ISSUE 15  AUGUST 12, 1999

NOTES AND ABSTRACTS FROM THE 1999 LEAFY SPURGE SYMPOSIUM
PLATEAU FOR LEAFY SPURGE CONTROL

Denise M. Markle and Rodney G. Lym Graduate Student and Professor, Department of Plant
Sciences, North Dakota State University, Fargo, ND 58105.

    Plateau has shown promise for leafy spurge control in North Dakota, but some injury to grasses
has been observed. The objectives of this research were: a) to determine the effect of various adjuvants
in combination with Plateau to maximize leafy spurge control and minimize grass injury, b) to determine
the most cost-effective rate of Plateau for leafy spurge control when applied alone or with various
adjuvants, c) to determine the most effective timing of Plateau application in the fall to maximize leafy
spurge control and herbage production, and d) to evaluate the combined effect of Plateau and biological
control agents on leafy spurge control. Plateau applied alone or with various adjuvants injured grasses in
greenhouse studies; however, Plateau did not decrease herbage production in field studies. Plateau
provided similar or better leafy spurge control than the standard treatment of Tordon plus 2,4-D in the
field. Plateau at 8 fl oz/A applied with a methylated seed oil (MSO) alone or with 28% N averaged 72%
leafy spurge control 12 months after treatment (MAT) compared to 40% control with Tordon plus 2,4-D.
Plateau provided maximum leafy spurge control when applied at 8 fl oz/A with a MSO either alone or with
28% N. Plateau applied with a MSO in mid-September provided the best leafy spurge control 12 MAT
compared to application in August or October.

    For instance, Plateau at 8 fl oz/A applied with a MSO in mid September provided nearly 70% leafy
spurge control 12 MAT compared to 50% or less leafy spurge control when applied in August or October.
Plateau applied over Aphthona spp. biological control agents improved leafy spurge control compared to
the insects alone, but reduced Aphthona density from 25 or 35 adults/m² by Tordon plus 2,4-D or the
control, respectively, to 15 to 20 adults/m² by Plateau. These results are based only on one location and
one year, further research needs to be conducted to determine if Plateau has a detrimental effect on
Aphthona spp. flea beetle population. Plateau will be a useful addition to a long-term leafy spurge control
program.

INTEGRATION OF THE FLEA BEETLE, APHTHONA NIGRISCUTIS FOUDRAS, AND
HERBICIDES FOR CONTROL OF LEAFY SPURGE, EUPHORBIA ESULA L.

Jeff A. Nelson, Rodney G. Lym, and Robert Carlson, Graduate Student and Professors, North
Dakota State University, Fargo, ND 58105.

    The combined treatment of the biological control agent, A. nigriscutis plus the herbicide treatment Tordon
plus 2,4-D generally provided better leafy spurge control compared to either method used alone. Leafy
spurge control from the combined treatment averaged 44% 12 months after application. Leafy spurge
with A. nigriscutis was oversprayed with Tordon plus 2,4-D with a minimal negative impact to the
A. nigriscutis population. The number of A. nigriscutis adults collected in the field was similar regardless
of herbicide application date. Leafy spurge root nutrient content was not affected by Tordon plus 2,4-D
applied in the fall. Soluble and insoluble carbohydrate and soluble protein concentrations in herbicide treated
plants were similar to concentrations in the untreated control. Leafy spurge plants harvested within an insect
confining screened cage had root nutrient concentrations similar to roots harvested outside the screened cage.
Uptake and translocation of ¹⁴C-Tordon and ¹⁴C-2,4-D was similar in plants damaged or unaffected by
A. nigriscutis larvae. Therefore, the observed increase in leafy spurge control from the combined treatment
was likely from the combined effect of herbicide toxicity to root tissue plus A. nigriscutis larval feeding on
leafy spurge root buds.

APHTHONA FLEA BEETLE ESTABLISHMENT DETERMINED
BY SOIL COMPOSITION AND ROOT GROWTH PATTERN.

    Aphthona spp. flea beetles have been used since 1992 as a control treatment of leafy spurge in North
Dakota. The reduction in leafy spurge where biological control was used ranges from excellent to poor
depending on location. The fair to poor location results prompted a study on the effects of soil composition
and root growth patterns of leafy spurge on flea beetle population levels.

    Forty one, four-year-old, Aphthona flea beetle release locations were sampled between 1996 and 1998
for soil composition and root growth pattern. The leafy spurge roots were extracted and measurements from
the soil surface to the first laterial roots, and the number of filament roots on laterial and tap roots were
recorded. The results were compared to adult flea beetle population levels at each location.

    To use Aphthona spp. for leafy spurge control appears to require a soil composition that will result in
root growth close to the soil surface. A silt loam, silt clay loam, clay loam, or loam soil with a ph of 6.8 -
7.9 and organic matter of 6.0 - 9.28 % produced the most adult flea beetles. The fine sand, loam fine sand,
or fine sand loam soils with a ph of 6.5 - 7.4 and organic matter of 0.90 - 2.8 % produced the fewest adult
flea beetles. Leafy spurge root systems in soil habitats that do not produce sufficient numbers of filament roots
and the laterial roots are more than two inches below the soil surface, will result in low Aphthona spp.
population levels and little impact on spurge stands.

SEEDBANK STUDY OF A LEAFY SPURGE INFESTATION.

    Approximately 15 to 20% of the Sheyenne National Grassland in southeastern North Dakota is
infested with leafy spurge (Euphorbia esula L.). The purpose of this research was to determine
seedbank composition, which may play a role in future site revegetation during leafy spurge control
efforts. Herbicide efficacy trial plots were established to determine herbicide rates to be used in
controlling leafy spurge in areas that also contain the western prairie fringed orchid (Platanthera
praeclara Sheviak and Bowles). These plots were also used to determine seedbank composition.
Three herbicides at two rates each were applied in the fall of 1997, Roundup plus 2,4-D (1.33 pt/A
plus 1 qt/A), Plateau (4 and 8 fl oz/A) plus Sun-It II plus 28% N and Paramount (1 and 1.33 lb DF/A)
plus Sun-It II. Soil cores 2.5 cm deep were taken in May 1998 and were washed through a 4 mm
sieve and a 0.2 mm sieve to remove coarse and fine materials. Samples were then spread 3 to 5 mm
deep on a layer of sterile sand (approximately 1 cm), which prevented contact between sample and
potting soil. Seed from a total of 56 composited soil cores were grown in the greenhouse. Seedlings
were counted and removed after identification. Identification continued until no further germination
was noted approximately eight weeks after planting. Seedlings were identified by species and placed
in categories of leafy spurge, forb, grass, grasslike and other species for statistical analyses.  Leafy
spurge comprised 40% of all germinated seedlings, with grasses 25%, forbs 22%, grasslike 10% and
other species 3%.
    Thirteen grass species were identified, four were desirable native warm season species
big bluestem, sideoats grama, little bluestem, and sand dropseed and three were desirable native cool
season species prairie junegrass, needle and thread, and green needlegrass. Eighty-five percent of all
grass seedlings that germinated were Poa spp. and would be considered undesirable at that level of
presence. Twenty-eight forb species were identified of which 86% were considered undesirable (23
species) while 14% (5 species) were considered desirable natives [white prairie aster, wild strawberry,
wood sorrel, common evening primrose and black-eyed susan. The competitive nature of leafy spurge
and its high representation in the seedbank will present continuing control problems for revegetation efforts.

EFFECTS OF PRESCRIBED BURNING AND HERBICIDE
TREATMENTS ON LEAFY SPURGE (EUPHORBIA ESULA).

C.W. Prosser¹, K.K. Sedivec², and W.T. Barker². ¹USDA, Agricultural Research Service, Northern
Plains Soil and Water Research Laboratory, 1500 North Central, Sidney, MT 59270. ²Animal and
Range Sciences Department, North Dakota State University, Fargo, ND 58105

    A 3-year experiment to evaluate herbicide treatments with prescribed burning to improve long-term
leafy spurge (Euphorbia esula L.) control compared to herbicide alone was established on the Gilbert
C. Grafton South Military Reservation in North Dakota. Six treatments were evaluated including an
untreated control, prescribing fall burning with no herbicide, spring applied Tordon plus 2,4-D applied
at 1 pt/A plus 1 qt/A and unburned, spring applied Tordon plus 2,4-D applied at 1 qt/A plus 1qt/A
and unburned, spring applied Tordon plus 2,4-D applied at 1 pt/A plus 1 qt/A following a fall burn, and
spring applied Tordon plus 2,4-D applied at 1 qt/A plus 1 qt/A following a fall burn. A prescribed burn
was conducted on the predetermined treatment plots in mid October of 1994 with herbicides applied in
1995 and 1996. Study objective was to evaluate burned and unburned treatments in conjunction with
differing rates of herbicide on leafy spurge control.

    All herbicide treatments, regardless of burning, reduced the density of leafy spurge compared to the
control. No differences were noted between the burned and unburned plots after 12 months and 24
months on any treatment. Burning alone did not affect leafy spurge stem densities as new spring growth
grew uniformly and with vigorous sprouting occurring following the fall prescribed burn. Leafy spurge
stems were reduced 69 % and 95 % on the normal and heavy herbicide rates of Tordon plus 2,4-D
on the burn treatment, respectively, compared to the control after 12 months of herbicide treatment.

    After 24 months of herbicide treatment on the burn plot, leafy spurge stems were reduced to 88% on
the normal herbicide rate of Tordon plus 2,4-D which was a reduction of 19% compared to 12 months
following treatment. No change in leafy spurge stems was noted on the heavy rate of Tordon plus 2,4-D
between the 12 months and 24 months herbicide application on the burned treatments. Leafy spurge
stems were reduced 62% and 82% on the normal and heavy herbicide rates of Tordon plus 2,4-D on
the unburned treatments, respectively, compared to the control after 12 months of herbicide application.
No change in leafy spurge stems was noted on either the normal or heavy rates of Tordon plus 2,4-D
between the 12 months and 24 months following herbicide application on the unburned treatments. A
fall prescribed burning program alone did not affect leafy spurge stem densities or improve herbicide
control when compared to unburned treatments. However, fall prescribed burning did enhance leafy
spurge control using Tordon plus 2,4-D applied at 1 pt/A1qt/A under a 2 year spraying program
compared to unburned treatment results.

SITE CHARACTERISTICS OF ESTABLISHED FLEA BEETLE
COLONIES IN WESTERN NORTH DAKOTA.

    A total of 59 USDA-APHIS flea beetle release sites were located and evaluated in 1998 on the
LittleMissouri Grasslands near Medora, North Dakota. Five hundred flea beetles were released at
each site during 1993, 1994, or 1995. Five flea beetle species were released: Aphthona cyparissiae,
A. czwaline / lacertosa, A. flava, and A. nigriscutis. Physical characteristics (PC) of release sties
measured were aspect, soil texture, landscape position and site micro-topography. Biological
information recorded was control area, leafy spurge density and cover, and cover of co-dominant
plant species in the control area. No pre-release site data was available. The data set was subjected
to principal component analysis which reduced the dimensionality and eliminated random background
variation. No PC’s were significant for any data set. However, area of leafy spurge control appeared to
be the parameter with the greatest influence in graphically separating sample units (release sites). Nine
sites having the greatest leafy spurge control (avg. 5,000 m²) separated when plotted on an XY-graph.
A stepwise comparison was then made on these nine sites to determine the magnitude of importance of
each physical parameter. The physical site variables ranked from most to least importance are as follows:
(1) aspect, (2) micro-topography, (3) landscape position, and (4) soil texture. The nine sites had aspects
ranging from 90E to 270E, a micro-topography of level to convex, were located on the upper portion of
the landscape (upland or summit), and had sandy to silty loam soil textures. These physical characteristics
would all contribute to the nine successful release sites having warm and dry habitats for the larvae to live in.

Richard Zollinger
NDSU Extension Weed Scientist
rzolling@ndsuext.nodak.edu

NOW IS THE TIME FOR GOOD FARMERS TO FINALIZE WEED MAPPING

    With the cropping season cutting back closer toward harvest, now is the perfect period to do some
farm management strategy on weeds. Yes, even this late a date those rascally, rabid, railroading, ranging,
rapacious, ravenous rascals called weeds must be revenged! Bring out your site-specific management
skills--even if you aren't on GPS (global positioning system) you can set up a GIS (geographic information
system) for your farm. Whether you are fleet of hand (via pencil drawings) or fleet on computer feats (via
spatial analysis software), now is the time to map the remaining weed problems in your fields in order to
plan your strategic maneuvers for next season.

    Scout your fields and determine the remaining weed pockets in each field. Evaluate this information
against the early season weed pressure to determine how well your management program worked this year.
Do comparison shopping across your fields and across neighbors' fields where tillage or herbicide programs
are known in order to evaluate what went well this year and what could be improved next year.

    Map out your current weed problems and any perceived trouble management areas. Specifically mark
your maps with each weed culprit's name so that you have a list of weed species that you are gunning for
this next year. Site down the specifics on each weed in your notes in order to get a clear shot at the weed
for next year: whether it is a perennial, biennial or annual; whether it is a broadleaf or grass; whether it was
poorly controlled with the strategy used this year or well controlled but still lingering within the field in small
numbers; whether it was a late-germinator or came into the field early; or, if it was controlled early so you
eliminated some of the problem or it produced seeds.

    The utility of precision agriculture technology in integrated pest management (IPM) is improvement in 1.)
mapping and relocating pest populations, 2.) applying control tactics selectively to pest populations that are
above your established thresholds, and 3.) keeping records over time in order to determine the impact of
both the location and timing of pest resurgence. Like a well-planned deer hunt, weed walloping requires the
dexterity of a devious, diabolical hunter with a diligent dossier on each of the weed species wanted to trap,
control and contain.

    Mapping the weed locations will allow you to observe any yield in the areas where weeds are prevalent
in order to determine if yield loss occurs (a combine equipped with a yield monitor will give you an excellent
idea). The maps will also provide you with a way to relocate the weed problem areas next year so that you
can hone your tillage and/or herbicide skills in on the pest problem. By applying additional knowledge of
location and timing of weed emergence to your pest problem, you can compare tillage techniques or herbicide
habitudes to determine if targeting trouble can selectively narrow down weed populations. This will save you
chemical costs and long-term weed control efforts. By maintaining a record of the weed problems over the
years, you can further refine your control strategy to get the most for your efforts against major weed problems.
This will also, over time, give you a better idea (with harvests) just how much weed control is economic on
your fields and will allow you to know where best to utilize field scouts in future monitoring programs.

Denise A. McWilliams
Extension Crop Production Specialist
dmcwilli@ndsuext.nodak.edu