shot hole bore carries a fungus that will very likely kill an already sickened chestnut tree by PC. If the tree was not already sick, the tree.s own healing response system can usually prevent a full infection of the fungus. It.s just not PC that can leave a chestnut tree vulnerable to a secondary infection, water stress from insufficient or excessive water can also leave a chestnut tree vulnerable to infections.


Contact Information:

Farm Location:
6160 Everson Goshen Rd
Everson, WA 98247
Ph: (360) 592-3397

Business Offices:
Washington Chestnut Company
6160 Everson Goshen Rd.
Everson, WA 98247
Ph: (360) 592-3397