Organic Fruit Production
Horticulture - Apple
Many horticultural practices are the same in organic and conventional systems. Key differences exist for orchard establishment and crop load management.
Orchard establishment
Apple replant disease is a common concern when renewing an orchard from
apples to apples. Soil fumigation is an effective control measure, but is
not allowed in organic systems. USDA-ARS research Mark Mazzola has been
studying biological alternatives for replant disease control (see http://organic.tfrec.wsu.edu/OrganicIFP/AppleReplantDisease/Index.html
) but no consistently effective alternatives are yet developed. Growers
can do a bioassay of their soil to learn how severe replant disease might
be. Some organic growers choose to fumigate their soil, start their organic
certification again, and then reach certification around the time the orchard
begins to bear fruit. This is allowed under the US National Organic Standard
(36 months after the last use of a prohibited material), but is more restricted
under the European standard.
Some growers modify their choice of rootstock for organic systems, as well as for particular sites. Going to a slightly more vigorous rootstock may help the young trees grow well despite potential challenges from weeds and slow-release organic fertilizers. Research is also underway for rootstocks that tolerate replant disease and tolerant or resistant to various insects and diseases. Commercialization of these rootstocks will greatly benefit organic growers. Information on tests conducted by the Washington Tree Fruit Research Commission can be found at http://jenny.tfrec.wsu.edu/wtfrc/ .
Most modern orchards are planted on a trellis system. Treated wood (with preservatives that are prohibited materials) are not allowed to be used in a new planting. Alternatives such as steel, wood, and cedar do exist, but can be considerably more expensive. Treated posts already installed in an existing block that is subsequently transitioned to organic are grandfathered in, but no treated replacements are allowed.
Weed control in new plantings can be a challenge. Growers use combinations of tillage, thermal weed control (flaming), mulching, mowing, and hand weeding. Plastic (non-PVC) mulch is allowed in organic fields, but must be removed at the end of its service. Tillage is allowed but cannot degrade soil or water quality. See Orchard Floor Management for reports from field trials on this topic. An extension publication from Michigan State is also helpful.
Crop load management
Organic apple orchards can be more prone to biennial bearing, which has
negative consequences for fruit quality and profitability. Historically,
thinning was done by hand, using blossom thinning, fruitlet thinning, or
both. Also, some crop load reduction can be accomplished during pruning.
Hand thinning was very expensive and accounted for the greatest increase
in production cost for organic growers. Over the past several years, fruit
thinning research by the Washington Tree Fruit Research Commission included
a number of chemical compounds with potential use in organic systems. One
of the best blossom thinners turned out to be lime sulfur plus fish oil,
a combination developed by long-time organic grower Harold Ostenson. Research
into the mechanisms of thinning is helping to understand the observed inconsistency
among years and varieties. No effective post-bloom thinners for organic
orchards are currently available. Mechanical
fruit thinners have been developed in Europe and are being tested here.
Also research on shade
manipulation for thinning is underway in Switzerland. Research reports
on thinning can be viewed on-line
, including a final
report on chemical thinning with organic compliant materials.
Other considerations
The organic standards include rules that impact several other orchard practices.
Only certain materials are allowed for use in grafting. Nursery planting
stock that is not organic cannot produce a certified organic crop until
after one year of organic management. Organic seeds (e.g. for cover crops)
need to be used unless none of equivalent variety and quality are available
in commercial quantities. If none are available, only untreated seed (no
fungicides or other prohibited materials) can be used. The use of treated
cover crop seeds has caused orchards to lose organic certification for three
years.
Biodiversity is encouraged in organic systems, both to help with pest management and with other ecosystems services (see Wild Farm Alliance . European standards have explicit requirements for biodiversity zones.
Organic fields need buffer zones to prevent contamination from neighbors. Since most orchards use airblast sprayers that can have considerable spray drift, organic growers need to create a buffer adequate to protect their crop. The standards do not specify a distance. Growers often use organic management up to the border of their orchards but harvest one or two rows on the outside separately and sell it as conventional fruit. Another potential contamination can be from public road department vegetation management with herbicides on road shoulders and ditches. Special arrangements and signage are necessary to curtail this on borders of organic fields.
Since organic growers have fewer, and sometimes less effective or persistent,
pest control measures, choosing a site without chronic pest problems is
important. Orchard sanitation is more important as part of preventative
management and may require alteration of horticultural practices. Trees
may need to be pruned and trained to allow more air drainage to help with
disease prevention.