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Publication #SS-AGR-41

Fireweed (Heartleaf Nettle) Control in Pastures1

J. A. Ferrell and B. A. Sellers2

Introduction

Fireweed (Urtica chamaedryoides) (Figure 1) is native to Florida, but has only recently become problematic. This winter annual species is commonly observed in north and central Florida pastures, particularly in bareground areas (near feeding pens and under fences), as well as along tree lines where forage grasses are less dense.

Figure 1. 

Fireweed (Urtica chamaedryoides).


[Click thumbnail to enlarge.]

Fireweed is particularly troublesome because it possesses stinging hairs that easily embed in skin. Once exposed to the toxin, severe irritation can occur for several hours. Though generally avoided by cattle, horses are more likely to browse fireweed and develop stress symptoms. These symptoms commonly manifest themselves as weight loss, or difficulty in swallowing and breathing for many days after consumption. In extreme cases, young horses have died after rolling in fireweed and becoming over-exposed to the toxins in the leaf hairs.

Biology

Fireweed leaves resemble that of a strawberry plant (Figure 2), but the plant as a whole has little resemblance to strawberry. The plant has square stems and small pale green flower clusters. Small stinging hairs are found on the stems, petioles, and leaves. These hairs contain irritants that have been shown to cause respiratory stress and local allergic reactions when ingested or inhaled.

Figure 2. 

Fireweed leaves.


[Click thumbnail to enlarge.]

Control

Little work has been reported for control of this seasonal species. Therefore, experiments were conducted to determine which pasture herbicides are most effective on fireweed.

It was observed that 2,4-D and Telar were ineffective on fireweed (Table 1). Glyphosate, which can be applied when pasture grasses are dormant, provided as much as 80% control. However, in other experiments, we have found glyphosate to be inconsistent on fireweed, sometimes providing as little as 30% control. Because glyphosate can severely injure pasture grasses that are not fully dormant and because of its inconsistency on fireweed, we do not recommend the use of this product.

Weedmaster at 1.5 qt/A did not provide acceptable levels of control, but GrazonNext HL, Remedy Ultra, and Pasturegard HL were found to be highly effective. Within 2 weeks of application, over 90% of the fireweed plants were dead, and the remaining individuals were yellow and dying. By 6 weeks after treatment, no fireweed could be found.

It is our recommendation that GrazonNext HL, Remedy Ultra (or comparable triclopyr ester product), or Pasturegard HL be used for effective control of fireweed. These herbicides can be applied any time of year to warm-season forage grasses. There are no grazing restrictions for beef cattle with these herbicides, but lactating dairy animals must be removed for 0 and 14 days with GrazonNext HL and Remedy Ultra, respectively, and one season for Pasturegard HL.

Mowing provides no benefit for control of this species. In fact, mowing has been found to result in smaller plants, but with many more stinging hairs. Additionally, the seed is surrounded by a sticky substance that can be transported by mower blades to areas not infested with this weed.

If not controlled, fireweed generally disappears in May with the onset of summer temperatures.

Table 1. 

Control of fireweed with various herbicides.

Herbicide

Rate

Product/A

Herbicide cost 1

$ per acre

% Control

2 wat2

6 wat

2,4-D amine

2 qt

6

10

0

Weedmaster

1.5 qt

7

33

65

Remedy Ultra

1 qt

14–20

93

100

Pasturegard HL

24 fl. oz

20

92

100

GrazonNext HL

24 fl. oz

8

95

100

Glyphosate

1 qt

3

70

80

Telar

0.5 oz

10

30

10

1These are approximate values taken from Approximate Herbicide Pricing at http://edis.ifas.ufl.edu/wg056 and do not include application costs.

2wat=weeks after treatment.

Footnotes

1.

This document is SS-AGR-41, one of a series of the Agronomy Department, UF/IFAS Extension. Original publication date: May 2006. Latest revision: August 2013. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

J. A. Ferrell, associate professor, Agronomy Department; B. A. Sellers, associate professor, Range Cattle Research and Education Center, Ona, FL; UF/IFAS Extension, Gainesville, FL 32611.

The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication do not signify our approval to the exclusion of other products of suitable composition. Use herbicides safely. Read and follow directions on the manufacturer's label.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.