NC State Extension Publications


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Trade Name: Princep, Simazine Common Name: simazine Formulations: 4 L, 90 DF

Preemergence control of many annual broadleaf and grass weeds in field-grown woody nursery stock, Christmas trees and warm-season turf.

Amount of Active Ingredient Amount by Formulation
4 L 90 DF
Per Acre 1.5 to 3 lb 1.5 to 3 qt 1.7 to 3.4 lb
Per 1,000 sq. ft. 1.1 to 2.2 oz 0.6 to 1.25 oz

Major Weeds Controlled

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Many annual broadleaf weeds including common chickweed, horseweed, wild mustards, pigweed, lambsquarters, galinsoga, groundsel, ragweed, and others. Annual grasses such as crabgrass, panicum, and foxtail are somewhat tolerant but can be controlled at the higher rates.

Major Weeds Not Controlled

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Velvetleaf and late-germinating summer annual grasses are often not controlled. Does not control nutsedges. Annual bluegrass is labeled but control is variable. Many species have developed resistance to simazine (a triazine herbicide), including groundsel, lambsquarters, ragweed, and pigweed.

For Best Results

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Apply prior to weed germination in combination with a preemergence grass herbicide such as oryzalin, pendimethalin, prodiamine, dimethenamid-p or s-metolachlor. Typically used in late winter to control spring germinating weeds and again in late summer to control fall germinating weeds. Follow label directions for such tank mixes. Needs 1 to 2 inches of water for optimum activity.

Cautions and Precautions

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Use lower rates on coarse-textured soils and soils low in organic matter. In nurseries, do not apply for at least one year after transplanting. Do not use on seedbeds or cutting beds. Do not apply to Christmas trees less than two years of age. Do not use until soil is firmly settled around roots. Simazine has been restricted or prohibited in certain locations where leaching potential is high; check the product label for specific guidelines.

Residual Activity

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Three to six months of broadleaf weed control can be expected, depending upon rate, soil type and environmental conditions.

Volatility and Leaching Potential

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Essentially nonvolatile. Moderate leaching potential. Leaching can occur on coarse-textured soils. Movement in surface runoff may also occur when heavy rains follow application.

Symptoms and Mode of Action

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Absorbed mostly through the roots. Translocated upward to leaves and growing points. Inhibits photosynthesis. Weed seedlings may emerge from the soil, then turn yellow and die. Symptoms of injury on nursery stock include interveinal chlorosis resembling iron chlorosis, marginal chlorosis and necrosis, reduced vigor, and general chlorosis of the new growth. See Photosystem II herbicide injury fact sheet. MOA Group 5.

Additional Information

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Worker Protection Standards REI: 12 hours (48 hours in Christmas trees)
PPE: coveralls, chemical resistant gloves, shoes plus socks
Manufacturer: Syngenta, many other registrants EPA Reg. # 100-526


Professor of Weed Science and Extension Specialist
Horticultural Science

Publication date: Feb. 27, 2015
Revised: Feb. 17, 2022

Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by NC State University or N.C. A&T State University nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your local N.C. Cooperative Extension county center.

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