Thrips, Resistance, and a Retail Contract in the Poinsettia House

A biological program cannot carry this crop on its own, and the calendar is the reason. Amblyseius cucumeris needs three to four weeks to establish and works best at 70 degrees F or above with relative humidity of 65-75%. This house runs 62 degrees F at night, and the calendar allows nine weeks. Starting beneficials against a population already at 45 thrips per card, with scarring visible, means the predator population has to build while the thrips population is still increasing, and the retailer's damage standard will be judged in nine weeks.

The defensible plan is a chemical knockdown followed by rotation, with biologicals reconsidered only if counts fall far below threshold and the label allows it:

• Spinosad (group 5) first for adult and larval knockdown, at the full label rate with thorough coverage of buds and bracts, since thrips hide in tight tissue.
• Abamectin (group 6) as the rotation partner roughly five to seven days later; it is translaminar and reaches tissue the spray does not wet.
• Pyriproxyfen (group 7C) as a follow-up because it suppresses juveniles and is softer on beneficials, but it will not knock down adults.
• No pyrethroids, given the suspected resistance and the contract.
• Check every product's label for reentry interval and any crop-specific restrictions before scheduling crews.

Rotation rules: never apply the same IRAC group twice in a row, never exceed two consecutive applications of a group within a generation, use full labeled rates (sub-lethal rates select for resistance), and keep a written log of date, product, group, rate, temperature, and thrips count before and after each application.

A workable nine-week sequence:

• Week 0: spinosad (5), full rate, high-volume coverage of the underside of leaves and the bracts.
• Week 1: abamectin (6), switching modes of action.
• Weeks 2-3: pyriproxyfen (7C) to suppress the next generation, then scout hard.
• Weeks 4-6: return to spinosad only if counts exceed the action threshold; otherwise hold and use Beauveria bassiana for low-level suppression, which is compatible with the retailer's restrictions.
• Weeks 7-9: no new chemistry except spot treatment, so residues and damage have time to clear before shipping.

Handling reentry: apply at the end of the workday so the reentry interval runs overnight and crews do not lose paid hours. Post the reentry time at every door, and never send an employee in for spacing or watering before it expires. Scout on sticky cards and plant inspection twice weekly so decisions come from counts, not from the calendar.

Scarring on bracts does not heal, and the contract is written around visible damage, so those plants are a liability no matter how well the spray program works. Cull or pull them out of the shipping blocks now, before more labor and space go into finishing them, and dispose of the plant material away from the house rather than piling it in a corner where it re-infests the crop. Moving that 15% (about 630 plants) out also thins the canopy, improves airflow, and makes coverage on the remaining plants better.

The culling changes the economics of the spray decision: with the most heavily infested plants gone, the population pressure drops, which improves the odds that a rotation program holds through shipping. Do not, however, treat culling as a substitute for the spray program, because the adults that produced that damage are still in the house.

Finally, document the scouting counts and the culls. If the retailer questions damage at delivery, records showing that the damaged plants were removed and that labeled, contract-compliant products were used are the difference between a resolved question and a cancelled order.