Tropical and subtropical fruits (2+1)

Weed Management

It is critical to have minimum or no weed competition at the time of planting new vines 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. Weed seeds located in the surface 4 inches of soil can be buried to depths where they cannot emerge with a soil-inverting plow such as a Kverneland plow; a moldboard plow will not sufficiently invert the soil to be effective.
Soil solarization

Soil solarization of the planned vine 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. Bury all sides of the plastic 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 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.
WEED MANAGEMENT AFTER PLANTING
Cultivation

• Mechanical cultivation uproots or buries weeds. Weed burial works best on small weeds, while larger weeds are better controlled by destroying the root-shoot connection or by slicing, cutting, or turning the soil to separate the root system from the soil. Keep cultivation shallow to minimize damage to crop roots and to avoid bringing more weed seeds near the surface to germinate.
• Perennial weeds with established root systems are difficult to kill with a single tillage operation. With tillage, the top is removed and a new top is generated using the underground reserves. For perennials, tilling 3- or 4-inches deep reduces the reserves, forcing the weeds to use a greater portion of the reserves available to regenerate. Several companies make cultivation equipment. Trip mechanisms on vineyard cultivators prevent damage to the vines. Even the best cultivators will not eliminate all weeds, thus hand hoeing is often needed. Hand cultivation alone may be effective on a small scale.
Mulches

• Mulches can also help with weed control in the vineyard. The mulch blocks light, preventing weed germination or growth.
  
• Many materials can be used as mulches including municipal yard waste, wood chips, straw, hay, sawdust, and newspaper.
  
• To be effective, mulches need to block all light to the weeds; therefore different mulch materials vary in the depth necessary to accomplish this.
  
• Organic mulches must be maintained in a layer 4 or more inches thick.
  
• Organic mulches breakdown with time and the original thickness typically is reduced by 60% after one year. Cover crops can be grown in the middles; in the spring "mow-and-throw" the mulch in around the base of the vines.
  
• Weeds that emerge through the mulch can be controlled using an organic contact herbicide or with hand hoeing.
  
• Do not plant cover crops under the vine row because excess competition may occur, possibly reducing grape yields.
Herbicides

• Several organic, contact-type herbicide products are registered for use.
• These soap-based (Scythe), clove oil based (Matran 2), or acetic acid based (All-Down) products all damage any green vegetation contacted, including the leaves and young stems of grape vines.
• Apply these products as directed sprays against woody stems and trunks. Because these herbicides only kill contacted tissue, good coverage is essential. Thus, adding an organically acceptable surfactant is recommended. Because these materials lack residual activity, repeat applications will be needed to control new flushes of weeds.