Moss Control in Lawns

Shawn Askew, Professor and Extension Turfgrass Weed Specialist

The following was an inquiry from a lawn care operator in Virginia.

QUESTION (LCO): "My client is trying to kill moss in their yard in central Virginia. The home is in a wooded area and no doubt the shade is a contributing factor to moss development. The homeowner has tried glyphosate and Scotts MossEx, but the moss just turns brown and in 3 weeks comes right back from the roots. Do you have any additional thoughts to aid in moss management?"

ANSWER (Dr. Askew): There aren’t any “easy” solutions for lawn moss. Practically all mosses are immune to glyphosate. They have evolved a different type of ESPS enzyme.  MossEx contains the fertilizer ferrous sulfate. Research has shown that extremely high rates of FS can suppress moss on putting greens, but I would expect about what your client observed on lawns: a slight burn followed by quick recovery.

The best product currently marketed for selective moss control is Quicksilver T&O Herbicide by FMC Corporation (the active ingredient is carfentrazone).  This product will cause a more substantial discoloration of the moss compared to MossEx and can be used in sequence with Moss EX, but it does not completely kill moss. For best results, consider the following:

  1. Treat with Quicksilver at recommended spot-treatment rate (9 milliliters product per gallon water per 1,000 ft2).
  2. Moss will turn brown within 4 days.
  3. Once moss reaches peak injury, use a vertical mower, garden rake, weed eater, or some means to aggressively dislodge the moss from soil.
  4. Rake or blow the moss debris away from the infected area and deposit in an area where moss would not be an issue or bag and discard.
  5. Seed the area with desirable turfgrass (consider shade-tolerant species such as the fine fescues, but this will depend on the lawn grass currently managed). Note: the ideal times to seed cool-season turfgrasses are in late summer to mid-fall and early-mid spring.
  6. Fertilize the area to meet turfgrass needs and use MossEx in conjunction with fertilizer. Iron is a foliar feed that bolsters turf competition while also burning any green moss.
  7. When moss starts to recover, treat again with Quicksilver after about 2 weeks. It will be safe to use over young, developing grass seedlings if seed has been planted.
  8. This entire practice may be needed twice annually to achieve near eradication of moss. The more turfgrass cover you can obtain, the less moss you will have.
  9. If environmental conditions are not changed to favor turf then consider removing trees, selectively trimming tree limbs to improve light penetration, conducting soil test, alleviate soil compaction, improve drainage and air circulation, ... etc.) then moss will begin to return in the next season and some level of routine maintenance will be required to keep it out.