Vegetable pesticide series: Can I use it in the greenhouse?

A greenhouse chemical usage guide for vegetable growers.

Pesticide use in the greenhouse

Vegetable growers often use greenhouses or hoop houses to start transplants for field production or for full-season protected culture. Certain types of pests and diseases can be reduced in these controlled settings, but the occasional outbreak may require treatment from a pesticide. Vegetable transplants can sometimes benefit from preventative applications of a fungicide before they reach the field.

Many foliar-applied pesticides have longer residuals in certain greenhouse settings. Usually, pesticides degrade with exposure to sunlight. Greenhouses that use UV-blocking materials remove a large spectrum of light between 10 and 400 nm that we cannot see with our own eyes, but contributes to pesticide degradation. Therefore, sidewalls and coverings that block UV light increase residual activity of pesticides.

Glass and acrylic sheeting and untreated polyethylene films allow the most amount of light across the entire spectrum to penetrate to the crop canopy. Fiberglass, polycarbonate and rigid PVC sheeting, as well as PVC and treated polyethylene films can either partially-block or fully-block UV light.

Greenhouse label language

The label is law. Label language will indicate whether a certain pesticide application is allowed in a greenhouse, and a restriction statement is usually found in the “Directions for Use” section. Very often, greenhouse applications are only allowed on certain crops or crop stages.

Some labels contain different rates and recommendations for the same crop inside and outside of a greenhouse. For example, streptomycin is an antibiotic that is only allowed on tomato transplants in the greenhouse as an effective control for bacterial diseases, and is not allowed for use on outdoor tomatoes at all.

Occasionally, a label will not indicate greenhouse restrictions, but also will not provide special instructions for greenhouse use. When the label is silent on greenhouse use, it is classified as an implied use, and can be used as long as the target crop is on the label.

How does Michigan define a greenhouse?

The Michigan Department of Agriculture and Rural Development (MDARD) defers to the Worker Protection Standard (WPS) for its definition of a greenhouse. The most recent update to the WPS has termed it “enclosed space production,” and defines it as “production of an agricultural plant indoors or in a structure or space that is covered in whole or in part by any nonporous covering and that is large enough to permit a person to enter”.

So, if a pesticide label does not allow its use in an “enclosed space production” area, then you cannot use it in a poly film hoop house even when the sidewalls rolled up and end walls are open. The Environmental Protection Agency (EPA) anticipates most greenhouses, hoop houses, high tunnels and similar structures will fall within the definition of enclosed space production, but a final determination will be made on a case-by-case basis applying the parameters of the definition to each situation.

Some operations will use “shade cloth” during certain production or market phases. Shade cloth used within a greenhouse would be subject to the “enclosed space production” procedures. Where shade cloth is the sole “covering,” the employer will need to determine if the particular material is porous or nonporous.

In addition, there are “porous” versions of Polyethylene (PE), Polypropylene (PP), Polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE) and Ethyl Vinyl Acetate (EVA). As there has not been guidance issued on these materials, consider the traditional greenhouse structures to be “enclosed space production” areas.

Worker pesticide safety and greenhouse applications

Greenhouse pesticide applications require compliance with re-entry and spray notification regulations under the WPS. The following table is modified from the “How to Comply with the 2015 Revised Worker Protection Standard” manual, and identifies the entry restrictions when applying pesticides for enclosed space production to ensure workers and other persons are not exposed to the pesticides being applied. The restrictions depend on the types of pesticides or application method used. Read the table by starting in Column A and following the scenario to Column D.

Entry restrictions during enclosed space production pesticide applications.

A. When a pesticide is applied:B. Workers and other persons, other than appropriately trained and equipped handlers, are prohibited in the:C. Until:D. After the ventilation time has expired, the restricted-entry interval:
(1) As a fumigant. Entire enclosed space plus any adjacent structure or area that cannot be sealed off from the treated area. *The ventilation criteria are met. Continues from the time of application.
(2) As a smoke, mist or fog, or as a spray using extra fine, very fine or fine nozzles.  Entire enclosed space. *The ventilation criteria are met. Begins for the entire enclosed space.
(3) Not as in (1) or (2), and for which a respirator is required for application by the pesticide product labeling. Entire enclosed space. *The ventilation criteria are met. Begins for the treated area.
(4) Not as in (1), (2) or (3), and from a height of greater than 12 inches from the planting medium, OR as a spray using medium or larger coarse nozzles. Treated area plus 25 feet in all directions of the treated area, but not outside the enclosed space. Application is complete. Begins for the treated area.
(5) Otherwise. Treated area. Application is complete. Begins for the treated area.

* When column C of the table specifies ventilation criteria must be met, ventilation must continue until one of the following conditions is met:

  • Ten air exchanges are completed.
  • Two hours of ventilation using fans or other mechanical ventilating systems.
  • Four hours of ventilation using vents, windows or other passive ventilation.
  • Eleven hours with no ventilation followed by one hour of mechanical ventilation.
  • Eleven hours with no ventilation followed by two hours of passive ventilation.
  • Twenty-four hours with no ventilation.

For example: When a pesticide is applied as a smoke, mist or fog, or as a spray using extra fine, very fine or fine (F) nozzles, workers and other persons, other than appropriately trained and equipped handlers, are prohibited in the entire enclosed space until the ventilation criteria are met. After the ventilation time has expired, the restricted-entry interval begins for the entire enclosed space.

A1: Since fumigants are primarily inhalation hazards, the ventilation time counts down along with the product’s restricted-entry interval (REI). If a fumigant had an REI of 48 hours and the grower chose to ventilate for 24 hours without ventilation, they must still wait another 24 hours because the REI is 48 hours total. If the fumigant had an REI of 12 hours and the grower chose to ventilate with 11 hours of no ventilation followed by one hour running the fans, then they would have to wait one more hour to re-enter.

A2: The REI is delayed for non-fumigants because they are considered a residual contact hazard. For a product with an REI of four hours and sprayed in an enclosed space with a fine nozzle, the grower would need to ventilate the entire space by any of those methods listed above before the REI would actually start ticking. If a grower chose to wait 24 hours without ventilation, then that REI is effectively 28 hours.

A3: Products that require a respirator usually have smaller droplet sizes. This increases inhalation hazard while spraying, but once dried and the air ventilated, the product would have a lower airborne likelihood from mechanical forces. An applicator or handler uses a respirator to protect themselves for the potential of inhalation due to mixing, loading or application methods used. No one is allowed into the entire space until it is vented. Then, the REI applies to just the treated area to limit residual contact activity of products.

A4: If the grower used medium nozzles using the same product as in the A2 example, then only the 25-feet around the treated area would need to be ventilated before the REI kicks in. For greenhouses, a treated area can be as small as one plant.

If the REI of the product is greater than four hours in an enclosed space or 48 hours in an outdoor space, a warning sign must be posted for all applications. If the REI is less than or equal to four hours in an enclosed space or 48 hours in an outdoor space, workers can be notified with an oral warning or a posted sign. Employers must also post application locations when a label requires “dual notification” regardless of the stated REI.

Vegetable pesticides that can be used in the greenhouse

So, what commonly used pesticides labeled for vegetable use can be used in the greenhouse? Below is a list in order by trade name. If the label is open to all greenhouse uses, we indicate “yes.” If the label specifically disallows greenhouse uses, we indicate “no,” or cautions against its use, we indicate “avoid.”

If the label makes specific uses allowable in certain crops or crop stages, we put “certain crops only, see label.” In the cases where a label implies a use by not including any greenhouse language, we indicate “silent.” Always double-check the label that comes with your specific product and formulation.

Download printable version of this table.

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