Weed And Disease Control In Organic Apple Orchards

Weed Control
Plans for weed control should be in place prior to planting the orchard. Many options have been investigated, and the perfect option remains elusive. Hay mulches and synthetic mulches harbor vole populations, and controlling weeds along edges of synthetic mulches is difficult because mowers snag the mulches. Some burn-down herbicides are approved for use in organic plantings, but these are expensive and must be reapplied frequently. Propane flamers sound like fun for pyromaniacs but are expensive and have proven only marginally effective over the long haul.

Wood chip mulch has provided acceptable weed control without harboring voles, but the transport and installation costs for a wood chip mulch can be substantial. Wood chip mulches must be renewed every several years, and perennial weeds such as Canada thistle can become a problem in wood chip mulches. Wood chip mulches provide some benefits for fertility and moisture retention, but long-term management is more complex than for weed control by tilling. Wood chips should never be tilled into the soil because they will tie up all of the available nitrogen for several years after incorporation. Thus, one cannot mix wood chips and tillage.

An option worth exploring would be a removable and re-usable synthetic mulch. Several companies manufacture durable plastic and/or fiberglass-based ground covers that have worked well to suppress weeds. When left in place during winter, these mulches harbor damaging populations of voles. However, it should be feasible to design a machine that would mechanically install the mulch in spring (perhaps in early May) and then recover that mulch onto a roll in mid-August so that it could be stored until it is reinstalled the next spring. A plastic mulch installer like those used for vegetables might be modified and off-set so that a ground cover could be installed on one side of a tree with the outside edge buried in soil to hold it in place. After installation was completed on both sides of a tree row (with separate 3-foot-wide strips of mulch on each side), the center overlap along the tree row would need to be manually stabilized to resist wind by inserting long wire “staples” into the ground or by weighting the center edge with rocks, wood chip mulch, or a long water-filled hose. Wood chip mulch installed over removable synthetic mulch could presumably be shaken to the ground when the synthetic mulch is removed in fall and then covered over with the synthetic mulch the next year. However, removable synthetic mulches need to be tested experimentally and will become practical only if their installation and removal can be mechanized.

Disease Control
Various plant pathologists working with organic apple production have all agreed that the two most problematic groups of diseases in organic apple production are rust diseases and summer fruit rots. Sulfur and liquid lime-sulfur (LLS) can be used to control most other diseases, although, as noted before, using these fungicides at the rates and intervals needed to control apple scab will cause yield reductions. To date, all of the organic fungicides promoted as alternatives to sulfur are more expensive and less effective than sulfur.

Fire blight is another potential problem with many cultivars, but streptomycin is currently acceptable within organic programs so long at is used only on an as-needed basis. Strategies for fire blight control are therefore similar in organic and conventional orchards.

Cedar apple rust and quince rust are very difficult to control with sulfur. Therefore, organic plantings that include rust-susceptible cultivars should be located at least 300 feet away from the nearest cedar trees. Powdery mildew can become a problem on some cultivars, but three or four applications of sulfur beginning at petal fall may suffice to keep mildew in check. Where mildew becomes established, however, the sulfur program should be initiated no later than pink.

Sooty blotch and flyspeck can be controlled by using low rates of LLS during summer. In trials in New York’s Hudson Valley, LLS applied at 1 quart per 100 gallons of dilute spray was very effective when applied on a 10-day schedule during July and August, whereas 2 quarts per 100 gallons were required for good control on a 20-day schedule. In regions where conditions favor development of flyspeck and sooty blotch, sprays with LLS must be continued into late September to prevent disease on late-maturing cultivars.

Unfortunately, LLS does not control summer fruit rots such as black rot, white rot, and bitter rot. Low rates of copper fungicide can be tank-mixed with LLS during late July and August LLS to increase activity of these sprays against summer fruit rots. However, organic apple growers may need to resort to sanitation measures to control summer fruit decays as plantings mature. In the northeast, much of the inoculum for summer fruit decays comes from fruitlet mummies that are retained after fruit set and that remain on the trees over winter. Manually removing all of these fruitlet mummies during winter pruning should significantly reduce problems with summer fruit rots. However, as is the case with many other aspects of organic production, that hypothesis has not yet been tested.

Leave a Reply

Featured Stories
Photo credit: Christina Herrick
Stone Fruit
September 28, 2016
New Research Gets To The Bottom Of Cherry Cracking
German researchers hope to identify root causes of rain-induced problem. Read More
Part of a sustainable cropping system includes desiging fields to wrap around hilly terrain to limit runoff and soil erosion.  Photo credit: Rosemary Gordon
Farm Management
September 28, 2016
Grants Available For Sustainable Ag In The West
More than $1 million is marked for grants to study, demonstrate, and improve sustainable ag practices. Read More
Organic farmer on tractor
Equipment
September 28, 2016
Small Tractor Sales On The Rebound
Retail sales of tractors under 40 horsepower gained more than 21% last month, while sales of larger tractors continued their double-digit declines. Read More
NOAA Temperature Outlook For Winter 2015-2016
Farm Management
September 28, 2016
The Time For Climate Change Denial Is Over [Opinion]
Extreme cold, droughts, flooding, record-setting temperatures have all been a part of this year’s growing season. Read More
Cosmis Crisp apples planting FEATURE
Fruits
September 27, 2016
Focusing On Phenomics In Specialty Crops
It’s not just the nature of your crops — the genomics — it’s also how they are nurtured. Read More
Bob Bender (center) accepts American Vegetable Grower's 2016 Grower Achievement Award from Lonny Smith of AgroLiquid, the award's sponsor, and American Vegetable  Grower editor Rosemary Gordon
Grower Achievement Award
September 27, 2016
Tasteful Selections Is The Recipient Of American Vegetable Grower’s 2016 Grower Achievement Award
The award was presented to Bob Bender of Tasteful Selections Sept. 13 at United Fresh's Washington Conference. Read More
Urban vegetable farm in rural Cuba
Fruits
September 27, 2016
Rodale Institute Launches An Organic Farming Association
A new national organization for organic growers is designed to provide advocacy, the latest research and education, and information-sharing among farmers. Read More
Marco Rubio tours a Central Florida citrus grove with industry dignitaries
Farm Management
September 27, 2016
Politicians May Be Taking Ag For Granted [Opinion]
Growers have become masters at ensuring a steady food supply, but warning, politicians: Ignore them at your peril. Read More
U.S. Capitol Building FEATURE
Citrus
September 26, 2016
Presidential Candidates Comment On Agricultural Issues
Hillary Clinton and Donald Trump weigh in on a number of topics of concern to growers. Read More
'Rave' is a cross between 'Honeycrisp' and an unreleased variety called ‘MonArk.' 'Rave' was bred by the University of Minnesota and will be grown and sold exclusively by Stemilt in the U.S. (Photo credit: Stemilt)
Apples & Pears
September 26, 2016
New Apple Variety Is One Stemilt Hopes Consumers Will ‘Rave’ About
University of Minnesota apple variety will be grown and packed exclusively by Stemilt. Read More
The Latest
Stone Fruit
September 28, 2016
New Research Gets To The Bottom Of Cherr…
German researchers hope to identify root causes of rain-induced problem. Read More
Farm Management
September 28, 2016
Grants Available For Sustainable Ag In T…
More than $1 million is marked for grants to study, demonstrate, and improve sustainable ag practices. Read More
Equipment
September 28, 2016
Small Tractor Sales On The Rebound
Retail sales of tractors under 40 horsepower gained more than 21% last month, while sales of larger tractors continued their double-digit declines. Read More
Farm Management
September 28, 2016
The Time For Climate Change Denial Is Ov…
Extreme cold, droughts, flooding, record-setting temperatures have all been a part of this year’s growing season. Read More
Fruits
September 27, 2016
Focusing On Phenomics In Specialty Crops
It’s not just the nature of your crops — the genomics — it’s also how they are nurtured. Read More
Grower Achievement Award
September 27, 2016
Tasteful Selections Is The Recipient Of …
The award was presented to Bob Bender of Tasteful Selections Sept. 13 at United Fresh's Washington Conference. Read More
Fruits
September 27, 2016
Rodale Institute Launches An Organic Far…
A new national organization for organic growers is designed to provide advocacy, the latest research and education, and information-sharing among farmers. Read More
Farm Management
September 27, 2016
Politicians May Be Taking Ag For Granted…
Growers have become masters at ensuring a steady food supply, but warning, politicians: Ignore them at your peril. Read More
Citrus
September 26, 2016
Presidential Candidates Comment On Agric…
Hillary Clinton and Donald Trump weigh in on a number of topics of concern to growers. Read More
Apples & Pears
September 26, 2016
New Apple Variety Is One Stemilt Hopes C…
University of Minnesota apple variety will be grown and packed exclusively by Stemilt. Read More
Grapes
September 26, 2016
Where Site And Growing System Meet In Th…
Vineyard manager uses growing systems to control vigor of winegrape varieties. Read More
Fruits
September 26, 2016
San Jose Scale Is An Old Pest That Is A …
Growers see increase in infestations due to changes in chemical control programs. Read More
Citrus
September 26, 2016
Florida Sugarcane Industry Strengthening…
Pot sweetens with promotions for three executive staffers of the state’s Growers Cooperative. Read More
Citrus Achievement Award
September 26, 2016
Hope Growing Around Bactericides As A Ci…
Citrus Achievement Award winner Marty McKenna is optimistic about new approach to staving off HLB. Read More
Cucurbits
September 25, 2016
10 Cantaloupe And Melon Varieties You Ne…
Browse this slideshow for more information on 10 cantaloupe and melon varieties you need to know about from the nation’s leading Read More
Farm Marketing
September 25, 2016
New York Governor Signs Additional Legis…
Bills allow farm wineries, breweries, and cideries to sell New York-made farm beverages by the glass. Read More
Farm Management
September 24, 2016
Water Woes Continue In Northeast
Hydrologist says this year’s conditions are bad but are part of a typical water cycle. Read More
Berries
September 24, 2016
Time Is Now For Florida Blueberry Grower…
Coming off a challenging season, industry players must continue to adapt to curveballs thrown by Mother Nature and market forces. Read More
[gravityform id="62" title="false" description="false"]