Organic Control of a New Apple Disease: Marssonina Leaf Blotch

Progress report for FNE20-957

Project Type: Farmer
Funds awarded in 2020: $13,949.00
Projected End Date: 02/28/2022
Grant Recipient: Elderberry Pond
Region: Northeast
State: New York
Project Leader:
Louis Lego, Jr.
Elderberry Pond
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Project Information


Elderberry Pond is a certified organic farm in the NY Finger Lakes. We farm  35 acres of fruits, vegetables and pastured animals.  We market through farmers markets a country food store and fine dining restaurant on our farm.  In all of these markets the most important crop is apples.  We have about 500 trees including about 50 varieties including Heirlooms, American classics, and new disease resistant cultivars. Through innovations, some SARE funded, we are able to produce high quality apples with very limited use of certified spray materials.  In midsummer we noticed that many of our trees were losing leaves and by September some were completely defoliated.  (Figure 1) 



We began getting calls from home orchardists that their trees had lost all of their leaves.  We had NO idea of what was happening.  We did a thorough online search and discovered that there was a new, very devastating apple disease called Marssonina Leaf Blight- MLB.  The disease started in China and Korea, moved through Europe and was discovered in Eastern NY in 2016.  All the previous research literature, which we reviewed extensively, was from Overseas.  Much of this research indicated that the only the most modern chemicals offered any protection and that organic orchards would be decimated.  Fortunately, we found a few US researchers from Cornell and Penn State that were familiar with the disease and were excited to work with us as technical advisors to test potential cultural and OMRI approved amendments. Our orchards, they felt are ideally suited for these tests and agreed to support us and through outreach other growers.


Project Objectives:

Projective Objectives

This project will guide organic and sustainable apple growers who have seen or are about to see the devastating effects of Marssonina Leaf Blotch in their orchards.  We will describe early warning signs and timing (with leaf photographs and diagnostic test reports) leading up to tree defoliation.  We will also report on which of the 50 varieties of apples we grow here in upstate New York we have found to be the most vulnerable and most resistant in 2019 and 2020. Tests conducted in our three separate organic orchards containing some of the same varieties will show which chemical and cultural preventive measures we have found to be the most effective in combating the disease outbreak.   We will compare the treatments to those we and others have successfully developed and routinely use for apple scab, a similar weather related fungal disease that threatens sustainably managed orchards.  This will, I believe, be the first controlled and documented field evaluation of this disease in orchards of the type described here in the northeast.  With the likelihood of more weather related diseases ahead I believe farmers, as first at the scene, have an obligation to carry out such on farm research.


Problem and Solution

In June of this year we noticed that some of our apple trees were losing many of their leaves.  By mid-August some of the trees were bare.  We had no idea why and were most surprised by the fact that the disease resistant varieties such as Gold Rush and Pristine were the most affected. As the season progressed the situation worsened and many, but not all, of the 50 apple varieties had lost many of their leaves.   We also got many calls from local gardeners and home orchardists asking why their apple trees were all defoliating.  Some articles suggested the problem was apple scab.  We doubted that this disease outbreak was apple scab.  On a previous grant that we performed in 2012 (SARE grant FNE 11-722) Growing Scab Free Apples Without Fungicides, we studied this long existing orchard disease in detail and had virtually eliminated scab in our orchards through extreme orchard sanitization and a minimum sulfur spray program. Also, and more importantly, the defoliation  was the worst on disease resistant cultivars that had been scab free for the past 15 years.  Further on line searches revealed that in the last year or so a new apple disease, Marssonina Leaf Blotch , MLB Marssonina coronaria. had been discovered in the Hudson Valley in September of 2017 (reference 1) and in Pennsylvania (reference 2), authored by our technical advisor, Dr. Kari Peter.  The description and photographs in these Cornell, and Penn State Extension articles and other reviews exactly matched the symptoms we had observed.  Nearly all the other articles we found in our online search were from Korea, Japan, India and Europe where the disease has advanced rapidly devastating their small commercial orchards.  Many of these small commercial orchards, like ours, rely on simple broad spectrum fungicides such as lime, copper and sulfur for disease control which did not appear to work.   One reviewed article from Germany (reference 3), however, suggested that these chemicals might provide moderate control when applied early enough. We could find no US tests of the efficacy of these organically approved products!

It is generally agreed that the disease is propagated and progresses in much the same way as apple scab.  Spores overwinter as the fungus Diplocarpon mali in leaf litter but perhaps unlike apple scab on twigs and buds in the trees.  In the spring ascospores are released which jump to newly forming buds and leaves causing a primary infection.  These infections then produce secondary spores which further spread the disease. It appears that the disease shows symptoms and progresses much faster that apple scab, defoliating trees in early summer. The disease does not always scar the fruit, at least in early years.  The early tree defoliation however causes fruit quality to decrease AND more importantly weakens  the tree in preparation for dormancy. Some articles suggest that the only cure is removal of the trees.   

 Marssonina may be the most serious threat to organic and IPM apple growers in 20 years.  Apple scab causes blemishes on the fruit, but does not kill the tree.  Field tests need to be done to discover what cultural or low impact chemical treatments organic growers can use to combat this new devastating disease.  If low impact chemicals and or new cultural  practices cannot not be found to prevent Marssonina Leaf Blotch and the resulting defoliation quickly, it would be a serious blow to growing organic apples in the Northeast.   Getting a start on this effort is the purpose of this proposed project.

The approach we will take on this project is similar to that used on the apple scab grant.   We will use our three isolated orchards containing identical verities to test and compare the effectiveness of practices and treatments on specific varieties. The instrumentation and equipment developed for the Apple Scab grant in 2012 will be upgraded to allow more disease modeling. 

Using the three separate orchards, one as a no change control planting, we will determine the effectiveness of the following practices

Orchard 1.   Further eliminating leaf and litter infection sources through improvements in our High Efficiency Orchard Vacuum built on the scab grant and some additional ground sanitization techniques.

Orchard 2.  Altering spray plan to include an early season tree sanitization targeting overwintering MLB ascosporic inoculum.  To guide spray timing data on leaf wetness duration, we will use our existing  weather sensors and data loggers  and a new leaf wetness sensor to time sprays.   No changes from 2019 in this orchard to orchard floor sanitization.

Orchard 3.  Control Orchard  - No changes to sanitization or spray materials or practices from 2019.


Click linked name(s) to expand
  • Dr. Kari Peter, Ph.D.
  • Abby Seaman


Materials and methods:

Materials and Methods

As mentioned previously we have three separate orchards with some of the same varieties of trees in each.  To try to determine what changes need to be made to our orchard management we will test two changes in two of the orchards and in the third we will use the same practices we used in 2019 when the serious MLB infection occurred. The three orchards can be seen in the farm orchard plan drawing (figure 5).


Figure 5. Farm Orchard Layout
Figure 6. Test Orchard 1 in Early Winter


Orchard 1- Specific Tasks

Orchard 1 had moderate MLB, and very little Apple Scab in 2019.  The focus on further reducing scab and MLB in this orchard will be on orchard and tree sanitization.  Early in spring while the trees are dormant we will work on the vacuum system. While it has worked well for apple scab there are still visible small dust particles escaping the leaf collection container that may include MLB spores.  We will replace the current leaf container box (figure 7) with 3 new fully contained bags that let air escape but filter out more of the dust.




We will then mow and vacuum the orchard floor thoroughly and treat areas under the trees with either lime, or burn them with a flame weeder.  In addition, Images from the European Journal of Plant Pathology  (figure 8) suggest that the MLB spores may overwinter in small cracks or crevices in the trees.  In this orchard we will spray the bare, dormant trees with an  OMRI approved sanitizer such as oxidate (hydrogen peroxide) which should penetrate cracks better than sulfur.


Figure 8- Disease Cycle -Unlike Apple Scab, Condia from MLB can overwinter in twigs and branches



We will also purchase an Omega  leaf wetness sensor which we can use with our current Omega data logging system to predict possible infections and spray sulfur only as needed  for apple scab in a  minimal spray program.

 It is our hope that these changes to our sanitization program solve the MLB problem and avoid the need for increasing the amount or type of spray that we need in the orchards. This would also be the preferred system to pass to other organic growers and home gardeners who are calling us for solutions to this new problem.


Orchard #2 Specifics  Tasks

In this orchard we will evaluate whether a spray system more intensive than our minimum spray program used in orchard 1 is of benefit in controlling MLB.  This orchard is divided in two by a stream.  In both sections we will use the same enhanced ground sanitization as in orchard 1.  The difference in this orchard will be a more intensive spray program with sprays based on timing rather than on modeled disease predictions.  The timing between sprays will be approximately every 10 to 12 days, as many of the chemical spray manufactures recommend.  Also in this orchard we will compare sulfur (Microthiol Disperss) on one side of the creek (Orchard 2A) to an OMRI approved copper based spray (Cueva) on the other side of the creek (Orchard 2B).  Each side has some of the same apple varieties including disease resistant and conventional varieties.  If we find a significant difference in the defoliation caused by MLB in these two orchard sections, we can assume that the difference is the result of the difference in spray materials.  If both sections are less impacted by  MLB than in orchard 1, the implication is that a more intensive spray program than our minimal program along with our enhanced vacuum cleaning and dormant tree sanitization is now required.  This would not be good news since treating MLB would take us back to the aggressive spray program that was required before we devised the vacuum sanitization system. This would be particularly problematic for home orchardists.



Orchard 3 Specific Tasks

In this orchard we will use the same orchard floor treatments and minimal spray program used in 2019. This “control” orchard will be a reference to compare the impact of the other spray and sanitation techniques we try.  No costs will be charged to the grant for the normal maintenance of this orchard.  Only recording and documenting the results for comparison to the test orchards will be charged.

As part of this project we will go through all of the recorded images of varieties most affected, and least affected by MLB in 2019 and their pedigree plots to see if there is any possible correlation between the pedigree and vulnerability of the variety to MLB. (Figure 9).  This was highly recommended by our Technical Advisor, Kari Peter from Penn State who thought it would be valuable to other growers and researchers.  Also as figure 8  suggests,  the waxiness of the leaf of certain varieties may be related to that varieties MLB susceptibility, with waxy leaves being less susceptible either by blocking spores, or we believe, by possibly reducing leaf wetness duration..  We will see if in our proposed orchard trials these correlations can be observed.

Figure 9. Jonafree and Its Pedigree- One of the most MLB resistant in 2019

We will work closely with our technical advisors from Penn State and Cornell to interpret the observations we make in the orchards and the significance of our observations.

Degree of Damage

We will compare the MLB damage between the same varieties in each orchard.  While it is difficult to measure the degree of damage we will use the a scale of 1-10 similar to the one used by Bohr & Mayr  in the MLB evaluations in 2017 in Germany (Reference 3)  .  The scale we will use is shown in figure 10.   We will also document the comparisons with photographs.  We should emphasize that we could find no such controlled field trials of this disease in the US.


Research results and discussion:


Research results and discussion:

We began the year pretty much as planned. In late spring after some early tasks in each orchard had been completed it became evident that the 2020 season in our area had been and would probably continue to be too dry ( fig.11) to cause a serious Marssonina Leaf Blight (MLB) infection.  This would in turn make it difficult to continue our research on finding organic remedies to this disease in our orchards.

Fig 11. Rainfall in Inches per Month 2019 vs 2020

In mid-August we contacted the NE SARE program office to request a 1 year no additional cost extension to our program.  The following discusses results of the work completed prior to the extension which in one instance proved to be very important to the project and to the planned work for 2021.

In orchard 1 we attempted a first quick leaf cleanup using the high vacuum “fast vac” system on our Ferris mower but the grass and leaves were too wet. A late fall or early winter mowing would have helped the process by reducing the cut grass volume before much of the leaves had fallen. We did do such a fall mowing at the end of 2020 in preparation for 2021 spring cleanup.

On 4/15 we sprayed all dormant tree trunks and branches in orchard 1 with Oxidate 2.0 as planned, to eliminate overwintering MLB. The spray that fell to the ground surrounding the tree which may have helped sanitize any leaf litter still present. We again went over the orchard more thoroughly with the vacuum system on 5/3. On 5/14 we sprayed all the trees with Microthiol Disperss and Nu film P spreader/sticker.  The trees were at full green tip and close to early bloom. During the remainder of the season no further fungicide sprays were applied to this orchard, and there were very few indications of either apple scab or Marssonina in any of the 20+ varieties in this orchard. This was in part due to the lack of rainfall during infection periods as discussed previously only 7.9″ vs. 18.4″ the previous year (fig 11). 


In Orchards 2E and 2W we vacuumed the orchard floors thoroughly and as in Orchard 1 and sprayed tree trunks and lower limbs with Oxidate 2.0.   In orchard 2W  THERE WAS ONE ADDITIONAL TREATMENT DONE WHICH TURNED OUT TO BE VERY IMPORTANT. In this orchard we selected a few varieties of trees which had two trees in close proximity that were seriously defoliated in 2019 by MLB.   The varieties we chose were Goldrush, Pristine and Keepsake.  In 2020 we had very little MLB in any of the orchards including Orchard 2 which had those varieties that we paired for testing, with one important exception, Goldrush.   In August, the tree that had not received the Oxidate bark and limb spray began to show signs of MLB and by November was totally defoliated (fig 12).













The tree that had received the Oxidate Bark Spray remained free of Marssonina Blight throughout the season and produced near perfect fruit (figure 13).



While this is only one test on one variety in one season, I believe it was dramatic enough that more of these comparative tests must be included in in the second year, 2021 MLB project.  We have also reported the tests on Goldrush to several other northeast organic apple growers as well as our technical advisors hoping that they would perform one or more of these two tree comparative tests in their own orchards in 2021.


In Orchard Three  we managed the trees as we had done in previous years with through cleanup of fallen leaves and a mid-May green tip spray of sulfur.  No bark or lower limb sprays of Oxidate were performed in this orchard.  Throughout the dry 2020 summer the trees remained nearly free of apple scab and MLB.


With the exception of Goldrush the varieties listed below (figure 14) present in one or more of the orchards and had various degrees of MLB infections in 2019 had minimal leaf or fruit disease in 2020.


Research conclusions:

Although the very dry weather led us to request an extension of the project into 2021, we did make some important discoveries that we think will shape not only our own project work in 2021, but hopefully will extend and perhaps validify the findings by other researchers we have reached out to test this significant new treatment for MLB.  This treatment involves early spring saturation of trunk and lower limb bark with a strong oxidizer such as Oxidate 2.0. We will continue during 2021 to extend the trials of this technique and to carry out the other approaches outlined in our original proposal.

Participation Summary
2 Farmers participating in research

Education & Outreach Activities and Participation Summary

1 Consultations
1 Curricula, factsheets or educational tools
1 Tours

Participation Summary:

5 Farmers
2 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

In December we sent out letters to several organic apple growers and to some educators which were either advisors on this grant or people we discussed the grant with which contained the information described in the previous section on the apparent success we had with Oxidate trunk and limb treatments in reducing Marssonina Leaf Blight on Goldrush apple trees.  Due to the extension of the grant into 2021 , and the lack of many conferences this year any outreach presentations or articles/press releases were delayed until next fall and winter.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.