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Orchard Floor Management

Introduction

Orchard floor management decisions impact the health of fruit trees and overall production and quality of fruit. The understory performs a number of interrelated purposes in the orchard. Soil condition, nutrient availability, water management, weed control, insect habitat, and prevalence of rodents all influence the growth, development and productivity of fruit trees. Orchard floor vegetative ground cover provides traction for tractors and machinery, protects the soil from erosion by wind and water, prevents runoff, facilitates water percolation and helps manage dust. Traditionally growers have used a grass drive row and an herbicide-treated band in the tree row for weed control (weed-free strip). Today, farmers and consumers alike are interested in the benefits of sustainable food production. Sustainable practices that are good for the soil and the environment will benefit producers and the consumer public. WSU researchers have been testing cover crops, mulches, tilling, and soil nutrition to gain a better understanding of the unique relationships among the interconnected systems making up the orchard floor.

Special Considerations

Organic growers have some extra challenges managing the orchard floor, especially with weed control, since they are not allowed to use synthetic herbicides. As a result, weed control can be more difficult, challenging and expensive. Another challenge is providing nutrients for the soil. Organic fertilizers are taken up by the roots more slowly than commercial fertilizers, and are expensive. Certified organic growers must demonstrate that their orchard floor management practices are maintaining or improving soil quality, as part of the certification process, a point highlighted in this technical note: The potential for legume cover crops in WA apple orchards, P. Pavek and D. Granatstein, USDA NRCS Technical Note 22. 34p. 2014.

Apple Replant Disease is a major concern for growers planting fruit trees on land that had previously been planted in fruit trees. Dr. Mark Mazzola, plant pathologist, at the USDA-ARS Tree Fruit Research Lab has identified an alternative treatment to fumigation, as the chemicals used for fumigation only provide short-term control of soil pathogens related to replant disease. He has found that a combination of yellow and white mustard seed meal mixed into the soil as a pre-plant treatment controls these organisms.
See New replant disease treatment, G. Warner, Good Fruit Grower, 2014; and the Organic & Integrated Tree Fruit Production Apple replant disease page. Additional information on replant disease can be found on the Soils and Nutrition page of this website.

Orchard Floor Sanitation

Orchard floor sanitation is very important in maintaining healthy fruit trees. Fungal pathogens over-winter on dried leaves, pruned limbs, and decaying fruit left on the orchard floor. Fungal spores produced on the leaves and limbs left on the orchard floor can inoculate healthy trees and fruit in the spring when temperatures are warmer and rain, irrigation water and wind spread the spores. Diseased branches that have been pruned need to be disposed of as soon as possible. Flail mowing of limbs and leaves on the ground will break them down more quickly and decrease the fungal inoculum. Dr. George Sundin, Michigan State University recommends urea treatments on apple leaves in the fall or spring, as the nitrogen speeds up the breakdown of the leaves where scab overwinters. Scab releases spores the following spring, and according to Dr. Sundin, it only takes 1% scab-infected leaves to cause infection in the orchard. This would be more important for apple production blocks west of the Cascade mountains that have more rainfall and conditions conducive to scab development. For more on orchard sanitation see: Four reasons to manage the orchard floor, R. Lehnert, Good Fruit Grower, 2014.

‘Manchurian’ crabapple trees used as pollenizers in apple orchards are highly susceptible to certain diseases, especially, Sphaeropsis rot (Sphaeropsis pyriputrescens) and Speck rot (Phacidiopycnis washingtonensis) that infect apples in the orchard, causing postharvest diseases in storage. These diseases are quarantine pathogens, that if found, can limit export of apples to China, for example. Fungal spores from the infected crabapple limbs and fruit infect the apple crop with symptoms manifesting in storage. Cankers on apple trees caused by S. pyriputrescens are not common in WA State, but infection of apple fruit is a concern. When infected crabapple limbs are pruned out, they must be disposed of and removed from the orchard, or they remain as a source of infection.  Because of heavy thorns, these limbs have been known to cause flat tires in farm equipment. Removal of infected wood from the orchard is critical to limit the disease. For more information about crabapple sanitation see: Guidelines on Pruning ‘Manchurian’ crabapple for fruit rot control and Guidelines for control of Sphaeropsis rot in apples.

Fire blight (Erwinia amylovora) infected limbs that have been pruned from apple and pear trees must be removed from the orchard, as the bacterial inoculum on shoots and limbs will also infect the healthy trees in the orchard. Infected cuttings from trees are usually destroyed by burning. Tools should be sanitized during and after this pruning process. For more information on fire blight visit The WSU Extension webpage Fire Blight and the Oregon State University webpage Fireblight of apple and pear.  (Accessed: 1/19/17).

If diseased limbs and debris on the orchard floor are removed from the orchard, the amount of pesticides needed for disease control can be reduced. This can help to reduce problems with resistance development to fungicides, for example. Fungicide resistance occurs from using the same or related fungicides repeatedly, over time in orchards. For more information see: Fungicide resistance management in the 2016 WSU Crop Protection Guide.

When fungicides and insecticides are applied in combination in apple orchards it is possible that synergism between these products can occur resulting in acute or chronic toxicity to honey bees. For more information see: Comparative toxicities and synergism of apple orchard pesticides to Apis mellifera (L.) and Osmia cornifrons (Radoszkowski), D.J. Biddinger, et. al., PLoS One, 8(9): 2013.

Cover Cropping

Orchard floor vegetation usually consists of perennial grasses that form sod, weeds, and cover crops. Legumes like white clover, vetch, or trefoil are sometimes used. Typical grasses used in orchard drive rows, depending on location include: orchardgrass, ryegrass, bentgrass, fescue, bluegrass, and timothy. Groundcover mixes designed for growth and growing conditions in orchards are used. For more information see: Cover crop resources and seed vendors for Oregon and Washington (A. Young-Mathews and P. Pavek, USDA-NRCS Plant Materials Technical Note 41). (Accessed: 1/19/17).

Researchers and fruit tree growers are testing cover crops in fruit orchards in the Pacific Northwest. Legume cover crops are used to provide usable nitrogen (N) to the soil. David Granatstein, WSU-TFREC, has conducted trials on orchard cover crops, and has found that cover crops affect the soil and orchard temperature and soil moisture (visit the TFREC page, and the WSU CSANR Cover crop page here). Some problems associated with cover crops are that they can compete with young trees for nutrients and water, and they can be a habitat for vertebrate pests such as voles and insect pests. Weed management can also be difficult in cover crops (reference: Cover crops influence meadow vole presence in organic orchards, M.R. Wiman, et. al., HortTechnology, 19(3), 2009.)

The irrigation system used in an orchard determines what type of cover crops can be grown. Some growers use drip irrigation to irrigate fruit trees in the tree row and under-tree sprinklers to irrigate cover crops in the row middle.

From an insect biological control standpoint, cover crops can also enhance habitat for predators and parasites of tree fruit pests. Dr. Elizabeth Beers, WSU-TFREC has conducted research on cover crops and natural enemies. Sweet alyssum used as an orchard drive row ground cover attracted Syrphids, which eat woolly apple aphids. For more information see her presentation on Cover crops: Inviting natural enemies into your orchard, E. Beers, 2011. Also see her 2013 Biological Control article entitled Flowers promote aphid suppression in apple orchards.  Additional information and links related to this topic can be found at the WSU Center for Sustaining Agriculture and Natural Resources Cover Cropping page.

Weed Management

Weed management is one of the most important areas of orchard floor management, as weeds compete with the trees for water and nutrients, inhibit adequate irrigation, and provide habitat for vertebrate pests. Weed species in orchards include annual and perennial broadleaf weeds, dandelions, grasses, and others. Weed management in orchards is achieved in many ways. Programs used depend on whether the orchard is under conventional or organic production. Conventional growers can use herbicide treatments for weed control, whereas organic growers must rely on other methods and organic herbicides. Some weed control programs used by growers include: mechanical/tillage, flaming, steaming, mowing, and mulching. Some methods work better than others, depending on your site and management system. See our Weed Control page for information on weed management strategies or watch the video Weed Control in Orchards.

Soil

Orchard floor management decisions affect the orchard soil quality and health which in tern is vital to tree health, and quality fruit production. Fruit trees require fertile soil, with good structure and water holding and draining properties.

Soil organic matter, composts, fertilizers, manures, green manures, and mulches are all used as soil amendments, depending on site-specific soil and ground cover needs. See our Soils and Nutrition page, and the WSU Organic & Integrated Tree Fruit Production Soil Management page for additional information.

Temperature and Sunlight

Orchard floor management decisions can influence orchard temperatures. Bare ground will absorb more heat during the day and release more heat at night than soil covered in vegetation. This can be particularly important during spring bloom timing when just a few degrees temperature difference can result in flowers being killed or not. Mowing tall cover crops will help with frost protection, as more solar heat will be absorbed by the ground during the day.

Finally, growers use reflective film materials on orchard floors to reflect sunlight back up into the trees to improve color on apples, and cherries, and other stone fruit. WTFRC research on reflective covers has also shown that reflective groundcovers improved Bartlett pear yields by increasing fruit set and/or size (reference) and increased yields of peaches and nectarines (reference). For more about the affects of reflective films see these Good Fruit Grower articles: Mylar machine moves fast, Reflective cover has marketing benefits, and How reflective cloth affects crop.

In closing, there are several orchard floor areas to manage, and the treatments for each may vary during the life of the orchard, in order to have fertile soil, balanced nutrition, weed control, and efficient irrigation, etc. The orchard floor combinations and management decisions are unique to each site and variety.

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