Hydrilla verticillata

Common Name: hydrilla

Family: Hydrocharitaceae

Common Synonyms: none

USDA Hardiness Zone: 5a-11

Growth Habit: Aquatic perennial herb

Origin: Warmer regions of the Old World

FISC Category: 1

FDACS Listed Noxious Weed: Yes

Introduction Date: 1960

IFAS Assessment:

• North: PROHIBITED
• Central: PROHIBITED
• South: PROHIBITED

Description

Aquatic, submersed, perennial herb with slender stems to 9 m long, many branched. Stems from rhizomes. Whorled leaves, 3-8 per whorl, with toothed margins, and 1-4 conical bumps on the underside of the midrib. Fleshy buds form in the leaf axils called turions, each with 3 sepals and petals, whitish and floating.

Habitat

Lakes, rivers

Comments

Similar to Egeria densa, also a non-native invasive, which has whorls of 3-6 leaves and no conical bump on midrib.

Control Methods

• Manual: Mechanical: Physical removal by raking or seining, but it will reestablish from any remaining fragments (Texas A&M).
• Chemical: Several chemicals have been successfully used to treat Hydrilla: diquat, endothall, flouridone, imazamox, penoxsulam, bispyribac-sodium, and flumioxazin. [Texas A&M: https://aquaplant.tamu.edu/management-options/hydrilla/, IFAS: http://edis.ifas.ufl.edu/ag370].
• Biological: NA

Control Notes

Note: Timing and herbicide concentration are important to consider in terms of efficacy and non-target damage to native species (IFAS).

References

Dave's Garden. 2014. PlantFiles: Hydrilla, Hydrilla verticillata. http://davesgarden.com/guides/pf/go/32040/. Accessed on June 20, 2014.

IFAS, Center for Aquatic & Invasive Plants. 2014. Plant Management in Florida Waters: An Integrated Approach. http://plants.ifas.ufl.edu/manage/control-methods/chemical-control/selective-application-of-aquatic-herbicides. Accessed on June 25, 2014.

Langeland, K.A., H.M. Cherry, C.M. McCormick, K.C. Burks. 2008. Identification and Biology of Non-Native Plants in Florida's Natural Areas-Second Edition. IFAS Publication SP 257. University of Florida, Gainesville, Florida.

Texas A&M, AgriLife Extension. 2014. AQUAPLANT, A pond manager diagnostic tool: Hydrilla. http://aquaplant.tamu.edu/management-options/hydrilla/. Accessed on June 25, 2014