2005 Annual Report for SW03-063
Factors Affecting Alfalfa Stand Longevity in Montana
Summary
Alfalfa is the major forage crop grown in Montana with over 1.8 million acres in production supporting the $2.5 billion livestock industry. Production in Montana is divided between dryland/rainfed (57%) and irrigated (43%) agriculture. Producers and extension agents throughout Montana have identified stand productivity and longevity as critical issues. Although not well recognized, an insect pest of alfalfa, clover root curculio (CRC) Sitona hispidulus (F.), can reduce stand longevity and has been reported in the state. The larvae cause damage by burrowing into the soil, feeding on alfalfa nodules and lateral roots, and 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, other insect pests, and alfalfa diseases as factors affecting stand longevity.
Objectives/Performance Targets
Objectives:
1. Conduct an extensive survey of pests and production practices in a variety of Montana production areas for effects on alfalfa stand longevity.
2. Identify the impact of clover root curculio, Sitona hispidulus, other arthropod pests, and plant diseases on alfalfa stand longevity.
3. Evaluate the impact of fall harvest timing on alfalfa stand longevity.
4. Evaluate the impact of nurse crops on alfalfa stand longevity.
5. Provide economic analysis of individual recommended and non-recommended practices from the results of research plots and from cooperating producer field level trials.
METHODS
Thirteen first-year alfalfa fields were visited spring and fall of 2005, although two fields were dropped from the original as they were older fields or had multiple planting dates within a single field. Ten plants per field including 6–8 inches of taproot were collected, returned to the lab, and assessed for insect, foliar, and root diseases. Taproot damage by clover root curculio was determined on a six-increment rating scale, based on rough visual estimates of percent damage: 0=no damage; 1= 1-10%; 2= 11-35%; 3= 36-65%; 4= 66-90%; 5= 90-100%. Plant foliage was tested for alfalfa mosaic virus using DAS-ELISA test kit on expressed plant sap.
Extension agents collected bi-monthly 25 sweep samples using s standarad 38 cm diameter sweep net. Insect samples were returned to the MSU-IPM lab for identification and processing. Differences in taproot damage were analyzed using PROC GLM (Tukey Test; P=0.05).
Accomplishments/Milestones
Participants in the project include: Extension Agent Cooperators:
Janna Kincheloe
P.O. Box 65
Forsyth, MT 59327
Steve Seleg
1523 Cartersville Rd
Rosebud, MT 59347
Mark DeCock
2114 Old Hwy 10
Forsythe, MT 59327
Gina Snyder
212 Broadway
P.O. Box 416
Culbertson, MT 59218
David Christoffersen
Box 325
Froid, MT 59226
Miles Knudsen
P.O. Box 734
Culbertson, MT 59218
Ron Carlstrom
901 N. Black
Bozeman, MT 59715
Ken Flikkema
Middle Creek Farms
8289 Huffine Lane
Bozeman, MT 59718
Paul Dixon
P.O. Box 35021
Billings, MT 59107
Roger & Cecilia Schwarz
64th St. W. Box 1243
Laurel, MT
Kent Williams
1010 Main
Miles City, MT 59301
Bill Griffin
HC 46 Box 114
Ismay, MT 59336
John Viall
HC 46 Box 7821
Miles City, MT 59301
Eric Miller
P.O. Box 81
Jordan, MT 59337
Tom Stanton
HC 60 Box 20
Brusett, MT 59318
Marko Manoukian
P.O. Box 430
Malta, MT 59538
Kevin Wiebe
HC 65 Box 6090
Malta, MT 59538
Karren Crawford
712 W. Main
Lewistown, MT 59457
Dee Boyce
95162 US Hwy 87
Lewistown, MT 59457
Degree day accumulation for each alfalfa forage cutting for irrigated alfalfa (41 F base temperature) was 1284.7 (SD = 208.3); second cutting was 2610.98 (SD = 277.8); and third cutting was 3796.2 (SD = 379.5). For dryland hay producers first cutting occurred at 1171.9 (SD = 170.8) and second cutting occurred at 2829.8( SD = 35.8). Alfalfa produced under irrigation yielded 5.1 tons/A (SD = 0.72) and dryland-produced hay had an average yield of 2.6 tons/A (SD = 0.63).
Clover Root Curculio. Adults collected from sweep nets were 61% S. hispidulus, 26% S. flavescens, and 12% S. lineelus. The clover root curculio is considered to be a complex of these three species, all of them known to cause similar damage (Bright 1994).
Most field sites showed no taproot damage in the early spring. Fall CRC ratings showed a strong correlation with soil type; sandy soils have significantly lower rates of damage than silty and clay soils (p=0.003). 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.
Plant Disease. Spring black stem (SBS) was present only in spring. Incidence of alfalfa mosaic virus (AMV) and crown/root rot increased in fall. Prevalence of alfalfa diseases did not seem to be correlated with CRC ratings.
Pest Management:
Insects: One producer practiced early cutting for alfalfa weevil control and two producers applied insecticide for alfalfa weevil management. No applications were made for aphid management.
Weeds: Two producers applied Sencor herbicide and two other producers each applied Pursuit and Buctril herbicides to their hay crop for weed management.
Plant Disease: No fungicide use was noted.
Impacts and Contributions/Outcomes
Most field sites showed no clover root curculio taproot damage in the early spring. However, damage had increased dramatically by the time of the fall survey; clover root curculio ratings showed a strong correlation with soil type; sandy soils have significantly lower rates of damage than silty and clay soils. These findings are consistent with findings of other researchers 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. Clover root curculio damage can be linked to soil type and was found to significantly damage alfalfa root systems in the first production year. Soil type may be useful in predicting damage by this insect pest.