Transcript Document

Taproot Damage by Clover Root Curculio, Sitona hispidulus (Coleoptera:
Curculionidae) and Other Factors Affecting Alfalfa Stand Longevity in Montana
Rebecca Baril, Cecil Tharp, Sue Blodgett, Ken
INTRODUCTION
Alfalfa is the major forage crop grown in Montana with
over 1.8 million acres in production supporting the $2.5
billion livestock industry. Montana producers and
extension agents have identified stand productivity and
longevity as critical issues. A well-known insect pest of
alfalfa, notorious for reducing stand longevity, is the
clover root curculio Sitona hispidulus (F.). The larvae
cause damage by feeding on alfalfa nodules and lateral
roots, eventually creating open feeding wounds on the
taproot that invite the entry of various pathogens. In
this first year of a three-year study, we looked at statewide incidence and severity of clover root curculio
(CRC) taproot damage and alfalfa diseases as factors
affecting stand longevity.
1
Kephart ,
and Dave
2
Wichman
Dept. of Animal and Range Sciences, Montana State University-Bozeman
1Southern Ag. Research Center, Huntley, MT 2Central Ag. Research Center, Moccasin, MT
S. hispidulus
Sitona spp.
RESULTS
Clover Root Curculio. Adults collected from sweep nets were 61%
S. hispidulus, 26% S. flavescens, and 12% S. lineelus. The clover root
curculio is thought to be a complex of these three species, all of them
known to cause economic damage (Bright 1994).
Producer Field
Roosevelt1
Roosevelt2
Custer1
Garfield
Phillips
Custer2
Rosebud1
Gallatin1
Rosebud2
Gallatin2
Fergus
Teton
Yellowstone
SBS
30%
10%
100%
none
20%
90%
none
40%
none
100%
30%
10%
50%
Spring
AMV
Crown/Root Rot
10%
none
none
none
none
none
10%
none
none
none
none
none
none
none
20%
10%
10%
none
10%
none
none
none
20%
none
30%
none
AMV
60%
10%
20%
20%
none
10%
none
70%
10%
33%
10%
30%
40%
Fall
Crown/Root Rot
30%
20%
none
30%
50%
10%
none
20%
30%
none
none
50%
80%
Table 1. Incidence of spring black stem (SBS), alfalfa mosaic virus
(AMV), and crown/root rot by producer fields
ROOSEVELT
PHILLIPS
TETON
FERGUS
GARFIELD
Plant Disease. Spring black stem (SBS) was present only in
spring samples (Table 1). Incidence of alfalfa mosaic virus
(AMV) and crown/root rot increased in fall (Table 1).
Prevalence of alfalfa diseases did not seem to be correlated
with CRC ratings.
ROSEBUD
CUSTER
GALLATIN
YELLOWSTONE
Fig. 1. Field sites by county
(A)
METHODS
Thirteen 1st year alfalfa fields in Montana (Fig. 1)
were visited in spring and fall of 2005.
•Ten plants per fields were dug and assessed for foliar
and root diseases.
•Taproot damage by CRC was determined on a sixincrement rating scale, based on rough visual estimates
of percent damage: 0=0%; 1=1-10%; 2=11-35%;
3=36-65%; 4=66-90%; 5=90-100.
•Plants were tested for alfalfa mosaic virus using
DAS-ELISA (Fig. 2).
•Bi-monthly sweep samples taken by extension agents
•Differences in taproot damage were analyzed using
PROC GLM (Tukey Test; P=0.05).
(A)
(B)
Fig. 3. CRC taproot damage in spring and fall 2005 showing
correlation with soil type
Fig. 4. Alfalfa diseases. (A) severe crown and
root rot (B) Spring Black Stem
FUTURE
Most field sites showed no taproot damage in the early spring (Fig. 3).
Fall CRC ratings showed a strong correlation with soil type; sandy
soils have significantly less damage than silty and clay soils (p=0.003;
Fig. 3). These findings are consistent with Pacchiolo and Hower
(2004) who demonstrated that silt-clay loam provided soil cracks
larger than 1.0mm for CRC larvae increasing access of first instars to
alfalfa root nodules. Sandy loams did not contain large enough pores
and the texture was abrasive to the larvae cuticle.
Fig. 2. (A) AMV ELISA test showing positive results
(blue) (B) Alfalfa leaf showing characterisitic AMV
patterns
LITERATURE CITED
Bright, D.E. 1994. Revision of the Genus Sitona (Coleoptera:
Curculionidae) of North America. Ann. Entomol. Soc. Am. 87(3):
277-306.
Pacchiolo, M.A. and A.A.Hower. 2004. Soil and moisture effects on
the dynamics of early instar clover root curculio (Coleoptera:
Curculionidae) and biomass of alfalfa root nodules. Environ.
Entomol. 33(2): 119-127.
(B)
Fig. 4. CRC damaged taproots
This statewide study will continue for two additional years.
Other factors to be looked at include: field management
practices, other insects, weeds, hay quality and yield.
Concurrent studies are researching the use of nurse crops
on alfalfa stand density and longevity, and at the
effectiveness of carbofuran applications on clover root
curculio taproot damage.
AKNOWLEDGEMENTS
We would like to thank all of the producers and county extension agents who are
involved in this study for their time and interest: Steve Seleg, Mark DeCock, David
Christoffersen, Mike Knudsen, Glenn Droge, Ken Flikkema, Roger Schwarz, John
Viall, Bill Griffin, Tom Stanton, Kevin Wiebe, Dee Boyce, Randy Parker, Dale
Sand, and Jerry Johns, Dave Phillips (Fergus County Extension), Dan Clark (Teton
County Extension), Paul Dixon (Yellowstone County Extension), Janna Kincheloe
(Rosebud-Treasure County Extension), Marko Manoukian (Phillips County
Extension), Steve Hutton (Pondera County Extension), Kent Williams (Custer
County Extension), Eric Miller (Garfield County Extension), Wade Crouch
(Cascade County Extension). This research is funded by the WSARE program.