Aphthona spp. flea beetles were released in the Little Missouri National Grasslands
(LMNG) in western North Dakota in 1999 to control leafy spurge (Euphorbia esula L.). The
changes in soil seed bank composition and leafy spurge density were evaluated on two
ecological sites five (2004) and ten years (2009) after Aphthona spp. release to monitor
the effectiveness of the insects on weed control and associated change in plant
communities. In 2009, leafy spurge stem density averaged 2 and 9 stems m-2 in the loamy
overflow and loamy sites, respectively, compared to 110 and 78 stems m-2, respectively, in
1999 and 7 and 10 stems m-2, respectively, in 2004. Leafy spurge constituted nearly 67%
of the loamy overflow seed bank in 1999 compared to 17% in 2004 and 2% in 2009. In the
loamy seedbank, the weed represented nearly 70% in 1999 compared to approximately
11% in 2004 and 15% in 2009. As leafy spurge was reduced, native species diversity and
seed count increased ten years following Aphthona spp. release. High-seral species
represented 17% of the loamy overflow seedbank in 2009, an increase from 5% in 1999.
However, Kentucky bluegrass, a non-target weedy species, increased over 250% in the
loamy overflow seedbank from 2004 to 2009. The reestablishment of native plant species
has often been slow in areas where leafy spurge was controlled using Aphthona spp. A
bioassay was completed to evaluate native grass establishment when grown in soil from
Aphthona spp. release and non-release sites throughout North Dakota. Native grass
production was not affected when grown in soil collected from established Aphthona spp. sites (1.5 g per pot) compared to soil without insects (1.6 g per pot). The cause of reduced
native grass production in sites with Aphthono spp. previously observed is unknown but
may have been due to a chemical inhibition caused by the insects within the soil that no
longer exists. The native warm-season switchgrass (Ponicum virgotum L.) may be an
alternative to corn for efficient biofuel production; however, control of cool-season grassy
weeds has been a problem in switchgrass production. Various herbicides were evaluated
for smooth bromegrass (Bromus inermis Leyss.) and quackgrass [Elymus repens (L.) Gould]
control in an established switchgrass stand near Streeter, ND and a weed-infested field in
Fargo, ND. Switchgrass yield was higher than the control 14 mo after treatment (MAT)
when aminocyclopyrachlor or sulfometuron were applied early in the growing season, but
no treatment provided satisfactory long-term grassy weed control. Herbicides were
reevaluated at increased rates for smooth bromegrass or quackgrass control in Fargo.
Sulfometuron provided 99% smooth bromegrass control when applied at 280 g ha-1 in the
fall but injured other grass and forb species as well. Sulfometuron would likely be
injurious to switchgrass and could not be used for biofuel production.
Aminocyclopyrachlor did not injure other grass species but only reduced smooth
bromegrass control by 76% when applied at 280 g ha-1 in the fall. No treatment provided
satisfactory long-term quackgrass control.
| Identifer | oai:union.ndltd.org:ndsu.edu/oai:library.ndsu.edu:10365/29318 |
| Date | January 2011 |
| Creators | Setter, Cassandra Marie |
| Publisher | North Dakota State University |
| Source Sets | North Dakota State University |
| Detected Language | English |
| Type | text/thesis |
| Format | application/pdf |
| Rights | NDSU policy 190.6.2, https://www.ndsu.edu/fileadmin/policy/190.pdf |
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