Weed problems have increased as strawberry growers have transitioned away from methyl bromide. Two of the most troublesome weeds in strawberry fields are yellow and purple nutsedge (Figures 1 and 2). Nutsedges are perennial weeds that spread via underground roots called rhizomes and vegetatively produced structures known as tubers. Yellow nutsedge produces fewer but larger tubers located at the end of rhizomes whereas purple nutsedge produces more, smaller tubers in a chain along the rhizome. Nutsedge is well adapted for growth in plasticulture production systems. It is able to penetrate the majority of commercially used plastic mulches and spreads rapidly.
It is important to keep the nutsedge population as small as possible. The grower should focus on year-round control to prevent wide-scale establishment and spread of this weed. This involves selecting and correctly applying a good fumigant system, spot spraying, applying postharvest herbicides and/or fumigants, and implementing fallow period tillage, herbicide, and cover crop programs.
For areas of a field that have a history of nutsedge problems, it is important to use a full fumigant system. Fumigant systems consisting of only 1,3-dichloropropene and/or chloropicrin, such as Telone® II and 100% chloropicrin or premixes like Telone® C35 and PicClor® 60, may not provide satisfactory control of nutsedge. In long-term trials the use of these systems actually increased the amount of nutsedge present in the field over time. Paladin is an alternative option that can provide excellent control. The use of a three-way system consisting of Telone® II, chloropicrin, and KPam® or Vapam® will also provide good to excellent control. When using KPam® or Vapam®, a minicoulter rig provides the best control of nutsedge; however, if using drip applications, good control can be achieved if the grower uses two drip tapes to maximize coverage of the bed. The use of totally impermeable films (TIF) instead virtually impermeable (VIF) or low density films can substantially reduce nutsedge density in the presence or absence of a fumigant.
Yellow and purple nutsedge will be a major factor in future fumigation decisions. Preventing this weed from obtaining a foothold may allow strawberry growers to use a reduced fumigant system, provided they are willing to spend time removing any escaped nutsedge populations from their production fields.
If nutsedge is emerging through plastic mulch, it is important to spot spray a glyphosate product (Roundup®, Touchdown HiTech®, Glyfos Xtra®, etc.) to kill the top growth as well as the tubers the plant is producing. Hand pulling will only result in removing the top growth, and repeat pulling may take all season before exhausting the root reserves of an established plant.
At the end of the growing season, either an application of a fumigant in the drip tape or a postemergent application of a glyphosate product will be needed to reduce the population of nutsedge tubers present in the soil. The use of a fumigant can also help in reducing disease and nematode populations.
Maintaining control of nutsedge requires an active management plan. The key is to break the rhizome that the tubers are attached to so as to maximize nutsedge emergence at a time when control measures can be applied. For example, use tillage to break the rhizome and follow that with an application of glyphosate after the nutsedge shoots have emerged. Follow the glyphosate application with a cover crop that will form a canopy quickly and hinder further nutsedge emergence. Broadleaf cover crops tend to develop thicker crop canopies and are well suited to preventing light from reaching the soil surface.
Initial infestations of nutsedge will come from the edges of the field (Figure 3) and may obtain a foothold at the end of the rows where the fumigant has not been properly applied. It is important to maintain good weed-management practices around the edges of the field. A little time spent at the early stages of infestation can help reduce the possibility of a nutsedge population increasing to the point where a full fumigant system will be required to keep the population below damaging levels.