How do I manage a white clover living mulch for weed suppression for my squashes and melons?
Answer: Here is some information on living mulches in general, along with some information specific to cucurbits.
Part One: Introduction to Living Mulches
A living mulch is a cover crop that is intercropped with an annual or perennial cash crop, primarily for weed suppression and as a soil management practice. Living mulches reduce soil erosion, suppress weeds, increase soil organic matter, improve trafficability, increase water infiltration, and increase nutrient cycling. Legumes used as living mulches fix nitrogen from the air and can replace or reduce the need for nitrogen fertilizers. Some living mulches also provide habitat for beneficial insects.
There are three basic ways to establish a living mulch:
 drilling or broadcasting a cover crop together with the primary crop at planting;
 drilling (interseeding) or broadcasting (overseeding) a cover crop at the last cultivation;
 drilling a cash crop into mechanically or chemically suppressed strips of a living cover crop.
Living Mulch Systems and Methods of Suppression
When managed incorrectly, living mulches can act like weeds and compete with the main crop for light, water and nutrients. Especially in low-growing vegetables—such as vine crops—an overgrown living mulch can interfere with flowering and fruit development. Thus, management of a living mulch is geared to getting good ground coverage and then suppressing its growth through chemical or mechanical means.
The first 4 to 6 weeks after planting is the most critical growth period for most crops. During this time, plant competition can reduce yields most severely, and living mulch growth may require suppression. Using a method of suppression becomes most critical where soil moisture is limited. When a vegetable crop is planted directly into strips of live vegetation, methods of suppression prior to planting may include application herbicides (at sublethal rates), mowing, tillage, flaming, and a technique known as rolling.
When an intercrop is established at planting or by overseeding, methods of suppression may include time of establishment (in the case of overseeding), use of dwarf type cover crops, application of herbicides at sublethal rates, and light mechanical cultivation.
Dying Mulch/Living Mulch Weed Suppression
A dying mulch is a cover crop planted out of season that puts on some growth—suppressing weeds as a living mulch—and then dies back out on its own without requiring the use of herbicides, mowing, or tillage to knock it back. Winter rye—planted in the spring—has been used successfully in this manner in several agronomic and horticultural crops.
Here’s how a dying mulch has been used by several Midwestern vegetable growers. In mid-spring, the field is overseeded with winter rye at 120 lbs. per acre to establish a living mulch. In order for winter rye to tiller and produce a seed head, it requires a period of cold treatment, or vernalization. Since it never receives vernalization and thus never tillers, it remains short and eventually just “cooks out” in summer, leaving a weed-suppressive duff.
The success of this system is dependent on proper timing and good luck. Timing is critical to get the rye established early enough to promote germination when the soil temperatures are still relatively cool, but at the same time, late enough that a cold spell is avoided. Since vernalization can occur when the rye is exposed to only 10 days of 45? F. night temperatures, a sudden spring cold snap can result in the cover crop performing in an other-than-expected manner.
Choice of Living Mulch Species
Cover crops, like any other crop, require fairly specific growing conditions. Both grasses and legumes are being used as living mulches. Of these, there are both cool season and warm season types to choose from.
Factors affecting choice of living mulch cover crop include the primary crop, rotation sequence, growing season, method of establishment, and intended use (i.e., dying mulch, winter killed mulch, etc.). Most important in the selection of a living mulch is that the plant species chosen be vigorous enough to provide the benefits of a cover crop, but not so vigorous that competition with the main crop cannot be managed without killing it. The region of the country (e.g., agroclimatic zone) is also of great importance in selecting a living mulch. For example, subclover is grown as a winter annual legume in the South, but as a spring annual in the North.
Some grass species used as living mulches include perennial ryegrass, dwarf ryegrass, turf type fescues, millet, and out-of-season winter cereal grains. Some legume species used as living mulches include white clover, hairy vetch, subterranean clover, Dutch white clover, dwarf English trefoil, Korean lespedeza, and crimson clover. Broad-leaved cover crops that have potential as living mulches include phacelia, buckwheat, and various crucifers. Rapid cycling brassica germplasm is under development at the University of Minnesota. These are low-growing, short-season brassicas that function as smother crops early in the growing season, then mature early and leave a weed suppressive duff.
ATTRA’s Overview of Cover Crops and Green Manures publication is a useful resource. It reviews the benefits and uses of cover crops and provides a number of useful resources on cover crops and seed sources.
Part Two: Notes on Living Mulches for Cucurbits (Squash and Melons)
In New England, drilling clover in between the rows after cucurbit crop establishment is a common way to raise cucurbits with living mulches, especially with winter squashes.
In fact, one Cornell research report—”Lana vetch winter rye living mulches in organic pumpkins: competition, weed suppression, and insect pest mitigation effects”(see below)—concluded that after-seeded living mulches were the most promising approach to living mulches in pumpkins.
The following selected resources address living mulches and cover crops for cucurbits, including a few select items geared to the Northeastern United States:
1. Cover Crop and Mulch Studies
Carrington Research Extension Center
North Dakota State University
Pumpkin cover crop and living mulch study
2004 2003 2002 2001
2. Evaluation of Living and Synthetic Mulches in Zucchini for Control of Homopteran Pests
Daniel L. Frank, Dept of Entomology and Nematology, Univ of Florida
_____ 46-page PDF
Investigate and compare the effects of reflective and living mulch on the population dynamics of homopteran pests, their associated natural enemies, and insect-transmitted plant impairments.
Investigate the advantages of using reflective and living mulch over standard bare-ground or white mulching systems.
Living mulch treatments had higher natural enemy populations than the synthetic mulch and bare ground treatments.
Synthetic mulches had significantly higher yields than those grown with living mulch or on bare ground.
Synthetic mulches cost more.
Living mulches require more time and maintenance.
Harvesting easier on synthetic mulches.
3. Cucurbit Pest Management — Weed Management & Cover Cropping
Iowa State, Colorado State, Univ of Minnesota project
We investigated the use of a hairy vetch/rye cover crop as an organic nitrogen source and as a living mulch to control weed.
The experiment was conducted at the ISU Horticulture Research Station and at the Muscatine Island Research Station. Treatments included a hairy vetch/rye cover crop with sidedressed chemical nitrogen, the cover crop alone, the nitrogen treatment alone, and a control without the cover crop or nitrogen addition.
The cover crop was planted in the fall prior to the muskmelon season (40 lb/A vetch and 30 lb/A rye), and was killed by rolling the crop with a cultipacker after flowering. A slit was made in the mulch using a chisel tooth, and transplants were inserted.
Cover cropping appears to be a successful, sustainable strategy for weed management.
4. Watermelon Cover Cropping with Wheat and Barley in Niigata, Japan
Agroecological Case Study
5. Selection of Vegetables for Intercropping as a Pest Management Strategy
Mark G. Wright & Michael P. Hoffmann
Department of Entomology, Insectary Building, Cornell University, Ithaca
_____ 10-page PDF
Organic Agriculture at Cornell University research report
6. Lana vetch winter rye living mulches in organic pumpkins: competition, weed suppression, and insect pest mitigation effects
Organic Agriculture at Cornell University research report
7. Guide to the Expert Farmers? DACUM Chart for “Manage Crop Rotation System”
_____ 27-page PDF
NEON — Northeast Organic Network
8. Cover Crops and Green Manures
Vern Grubinger, Univ of Vermont
Coleman, Eliot. 1989. Fertilizer from the garden. Mother Earth News. September-October. p. 112, 114, 116-120.
Foulds, Chantal. 1989. Interseedings in vegetable production. REAP Canada. Vol. 2, No. 4. p. 6-7, 14.
Foulds, C.M., K.A. Stewart, and R.A. Samson. 1991. On farm evaluation of legume interseedings in broccoli. p. 179-180. In: W.L. Hargrove (ed.) Cover Crops for Clean Water. Soil and Water Conservation Society, Ankeny, IA.
Grubinger, Vernon P. 1990. Living Mulch for Vegetable Production. University of Vermont Extension Service, Windham County. 14 p.
Hofstetter, Bob. 1993. Smother crops: Plant a grain in the “wrong” season for the right cover. New Farm. May/June. p.39-41.
Jurchak, Thomas. 1989. Growing vegetables with the living mulch. American Vegetable Grower. May. p. 22-25.
Lanini, Tom. 1989. Subclovers as living mulches for managing weeds in vegetables. California Agriculture. November December. p. 25-27.
Further Reading on Living Mulches:
Anon. 1993. Alternate vegetable systems tested in new ?living lab.? Innovations in Sustainable Agriculture. Fall. p. 1, 6-7.
Butler, Jack D. 1986. Grass interplanting in horticulture cropping systems. HortScience. Vol. 21., No. 3. p. 394-397.
Brown, Martha. 1990. Cover crops: soil and water management options. The Cultivar. Winter. p. 1-2, 15.
Brown, Martha. 1990. Cover crop study concludes second year. The Cultivar. Summer. p. 3-4.
Cook, Tom. 1982. The potential of turfgrasses as living mulches in cropping systems. p. 23-35. In: J.C. Miller, and S.M. Bell (ed.) Crop Production Using Cover Crops and Sods as Living Mulches. International Plant Protection Center, Oregon State University, Corvallis, OR.
Cramer, Craig. 1988. High value hillsides. The New Farm. September-October. p. 54-55, 59.
DeGregorio, R.E., and R.A. Ashley. 1985. Screening living mulches and cover crops for weed suppression in no till sweet corn. Proceedings of the Northeast Weed Society. Vol. 39. p. 80-84.
Eberlein, C.V., C.C. Sheaffer, and V.F. Oliveira. 1992. Corn growth and yield in an alfalfa living mulch system. Journal of Production Agriculture. Vol. 5, No. 3. p. 332-339.
Elkins, D.I. et al. 1983. Living mulch for no till corn and soybeans. Journal of Soil and Water Conservation. Vol. 26. p. 431-433.
Enache, A.J. 1989. Weed Control by Subterranean Clover (Trifolium subterraneum) Used as a Living Mulch. Ph.D. Dissertation. Rutgers University. 137 p. Dissertation Abstr. Int’l., Volume: 50 11, Section: B, page 4825.
Enache, A.J., and R.D. Ilnicki. 1990. Weed control by subterranean clover (Trifolium subterraneum) used as a living mulch. Weed Technology. Vol. 4, No. 3. p. 534-538.
Enache, A.J., and R.D. Ilnicki. 1993. Chapter 19, Subterranean clover: Nitrogen contribution. p. 215-226. In: M.G. Paolettie, W. Foissner, and D. Coleman (ed.) Soil Biota, Nutrient Cycling, and Farming Systems. Lewis Publishers, Boca Raton, FL.
Fischer, A.J. 1988. Intra and Interspecific Interference Between Sweet Corn (Zea mays L.) and a Living Mulch of White Clover (Trifolium repens L.). Ph.D. Dissertation. Oregon State University. 151 p. Dissertation Abstr. Int’l., Volume: 50 05, Section: B, page 1697.
Fischer, Albert, and Larry Burrill. 1993. Managing interference in a sweet corn white clover living mulch system. American Journal of Alternative Agriculture. Vol. 8, No. 2. p. 51-56.
Grossman, Joel. 1993. Fighting insects with living mulches. IPM Practitioner. October. p. 1-8.
Grubinger, Vernon. 1989. Augmenting a Low Rate of Nitrogen Fertilization for Sweet Corn Production with Strip Rototilled White Clover Living Mulch (Fertilizer, Corn, Clover). Ph.D. Dissertation. Cornell University. 170 p. Dissertation Abstr. Int’l., Volume: 50 07, Section: B, page 2682.
Grubinger, Vernon P., and Peter L. Minotti. 1990. Managing white clover living mulch for sweet corn production with partial rototilling. American Journal of Alternative Agriculture. Vol. 5, No. 1. p. 4-12.
Ilnicki, R.D., and A.J. Enache. 1992. Subterranean clover living mulch: an alternative method of weed control. Agriculture, Ecosystems and Environment. Vol. 4. p. 249-264.
Nicholson, A.G., and H.C. Wien. 1983. Screening of turfgrasses and clovers for use as living mulches in sweet corn and cabbage. Journal of the American Society of Horticultural Science. Vol. 108. p. 1071-1076.
Reiners, S. and O. Wickerhauser. 1995. The use of rye as a living mulch to control weeds in bell pepper production. HortScience. July. p. 892.
Sarrantonio, Marianne. 1992. Opportunities and challenges for the inclusion of soil improving crops in vegetable production systems. HortScience. Vol. 27, No. 7. p. 754-758.
Schonbeck, Mark, Judy Browne, and Ralph DeGregorio. 1990. Cover crops for weed control in lettuce. New Alchemy Quarterly. Fall. p. 8-11.
Schonbeck, Mark, Peggy Elder, and Ralph DeGregorio. 1995. Winter annual cover crops for the home food garden. Journal of Sustainable Agriculture. Vol. 6. No. 2-3. p. 29-53.
Scott, Thomas W., and R.F. Burt. 1985. Cover Crops and Intercrops for New York. Cornell Field Crops Fact Sheet 452. 4 p.
Vrabel, T.E., P.L. Minotti, and R.D. Sweet. 1981. Legume sods as living mulches in sweet corn. Proceedings of the Annual Meeting &—Northeast Weed Science Society. Vol. 35. p. 158-159.
Vrabel, Thomas Edward. 1983. Effect of Suppressed White Clover (Trifolium repens L.) on Sweet Corn (Zea mays L. var. Rugosa Bonaf.) Yield and Nitrogen Availability in a Living Mulch Cropping System. Ph.D. Dissertation. Cornell University. 176 p. Dissertation Abstr. Int’l., Volume: 44 06, Section B, page 1670.
Waters, M., and Ilnicki, R.D. 1990. Use of subterranean clover as mulch for weed control in summer squash. Proceedings of the Northeast Weed Science Society. Vol. 44. p. 58.
Wiles, L.J. et al. 1989. Analyzing competition between a living mulch and a vegetable crop in an interplanting system. Journal of the American Society of Horticultural Science. Vol. 114, No. 6. p. 1029-1034.
William, R.D. 1987. Living Mulch Options for Precision Management of Horticultural Crops. Extension Circular 1258. Oregon State University Cooperative Extension Service. 5 p.