Highly invasive Pennisetum purpureum, aka Giant King Grass, as requested by Richard R. Rodriguez, CPA in a comment post request

Pennisetum purpureum (Schumach. 1827)
NPS photo by National Tropical Botanical Gardens

Richard R. Rodriguez, CPA, asked me to post his comment on my blog from October 09, 2012 Pennisetum purpureum - Biofuel, ornamental specimen, invasive species, weed with a tendency towards hybrid cultivars with common names like Napier grass or king grass,

Normally I would just post his comment, but given the nature of hiscomments, I thought he was owed a more detailed response.

Here are his comments: 

"Need more information from your research to agree with your statements. Giant King Grass is NOT invasive.Giant King Grass actually has 80% of its roots mass in the top 18 to 24” of the soil. The other 20% are small hair like roots that can ...go deeper and break down each year and regenerate new roots. In summary, very little of the root system is deeper than 24”. The roots could never get to an aquifer. A major benefit of GKG is its ability to stop run off water and erosion loss of surface water that would normally run into the ocean". 

Mr. Rodriguez, CPA, in his request for more information on this invasive plant mentions root depth which is not part of any weed risk assessment currently used in the United States (or for that matter anywhere else I know about).

Here, then is the information from the University of Hawai'i's risk assessment of the highly invasive species Pennisetum purpureum (Schumach. 1827) as requested by Mr. Richard R. Rodriguez, CPA:

4.01      Produces spines, thorns or burrs     y=1, n=0            n            No evidence of spines, thorns or burrs.           Wagner,W. L., D. R. Herbst & S. H. Sohmer. 1990. Manual of flowering plants of Hawaii.University of Hawaii at Press. Honolulu.

4.02      Allelopathic    y=1, n=0            n            Not allelopathic.               http://plants.usda.gov/cgi_bin/topics.cgi

4.03      Parasitic           y=1, n=0            n            No evidence.  

4.04      Unpalatable to grazing animals         y=1, n=-1          n            (1)Medium palatability. (2)The grass is valued for its … palatability…'               (1)http://plants.usda.gov/cgi_bin/topics.cgi   (2)Bogdan, A.V. 1977. Tropical pasture and fodder plants. Longman, London

4.05      Toxic to animals          y=1, n=0            n            "(1)Not toxic.   (2)Seiler et al. (1979) report fatal nitrate poisonings in cattle whose diet consisted solely of Napier grass. Levels of nitrate averaged 28.3 mg/g with some samples as high as 44 mg which levels in the same species from non-toxic areas was 3.9 mg/g. (due to grown in soil with excessive N) 3)It is one of the most valuable forage, soilage and silage crops in the wet tropics

"             (1)http://plants.usda.gov/cgi_bin/topics.cgi  (2)http://www.hort.purdue.edu/newcrop/duke_energy/Pennisetum_purpureum.html#Toxicity 3)http://www.ecoport.org/default.htm

4.06      Host for recognized pests and pathogens   y=1, n=0            n            This website lists 88 species of fungi that are found on P. purpureum (only a few generalists are economically important.)      http://nt.ars-grin.gov/fungaldatabases/all/FindRecOneFungusFrame.cfm

4.07      Causes allergies or is otherwise toxic to humans  y=1, n=0            n            No evidence.         

4.08      Creates a fire hazard in natural ecosystems             y=1, n=0                           Not fire resistant and high fire tolerance.      http://plants.usda.gov/cgi_bin/topics.cgi

4.09      Is a shade tolerant plant at some stage of its life cycle       y=1, n=0            n               Shade intolerant.         http://plants.usda.gov/cgi_bin/topics.cgi

4.1         Tolerates a wide range of soil conditions (or limestone conditions if not a volcanic island)           y=1, n=0            y             1) It is a rapid colonizer of disturbed areas and prospers in a broad range of conditions. 2)Requires a rich soil 3)However, it will also grow on poorly drained soils to dry sandy soils of low fertility.        1) http://aquat1.ifas.ufl.edu/mcplnt1p.html 2)http://www.hort.purdue.edu/newcrop/duke_energy/Pennisetum_purpureum.html 3)http://www.ecoport.org/default.htm

4.11      Climbing or smothering growth habit          y=1, n=0            n            No evidence. Not a vine.

4.12      Forms dense thickets              y=1, n=0            y               'Forms dense perennial stands, difficult to penetrate, which inhibits establishment of other vegetation.'                http://www.hear.org/pier/pepur.htm

5.01      Aquatic             y=5, n=0            n            Semi-aquatic grass               http://aquat1.ifas.ufl.edu/mcplnt1p.html

5.02      Grass   y=1, n=0            y             Perennial grass.               http://plants.usda.gov/cgi_bin/topics.cgi

5.03      Nitrogen fixing woody plant               y=1, n=0            n                          

5.04      Geophyte (herbaceous with underground storage organs -- bulbs, corms, or tubers)              y=1, n=0            n                          

6.01      Evidence of substantial reproductive failure in native habitat     y=1, n=0            n               No evidence.  

6.02      Produces viable seed.              y=1, n=-1          y             if grown from seed, it is started in a nursery and transplanted               http://www.hort.purdue.edu/newcrop/duke_energy/Pennisetum_purpureum.html

6.03      Hybridizes naturally y=1, n=-1                         (1)P. purpureum hybridizes with P. americanum readily under artificial conditions. No evidence of natural hybridization.  (2) 'Many cultivars and hybrids occur, a well known example is Banagrass, a cross with P. glaucum.' - again no evidence that this occurs naturally.            Bogdan, A.V. 1977. Tropical pasture and fodder plants. Longman, London

6.04      Self-compatible or apomictic             y=1, n=-1          y             A selfed progeny of the 'Merkeron' cultivar was produced (also, likely to be apomictic)               http://www.hort.purdue.edu/newcrop/proceedings1993/V2-294.html#Napiergrass

6.05      Requires specialist pollinators          y=-1, n=0          n            Probably not. Most grasses are wind pollinated - the flower morphology does not reveal adaptation to a specialist pollinator.

6.06      Reproduction by vegetative fragmentation              y=1, n=-1          y             is sometimes stoloniferous with a creeping rhizome. (sreads slowly this way)               http://www.ecoport.org/default.htm

6.07      Minimum generative time (years)                 1 year = 1, 2 or 3 years = 0, 4+ years = -1            See left               1            R. Criley, UH department of Horticulture (but assessment was given with low confidence, could required 2 years) 

7.01      Propagules likely to be dispersed unintentionally (plants growing in heavily trafficked areas)         y=1, n=-1          n            Propagules do not have any means of attachment.   

7.02      Propagules dispersed intentionally by people         y=1, n=-1          y             Pasture grass, sometimes grown as an ornamental.             

7.03      Propagules likely to disperse as a produce contaminant  y=1, n=-1          y               "Weed: potential seed contaminant (fide Weed CIBA)

(Stalks are cut and transported for feeding livestock. Some seeds are likely transported (accidentally) in the process)"          http://www.ars-grin.gov/cgi-bin/npgs/html/taxon.pl?27208

7.04      Propagules adapted to wind dispersal         y=1, n=-1          y             plumose spikelets          

7.05      Propagules water dispersed               y=1, n=-1          n                          

7.06      Propagules bird dispersed    y=1, n=-1          n                          

7.07      Propagules dispersed by other animals (externally)          y=1, n=-1          n               Propagules do not have any means of attachment.             

7.08      Propagules survive passage through the gut            y=1, n=-1          n            No evidence.         

8.01      Prolific seed production (>1000/m2)          y=1, n=-1          n            'Pennisetum purpureum produces, with occasional exception little or no seed, …'     Bogdan, A.V. 1977. Tropical pasture and fodder plants. Longman, London

8.02      Evidence that a persistent propagule bank is formed (>1 yr)       y=1, n=-1          n               (1)Caryposis 2 mm long.   (2)'Pennisetum purpureum produces, with occasional exception little or no seed, …'3)Does not readily produce viable seed in many countries,               (1)Wagner,W. L., D. R. Herbst & S. H. Sohmer. 1990. Manual of flowering plants of Hawaii.University of Hawaii at Press.   (2)Bogdan, A.V. 1977. Tropical pasture and fodder plants. Longman, London 3)http://www.fleppc.org/pdf/Pennisetum%20purpureum.pdf

8.03      Well controlled by herbicides             y=-1, n=1          y             "(1)Foliar application of 1%-3% Roundup Pro. If non-target damage is a concern, cut stems to ground level and allow sprouts to reach 8-12 inches and treat the same as Neyraudia above. Broadcast 3-5 quart/acre Roundup Pro, 2 quart/acre Arsenal, or 1 quart Arsenal and 2 quart Roundup Pro.

(2)The herbicide glyphosate provides acceptable control in aquatic sites "               (1)http://edis.ifas.ufl.edu/BODY_WG209#TABLE_1  (2)http://aquat1.ifas.ufl.edu/mcplnt1p.html

8.04      Tolerates, or benefits from, mutilation, cultivation, or fire             y=1, n=-1          y               1) No resprout ability. 2)Resprouts easily from small rhizomes left after mechanical control 3) regrows following frequent clipping (harvesting for animal fodder)              1) http://plants.usda.gov/cgi_bin/topics.cgi 2)http://www.fleppc.org/pdf/Pennisetum%20purpureum.pdf 3)http://www.hort.purdue.edu/newcrop/duke_energy/Pennisetum_purpureum.html

8.05      Effective natural enemies present locally (e.g. introduced biocontrol agents)   y=-1, n=1                 Biological controls for napier grass are unknown in Florida.                http://aquat1.ifas.ufl.edu/mcplnt1p.html

               Total score:                    16          -> Highly Invasive

Risk assessment from University of Hawai'i