Long-term
Strategies to Control Multiflora Rose
Jerry
Doll and Raymond Saxby*
Multiflora rose is an
infrequent pasture weed problem in several southern Wisconsin
counties. While not widely distributed, it can be a serious
problem if left uncontrolled. Research done in Grant and
Columbia counties found several products effectively control
multiflora rose. However, there is little information on which
product, method of application and the number of years
treatments most quickly and economically suppresses an
infestation.
In 1987, we started a
trial to compare various management strategies over a five-year
period, including the costs of each one. These strategies either
used the same treatment for five years or started with a
particular treatment and then shifted to a different product and
usually a different method of application. We also evaluated the
effects of single or multiple mowings on multiflora rose bushes.
Methods Used
The test site was an
unused pasture in Caledonia township of Columbia County in south
central Wisconsin. Plots were established in a randomized
complete block design in areas where multiflora rosa was rather
uniformly distributed and typical of infested pastures in the
region. Plots were 35 by 50 ft, replicated three times, and
contained an average of 16 bushes each at the start of the trial
in 1987 (equivalent to 373 bushes/acre).
Table
3 gives the products; their concentration, rate, method and
time of application; and cost per bush. Banvel was applied in
early spring when bushes were dormant or breaking dormancy with
a spot-gun applicator that delivered 5 ml per pull of the
trigger. Each bush received 2 ml of Banvel by applying 20 ml of
a 10% (v/v) Banvel solution. The 5-ml aliquots were applied in
four spots around the immediate vicinity of the base of plants.
Spike was also applied
as an early spring treatment. A canister with the pelleted
product consistently dispensed 0.25 oz of 20% active ingredient
pellets with each pull of the "trigger". The quarter
ounce of pellets was distributed to treat the soil at the base
of six bushes.
Foliar sprays were
applied in mid to late June when plants were fully leafed out
and often in the early bloom stage. A knapsack sprayer fitted
with an adjustable nozzle cone was used. Over the 5-yr period,
an average of 60 ml/bush of spray solution was applied for the
foliar treatments. A colorant was added to the spray solution to
aid in identifying treated bushes as applications were made. The
number of bushes treated was recorded at each application.
Visual evaluations were taken 6 to 8 weeks after application and
at the end of the growing season. Results were comparable and
only the late season results are presented. Analyses of variance
were performed and LSD values calculated on the evaluations and
multiflora rose populations.
The cost of each
strategy was determined using 1992 herbicide prices. Because the
populations varied among strategies at the start of the trial,
we adjusted the initial population to the average for the entire
area, 373 plants/A for the economic analysis. For 1987, the cost
per bush for each treatment (Table 3)
was multiplied times 373 to obtain the cost per acre. For
subsequent years, we used the actual multiflora rose population
in the plots for each strategy and calculated the percentage
change relative to the base year, 1987. This percentage was
multiplied times 373 to give the expected population if that
treatment had been applied to this population density. For
example, a strategy that had 400 treated plants/A in 1987 and
200 in 1988, was a 50% reduction. To calculate the costs in
1988, we took 50% of the average population (373) and multiplied
the cost per bush for that treatment times 187. The same
procedure was used for the other years and the total cost for
the 5-yr period was computed.
To evaluate the
effects of mowing on multiflora rose, individual bushes were
identified in 1990 and 1991. In one trial, we cut bushes at the
soil surface or 2, 4 or 6 inches above the soil. Other bushes
were identified and cut once, twice or three times at a 4 to 6
inch height. In 1990, we included a treatment of 50% Roundup
(volume/volume) to cut canes that were 6 inches in height. Cut
bushes were observed at the end of each season and the following
year to determine if they had survived.
Results and
Discussion
Banvel applied
annually to the soil as a spring dormant treatment gave 28 to
88% control and also gave less control than other treatments
when applied following foliar applications, except when
following Weedmaster (Table 2). Control
ratings for Roundup were between 77 and 100%. Even though the
control was sometimes less than that of other treatments, very
few Roundup-treated bushes survived the winter following
application. All other control strategies tested resulted in 85%
or better multiflora rose control. Spike and Crossbow gave the
most consistent control.
Of more importance in
this study was the impact of each strategy on multiflora rose
population over time. Populations varied greatly among
strategies (Table 3). Banvel applied
each season as a spring dormant treatment and Banvel following
foliar applications of other products was the least effective of
all strategies. Several strategies eliminated the population
after 3 or 4 yr, but reinfestation from seed always occurred.
Thus control strategies must be carried out for a long period to
assure eradication of multiflora rose. The average number of
bushes for all strategies shows that after 5 yr, only 18
bushes/A were present and six of the strategies had 8 or fewer
bushes/A.
To further compare the
effectiveness of each strategy on the populations, the
percentage reduction in comparison to the initial population was
calculated (Table 4). The relatively
poorer control from Banvel as a spring dormant treatment is seen
again. In several strategies, populations increased markedly
after 1987. An explanation could be that we failed to treat
plants because they had little if any new growth because they
were dormant and thus were missed. If this were true, we should
have seen similar population increases for Spike because it too
was applied when bushes were dormant. Perhaps the same bushes
were treated with Banvel from year to year as the control
ratings were lower than for other treatments. Most strategies
show a rapid and continual decline in percentage of bushes
remaining. The average over all strategies dropped to 30% by
1989 and to 6% by 1992. The most effective strategies reduced
the population to 18% of the original by 1989 and achieved
stable levels by 1990. This suggests that after 3 yr of
effective control, treatment frequency can be reduced to a
maintenance program.
Economic
Analysis
The cost of each
strategy is a function of product price and number of bushes
treated. Any economic evaluation is based on certain
assumptions. Our included the following. For simplicity, we used
estimated prices for 1992. This has probably overestimated the
cost somewhat. We assumed 100 ml of solution were used per bush.
We actually applied and average of 60 ml but believe that
producers and others would tend to apply more than we did. The
amount applied naturally varies with the size of bushes, nozzle
type and applicator experience. We did not include the cost of
the application. Our objective was to make relative cost
comparisons among strategies and Table 5
gives the results obtained.
Banvel applied
annually was the most costly treatment, both in 1987 (when we
assumed the number of bushes treated was identical for all
strategies), and when it followed any foliar application except
Banvel + 2,4-D. We have no explanation for this exception. The
higher cost of this strategy is due to the relatively high cost
per bush (3.70 cents) and to its slow effect in reducing the
population relative to other strategies. The average 5-yr cost
of strategies with Banvel as a spring dormant treatment was
$36.40/A.
Spike was the next
most expensive treatment (2.60 cents/bush) the first year, but
because it rapidly reduced the population, was an economical
treatment in 1988 to 1991. The average 5-yr cost of strategies
that included Spike was $14.60/A.
The most economical
strategies were those based on foliar applications. The total
cost per acre for strategies that included foliar sprays of
Banvel + 2,4-D averaged $6.00; for Roundup strategies, $7.20;
and for Crossbow strategies, $8.30 over the 5-yr period.
Naturally, all costs presented are based on the population at
this site. A population of 373 bushes/A means plants are
approximately 10 ft apart. In more heavily infested areas, the
cost would rise accordingly.
We knew at the start
of the project that the spring dormant treatments were the most
expensive alternatives and to use Banvel or Spike as a single
strategy was expected to be the least logical approach. Based on
economics this was definitely true for Banvel but less so for
Spike. Another consideration with Spike is that it is a soil
sterilant. All vegetation in the treated area is killed for at
least 2 and often 3 yr. In level areas, the spot killed is a
circle about 12 in. in diameter. On slopes, lateral Spike
movement can kill vegetation 2 ft from the site of application.
Thus its use in areas with dense populations and on sloping
terrain (which is typical of pastures in Wisconsin) should be
evaluated carefully.
The foliar
applications were both effective and economical during the
period of this study. There was no apparent advantage to
rotating products from the one used the first year. The kill of
forage species under and near the Roundup-treated plants was
temporary and did not lead to an invasion of weedy species.
After 2 or 3 yr, grass forage species reinfested the killed
areas. However, it would seem logical not to use Roundup in
pastures highly infested with multiflora rose as the impact on
desired forbs would be significant. The population of 373
bushes/A means that there was one plant/117 sq ft. If a 3-ft
diameter circle is killed around each bush, 6% of the total area
(7 sq ft) is killed. Therefore, starting with a selective foliar
treatment and shifting to Roundup when the density is reduced
seems appropriate.
There are several
strategies that producers can use to manage multiflora rose
infestations. Regardless of the one used, it is important to
continue the management program until the population is nearly
eradicated. This appears to be at least for 3 yr with annual
treatments and then alternate year applications should continue
until the seed bank is depleted. |
