Growing Scab Free Apples Without Fungicides

Project Overview

Project Type: Farmer
Funds awarded in 2011: $6,732.00
Projected End Date: 12/31/2011
Region: Northeast
State: New York
Project Leader:
Louis Lego, Jr.
Elderberry Pond


  • Fruits: apples, general tree fruits


  • Crop Production: application rate management
  • Education and Training: demonstration, farmer to farmer, on-farm/ranch research
  • Pest Management: compost extracts, cultural control, field monitoring/scouting, flame, prevention, sanitation
  • Production Systems: holistic management, organic agriculture
  • Soil Management: soil analysis

    Proposal summary:

    The problem is apple scab (Venturia inaequalis)(see Apple Scab Image below). It is a fungal parasite that has been present in apple orchards for centuries and that is the most damaging of all apple diseases. In a good year the disease will be manifested in round grey spots on the leaves and fruits, and in bad years will defoliate trees and severely misshape apple fruit (see figure 1 in appendix). In 2009 over 20 percent of the New York apple crop was lost to apple scab, and much of this was in commercial orchards where fungicide sprays were applied on a seven to ten day schedule. 2009 was a very bad year due to extended periods of leaf wetness during the primary scab (ascosporic) infection period that resulted in an extended secondary (conidian) spore infections that continued throughout the summer.

    The problem in 2009 was made worse by the fact that many of the new “low risk” fungicides that had become prominent were found to be ineffective due to new fungicide resistant strains of scab. The really bad thing is that with widespread resistance to the low risk Sterol Inhibitor (SI) and strobilurin (Stroby) fungicides, conventional growers have largely gone back to more toxic contact fungicides such as Captan and Mancozeb, a real setback in sustainable apple production. For organic growers like ourselves, Sulfur and Copper remain our best defense, and were not very effective in 2009. We lost over 30% of our crop in 2009 in spite of a diligent and frequent sulfur spray regime. Out of the disastrous 2009 apple year came one bright note. The small (2 acre) orchard on the northwest corner of our property fared much better than our other orchards. We believe that the reason this orchard did so well was due to the layout and management of the orchard which exploits a serious weakness in the life cycle (figure 3) of this otherwise robust and successful fungal parasite: its overwintering stage.

    Unlike destructive fungal spores that cause tomato late blight and those that cause downy mildew in cucumbers and netted melons, the apple scab spores are not imported from the southern states each year on winds or on infected bedding plants. Apple scab spores overwinter in leaf debris in the orchard. In this project we will hopefully demonstrate a long term systems approach to orchard design and maintenance that will greatly reduce or even eliminate the local spores during the winter and early spring dormancy period. The three important steps in this process which will be described in detail in the following sections are:

    1.Orchard Design
    2.Orchard pruning and undercover selection and maintenance
    3.Orchard sanitization, debris breakdown, and fertilization

    It is this process that we believe resulted in the much better yield from this orchard compared to our other orchards. We will carry out items 2 and three in a rigorous and well documented fashion during this project.

    The issue this project addresses is that here in the Northeast, it has proven difficult, if not impossible, to grow the best varieties of apples without the use of organic or chemical fungicides. These fungicides, whether chemical or organic, are expensive, time consuming to apply and potentially dangerous. In addition, application can be damaging to beneficial insects and soil health. Several years ago we designed and planted an isolated two acre orchard specifically to test techniques for very low carry-over of apple scab inoculum. This orchard has both new disease resistant and classic non-disease resistant varieties. With what we have learned, I believe we can now produce quality fruit without fungicide sprays. In typical NY organic orchards, including ours, this would eliminate 5 to 10 sprays. We propose using use three specific procedures prior to the primary scab infection period to eliminate overwintering ascospores. By avoiding primary ascosporic infections and the resulting secondary conidial spore infections a summer and fall crop of scab free apples will result. The project involves risk to our 2011 farm apple production. If the method does not work we could lose about 20 percent of our total apple crop, but if it does work we will feel confident to apply the technique to all of our orchards. We can also then provide those interested in establishing new organic or sustainable orchards a proven method of planning and maintaining orchards that will greatly reduce or eliminate the most damaging of all apple diseases.

    Project objectives from proposal:

    The test orchard was planted in 1994 (See document 3 Project Test Orachard). It is approximately 2 Acres and has about 80 trees. It is on the northwest side of the property and is flat, well drained and open to winds from the north and west. The trees are a mixture of dwarfing M9, Mark and a few M7 rootstocks. The trees are planted on a wider than normal grid to allow for good air circulation. Apple varieties are mixes of disease resistant varieties with disease susceptible varieties in alternating rows to minimize the amount of scab infected debris. The orchard floor is a mixture of fine bladed grasses. For more apple Scab information, see Document 1: Scab Cycle and Document 2: Leaf Wetness/Apple Scab Control, below.

    Task 1 – Late Winter and Spring Orchard Cleanup.

    As of this writing in November, the orchard (figure 2 in appendix) is wet, and not all of the leaves or even unpicked apples have fallen. During dry, windy days in December the orchard will be mowed to break up leaf and fallen apple debris. This effort will be done by myself and my son (Chris) and will proceed the beginning of any grant effort.

    In early spring, approximately mid to late March we will begin the grant project if awarded.

    Task 1.1 The first effort will be to modify our 48 inch zero turn commercial mower to a mower/mulcher/vacuum. This project will involve the installation of newly available “high lift” mower blades which create a strong suction under the mower, a skirt to prevent debris from leaving the mower deck sides, and a Husquavarna designed adapter to connect the mower grass chute to a flexible pipe that connects to 2 large (40 gallon) collection vessels (Rubbermaid Brutes). This modification is a take-off on a commercially available grass bag attachment that is available from the mower manufacturer for about $2000. I believe our design will be more effective for debris pickup than the grass bag attachment and our well equipped shop and my own engineering background will help make this an effective new tool for organic orchardists.

    Task 1.2 This mulcher/vacuum will be used to scour the orchard floor and pick up as much debris as possible from the orchard floor before bud break in the orchard. Over the period of about a month the orchard floor will be cleaned (and the debris burned at a remote site) three to four times. Even if some debris is missed on a pass it will at least be turned over randomly allowing air and sunlight to help destroy ascosporic sites.

    The mulcher/vacuum machine will also be used in the other apple orchards on the farm to prevent drift of infected material from these orchards into the test orchard. Just before bud break these other orchards, which are about a quarter of a mile away, will be sprayed with organically approved fungicides hopefully preventing any early primary scab infections. Note: there is little possibility of primary scab infections prior to any green appearing at the bud tips and at temperatures below 40 deg F. See Mills chart (Figure 4 in the appendix).

    Task 2. Orchard Tree Pruning and Cleanup

    This is the most time consuming and perhaps the most difficult part of the project. In our normal pruning operations we simply prune the tree using thinning cuts to prevent crossing branches, branches that are growing toward the center of the tree, and heading cuts to shorten branches that are too long to support the weight of the fruit or put the fruit too high for us to pick with our orchard ladders. For this project we will pay particular attention to preventing tight clusters of branches or leafs that may not get sufficient air circulation to dry quickly after a wetting period. Ascosporic production is a function of both the temperature and of the time a particular leaf is wet (figure 3). Our intention will be to prune this orchard more and more carefully than our others to allow for exceptional sun and air penetration of the tree canopy. Our normal spring pruning time per tree is about 30 to 40 minutes per tree and for this orchard this year we will estimate about 60 minutes per tree.

    Immediately following pruning the cut branches will be removed from the orchard and the orchard will be again be “swept” with the vacuum/mulcher.

    Task 3 Orchard Fertilization and Debris Breakdown

    This is the part of the task that equates to the use of Urea to speed up decomposition of any remaining leaf or apple debris. There is probably no organically approved material that has as high nitrogen content and quick release as urea to perform this function. We must find an organically approved substitute for our decomposer and fertilizer. On the other hand in the tests where urea was used successfully, much less attention was paid to debris pulverization and removal than we will be doing in this test. Also, the material we do use to perform this function will be far safer to apply and will provide more balanced and slower released nutrition to the trees and undercover. In some tests of the use Urea for a leaf matter breakdown, the high nitrogen pulse accelerated leaf tissue emergence increasing the susceptibility of the trees to early scab infection. We believe the best organic solution is to apply a fairly high N product that will aid in rapid leaf matter breakdown and also provide some tree fertilization as well.

    For this project we have decided to use an application of certified organic OMRI approved cow Compost- Fessenden TLC mixed with our own green compost and chicken litter and apply it with a compost spreader, or to brew a tea and apply it with a sprayer to the orchard floor.

    The Fessenden compost is produced here in Cayuga County and we can purchase it directly from the Fessenden farm. We also like the idea that we can specify the maturity of the compost for our particular application. Approximately 50 cu yards of the compost will be used in our mixture

    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.