Effects of Aphthona species and integrated management on leafy spurge and native plant communities of Mount Sentinel

Cynthia Buckalew

The University of Montana IBS-CORE Program

Mentor- Marilyn Marler

Introduction

Euphorbia esula L, commonly known as leafy spurge, is a noxious weed that has invaded most of the western United States and Canada. It competes for soil nutrients and water with native flora, thus reducing the diversity and abundance of native plant species (Sheley, 1998). This reduction leads to changes in an ecosystem affecting not only native flora diversity but also the foraging of animals. Livestock carrying capacity is largely reduced as leafy spurge competes with rangeland grasses (EAP, 1991). This causes problems for ranchers with leafy spurge infestations and requires effective control methods to be established. Management control has focused on eradicating leafy spurge but has neglected the responses of native plant communities.

Leafy spurge is a perennial plant that easily spreads by seed and its extensive root system. Its root system stores nutrients that allow it to sustain many harsh conditions, including control methods (Lym, 1995). The roots are also capable of regenerating from most soil depths (NPS, 1998), requiring control methods that extensively attack the root system. Leafy spurge also contains a milky latex in its system, which causes irritation to most species when ingested (Lym, 1998). This prevents cattle from grazing on leafy spurge and only allows for sheep and goats to be effective grazers.

In order to completely control and eradicate leafy spurge both the root and stem systems must be destroyed (Lym, 1998). This allows for leafy spurge to become susceptible to control methods by weakening the plant systems. Grazing and mowing only attack the vegetative buds while plant competition attacks the root system. Herbicides and flea beetles attack both the vegetative buds and root systems (Lym 1995), but due to expenses for herbicides and lengthy control for flea beetles they are not always practical control methods when used alone. An integrated management plan is the most successful at containing and eradicating leafy spurge by attacking the plant in short-term and long-term aspects.

This project studies the effects different control methods have on native plant species. It will help us understand what control methods are most useful for not only leafy spurge eradication but also restoration of our natural lands. The first study addresses whether management goals are being met by introducing bio-control agents. The effects Aphthona spp., flea beetles, have on native plants is as important as their effects on leafy spurge. Previous studies show a decrease in leafy spurge after flea beetle establishment has occurred, but they do not consider how the native flora is affected.

The second study addresses the effects mowing, grazing, reseeding, herbicides, and biological controls have on native plant species. Each control method is used alone and in combinations in the study. Integrated management plans are successful in leafy spurge control due to the combination of short and long-term control strategies both affecting the noxious weed. When successful control methods promote native plant restoration these are the methods that should be used most commonly.

The hypothesis for the first study is that flea beetles will not negatively impact native flora, but will help natives compete with leafy spurge by reduction in spurge seed production and root mass. This leads to the following research questions:

· How do flea beetles affect native flora species in leafy spurge patches?

· What is the long-term affect of flea beetles on native flora?

The hypothesis for the second study is that mixtures of control methods will have a higher decrease in leafy spurge density, allowing for native flora to compete and survive better in leafy spurge patches. This leads to the following research questions:

· What effects do combinations of various control methods have on leafy spurge when used alone and combined?

· What effects do combinations of various control methods have on establishment of native plant species?

· What combinations of various control methods work best for leafy spurge eradication?

· What combinations of various control methods work best for native plant species restoration?

When considering the big picture of research for leafy spurge this study looks at the effects leafy spurge control methods have on native flora. Most research only concentrates on the eradication of leafy spurge while it ignores the restoration of native plant species. If a control method only kills leafy spurge and does not allow for native flora to restore the weed infested areas, then it is only doing half of its job. The establishment of native flora reduces the establishment of noxious weeds. This will inform those with a leafy spurge problem on what works best for native flora restoration and what is less successful.

Research Methods

The first study looks at five different leafy spurge patches located on Mt. Sentinel containing flea beetles released in the summer of 1999. The number of beetles and dates of release in 1999 are shown in Table 1. The number of leafy spurge stems, percent cover of leafy spurge, bare ground, and all other plant species was collected at each release site. Site #1 is not shown in the study because it is in an area of another research study and is not relevant to this study. Each site was marked with a wooden or metal stake at the exact spot of release and 30 feet north, south, uphill, and downhill from the release site to mark the parameters for data collection. Data was collected in late June using a 0.25m² square quadrant. A micro-plot was taken every five feet starting one foot from the release site and ending at the 26-foot mark. Plots #4 and #6 did not have any visible flea beetles during data collection so more beetles were released at each plot on July 12, 2000. Plot #4 received 4,000 Aphthona nigriscutis and plot #6 received 2,000 Aphthona nigriscutis. Plot #6 was accidentally sprayed with Tordon on 6-20-00 and plot #5 was accidentally burned in September of 1999.

Table 1. Number, species, and date of flea beetle release for 1999.

Plot number	Number of individuals released	Species	Date
#2	2,500	A. lacertosa	6-25-99
#3	1,000	A. nigriscutis	7-14-99
#4	2,000	A. cyparissiae	7-9-99
#5	1,000	A. nigriscutis	7-14-99
#6	2,000	A. lacertosa and A. nigriscutis mix	7-30-99

The second study took subsamples within the permanent study plots established during the summer of 1999. Forty-two plots previously treated with mixtures of control methods along with four control plots were studied. The mixtures for each plot are as follows:

Grazing only

Grazing and Reseeding

Grazing and Bio-controls

Grazing, Bio-controls, and Reseeding

Bio-controls only

Bio-controls and Reseeding

Mowing only

Mowing and Reseeding

Mowing and Bio-controls

Herbicides and Reseeding

Herbicides only

Mowing, Bio-controls, and Reseeding

Herbicides and Bio-controls

Herbicides, Bio-controls, and Reseeding

Data was collected between mid-May and mid-June using a 0.25m² square quadrant to record the number of leafy spurge stems, percent cover of leafy spurge, bare ground, and all other plant species. Each plot is 5m x 5m and marked with a wooden or metal stake in its four corners. Nine randomly located micro-plots were collected in each site. Data collection started with selecting one point between 0 and 3 from a random numbers data sheet to determine which point would start transect one along the vertical axis of the plot. Three micro-plots were then taken horizontally from the random number starting at 1ft and moving 6 feet along the measuring tape for the next two. The next six micro-plots were taken using the same method but moving up 5 feet along the vertical tape measure each time. After data collection was complete 5 sheep along with a lamb were grazed on plots #1-12 until most of the leafy spurge top growth was gone. Plots #17-21, #25-29, and #31-32 were mowed using a weed eater. During the mowing application native plants were purposefully missed. The herbicide and reseeding treatments will be applied every two years and thus were not applied this year.

Results

Graph 1. Percent distribution in study #1 for 1999 and 2000.

Graph 2. Average number of leafy spurge stems in study #1 for 1999 and 2000.

The results for the first study show a drop in percent cover for leafy spurge in all of the sites except #5, which stayed about the same. Site #2 is the only one that dropped in percent cover for other plant species. Site #4 has the highest percent (90-100%) of other plant species for both 1999 and 2000 while it also has the lowest percent bare ground (1-5%) for both years. The number of leafy spurge stems in the plots increased for all of the sites except #3, which stayed about equal. Plot #5 did not increase for leafy spurge stems by much while its percent cover of bare ground more than doubled.

Graph 3. Percent distribution in study #2 for 1999.

Graph 4. Percent distribution in study #2 for 2000.

For the second part of the study we see that the plots treated with herbicides have the highest average percent of bare ground, but also have the lowest average percent of leafy spurge. The grazing only plots have the highest average percent of others, while grazing with bio-controls has the highest percent of leafy spurge and the lowest percent for bare ground.

The herbicide/bio-controls along with the herbicides/bio-control/reseeding have the lowest percent cover of leafy spurge and the highest percent cover of bare ground. The mowing only, grazing/reseeding, and grazing/bio-control/reseeding are the only plots that have dropped in percent cover of others. The mowing only plots also have the lowest percent cover of others.

Comparing the 1999 and 2000 data, we see that all of the plots have a huge decrease in leafy spurge percent cover except for the grazing/bio-control plots. An increase in percent cover of others is seen in all of the plots except for mowing only, grazing/reseeding, and mowing/bio-control/reseeding, while grazing/bio-control/reseeding is about the same. Bare ground percent cover increased for all of the plots except for the grazing/bio-control plots.

Discussion

The first study shows a drop in percent cover for leafy spurge in all of the sites except #5 can be due to the flea beetles starting to affect the leafy spurge, but since they have only inhabited the patches for a year this is highly unlikely. Another disagreeing factor that this is due to the flea beetles is that sites #4 and #6 did not show any evidence of flea beetle establishment. The drop in leafy spurge percent cover is more than likely due to the drought we encountered this past summer.

The drop in percent cover of other plant species, which only occurred in #2, is not clear on why it occurred. The occurrence of site #4 having the highest percent cover of other plant species along with the lowest percent cover of bare ground can be explained together. These two factors correlate with each other because there is more cover from the higher percent of other species leading to less bare ground.

The high increase of percent bare ground for site #5 is due to the fire that burned the plot in September of 1999. The fire cleared the area of excess plant litter leaving more bare ground in the area. Weeds also have a higher chance of inhabiting this plot due to the fire disturbing the land. The lack of site #5 increasing in leafy spurge stems can also be due to the fire.

The overall increase in leafy spurge stem numbers and decrease in leafy spurge percent cover leads to the conclusion that there is a decrease in the number of large leafy spurge plants. This decrease results in less percent cover of leafy spurge while there is an increase in the number of baby leafy spurge plants. The increase in baby leafy spurge gives us more stem numbers but also results in less percent cover.

The second study shows the occurrence of the herbicide plots having the highest percent of bare ground and lowest percent of leafy spurge is due to the herbicides eradicating the leafy spurge faster than the other treatments. This is because it attacks the roots and the stems quickly killing the plant. Herbicides also attack native flora and this results in a reduction of percent cover of other plant species as well as leafy spurge. The reduction in plant species increases the percent bare ground allowing for increased soil erosion in the area, which may lead to easier establishment of other weeds in the area.

Grazing only plots have the highest percent other plant species, which may be due to the sheep spreading native plant seeds and aiding in their establishment. The sheep avoid grazing on Linaria dalmatica and Balsamorhiza sagittata, this helps the increase in percent cover of others since these plants are avoided.

The grazing/bio-controls plots have the highest percent cover of leafy spurge and the lowest percent cover of bare ground. These two factors may correlate with each other in that the high percent of leafy spurge covers more of the area reducing the percent cover of bare ground. The grazing and bio-controls will take more than one year to show a decrease in leafy spurge densities thus not showing a decrease this year.

The mowing only plots have the lowest percent cover of others. This can be explained by all of the plant species in the plots being reduced preventing them from flowering and seeding. Some of the native flora was avoided during the mowing application but many of the natives were cut down with the leafy spurge. The mowing only, grazing/reseeding, and grazing/bio-controls/reseeding plots are the only ones that have dropped in percent cover of others in the last year. This is due to the prevention of the native plant species, along with other noxious weeds, from reproducing and forming seeds since they were cut or grazed before reproduction could occur.

Comparing the 1999 and 2000 data we can see that all of the plots have a huge decrease in leafy spurge percent cover, except for the grazing/bio-control plots. This decrease may be due to differences in the quadrant size used and to the drought this past summer.

Most of the plots also show an increase in percent cover of others except for mowing only, grazing/reseeding, and mowing/bio-controls/reseeding plots which all show a decrease. Grazing/bio-controls/reseeding plots are about the same with percent cover of other plant species. The increase in percent cover of others can be due to the difference in quadrant size along with the effects of the control methods starting to weaken the leafy spurge.

Since this study is only one year into its research it is hard to determine what effects the flea beetles and integrated control methods have on native flora. This project needs continual research for many more years in order to fully understand how different control methods affect native flora. As research on this project continues I expect to see fewer leafy spurge density in plots with mixtures of control methods. Higher native flora density is expected in reseeding plots and less native flora in grazing and mowing, due to the failure of the natives to produce seeds and lower diversity of all species is expected in plots treated with herbicides. I do not expect flea beetles to cause a negative effect on the native flora, since they are not seen feeding on other plants in the field.

Acknowledgements

This work was funded by an IBS-CORE Undergraduate Research Fellowship to Cynthia Buckalew through a grant from the Howard Hughes Medical Institute to the University of Montana. I would like to thank Marilyn Marler for guidance and aid in my research. Kathleen Kennedy, Morgan Valiant, William Schlegel, Kevin Schreiner, and Kristin Wellman for helping me gather information in my study sites. I’d also like to thank John Stahl for allowing me to use his sheep for my grazing plots.

Literature Cited

Ecological Agriculture Projects. 1991. Control of Leafy Spurge with Spurge Beetles. [http://eap.mcgill.ca/PCBCW_2.htm] Accessed on 10/02/00.

Lym, R. G. 1998. The Biology and Integrated Management of Leafy Spurge Euphorbia esula on North Dakota Rangeland. Weed Technology 12:367-373.

Lym, R. G.; R. K. Zollinger. 1995. Integrated Management of Leafy Spurge. [http://www.ext.nodak.edu/extpubs/plantsci/weeds/w866w.htm] Accessed on 10/9/00.

National Park Service. 1998. Leafy Spurge. [http://www.nature.nps.gov/wv/ipm/spurge/htm] Accessed on 10/02/00.

Sheley, R.L.; B. E. Olson; and C. Hoopes. 1998. Impacts of noxious weed on the ecology and economy of Montana. Montana State University Extension Service.

Executive Summary

Leafy spurge is an invasive weed that must be contained before it causes more damage to Montana’s ecosystem. This study looks at how flea beetles and mixtures of control methods affect not only leafy spurge but also native plant species. It is important to restore Montana’s lands back to their historic status, and this requires that native plants reestablish in areas infested with noxious weeds. Control methods that eradicate leafy spurge and also allow native plant species to flourish should be the methods most commonly used to control and kill leafy spurge.

Flea beetles are insects that feed on the root and stem systems of leafy spurge weakening the plant. They can control a leafy spurge patch but it takes many years before a population can establish and affect the plant. The first part of this study looks at how flea beetles not only affect leafy spurge but also native plant species. This research will allow us to know if native plant restoration naturally occurs with the use of flea beetles, or if another method for plant restoration should be used with the flea beetles.

The most efficient management for leafy spurge is the mixture of control methods on a leafy spurge patch. This is due to the control methods attacking both the roots and stems of the plant, weakening all of its reproductive systems. Mixtures of control methods also allow for short and long-term control. This means that one method fights the leafy spurge right away, i.e. herbicides, while the other method fights the leafy spurge in the long run, i.e. flea beetles.

The second part of this study looks at how mowing, herbicides, grazing, reseeding, and flea beetles affect leafy spurge and native plant species. Each method is used in combination with each other to determine how effective they are at controlling leafy spurge and allowing for native plant restoration. This research will allow us to know if native plant restoration occurs with the use of integrated control methods or if other methods for restoration should be applied.

Since the study is only one year into its research the results are not very conclusive on how native plants are being affected by the different control methods. Differences in percent cover of leafy spurge, bare ground, and other plant species occurs in all of the plots though these are commonly due to issues other than the control methods. After more years of research the results will be more conclusive to the effects control methods have on native plant communities.