Managing Weeds in Woody Nursery Stock: Introduction

Excerpt from 2008 Chapter 16, Publication 75, Guide to Weed Control, Order this publication

Introduction

• A successful weed control program must integrate cultural and chemical weed control practices. The best weed management system for Nursery Crops uses a combination of chemical weed control with cultivation and other techniques. See Chapter 1, Principles of Integrated Weed Management.
• Cultural Weed Control -See notes on Cultural Weed Control in Fruit Crops section.
• Field Grown Nursery Stock: Mechanical weed control such as cultivation and hand hoeing will provide weed control in sensitive species as well as provide control of weed escapes. Cultivators are available which will work in between trees and in the row.
• Container Beds:
  • Prepare the container bed area with a gravel layer and/or ground covers such as black plastic or opaque woven material. It is important that these surface covers exclude light in order to be effective in preventing weed seed germination. These ground covers can be used for a number of years before being replaced.
  • Keep the container beds and roadways free of weeds by physical removal or chemical mowing. Prevent weeds from setting seed in adjacent uncropped areas by using cultural or chemical weed control measures. Mowing at regular intervals will prevent many weeds from flowering. Try to control weed escapes before they set seed by cultural removal or chemical mowing. In some situations, such as along fences, tools such as a weed whip may be useful. Look for the source of weeds that disseminate into container areas such as poplars, willows, willowherb and Canada fleabane.
  • Control weeds around irrigation ponds so that small seeded weeds are not being sown into container stock with each watering. A vigorous grassed bank will help reduce weed infestations as well as providing bank stabilization. A filtering system in the irrigation line will remove weed seeds.
  • Removal of existing weeds from container stock before they flower must be a priority job. Once a weed flowers it can disseminate hundreds of seeds by wind or by catapulting seeds. Many container weed species have several generations per year because their seeds do not need to overwinter before germinating. Remove and discard all pulled weeds well away from the growing area so that seeds are not disseminated into nearby containers.
  • Since many species of container weeds overwinter in the protected environment of a polyhouse, it is important to thoroughly weed container stock in the fall. Be sure to remove the rosettes of winter annuals such as shepherd's-purse and Canada fleabane and established plants and seedlings of common and mouse-eared chickweed. If not removed, these plants will be flowering by May or earlier.
• Container Stock in Poly Houses: Do NOT apply herbicides within covered polyhouses, or within four weeks before covering. Certain types of container stock may be injured by the following herbicides. Check manufacturer's directions for labeled species/cultivars before use.
• Site Preparation Before Planting - see Chapter 6, Special Methods of Weed Control
• All treatments should be applied in 150-300 L/ha (60-120 L/ac) water.
• Recommended rates /ha or /ac refer to area actually treated with herbicide.
• To convert kg/ha or L/ha to g/100m² or mL/100m² - Multiply by 10 and change units.
  For example - 11 kg/ha becomes 110 g/100m²; 28.4 L/ha becomes 284 mL/100m²
• Herbicide Application Timings:
  • Soil Applied Treatments include:
    • Preplant (PP) - Also see Chapter 6, Special Methods of Weed Control for details of products, rates and remarks.
    • Preplant Incorporated (PPI) - Two incorporations at right angles operating at a depth of 10 cm using a double disk (7-10 km/hr) or vibrating shank S-tine cultivator (10-13 km/hr) are required unless otherwise stated. Cultivation-type equipment used for herbicide incorporation is known to spread perennial weeds to previously uninfested areas. Special attention should be directed toward machinery cleanliness, and/or treating fields with perennial weeds last.
    • Preemergence (PRE) - Rainfall of 15-20 mm within 7-10 days after application is necessary to activate preemergence treatments. Shallow cultivation, rotary hoeing or harrowing will control weed escapes and improves herbicide activity in the absence of rainfall.
  • Postemergence (POST) - Leaf stage of the weeds is critical for good weed control. Smaller weeds are generally easier to kill but there needs to be enough leaf surface to intercept the herbicide. Apply according to recommended leaf stages. Crop stage is important to optimize crop safety. Adjuvants will frequently improve the weed control when used as directed. Weather or other conditions may influence the optimum rate of adjuvant, see the product label for more details. Always use appropriate drift management technology.
• WARNING - Refer to manufacturers' instructions for waiting period required after planting.
• WARNING: Certain types of woody nursery stock may be injured by the following herbicides. Check manufacturer's directions for labeled species/cultivars before use.

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Related Links

• Weeds in Ontario
• Nursery and Landscape Plants in Ontario
• Problem Weed Control in Field Crops
• Integrated Pest Management (IPM)
• Pesticide Application and Safety
• Pesticide Companies and Agents
• OMAFRA Sprayer Calibration Calculator
• Search the PMRA website
• OMAFRA Publication 505: Ontario Weeds
• OMAFRA Publication 75: Guide To Weed Control

   

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