Organic Orchard Management:  Organic Orchard Design

Orchard design and cultivar selection have a long-term impact on pest control and fruit quality.  In organic orchards where pest control tools are limited, it’s important that orchards be designed and planned to use the cultural (e.g. rootstock and scion selection) and organically approved pest management tools (e.g. mechanical or mulch-based weed control) to the grower’s greatest advantage.  Rootstocks and cultivars should be selected for vigor, hardiness and disease resistance to overcome the challenges of weed competition and limited organic controls for pests like fire blight, scab or wooly apple aphid (see Table 1).  Drip or micro-sprinkler irrigation should be designed to avoid spraying the canopy and spreading disease as well as reduce watering unwanted vegetation.  Additionally, irrigation should designed to allow for easy mechanical weed management.  See Chapter 8 Orchard Floor and Weed Management for more details.

If an existing orchard is being used to establish new trees, attention should be paid to the potential for new trees to be stunted by replant disease.  Replant disease has nonspecific causes that often differ from one site to another but are largely thought to be attributed to soil organisms including pathogens and parasitic nematodes (Hewavitharana, et al.).  Multiple biotic and abiotic factors are involved in replant disease.  Organic growers have limited options for control, which conventionally consists of soil fumigation, a practice not approved in organic production.  Replant resistant rootstocks are available for apple (See Table 1), but not other tree fruits (Hewavitharana, et al.).

Table 1: Cold Hardy Apple Rootstalks for Organic Production

Root Stock Vigor Fire Blight Woolly Apple Aphid Replant
G935 Moderate Very Resistant Susceptible Tolerant
G30 High Very Resistant Susceptible Tolerant
G210 High Very Resistant Resistant Tolerant
G41 Low Very Resistant Resistant Tolerant
G11 Low Resistant Susceptible Moderately Tolerant
G16 Low Resistant Susceptible Moderately Tolerant
G213 Low Very Resistant Very Resistant Tolerant
M7 Moderate Very Resistant Susceptible Susceptible
M26 Moderate Susceptible Susceptible Susceptible
M106 High Susceptible Resistant Susceptible
MM111 Low Susceptible Resistant Susceptible
B9 Low Moderate Resistance Susceptible Susceptible
B118 Moderate Moderate Resistance Susceptible Moderatley Tolerant

In addition to careful rootstock selection, avoiding original rows, or applying other organic approved soil treatments may help.  Pre-planting cover crops of marigold flowers, certain oilseed rape cultivars, and Sudan grass hybrids, may provide partial control of replant disease in some orchards.  Replacing soil from the planting hole with a mixture of fresh soil and compost may also be helpful. Other factors that may alleviate replant disease include allowing a fallow period before planting, soil pH adjustment, minimizing soil compaction, improving soil drainage, correcting nutrient deficiencies, and providing supplemental irrigation immediately after nursery trees are planted in the orchard.  New research has shown some benefits to amending soil with brassica seed meal and Anaerobic Soil Disinfection (Browne, et al., Mazolla, et al.).

Additionally, encouraging beneficial insects and biodiversity in the orchard can improve long-term pest management.  Edge habitats can be beneficial for wildlife biodiversity by providing habitat for beneficial insects.  They also act as a tool in resistance management of key insect pests, such as codling moth, peach twig borer, or western cherry fruit fly as wild-type individuals from surrounding habitat migrate into your orchard and mate with the resident pest population. Having these two gene pools intermix will help delay the development of pesticide-resistant pests.  The tradeoff, however, is that such migration may interfere with the effectiveness of chemical controls if pests migrate after spraying has taken place.  Ultimately growers should rotate chemicals, using products with different modes of action to avoid any pest, weed, pathogen or insect, developing resistance.