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UC Pest Management Guidelines


Plum

Weed Management in Organic Orchards

(Reviewed 5/06, updated 4/09)

In this Guideline: More about weeds in plum:

Weed control in organically managed orchards requires special attention to preventing weed problems before they start. Cover crops planted in middles and mechanical control of weeds in the tree row is key components of an organic weed management program.

Before planting. It is critical to have minimum or no weed competition at the time of planting new trees so weed control before planting is important. Take measures to deplete the soil weed seed bank. A summer fallow treatment of irrigation followed by tillage and then drying can reduce weed seed numbers in the soil. Repeat this cycle several times to further deplete weed seeds in the soil. If most of the weed seeds on the site are located in the surface 4 inches, a soil-inverting plow such as a Kverneland plow can be used to bury them to depths where they cannot emerge; a moldboard plow will not sufficiently invert the soil to be effective.

Soil solarization. Soil solarization of the planned tree row can also significantly reduce weed populations. The soil must be moist and the width of the solarized area should be at least 6 feet. All sides of the plastic must be buried to create a seal on the soil; this also helps prevent the plastic from being blown away by wind. Machines that lay down the plastic are available to automate the process.

Solarization must be done during the summer and should be started at least by the beginning of August to have sufficient time (4 to 6 weeks) to complete the process. Clear plastic or a plastic with a coating that suppresses weed seed germination can be used. Black plastic suppresses weed seed germination but will not heat the soil sufficiently for solarization. Plastic mulches may not be successful in suppressing species like nutsedge.

After plantingtree-row management. Similar to many conventionally managed orchards, weeds in the middles of organic orchards are commonly managed with cover crops and/or mowing. However, weeds in the tree row must be managed nonchemically with in-row cultivation, cross discing, mulches, hand hoeing or flaming. The choice of method depends in part on the type of irrigation system.

Furrow-irrigated orchards. Furrow-irrigated orchards are amenable to in-row cultivation. Several companies make cultivation equipment. Trip mechanisms on orchard cultivators prevent damage to the trees. Cross discing of young trees is also possible but requires furrowing after each discing. Weeds close to the trunk of the tree can be removed by hand hoeing, flaming, or an organic herbicide.

Sprinkler-irrigated orchards. In-row cultivators move in and out of the tree row to control weeds and they may damage sprinkler systems. In-row cultivation or mowing may be possible if extra protection is provided to ensure proper operation of the trigger mechanism on the cultivator so that the cultivator moves away from the sprinkler as it does for the tree.

Microsprinkler-irrigated orchards. Few options are available in organic orchards with microsprinklers. In-row cultivators may damage irrigation lines and emitters. Surface lines can be suspended in the trees or on stakes to allow for in-row mowing, cultivation, or flaming underneath. The microsprinklers are suspended upside down. Hand weeding and possibly flaming could be used for weed control. Flaming may be effective on weeds that are typically smaller than 8 leaves. When flaming is used repeatedly, grasses will eventually become the dominant weeds because their growing points are close to the ground. Also, perennial weeds are not controlled with flaming. Protect trunks of young trees from flamers to avoid injury to the cambium layer of the tree; also keep flamers away from the plastic irrigation tubing. Mulches can suppress weed growth. Weeds that emerge through the mulches must be removed by hand weeding.

Drip-irrigated orchards. Weed control options for drip-irrigated orchards are similar to those available for micro-sprinklers. However, if subsurface drip irrigation is used, free moisture near the soil surface is limited and summer annual weed will not germinate, assuming rainfall does not occur. Cultivation, flaming, or mulches can all be used with a subsurface drip system.

Geese can often be used to manage grass weeds in orchards. Generally, about 4 geese per acre are needed. They require water for drinking, and some form of protection from predators (dogs, coyotes, etc.). Young geese are preferred, as they eat larger quantities of food, although having at least one older goose, helps to protect the younger birds. Consult the following Website for further information on geese: http://www.metzerfarms.com/weeder.htm

After plantingmiddles management. Consider planting a cover crop in the area between tree rows. Resident vegetation does not usually grow uniformly enough to compete well with newly invading weeds. In addition, resident vegetation includes weed species that continually colonize the tree row. An annual cover crop that reseeds itself will compete against weeds and reduce the potential for problems in the future. If there is a potential for frost and the cover crop is tall, mow once before bloom to minimize frost damage; the cover crop will regrow and flower later in the season. However, the cover crop will be most competitive if mowing can be avoided. After most species in the cover crop have produced seed, mow or roll it using a ringroller. The ringroller will allow more seed production and also create a surface mulch that will prevent emergence of weed seeds.

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Plum
UC ANR Publication 3462
Weeds
A. Shrestha, Kearney Agricultural Center, Parlier
W. T. Lanini, Weed Science/Plant Sciences, UC Davis
F. J. A. Niederholzer, UC Cooperative Extension, Sutter-Yuba counties

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