Wax myrtle is the main brush problem on south Florida pasture, especially on wet soils where they can completely takeover and eliminate forage production. Myrtle can be kept in check by burning, which is done on range, but most pasture is heavily grazed, especially in winter, and there is not enough fuel to carry a fire. In addition most ranchers wait until myrtles are four to six feet tall before attempting control, and then myrtles are a real problem. We have been field testing the herbicide, Remedy* for the past five years for control of wax myrtle on several ranches in south Florida. In Florida tests Remedy has been effective against blackberry briars, persimmon, Brasilian pepper and other woody plants.

The herbicides and rates listed in the table were applied on either (not both) 29 March or 23 August 1988. Myrtles averaged 2.2 feet tall in March 1988, but had grown to 3.2 feet in August, 1988. By April 1989, when treatments were evaluated, myrtles had grown to 4.5 feet in untreated plots. Myrtle density was about one plant per 50 square feet About 850 plants per acre).

Results of the field test are presented in the table. Defoliation and plant mortality depended on both herbicide treatment and date of application. Greater rates of Remedy resulted in greater defoliation and mortality than lower Remedy rates or treatment with Banvel** or Crossbow*, which contains the active ingredient in Remedy along with 2, 4-D. We suspected that repeated application of low rates would result in mortality than one application of a high rate, but we are still waiting for results of the double application.

Mortality was related to myrtle size For example when treated in August with Remedy at one pound per acre there was 100 percent mortality in myrtles less that two inches tall, but there was 71 percent mortality in myrtles greater than two inches tall.

Slightly better defoliation and mortality was observed with Remedy and Crossbow when applied in August compared to March. We measured carbohydrate content or energy reserves in roots on 28 day intervals throughout the year and found that carbohydrate content, which was mostly starch, followed a natural cycle where content was greater in March and April, declined until reaching a low in August, then rose steadily in the fall and winter. We suspected this, and it seems that treating the myrtle during "dog days" of August provides better control because plants are naturally weaker than they are in the spring.

It appears that Remedy applied at .5 to one pound per acre in August to wax myrtles under two inches tall is most effective. Remedy is an organo-auxin herbicide, so the provisions of Florida's pesticide law apply. Like 2, 4-D, even small amounts of Remedy and other organ-auxins can cause damage to tomatoes and other sensitive crops, so care must be exercised in application.

Editor's note: Rob Kalmbacher is an agronomist with Ona AREC, and Joe Egar is with Dow chemical, Tampa.

Percent defoliation and mortality of wax myrtle treated either 29 March or 23 August 1988 and Evaluated on 18 April 1989 at Deseret Ranch, Deer Park.
		Defoliation		Mortality
Treatment Herbicide	Rate lb ai/A	March	August	March	August
		-%-
Remedy*	1.00	93a†	99a	67a	79a
Remedy*	0.50	80b	88ab	28b	41ab
Remedy*	0.25	47d	67b	3c	30b
Crossbow*	1.50	75c	83ab	27b	32b
Banvel**	1.00	31e	22c	0c	1c
Untreated	-	0f	0d	0c	0b
† Means within a column followed by the same letter are not statistically different (P<0.05).
* Trademark of The Dow Chemical Company.
** Trademark of Sandez Chemical Company.

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