Dr. Ron Strahan (Associate Professor, LSU Extension Weed Specialist), David Sexton (LSU Extension Research Associate Specialist), Stuart Gauthier (County Agent/Regional Horticulture Agent, LSU AgCenter)

Weed management continues to be one of the major issues facing blackberry growers in Louisiana.  Grower concerns prompted LSU AgCenter, Weed Scientist Dr. Ron Strahan and St. Martin Parish County Agent, Stuart Gauthier to look at current weed control options. The efficacy of synthetic and organic herbicides as well as organic mulches, inorganic plastic mulch and landscape fabric were evaluated at an on-farm weed control demonstration trial established at the D&D Blackberry Farm in Breaux Bridge, LA in late winter 2020.  Herbicides and mulches were fully installed by March 3rd.  A non-selective herbicide was used to destroy existing weed populations prior to mulch installation and herbicide applications. 

The herbicides evaluated in the weed control demonstration included synthetic preemergence herbicides Princep (simazine), Surflan (oryzalin), Devrinol (napropamide), and Sinbar (turbacil).   Organic herbicides evaluated included Preen Garden (corn gluten), a preemergence herbicide and Scythe (pelargonic acid), a postemergence herbicide. The organic herbicides were applied monthly for the duration of the study.  Organic mulches evaluated at this location included pine bark, pine straw and sugarcane bagasse. Two Inorganic row coverings, GCI 500 Series Landscape Fabric and 1.25 mil black non-degradable plastic mulch were included in the weed control demonstration as well.   Weed control plots were evaluated monthly. 

All mulches tested were equally effective in managing annual weed populations.  Combinations of mulches + preemergence herbicides were highly effective as well.  However, perennial weeds such as bahiagrass, bermudagrass, blue vervain, Virginia buttonweed, and yellow and purple nutsedge were the most common weeds infesting test plots regardless of weed control method used.

Bagasse is a free mulch option in sugarcane production areas of Louisiana
The combination of pine straw mulch and heavy crop canopy suppressed weeds

Earlier weed control work conducted in the fall of 2019 at D & D Berry looked at the winter weed control of annual bluegrass and other winter annuals using a similar line-up of herbicide options.   Napropamide 50 DF (Devrinol) provided the best winter weed suppression in the trial.  

Devrinol at 80 days after treatment
Simazine at 80 days after treatment

Learn more about blackberry weed control options from Dr. Ron Strahan, LSU AgCenter Weed Scientist: