Weed Science Research & Herbicides

Preemergence herbicides should be recommended as the “backbone” of a landscape weed control program. Achieving satisfactory weed control generally requires repeated applications of one or more herbicides (Gilliam, 1989). Two applications, one in the spring (March) and one in the fall (August) of preemergence herbicides are recommended. Using less than two, in most situations, will result in more frequent use of postemergence herbicides and thus increased potential injury to ornamental plants. The use of postemergence herbicides versus preemergence herbicides is always a high-risk behavior!

Also rates have declined with newer preemergent herbicides, released to the ornamental market, further increasing their safety around ornamental plants and in the environment (Table 1). The lowest use rate in the ornamental market today is with (indaziflam)(Table 1), followed by BroadStar, FreeHand and Biathlon (Table 1). OHP, Inc., Mainland, PA launched the granular Marengo in September, 2013 for nursery containers. The Marengo SC formulation had been released in 2012. Indaziflam is also registered for landscape use as Specticle G. The attributes of indaziflam are long-lasting, soil degradation not occurring until 150 days after treatment (DAT), non-volatile, non-mobile in soil once watered in and less required applications. Indaziflam also requires only 0.25” of irrigation or rainfall to activate, half that required for other products and it is effectively incorporated up to 21 DAT. In addition, the Verge ™ granule used for Marengo G and Biathlon 2.75G, further reduces injury to desired plants while maintaining exceptional weed control (efficacy) and residual control. Continue to read the Full Article here.

Table 1. Standard use rates of common granular preemergence herbicides used in landscape beds and nurseries comparing older products to newer products released on the market in the past 5 years.

Trade name Landscape rate lb./ac Active ingredient (ai) names lb. a.i./ ac
Snapshot 2.5 TG 150 Trifluralin + Isoxaben 3.75
Rout 100 Oxyfluorfen + Oryzalin 3.0
OH-2 100 Oxyfluorfen + Pendimethalin 3.0
Regal Star 100 Oxadiazon + Prodiamine 3.0
Ronstar G 200 Oxadiazon 4.0
BroadStar 0.25G 150 Flumioxazin 0.375
FreeHand 1.75 G 150 Dimethamid-p + Pendimethalin 2.63
Biathlon 2.75 G 100 Oxyfluorfen + Prodiamine 2.75
Marengo G 200 Indaziflam 0.0448