General Information


FENSTOP is a sprayable, broad-spectrum foliar fungicide for control of certain plant diseases of ornamentals. It can be applied as a drench or foliar application to greenhouse grown ornamental plants. Use of FENSTOP should be integrated into an overall disease, pest management, or IPM program. FENSTOP may be used with disease forecasting or Extension advisory programs, which recommend application timings, based on environmental factors favorable to disease development. Applications may be made at the longer spray intervals or lower rates under low to moderate disease pressure while the higher rates in the rate range or shorter spray intervals may be required under conditions of heavy infection pressure, highly susceptible varieties, or when disease conductive environmental conditions exist. FAILURE TO FOLLOW THE DIRECTIONS AND PRECAUTIONS ON THE LABEL MAY RESULT IN POOR DISEASE CONTROL, AND/OR CROP INJURY.

Fungicide Resistance Statement

OHP, Inc encourages responsible resistance management to ensure effective long-term control of the fungal diseases on the label.

Fungal pathogens can develop resistance to products with the same mode of action when used repeatedly. Because resistance development cannot be predicted, use of the product should conform to resistance management strategies established for the particular crop and use area. Consult your local or state agricultural authorities for resistance management strategies that are complimentary to those in the label. Resistance management strategies may include rotating and/or tank-mixing with products having different modes of action or limiting the total number of applications per season.

FENSTOP is an imidazolinone fungicide that exhibits no known cross resistance to fungicide chemistry such as sterol inhibitors, dicarboximides, benzimidazoles, anilinopyridines or phenylamides.

FENSTOP is an inhibitor of the Qo (quinone outside) site within the electron transport system (QOI inhibitor) in several plant pathogenic fungal species. FENSTOP does exhibit cross-resistance, in certain plant pathogenic fungi, to fungicides of the QOI group; this includes certain strobilurin compounds such as azoxystrobin and trifloxystrobin.

Do not use a fungicide from The QOI group for more than 1/2 of the total sprays in any one season. Do not use a QOI fungicide for more than 3 sequential applications or more than 6 times per season (including in mixtures). Avoid alternation of FENSTOP with other fungicides in the QOI group.


Ground Application

Apply in a minimum of 15 gallons of water per acre. Thorough uniform coverage is essential for effective disease control.


FENSTOP alone or in tank mixture with other pesticides which are registered for overhead, microjet, or drip application may be applied in irrigation water at rates recommended on the label. Follow the label directions for the most restrictive of label limitations and precautions. The product cannot be mixed with any product containing a label prohibition against such mixing. Apply the product only through an overhead, microjet, or drip irrigation system. Do not apply the product through any other type of irrigation system. Plant injury or lack of effectiveness can result from nonuniform distribution of treated water. If you have questions about calibration, you should contact State Extension specialists, equipment manufacturers, or other experts. Do not connect an irrigation system (including greenhouse systems) used for pesticide application to a public water system unless the pesticide label-prescribed safety device for public water systems are in place. A person knowledgeable of the chemigation system and responsible for its operation, or under the supervision of the responsible person, shall shut the system down and make necessary adjustments should the need arise. Public water system means a system for the provision to the public of piped water for human consumption if such system has a least 15 service connections or regularly serves an average of at least 25 individuals daily or at least 60 days out of the year.


- The system must contain a functional check valve, vacuum relief valve, and low pressure drain appropriately located on the irrigation pipeline to prevent water source contamination from back flow. Chemigation systems connected to public water systems must contain a functional, reduced-pressure zone, back-flow preventer (RPZ) or the functional equivalent in the water supply line upstream from the point of pesticide introduction. As an option to the RPZ, the water from the public water system should be discharged into a reservoir tank prior to pesticide introduction. There shall be a complete physical break (air gap) between the outlet end of the fill pipe and the top or overflow rim of the reservoir tank of at least twice the inside diameter of the fill pipe.

- The pesticide injection pipeline must contain a functional, automatic, quick-closing check valve to prevent the flow of fluid back toward the injection pump.

- The pesticide injection pipeline must also contain a functional, normally closed, solenoid-operated valve located on the intake side of the injection pump and connected to the system interlock to prevent fluid from being withdrawn from the supply tank when the irrigation system is either automatically or manually shut down.

- The system must contain functional interlocking controls to automatically shut off the pesticide injection pump when the water pump motor stops.

- The irrigation line or water pump must include a functional pressure switch which will stop the water pump motor when the water pressure decreases to the point where pesticide distribution is adversely affected.

- Systems must use a metering pump, such as a positive displacement injection pump (e.g., diaphragm pump) effectively designed and constructed of materials that are compatible with pesticides and capable of being fitted with a system interlock.

- Do not apply when wind speed favors drift beyond the area intended for treatment.

- Prepare a mixture of FENSTOP in water, and inject this mixture into the system. Injecting a larger volume of a more dilute mixture per hour will usually provide more accurate calibration of metering equipment. Maintain sufficient agitation to keep the fungicide in suspension.

- Meter into irrigation water during the beginning of the irrigation cycle.

- With overhead or microjet systems, apply enough water to thoroughly wet the potting media.

Precaution for irrigation applications: Where distribution patterns do not overlap sufficiently, unacceptable control may result. Where distribution patterns overlap excessively, injury to desirable plants may result.


Use FENSTOP on ornamentals such as Alyssum, Azalea, Bee Balm (Monarda), Easter Lily, English Ivy, Geranium, Hybrid Tea roses, Ivy, Lilac, Pelargonium, Poinsettia, Rhododendron, Spathiphyllum and Vinca, grown in greenhouses for control of diseases caused by Pythium, Phytophthora, and downy mildew. Applications should be made prior to disease development and should be made in conjunction with good cultural management practices. Use the higher rate and/or shorter interval when disease pressure is severe. Do not exceed recommended rates or apply more frequently than at specified intervals or plant injury may occur.


Plant tolerances to FENSTOP have been found to be acceptable in the specific genera and species listed on the label. It is not possible to evaluate every species or variety of ornamental plant for its tolerance to FENSTOP. The user should test for possible phytotoxic responses in other plants on a small area basis using recommended rates prior to commercial use.

Limitations, Restrictions, and Exceptions


- For Pythium and Phytophthora control, mix 7.0 to 14.0 fl. oz. of product with 50-100 gallons of water and apply to 400 sq. ft. (equivalent to 1-2 pts. solution per sq. ft.) Repeat as necessary on a 28-day spray schedule. Do not apply more than four applications of the maximum rate per crop per season.

Restricted Entry Interval

12 hours