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Orchard Cleanliness Reduces Apple Scab

The following was authored by Louis Lego of Elderberry Pond,  with assistance from Brian Caldwell of Cornell University.


Apple Scab is perhaps the most devastating of all disease or insect disorders impacting apple production in the Northeast. While there are many new scab fungicides including some with systemic and reach-back capabilities (can be applied post infection), none of these spray materials are permitted in organic production. In addition the cost of these fungicides is often prohibitive in conventional orchards. One of the fundamental premises of apple scab control whether organic or conventional, is that orchard floor clean-up at the end of a season can help prevent serious infection the following year. This is based on the fact that the scab fungus, (Venturia inaequalis) overwinters only on fallen debris. So the question that you might ask is, What if you cleaned up ALL debris through brushing, vacuuming, applying early compost to decay remaining bits of leaf and fruit debris? Could you eliminate apple scab in the orchard and not have to spray fungicides at all? Or alternatively would there be some residues in adjacent fields or orchards that would move into your orchard and cause infections. The purpose of this project was to try an extreme cleanup in a small 2 acre orchard that was somewhat isolated from other orchards on our farm that are managed organically. This orchard was thoroughly cleaned, compost applied in spring to accelerate ground leaf decay, and early, vigorous pruning to allow air and sunshine to infiltrate the orchard (a standard organic orchard procedure). The results were very encouraging even in a very wet year with many scab infection periods. The test orchard (with no fungicide sprays) had less apple scab than the organically managed orchard where 5 sulfur sprays were applied. Comparisons were made on the same varieties (Macoun, Empire, Honeycrisp, Fuji, Red Yorking and Northern Spy). The results were encouraging enough that we have purchased a large vacuum system to begin applying the ultra clean practices demonstrated in this project to all of our orchards. The remainder of this report details the methods used and the results obtained.


1. Goal

The goal of this project was to determine if Apple Scab (Venturia inaequalis) could be controlled or even eliminated in a two acre isolated orchard by using three processes aimed at removal and/ or destruction of overwintering fungus on the orchard floor. If all or nearly all of the overwintering scab fungus could be destroyed or removed there would be no primary or secondary infections and no need for fungicide sprays during a growing season. This could result in saving the labor and material costs associated with from five to ten sprays in a given season. It would also be very good for beneficial insects including bees which can be harmed by fungicide sprays both conventional and organic (sulfur).

2. Farm Profile

Elderberry Pond is a 100 Acre certified organic farm. In any year we have about 35 acres of certified organic fruits, vegetables and pastures. Our mission at Elderberry Pond is to use the farm as a model of how sustainable agriculture can operate to fuel local food systems. The farm is operated by my wife and I and our son Christopher. We hire a few summer students and interns to work with us during the summer months. We market our produce and meats through an on-farm country food store, at local farmers’ markets and through a fine dining restaurant “The Restaurant at Elderberry Pond” which is located in a woodlot overlooking the farm. The farm produces a very wide variety of produce and meat to meet the needs of the store and restaurant. All of the salad greens, vegetables, potatoes, dessert fruits and many of the meats for the restaurant are grown on the farm. Apples are one of the most important crops grown on the farm. We grow about 100 varieties of apples. Because we believe orchards serve many purposes on a diversified farm our fruit trees are not planted in large single blocks, but rather are scattered around the farm in long thin plantings serving as windbreaks and as habitats for beneficial insects as well in small blocks that can be used for pastures and shade for livestock. Because our orchards are spread around the farm, and we have summer help working it is important that we find ways to control insects and disease using as few organic spray materials as possible. With this objective in mind we have tried each year to have one on farm research grant aimed at methods to reduce or eliminate the use of sprays. We have pursed spore exclusion, unique trapping techniques, and in this case a way to reduce or eliminate overwintering disease spores. These on farm research efforts are very important to the operation of our farm and to our mission of improving and promoting sustainable agriculture practices.


Along with my own work on this project, my son Chris helped with orchard mowing, flaming and pruning, and our Technical Advisor, Brian Caldwell advised us on issues of scab overwintering and the vulnerability of specific cultivars.

4.Project Activities

The project followed our proposed approach with a few adjustments that were due to the very snowy fall and the wet spring we had in upstate New York… the wettest on record. The very wet spring was good in a sense because the disease pressure was extreme, with over 7 scab infection periods. We started the project in the beginning of April with orchard floor cleanup. We found that our large three blade mower with hi lift blades was not picking up much of the debris. This was due to the fact that the ground was soaked and the leaves were stuck together. We then tried a small “Billy Goat” we rented from Taylor Rental. This was a much smaller machine with more suction per unit area. It worked better, but was still not doing the job. We then tried a small (20”) rotary mower with an ultra- lift mulching blade and a bagger. With a blade height setting of 3 inches, this worked well, sucking everything except the earthworms from the orchard floor. Doing the 2 acre orchard with a twenty inch mower took many hours (days), particularly since the bag filled every 10 to 12 feet. The result however was really good. Except in the very close proximity of the trees, there was almost no leaf debris remaining. See Figure 2. In the vicinity of the tree trunk we carefully flamed the remaining debris with a hand wand flamer.

Following Orchard Floor Cleanup we began pruning. The idea here was to prune the trees early and more aggressively than we normally would. The purpose of this aggressive pruning is to allow more sunlight penetration onto the well cleaned orchard floor and to permit more airflow through the orchard. This is exactly opposite to what happens in a conventional block orchard or in a high density orchard. An example of our pruning is shown in the before and after photos of.

The final Step in the process was to spread compost on the orchard floor. We used a combination of composted cow manure (Fessenden TLC) which we put in the vicinity of the tree and pelletized chicken manure (Kreher) which we used in the rows between the trees. Both are approved for Organic production. In this system the compost serves three purposes: 1. Help to decay the remaining debris which may contain overwintering scab spores 2. Provide spring nutrients for the health of the trees 3. Provide for very rapid growth of the orchard grass early in the spring This third advantage was one that was discovered during the project. With the grass mowed very low during the pre-growth period in the spring, and then fertilized, the spring rains in early May cause an amazing spurt in growth of the grass. I believe this rapid grass growth helps to shield the new spring growth on the trees from ascospores that may be released from the fruiting bodies of any remaining overwintering fungus. We allowed the grass to grow until the spring primary scab infection period was over. To provide for a comparison of the results of the scab infection rate in this orchard we had a second orchard plot which we maintained using standard organic orchard maintenance (5 sulfur sprays). This second control plot had many of the same scab susceptible varieties as the test orchard including Macoun, Honeycrisp, Fuji, Empire and Northern Spy as well as inter-planted disease resistant varieties such as Pristine and Jonafree. We have traditionally mixed scab free varieties with scab susceptible varieties to decrease the overwintering infected leaves in the orchard. There is however some risk to mixing scab resistant varieties with the Vf M.Floribunda gene resistance gene with standard cultivars. The risk is that a rare mutation of the normal scab fungus could infect the resistant variety and cause the breakdown of the resistance in that cultivar.

5. Results

The results of the test were fairly dramatic in one of the worst scab years we have had in 20 years. We began looking for primary scab infections when the leaves were just beginning to form on the early varieties. Early in the season there were no signs of infection on any of the trees in the no spray test orchard or in the organically managed orchard. We believed that we had prevented primary scab infections in all orchards, however in August we began to see both leaf and fruit lesions on Pink Pearl, Caville Blanc, and Summer Treat in the sulfur treated organic orchard. These very susceptible varieties were not in the no-spray test orchard. It was not until September that we found very small scab infections on Macoun in both the test and organic orchards.

The small scab spots were few and far between and were mostly in the line of trees that were adjacent to the clover field just to the east of the orchard. It is possible that some overwintering leaves had been trapped in the clover and spores from these infected this first row of trees. In the main part of the no spray orchard there were no visible scab infections. We cut branches from similar sized trees of the same variety in both the no-spray and the sulfur treated orchards, and compared them for visible infections. In all varieties that were in both orchards (N.Spy, Honeycrisp, Macoun, and Fuji) there were slightly ( about 5%) fewer visible infections in the no spray orchard. This may have been the result of the badly infected Caville Blanc and Pink Pearl trees that were present in the sulfur treated orchard and not in the no-spray test orchard. In any event I now believe that extreme sanitization may be the best approach to scab control in an organic orchard. It may be that these very susceptible heirloom varieties should be planted in a separate orchard and managed differently. I have begun to reconsider mixing the varieties of differing susceptibilities to lower overall infected debris on the orchard floor. Perhaps separate orchards ,each with different management practices is the best approach.

6. Conditions

As mentioned previously the spring/summer of 2011 was one of the worst for scab infection periods. Our first infection period was on April 26th when we had unusually high temperature of 67 degrees and a leaf wetness period of about 10 hours. Then on May 16th and 17th we had temperatures in the high 40’s and a leaf wetness period of over 28 hours. Figure 5 shows the timing of these infections. There were of course many more scab infection periods but all of these were following the primary infection period. The primary infection period is usually over by approximately 1000 degree days at Base 32 degrees. This occurred on about May 20th at Elderberry Pond. If all of the primary spores were expended and no primary infections occurred there would be no secondary infections. This was not the case in our orchards. Our scab infections, although minor were most likely caused by secondary infections following June 22nd, from a small number of unobserved primary infections.


The Time it took us to thoroughly clean the two acre orchard with a 20 inch rear bagger mower offset any cost advantage from not having to apply 5 sulfur sprays. Having said this the time in the late fall and early spring when this cleaning is taking place is not as busy a time for us during April, May and June. I believe that with a more efficient vacuum cleaner we can greatly reduce the cleanup time.

8. Assessment

This project has convinced me that extreme cleanup is the most practical and sustainable approach to organic orcharding. I believe that the continued use of large numbers of copper and sulfur sprays will not work in the long run. I also have come to believe, in part based on the results of this project, that it may be better to separate orchard plantings by scab susceptibility. Perhaps all scab resistant varieties should be planted together and managed with no scab sprays. Those varieties that have very high susceptibility like Caville Blanc and Pink Pearl should be planted in a separate orchard and managed as required using sprays to minimize resistant fungi development. All other varieties (with moderate scab susceptibility) should be managed using the techniques I have tested in this project.

9. Adoption

We do definitely plan to use the approach we tested on this project on our orchards. To this end we have purchased at our own expense a used leaf collection bin and vacuum fan which we have just finished adapting to an older Gravely Lawn Tractor. The Lawn Tractor Deck was modified to take high lift mulcher blades and feed the vacuum fan through a large flexible hose. See figure 6. The plan is to use a smaller zero-turn mower to lay the debris from near the trees to a middle isle where the vacuum machine will pick them up. We are also configuring a manually held hose attachment to the vacuum machine to use directly under the trees. We will continue to spread compost on the orchard floor for decomposition of remaining leaf debris, and to fertilize the trees and grass.

10. Outreach

We are scheduled to present the results of this project at the NOFA Organic Research Symposium in Saratoga Springs, NY on Friday, January 20th, and at the PASA Farming for the Future Conference at Penn State University on Saturday, February 4th. We will also present and demonstrate the extreme cleanup process at our 2012 Organic Orcharding Class here on the farm in April 2012. The extreme cleanup method of scab prevention will also be described to those attending our weekly farm tours at Elderberry Pond.

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Dwarf Rootstock Mortality in Cold Climates

The following is good reading when considering dwarf rootstocks in the colder climates. This is one of the many studies done through the US SARE system. (Look for more SARE project posts on our website.)

Authored by John O’Meara of O’Meara Family Farm with assistance from Renae Moran (U of Maine) :


This project attempted to determine the usefulness of dwarf rootstocks in a zone 3 orchard. Conducted over the course of four years, this project compared the growth and survivability of three dwarfing rootstocks with a standard, cold-hard rootstock normally used for extreme climates. Ultimately, the dwarf rootstocks did not survive well and generally showed poor performance at this location. The results of this project point to Antonovka rootstock as the most viable rootstock in a zone 3 location, especially when the orchard is under organic management.


This project aimed to test new dwarfing and semi-dwarfing rootstocks in a zone 3 climate. Rootstocks G. 41 (dwarfing) and G. 935 (semi-dwarfing), developed at the USDA/ Cornell University Apple Rootstock Breeding Program in Geneva, New York, could offer the hardiness required of a zone 3 climate combined with the benefits of a dwarfing tree. Dwarfing trees could allow the northern grower the advantages of fruit-bearing precocity, ease of harvest, and high orchard density. In addition, G. 41 and G.935 have been bred to be resistant to serious apple diseases, which may make them particularly valuable to growers in various climates. To test the hardiness of G. 41 and G. 935, this project compared the survivability and growth of the two new rootstocks to Bud. 9, a commonly used hardy, dwarfing rootstock, and Malus antonovka, a hardy standard-sized rootstock.



In the spring of 2009, we grafted 200 trees for this project. Liberty scionwood was used for all 200 grafts. 50 grafts were done on G.41 rootstock, fifty on G.935, fifty on Bud. 9, and fifty on Antonovka. The G. 41 and G. 935 rootstocks were provided by Dr. Fazio. The Antonovka and Bud. 9 rootstocks were acquired from Lawyer Nursery in Montana, the usual source of our rootstock. Success rate of grafting was recorded in the beginning of the first growing season. In the fall of each year, the trees were protected from rodent damage, in preparation for winter. During four growing seasons (2009,2010,2011, and 2012), the trees were weeded. They were also monitored for vigor, survivability, growth, and the presence of disease.


Grafting success: The trees were grafted in April, 2009 and planted on May 4th, 2009. As of June 4th, 2009, the following numbers of grafts were successfully growing, by variety. G.935 16/50 G.41 30/50 Bud 9 13/50 Antonovka 35/50 The G. 41 and Antonovka had significantly better grafting success than the other two varieties. Although every effort was made to acquire rootstock of comparable size and quality, the G. 935 was of larger diameter than the other rootstocks, requiring that the grafting was done a little differently. In addition, the Bud 9 rootstock lacked vigor from the start and did not grow well in general. Although these initial problems may have affected grafting success, we proceeded with the project with the belief that the project would still provide important data about the survivability and overall growth of the rootstocks in question, over the long term. Fatalities: Some rootstock died during the course of this project. As stated above, the Bud 9 rootstock arrived from our supplier nursery in poor condition. An unusual percentage of those rootstocks were dead on arrival or perished the first season. Deaths among the roostocks: 2009– recorded September G.935 5/50 G. 41 2/50 Bud 9 12/50 Antonovka 0/50 2010—recorded August G.935 42/50 G.41 13/50 Bud 9 25/50 Antonovka 2/50 2011– recorded August G.935 2/50 G.41 20/50 Bud 9 11/50 Antonovka 0/50 Total fatalities– 2009-2010 G. 935 49/50 (98%) G.41 35/50 (70%) Bud 9 48/50 (96%) Antonovka 2/50 (4%) Total fatalities– 2012 G. 935 49/50 (98%) G.41 47/50 (94%) Bud 9 48/50 (96%) Antonovka 2/50 (4%)


Clearly, the dwarfing rootstocks have displayed some serious problems during the course of this project. Although the Antonovka performed as it has for several years on this farm, the dwarfing rootstocks suffered severe problems of survivability. One cause of this may have been a weed problem that developed in the nursery during 2009. Quack grass became more prevalent in the nursery and possibly inhibited the vigor of the rootstocks in general. The more vigorous Antonovka was more able to compete with the weeds. On the other hand, the rootstocks that did survive performed well, indicating that weed pressure may not have been the major problem. Our advisor, Renae Moran, has expressed the opinion that weed pressure is probably not the primary cause of the fatalities among the dwarf rootstocks. Severe winter weather is a problem for fruit nurseries in our climate. This project was intended primarily as a test of the winter hardiness of these dwarfing rootstocks. Because the winter of 2009/2010 was one of the warmest winters in our location on record, as seen in the temperature log, and cold winter temperatures would not seem to be the cause of the high mortality of the dwarfing rootstocks. The winters of 2010-2011 and 2011-2012 have also been moderate in New Sweden. The problem may be tardiness in hardening off among the dwarfing rootstocks. Although the winters have not been very cold, G.935 and G. 41 may be slower to harden off in fall; the fall temperatures of Aroostook County may be causing a higher mortality among rootstocks not adapted to a zone 3 climate.

2009 Daily temperature log

2009 was an unusual year in northern Maine, weather-wise. April and May were unusually warm and almost incessantly windy. June and July were exceptionally rainy. Low and high daily temperatures were recorded daily 2010 also had some unusual fluctuations in weather. There were long dry spells during the summer but no exceptionally cold weather during winter months. 2011 was the wettest summer on record in Caribou, Maine. Although the exceptionally wet weather may have caused even more problems among the dwarfing rootstocks, the Antonovka were unaffected. During 2012, the dwarfing rootstocks used in this project continued to perform poorly. Only 1 G. 935, 3 G. 41, and 2 Bud 9 survived, as of October 2012. In contrast, only 2 of the 50 Antonovka rootstock have died since 2009.


This established that though the rootstocks in question may have utility in other locations, they did not serve well or succeed in our northern, organic orchard. The Antonovka rootstock outperformed all of the dwarfing rootstock in this project. Although there are disadvantages to using standard rootstocks, the dwarfing rootstooks tested over the past four years did not survive well enough to be viable options in our orchard.

The results of this project point to Antonovka rootstock as the most viable rootstock in a zone 3 location, especially when the orchard is under organic management.


An article on this project has been written and submitted to Farming magazine for Spring 2013 publication.

Northern Apple Rootstock Future Recommendations

Although the dwarfing rootstocks tested in this project did not do well in our orchard, our results point to the need for more testing in more locations and in different conditions. Perhaps a slightly more temperate location would allow for more survivability among the dwarfing rootstocks.

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Newly Grafted Trees

Young grafts should be treated closer to vegetable starts than to trees. A nursery bed for that first year, at least, is required. Although the tree will require different environmental and nutritional needs than an annual, they do need the same sort of babysitting. Consider water and warmth as the “fertilizers” of first importance. This latter point is all to often left out of the equation. This also means keeping the humidity up, especially if the union is not healed so well. (Drying out the scion may not simply kill it, it may be just crummy growth). Also, make sure it is the growing conditions and not the grafting procedure that is causing slow growth. This especially means aftercare for proper heal. When they are growing, give them the attention you would give to your little tomatoes, including mulching and weeding.

There will be a disconnect in how the baby is treated in this first year or two, and how it will receive nutrition as an adult. Later in life in a healthy system, it will do well with gradual release through organic matter, in conjunction with good mycorrhizal fungal connections. Now, in a bed that has been prepared with forethought (fungal connections partially in place) and living soil, good growth is possible. Even in this situation, some supplementation is helpful. A foliar application is great, but a sustainably derived fertilizer in that bed is a good idea as well. They benefit from a bit of nitrogen which, being easily available in a mineralized form is an easy one, as is K. But, P and other micronutrients really should have been developed in that living soil. It is when the quick fix is needed that growers turn to industrial farming methods like triple superphosphate, miracle grow and 20 20 20 .

Having done this quite a bit commercially, I find that that first year never really is all that spectacular for growth, whether that is seedling plants or grafted fruit trees. I think they are pissed from being moved around and violated, and they need to be at peace again. That second year is always awesome, for most. But, if the soil is a mess and it is too late to fix it, foliar sprays, watering on time, and keeping things in the low 70’s will give the best growth rates.

If the little guys are stunted in that first year or two, it will take a few more to get things back on track, in my experience. That said, a small tree is not always a poor tree. (Charlie Brown knew this) As long as it is healthy, slower can also mean denser and more resilient wood. I would put our smaller gritty trees up against the overly succulent fertilizer pushed trees any day of the week.

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Ask the Farmer : Tree Irrigation ?

Do you see many orchards around here choosing to irrigate?

Irrigation of course, can mean a lot of things. What is being asked here I think is whether or not a constructed system is put in place to deliver the water.

Irrigation, as in drip-line, is used for high density dwarf systems. In these arrangements, whether they cultivate or not, it is usually recommended due to the meager root system. Trees using size reduction rootstocks (dwarf), require a good deal more pampering with respect to water. Traditionally this was delivered through open canals, overhead sprinklers, etc. Modern techniques include soil drenching through plastic emitters in miles of plastic tubing. It is an absolute must in many of the dryer regions of the northwest and California, but is popular throughout the country.

In the wet northeast, with standard  trees it is unnecessary. Trees obtaining their natural large stature will have roots mining for water over a very large area. Roots can extend meters down and in circumference at least twice the distance of the canopy. This means resilience during dry spells, and buffering against extreme cold.

Irrigation can confine roots to the pampered area in many cases. If the rooting mass is confined to shallow, smaller areas due to trickle irrigating, later stresses like cold or drought can lead to mortality. The mechanism here (and backed up with numerous studies) is the tendency for roots to amass in areas of ideal culture. That is, where it has good nutrition and soil moisture content. While this is good for the tree in general, it does limit the yardage the roots will occupy. This is pronounced if the outlying area is dry. Roots do not really grow toward ideal soil, they just don’t proliferate where it is poor. An example of the possible danger is when irrigation is confined to a shallow depth by continuous light applications. Roots will be largely clustered in this same shallow zone. In colder areas, this can lead to root damage or death . It can also have such consequences in warmer, dryer areas if there is a pause in irrigating (ie- broken lines or power outages).

Some alternatives include:

  • Increase the organic matter in your soil. Fully composted materials are advised if you are incorporating it directly.
  • Surface application of organic materials. This is the place to put the coarser materials, and higher carbon detritus. If it is a continuous application, we call it mulch. Bark, hay, straw, leaves and wood chips all fit in this category.
  • A 5 gallon pail of water really isn’t all that heavy. At 8 pounds a gallon, that’s 40. One in each hand (filled 4/5 so it doesn’t spill on you) is 64 pounds. That’s all you need to deal with during the occasional drought for your young tree.
  • Grow standard trees. These are those with a natural seedling rootstock that will let a tree grow to its full size. They can be pruned to be less tall and still have a large canopy and extensive root system. Think of this route as raising self sufficient children.

We suggest watering during that planting year, especially during dry spells, for better growth. Sandy soils of course will need more attention than heavier ones. Mulching is a great way to conserve that moisture ( keeping  it away from the trunk) and do it initially after the soil is wet.

Here is something to consider : The US Geological Survey posts on their site that a mature oak can transpire 40,000 gallons of water in a year. That’s one tree. Now, an apple tree is a whole lot smaller than an oak, so in the interest of fair play, let’s reduce that figure 40 times. That leaves us with 1000 gallons for a mature apple. However, if the tree is transpiring that much as water, it must also be absorbing  more to use in metabolic processes. Then there is the issue of delivery versus root uptake. That is, the soil must contain more than this amount of water to begin with. Irrigation through precipitation or human intervention must exceed the volume absorbed by the tree. To make an impact, it would seem a very large volume would have to be delivered indeed.

In conclusion, a plant with a small root system will require a good deal more attention as regards water. This lines up nicely, since a small root system stands the chance of benefitting from the amount of water we are likely to be able to deliver. This is why farms tend to irrigate their high end vegetable plots but not irrigate hay fields and cider orchards.

Water is the single greatest and most overlooked of fertilizers for plants. Time and money are the single greatest commodities of the human being. With proper decisions, nature can do a good deal of the work for us.

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Wasp damage diagnosis

Characteristic damage of fruit from wasp species. This was created from yellow jacket wasps, but similar damage is caused by bald faced hornet and various other wasps and true hornets. Additionally, beetles (ie japanese beetle) and chafers can cause excavated cavities in the fruit like this. Although any loss to the crop is undesirable, these types of attack are often within acceptable tolerances.

Damage to apples from Yellow Jacket Wasp
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Cold damage to Roots

It should be understood that plant roots and aerial portions of those same plants vary in their resistance to cold damage. Apple tree roots for instance, can be more than 60 degrees (F) more susceptible to damage or death from cold than their above ground counterparts. The reason for the difference is still under study, but some interesting information is available on the subject.

A Cornell study in 1921 shed some light.  Apple and pear trees were manipulated as to have their roots under different exposures to soil, oxygen, and light. By allowing the tree roots to be exposed (above the soil), a physiological transformation of the roots occurred. The excavated roots soon took on the appearance of trunk and other above ground parts. Roots that were uncovered many months before cold temperatures arrived showed no damage at temperatures of at least 3 degrees F. Roots uncovered directly before were killed at 13 degrees F. It was unclear to the researchers if roots could eventually attain as much resistance to cold as normal aerial parts (ie- trunk and branches).

The same aforementioned  study showed that trunk sections can undergo a reverse type of transformation. Fameuse trees planted were planted deep enough to have about 10 inches of scion covered with clay soil. They grew in this condition for a full season, were dug and then exposed to 3 degrees F. All tissue was killed below where the soil line existed. Control trees of same cultivar and grown with all scion tissue above soil showed no damage at the same temperatures. This shows a regression of cold hardiness resistance of the same type of tissue, when covered with soil for a certain period.  There is evidence also that the more (ie- deeper) the material is buried, the less cold resistant it becomes.

The type of soil does apparently have bearing. In a 1922 study, Jonathan apples planted a foot deep in sandy soil and later excavated showed no damage to the parts in question at 2 degrees F. In the 1921 study the soil type was much heavier (higher density clay material). A similar test showed no damage on parts as low as -15 degrees F.

Older roots generally are more resistant to cold than finer, younger specimens.

This can be of practical importance in that growers can prevent any root excavation in their practices when said practice is approaching cold weather. This can happen during cultivation, raking, or mulch redistribution. It also means that older roots that have been exposed to the surface for a long period are likely not to be easily damaged by cold temperatures.

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Rootstock Crowding Study

I wanted to bring attention to a study we are doing at Walden Heights. In both research and direct observation, there is evidence that crowding of root systems leads to some dwarfing effects. Apples in particular tend to avoid growing in the same soil regions that other members of their species do. ( Atkinson D, Naylor D, Coldrick GA (1976) The effect of tree spacing on the apple root system. Hortic Res 16: 89-105 ). Additional consideration is that direct competition of many other species in the vicinity should lead to an overall size reduction. By creating a full block planting, roots will be forced to compete 360 degrees.

We have planted two sections to standard stock apple, one as an 8×8 foot grid, one as an 4×8 foot grid. We also, for comparison have standards at 15 x 15, and 30 x 30. We also have apples (part of another test) in a high tunnel at 8 foot spacing. Since we alot of scionwood collection for the nursery, if the fruit production is, well, unfruitful, there is still merit in the exercise. We are forced by necessity since we need to find room for what is closing in on 500 varieties, without resorting to dwarf stock or excessive topworking. It gives us an opportunity to run such a test without risking too much. We will keep everyone posted on the progress. There are about 500 trees in the two blocks, of 6 standard rootstocks and roughly 300 scion varieties.

Obviously precocity isn’t necessarily being addressed, at least at first glance. Since stress often leads to early bearing, who knows. If excessive pruning is needed in the early years, this may actually delay bearing. Our goals here have never been for rushing the crop- thats what berry bushes are for. Tree longevity and low maintenance plants are. If we can couple this with a tree that can more within reach for spraying, harvesting and scion collection, it may have a place in many a farm plan. Not as a replacement, but as an addition to the overall system.

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Dwarf Apple Trees and Cold Hardiness

For those interested in planting a dwarf apple orchard in the cold climates of North America:

Walden Heights is zone 3 NE Vermont at 1700ft, and has seen -40 this decade. The lower snow cover and temperature swings lately will likely test the marginal species here.  Of the dwarfing stocks we have only tried in any real way the bud 9, since in literature it was touted as the hardiest commercially available dwarf stock. We did plant and are watching some bud 490, bud 146, bud 233 (and I think 491 is out there somewhere). 

The bud 9 trial (over 100 grafted trees in 2002) has been a near total failure. In terms of their susceptibility to the climatic conditions here they are third rate. This doesn’t necessarily point to cold temps  as we have not witnessed any dramatic tissue damage. What I am seeing is classic “failure to thrive” syndrome. When we trial things here, we treat them as the average homesteader will, and like we treat our standards. Not neglect, but not pampering either. The roots are horribly brittle even after years of growth, grow very slowly in our zone without heavy fertilizing and drip irrigation, and are highly attractive to borers. I have had 12 year old trees killed by a single borer. Burr knots have occurred on nearly all. Of the 100+ there are a couple of dozen left. Having seen better luck at orchards who use heavy applications of conventional fertilizers, or high nitrogen  and irrigation, folks who grow with a more heavy handed approach may be happy with them, and dwarf trees in general. To come full circle here, I believe the colder climates stress trees, delaying their growth or occasionally stunting them, in the same way that forest species are stunted at high elevations. Adding a paltry root system to the mix can be frustrating. The “bow echo” winds (90mph) that rolled through here on July 4 flattened another half dozen(broken at the base), but no standard apples were damaged.  I should also mention every one of our standards (same age and scion cultivar in this trial) offered fruit before the dwarf trees did. There was no more cold or other damage to the grafted portion of the dwarf trees, mortality and damage always occurred to the stock itself.

We have had extremely good luck with standard seedling here including: dolgo, ranetka, antonovka, prunifolia, Selkirk, bud 118(clonal); fairly good luck with robusta, and just began with baccata. Many of the Alaskan growers we ship to will only take ranetka and baccata and I know of none who will touch a size reduction clonal stock.

All the Malling and many of the other dwarfing stocks are rated zone 5 so we have not bothered with them in zone 3.

A caution- nearly all temperate trees will experience damage when the root system is subjected to 19 degrees ABOVE zero. Additionally, the root collar/lower trunk is particularly vulnerable, which is why we are experimenting with clonal stock as an interstem, and high grafting scions

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taking up no room at all
Newsam Park in the UK

The espalier (that’s ess-pal-yay)  is a fancy word for a fancy tree. Specifically it is a tree or bush that is trained to grow in one plane, give or take. It really can be grown anywhere, but it took its beginnings from already existing structures like walls and fences. As the photos following will attest, you can get pretty involved if you have the passion.

a fence from the french
espalier in Sussex
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Scab, Fiend or Friend ?

Salvestrol is one of the new words around town. It is apparently another helpful substance in the fight against cancer. Fitting in nicely with the other health benefits of eating fresh fruits, it also is helpful in giving us pause to reconsider the way we go about things in modern agriculture. The thing is, salvestrol production is pumped up when a fruit reacts to an affront, like say a fungal infection. That is the chemical is produced by the plant cells to help combat the pathogen. Without the attack, the presence of the salvestrol is low or nonexistant.

that levels of salvestrols are up to 30 times higher in organic produce, but almost absent in some commercially grown varieties. Some varieties of fruit have 40 or 50 times higher levels than others.

The point here is, in an effort to do away with a problem we have perhaps designed less healthy fruit. So maybe those folks who don’t think eating scabby fruits is beneath them may just be staying a bit more healthy than those with, well, refined cuisine.

In research published in the British Naturopathic Journal, Gerry Potter, Professor of Medicinal Chemistry, and Dan Burke, Emeritus Professor of Pharmaceutical Metabolism, explain how salvestrols work. A good deal more on the subject can be found online.

There have been reports from growers that higher sugar levels occur in scab infected apples. We have not been able to find any scientific studies on the matter yet, but will keep you posted.

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extreme watercore in apple (image : Red58bill)
This is appearing in the disease section, but does not really fit within this category. It is however often thought of as such. Really an affliction of poor management, but with some varieties being far more prone than others. The above photo is an extreme example, most affected apples show only a small degree of damage. It is usually a  sign of boron/calcium imbalance. The sugars are concentrated in the area, and such apples are sometimes sought, but normally is considered less than desirable.

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Apple Scab

Fungal spores that cause apple scab disease (Venturia inaequalis) erupting through the cuticle of a crabapple leaf. Magnified about 1500xPhoto by Charles Krause

Apple scab (Venuria inaequalis) is a fungal disease of malus species specifically, affecting all species and nearly all varieties of apple and crabapple.

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Lichens : Do we Like ’em ?

lichen on the twigs of a 50 year old apple tree at the farm

We get many inquiries about this one from worried growers. “What is this awful disease growing on my apple tree?” they wonder. Well, its not a disease, and it isn’t a worry either…its a lichen. Lichen if you don’t know already, is a symbiotic arrangement. A fungus teams up with an algae or cyanobacteria  and they become something else entirely in the process. The fungus supplies out protection and structure, the algae supplies food(sugars) through photsynthesis.  Lichen is an epiphyte, that is it lives upon another organism, but not as a parasite.

This from David J. Goerig and James A. Chatfield ,  Ohio State U. Extension publication:

The short answer is no; lichens do not cause plant damage. The lichen symbiosis is not damaging bark in any direct ways. It does not rob bark of significant amounts of moisture. The fungal symbionts of the lichen do not parasitize living plant cells, and lichens do not appear to be associated with providing entranceways for pathogens into plant tissue. So why do so many people, including many horticulturists, think lichens damage plants? Perhaps it is because when branch decline occurs due to other factors, lichen growth sometimes proliferates. This is due to increased sunlight that penetrates to the bark which favors the algae that are photosynthesizing, resulting in enhanced growth. The lichens did not cause the branch decline, but rather, one of the effects of the plant decline was an increase in lichen growth.

Our experiences :

Lichens usually take hold in earnest when growth becomes meager. I often encounter them on the very oldest apple trees when growth has slowed significantly, even near the tips as new shoots rarely grow more than a few inches. As a matter of course, lichen gets removed from trees in our orchard because we gently rub the coarser bark away from trunks and branches in an attempt to knock off overwintering pests pupae and eggs from crevasses. The light colored lichens can be helpful in reducing sunscald. Since they are a good indicator of clean air (they do very poorly in polluted environments), they probably should be viewed more in a positive light than in a worrisome one.

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Tree Healing : Compartmentalizing

A tree under repair does not truly heal in the classic sense of the word. The damaged tissue does not undergo the same sort of process that, for example, a human wound does. Most of the exposed tissue simply dies, that is digresses to dried xylem for the most part. This portion may even become punky and infected with decay organisms. This does not normally spell trouble for the tree. The course of action is that of compartmentalizing. This is the formation of a distinct division between sound and dead material. We liken it to a damaged ship closing off bays to prevent sinking. Callus tissue and further growth eventually will surround the wound and encase it. A later observer coming  to the site may surmise the wound had healed, but if the tree were to be cut open it would still reveal the damaged part hidden inside and clearly defined. Below is a photo from our woods which shows new growth beginning to envelop a scar in a maple tree (the wound is the gray wood in the center). If we return in a few years the wound will be invisible, hidden inside the new tissue layers of the ever expanding cambium.

wound callus and compartmentalized zone in maple
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Seedling Rootstock and Fireblight Resistance

     Seedling apple trees will have variable susceptibilities to the Fireblight bacterium erwinia amylovora simply due to genetic differences in each plant. There are, however, several  factors inherent in the general behavior of most seedling trees. Pear trees may be considered similar in many of these respects, but it should be remembered that most pear rootstocks, seedlings included are considered highly susceptible to blight.

      The factors of resistance in seedling stocks will be dealt with here as a comparison of their behavior as compared with dwarfing stocks. Vigorous clonal stocks will behave similar to seedling in these respects.

–          Seedling rootstock will produce a tree which will delay flowering until such time as a large and strong trunk and branching system has been established. Since fireblight often gains entry via the flowering system, it is advantageous to have a hardier structure in place. Older and more developed limbs and trunk are often less prone to attack or spread.

–          A seedling will produce a very large and crowded branch area, thus it is less likely to produce blooms in the interior nearer the trunk. This puts the susceptible flowers out toward the periphery. Since the protocol in fireblight management is removal of infected wood, it is more easily and completely dealt with. This is the difference between pruning out limb portions versus performing trunk surgery.

–          Most seedling rootstocks are less likely to sucker compared with many dwarfing stocks. Fireblight often attacks the vigorous tender growth of suckers.

–          The layout in the standard tree orchard places large distances between trees. Dwarf tree high density plantings are quite the opposite, often with trees branches comingling. In the event of outbreak of blight, a seedling orchard is far less likely to receive the devastation possible in the high density plantation. 

–          The large canopy of the  seedling tree will buffer the damage due to hail, keeping wounds to tissue at the extremities.

–          It is important to keep in mind that management techniques can affect the susceptibility of trees to blight. The above considerations are based on a system that allows standard trees to grow in a more natural way. Excess pruning, for instance will often result in excessive and vigorous new growth, which is susceptible to blight attack. Succulent growth attracts insects which open wounds for infestation by the bacteria. This is especially true with regard to pear. Growing season pruning will also open tissue to attack.

Some of these points are mentioned in a paper by Cummins and Norton 1974 in the publication Plant Sciences.

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Apple Nutrition

An apple a day keeps the doctor away. Ok here’s why.

Calories 81
Carbohydrate 21 grams
Dietary Fiber 4 grams
Soluble Fiber
Insoluble fiber
Calcium 10 mg
Phosphorus 10 mg
Iron .25 mg
Sodium 0.00 mg
Potassium 159 mg
Vitamin C 8 mg
Vitamin A 73 IU
Folate 4 mcg


In addition to this is that there is a fair amount of pectin in the apple. Recent studies have hinted that pectin can help to reduce cholesterol levels. They are also high in dietary fiber which can keep things running smoothly, and reduce the risk of cancers of the digestive system. More to come…

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Cultivars for the Far North

This list is evolving, but here is a list of cultivars that have proved well in zone 3 (some will do well in colder zones as well) :

antonovka selections

duchess of oldenburg

red astrachan

yellow transparent

heyer selections


centennial crab

chestnut crab

dolgo crab


baccata selections

Selkirk selections





more to come….