Greenhouse Rose Fungicide Tank-Mix Conflict
A commercial applicator is called to a 2,400-square-foot glass greenhouse in Ward 5 where cut roses show white powdery patches on upper leaves and distorted new growth. The house is closed, air temperature is 86°F, and relative humidity is 70%. The applicator has two products on the truck. Product A is a wettable-powder fungicide labeled for greenhouse roses at 8 oz per 100 gal; its label states: “Do not tank-mix with emulsifiable concentrates or adjuvants containing petroleum distillates.” Product B is an emulsifiable-concentrate fungicide labeled for powdery mildew on ornamentals, but its label states: “Do not apply in greenhouses or other enclosed structures.” The applicator proposes to mix A and B plus a petroleum-distillate oil to improve coverage, then spray the entire house before vents are opened. The grower wants the problem gone before a weekend open house. Product A is a FRAC group 11 fungicide; Product B is group 3.
1. What should the applicator do before mixing, and may the proposed tank mix be made? Explain the label and compatibility reasoning.
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No. Product B’s label prohibits application in greenhouses or other enclosed structures, so it cannot be used in this glass house regardless of tank-mix compatibility. Product A’s label prohibits tank-mixing with emulsifiable concentrates or adjuvants containing petroleum distillates; Product B is an EC and the proposed oil contains petroleum distillates, so the A+B+oil mix is also prohibited. The applicator should read both labels and the oil label, check the site (greenhouse roses) and pest (powdery mildew) on each, and not rely on verbal advice. Because the house is closed at 86°F, even a legal product may volatilize or injure foliage; the applicator should ventilate, test on a few plants, and follow reentry and PPE requirements. If A is used alone, confirm the 8 oz/100 gal rate and whether the label allows an adjuvant; choose a non-petroleum adjuvant only if the label permits. Document the decision.
2. Assuming the applicator uses only a legal product, outline a treatment and resistance-management plan for the greenhouse, including PPE and ventilation.
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Use Product A alone only if its label permits the site and rate; do not add the prohibited oil or B. Because A is FRAC 11 (QoI), resistance risk is high, especially with repeated use. Apply at the labeled 8 oz/100 gal interval, but plan to rotate to a product with a different FRAC group and a different site of action after the labeled number of applications; do not rotate only among group 11 products. Improve cultural controls: increase air movement, avoid overcrowding, water at the base, remove badly infected leaves, and avoid working wet foliage. Ventilate the house before, during, and after spraying to reduce inhalation and phytotoxicity; use the label-specified respirator, gloves, coveralls, and eye protection. Post reentry signs and observe the reentry interval. Recheck plants 3–5 days later; if no improvement, do not simply retank-diagnose the disease and confirm the product was mixed correctly.