2008 Bentgrass Tolerance to Citrus Oil, Worry Free Moss and Algae Control, Garden Safe Moss and Algae Killer, and Lilly Miller Moss-Out Applications to Control Lawn Moss


The objective of this trial was to compare two formulations of citrus oil (d-limonene) at three rates with three commercial standards (Worry Free Moss & Algae Control, Garden Safe Moss & Algae Killer, and Lilly Miller Moss-Out) sprayed at 2x label rate to determine bentgrass tolerance to these products.

Materials and Methods

The trial was initiated on February 20th at the Lewis-Brown Horticulture Farm in Corvallis, Oregon. The trial site was a stand of different varieties of colonial bentgrass which was planted several years ago and was growing on a silty clay loam soil with a pH near 6.0.

The weather on the date of application was foggy in the morning and overcast until 1 p.m. The products were applied between 2:20 pm and 3:45 pm. The sun was out during the application of all the products. The temperature and relative humidity at 2:20 pm was 53 degrees Fahrenheit and 71%, respectively.

All treatments were applied with a CO2-powered plot sprayer with a 5 foot boom using TeeJet 80015 flat fan nozzles spraying 2 gallons per 1,000 square feet. All products were applied at a spray volume of 6 gallons per 1,000 square feet by spraying each plot three times.

Because of cold temperatures and adequate rainfall, the plots were neither mowed nor irrigated during the duration of the trial.

The trial was set up as a randomized complete block design with three replications using a plot size of 5 X 5 (25 square feet).

Visual turf injury ratings were made on February 23 (3 DAT), February 27 (7 DAT), March 5 (14 DAT), March 18 (4 WAT), and April 18 (8 WAT). The data for each rating date were subjected to analysis of variance (ANOVA) and differences between means were determined by LSD at the 5% level.

The treatments applied were as follows:

Trt #ProductsRate (oz)
Product per 1,000
Spray Volume
Gallons per 1,000
1Moss-1 70 % ai (d-limonene)116
2Moss-1 70 % ai (d-limonene)226
3Moss-1 70 % ai (d-limonene)336
4Moss-2 70 % ai (d-limonene)116
5Moss-2 70 % ai (d-limonene)226
6Moss-2 70 % ai (d-limonene)336
7Lilly Miller Worry Free Moss & Algae*646
8Garden Safe Moss & Algae Killer (22%)*1606
9Lilly Miller Moss-Out (9.75 % iron)*1286

* The active ingredient in the Worry Free Moss & Algae Control product is 15% sodium lauryl sulfate and 6% citric acid. The active ingredient in Garden Safe is potassium soap of fatty acids. The active ingredient of Moss-Out is ferric sulfate.


With the exception of treatments 3 and 8, all the treatments had at most only minor leaf tip burn which recovered within 28 days. Although the leaf burn was severe in the case of treatments 3 & 8 (Moss-1 at the 33 oz rate & Garden Safe Moss & Algae Killer), no turf death occurred and the turf showed only minor injury after 28 days after treatment (See turf injury data and photos on page 3). There was no turf injury observable 8 weeks after treatment.

Table 1: Turf Injury Ratings

   Injury Ratings 1 - 9; 1 - no injury
Trt #ProductsRate (oz)
Product per 1,000
3 DAT* Avg
7 DAT Avg
14 DAT Avg
4 WAT* Avg
8 WAT Avg
1Moss-1 70 % ai (d-limonene)1111111
2Moss-1 70 % ai (d-limonene)
3Moss-1 70 % ai (d-limonene)336.36.351.31
4Moss-2 70 % ai (d-limonene)1111111
5Moss-2 70 % ai (d-limonene)2211111
6Moss-2 70 % ai (d-limonene)333.33.33.321
7Worry Free Moss & Algae Control6411111
8Garden Safe Moss & Algae (22%)1607.37.36.331 
9Lilly Miller Moss-Out (9.75 % iron)12833311
  LSD @ .050.650.650.730.6na

* DAT = days after treatment; WAT = weeks after treatment