Orchard Weed Management

What would the world be, once bereft
Of wet and wildness? Let them be left,
Oh let them be left, wildness and wet;
Long live the weeds and the wildness yet.

Gerard Manley Hopkins

What is a weed?

There are many reasons why certain plants are or become weeds in orchards or organic farming operations.

Conventional methods of broad scale systemic or selective weed suppression can have many undesirable effects on soil microbes and healthy soils.

Plants are commonly defined as ‘weeds’ if they exhibit one or more of the following characteristics:

• compete with plants for water (most plants);
• compete with plants for nutrients (most plants, especially non-legumes);
• interfere with water distribution from low-level sprinklers (most plants);
• poison livestock;
• harbour or encourage non-beneficial pests;
• produce spiky seeds/thorns that may injure workers or contaminate produce;
• interfere with harvest or other orchard operations;
• compete with more desirable cover crops;
• have the potential to invade neighbouring properties where they can exert their undesirable qualities;
• Are noxious or declared by the local Rural Lands Board / Council

When weeds are not weeds…

The real vs. perceived status of a weed can vary from grower to grower. Many agricultural weeds have been defined as such because of their negative impact in pasture and grain cropping systems and/or livestock, the dominant form of agriculture in Australia. E.g., grasses are often encouraged in cool climate orchards/vineyards on fertile soils where their competition for nitrogen is used to reduce excess vigour. On naturally poor soils of some hot, dry regions however, summer grasses tend to be discouraged, because they compete for water and nutrients – major issues for some regions. Summer ground cover does however help reduce soil temperatures and dust.

Beneficial ‘weeds’

Some ‘weeds’ provide benefits of value to organic systems, and these benefits need to be weighed against any negative characteristics of the weeds. Some benefits of weeds are listed below:

• Soil protection – Most plants protect otherwise bare soil from the effects of sun, wind and rain (erosion).
• Food source for beneficial insects – Many flowering plants produce pollen or nectar that is a useful food source for beneficial insects such as hover flies and lacewing insects (predators of mealybugs, scales and other pests) and predatory mites. They also provide a haven for bees and other pollen spreading insects, which is particularly important in an orchard setting.
• Other plants, like thistles, support aphids which provide a food source for beneficial insects and help maintain populations of those beneficial species.
• Nutrient recycling – Deep-rooted plants play a useful role in nutrient recycling by absorbing nutrients from lower in the soil profile and redistributing them when the plants decompose.
• Weed suppression – heavy growth of some ‘weeds’ like grasses, can suppress the establishment and growth of less desirable weeds.

Next I will look at weed control methods that i have used in the orchard, and some trialing of a certified weed supressant.

References:

Organic Farming: Vineyard Weed Management (2007), David Madge,
Department Of Primary Industries, Victoria, ISSN – 1329-8062
web site: http://www.dpi.vic.gov.au/notes

Soil Management for Orchards and Vineyards (1993), G O’Conner, J Strawhorn, K Orr, AGMEDIA – Department Of Agriculture, Victoria, ISBN – 0 7306 3018 8

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