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Greenhouse Updates: Mar 16, 2020

Season Kick-Off Considerations, Pavement Ants
March 16, 2020

Season Kick-Off Considerations

Mild temperatures and lack of snow cover during the second half of the winter have accelerated the pace of preparation and activities around greenhouse crop production. If the pattern stays as it is, it looks to be an early season. With that said, it is easy to get caught up in the hustle and bustle and overlook some of the details. The following are important points to cover as we transition from winter to spring:

  • Spring into cleaning - Plugs and seeds are being planted at this time, and young plants are being moved into greenhouses. Before moving in new plants, be attentive to sanitation to help curb existing pest populations. That means tidying up, cleaning up debris, and thorough cleaning and disinfection.
  • Take a look - Be sure to carefully monitor all overwintering plant material for pest activity. Leafhoppers were observed last week on overwintering rosemary plants. Whiteflies and twospotted spider mites are other common culprits. Don’t forget to also inspect incoming plant material for pest presence and consider dipping plugs and cuttings.
  • Nip it in the bud - Eradicate weeds both inside of and outside of the greenhouse, as weeds can be a reservoir for pests and pathogens. Thrips have been observed recently on pepper and tomato seedlings, and the suspected cause is that they overwintered on weeds in a weedy greenhouse.

Careful attention to pest activity at this time will pay dividends all season in the form of lower pesticide use, better performance from biological controls, reduced management attention, and ultimately, higher quality plants.

Pavement Ants in the Greenhouse

Pavement ants (Tetramorium caespitum) were reported damaging petunia plants in a greenhouse last week. The plants were in pots placed on a pallet on the floor of the greenhouse. Symptomatic plants displayed a yellow coloration.

Damage to greenhouse crops by ants is a rare occurrence, but not unheard of. Several years ago, injury to bedding plants including petunia, marigold and pansy by pavement ants was reported in Maryland (UMD Extension Greenhouse IPM Report, March 18, 2011). The ants can damage the roots and girdle the stems of plants causing them to turn yellow and collapse.

Pavement ants get their name because they often nest under sidewalks, driveways and building foundations. The ant workers are about 2.5-4 mm long and vary in color from dark brown to black, with light colored legs and antennae. The waist (pedicel) has two nodes. There are distinctive parallel ridges or grooves on the head and thorax. The thorax has a pair of small spines on the upper back.  See additional identification information with pictures from Universty of Nebraska Extension:

Pavement ants that are are causing plan injury can be controlled by using DuraGuard ME (chlorpyrifos) as a drench or as a spray to the surface of the soil. Do not use on Kalanchoes (refer to the label for complete plant list and rates). Pavement ants can also be managed by incorporating or treating the growing media with granular Talstar (bifenthrin) insecticide, or applying the flowable formulation of Talstar to containers to the point of saturation.


- Jason Lanier and Geoffrey Njue, UMass Extension, with Jim Mussoni, Private IPM Scout