Thrips Never Go on Vacation

Despite early intervention with biocontrols and the judicious use of crop protectant chemistries, these pests always seem to regroup and launch a new attack. In the greenhouse environment, thrips management can be made a little easier by utilizing micro screening to keep migrating thrips out. Still, their population can explode once flowering annuals and baskets leave this protected environment for a consumer’s landscape.

Like many gardeners, I dutifully purchase calibrachoas for planters on my front porch each spring. Initially, the calibrachoas will thrive on my porch, and as the dog days of summer approach, the thrips population explodes, and my calibrachoas begin to suffer. I carefully inspect each pot at the local greenhouse for signs of an active thrips population on my plants. While I am thorough in my scouting, I probably will not detect thrips pupae that may be lying in wait on the surface of the potting media below the plant canopy.

While I am well acquainted with the various commercial chemistries that can be used to limit thrips populations in the greenhouse, the number of labeled effective products for home gardeners is quite limited. Releasing biocontrol agents would be a great defense, but few garden centers in my area market sachets of predaceous mites that home gardeners can use to protect their plants once they leave the sales floor.

When confronted by thrips on herbaceous plants in the landscape, commercial landscape managers and home gardeners could opt for using the biopesticide Beauveria bassiana as a softer, earth-friendly approach to thrips management. Horticultural oils and insecticidal soaps will often work equally when trying to curtail a burgeoning thrips population. However, horticultural oils and insecticidal soaps can cause plant injury if the air temperatures are high (over 85° F).

Beauveria bassiana, commonly sold as BotaniGard or Mycotrol, works best when the air temperatures are cooler, so I recommend applying it to the foliage and to the media (for pupating thrips) in the evening so it can be more effective in colonizing the targeted pest. Insecticidal soaps and some horticultural oils can also be tank-mixed with some Beauveria bassiana formulations for increased efficacy against this pest. Please review all pesticide labels carefully before making any application.