Skip to main content

Thomas Björkman Lab

Research Publications

Check out my ResearchGate profile

Liebert, Jeffrey, Rebecca Benner, Rachel Bezner Kerr, Thomas Björkman, Kathryn Teigen De Master, Sasha Gennet, Miguel I. Gómez, Abigail K. Hart, Claire Kremen, Alison G. Power and Matthew R. Ryan. 2022. Farm size affects the use of agroecological practices on organic farms in the United States. Nature Plants.

Stansell, Zachary, Mark Farnham and Thomas Björkman. 2020. From landrace to modern hybrid broccoli: the genomic and morphological domestication syndrome within a diverse B. oleracea collection Horticulture Research 7(1) doi:10.1038/s41438-020-00375-0 Open Access

Stansell, Zachary, Mark Farnham and Thomas Björkman. 2019. Complex Horticultural Quality Traits in Broccoli Are Illuminated by Evaluation of the Immortal BolTBDH Mapping Population. Frontiers in Plant Science 10:1104 doi:10.3389/fpls.2019.01104 Open Access

Coles, Phil, Jiayi Dong, Miguel I. Gómez and Thomas Björkman. 2019. Produce Buyer Quality Requirements to Form an Eastern Broccoli Industry. J. Food Dist. Res. 50: 63-82 Open Access

Stansell, Zachary, Katie E. Hyma, Jonathan Fresnedo-Ramírez, Qi Sun, Sharon Mitchell, Thomas Björkman and Jian Hua. 2018. Genotyping-by-sequencing of Brassica oleracea vegetables reveals unique phylogenetic patterns, population structure and domestication footprints. Horticulture Research 5(1) doi: 10.1038/s41438-018-0040-3 Open Access

Stansell, Zachary, Thomas Björkman, Sandra Branham, David Couillard, and Mark W. Farnham. 2017. Use of a Quality Trait Index to Increase the Reliability of Phenotypic Evaluations in Broccoli HortScience 32:1490-1495. doi: 10.21273/HORTSCI12202-17

Jordan, Lindsay M., Thomas Björkman and Justine E. Vanden Heuvel. 2016. Annual Under-vine Cover Crops Did Not Impact Vine Growth or Fruit Composition of Mature Cool-climate Riesling Grapevines. HortTechnology 26:36–45. Open Access

Björkman, Thomas, Carolyn Lowry, Joseph W. Shail, Jr., Daniel C. Brainard, Daniel S. Anderson, and John B. Masiunas. 2015. Mustard Cover Crops for Biomass Production and Weed Suppression in the Great Lakes Region. Agron. J. 107:1235–1249. doi:10.2134/agronj14.0461   Open Access

Duclos, Denise V. and Thomas Björkman. 2015. Gibberellin Control of Reproductive Transitions in Brassica oleracea Curd Development. J. Amer. Soc. Hortic. Sci. 140:57–67.    Request reprint

Björkman, Thomas and Stephen Reiners. 2015. Meeting initial snapbean seedling requirements with starter phosphorus or bicarbonate to solubilize soil phosphorus in high-phosphorus soils. HortScience 50:590-596.    Request reprint

Attalah, Shadi S., Miguel Gómez and Thomas Björkman. 2014. Localization effects for a fresh vegetable product supply chain: Broccoli in the eastern United States. Food Policy 49:151-159.   Blog post about article

Björkman, Thomas and Stephen Reiners. 2014. Application of bicarbonate to high-phosphorus soils to increase plant-available phosphorus. Journal of the Soil Science Society of America 78:319-324. doi:10.2136/sssaj2013.08.0359   Open Access

Björkman, Thomas and Joseph W. Shail, Jr. 2013. Using a Buckwheat Cover Crop for Maximum Weed Suppression after Early Vegetables. HortTechnology 26:575-580    Request reprint

Mastouri, Fatemeh, Thomas Björkman and Gary E. Harman. 2012. Trichoderma harzianum enhances antioxidant defense of tomato seedlings and resistance to water deficit. Molecular Plant-Microbe Interactions doi:10.1094/MPMI-09-11-0240

Cerveny, C.B., W.B. Miller, T. Bjorkman, and N.S. Mattson. 2012. Soaking Temperature of Dried Tuberous Roots Influences Hydration Kinetics and Growth of Ranunculus asiaticus (L). HortScience 47(2):1-5.

Farnham, M. and Thomas Björkman. 2011. Breeding Vegetables Adapted to High Temperatures: A Case Study with Broccoli. Hortscience 46:1093-1097

Farnham, M. and Thomas Björkman. 2011. Evaluation of experimental broccoli hybrids developed for summer production in the Eastern United States. Hortscience 46:858-863.

Mastouri, Fatemeh, Thomas Björkman and Gary E. Harman. 2010. Seed treatment with Trichoderma harzianum alleviates biotic, abiotic, and physiological stresses in germinating seeds and seedlings. Phytopathology 100: 1213-1221. doi:10.1094 / PHYTO-03-10-0091

Duclos, Denise V. and Thomas Björkman. 2008. Meristem gene expression during reproductive development in Brassica oleracea. Journal of Experimental Botany 59: 421-433    doi:10.1093/jxb/erm327

Mochizuki, Maren J., Anusuya Rangarajan, Robin R. Bellinder, Thomas Björkman, Harold M. van Es. 2008. Rye mulch managment affects short-term indicators of soil quality in the transition to conservation tillage for cabbage. HortScience.  43:862-867.

Harman, G.E., T. Björkman, K. Ondik, M. Shoresh. 2008. Changing paradigms on the mode of action and uses of Trichoderma spp. for biocontrol. Outlooks in Pesticide Management. 19:24-29. doi: 10.1564/19feb00Cover picture with various broccoli and cauliflower forms

Mochizuki, M.J., A. Rangarajan, R.R. Bellinder, T. Björkman, H. M. van Es. 2007. Overcoming compaction limitations on cabbage growth and yield in the transition to reduced tillage. HortScience.  42:1690-1694.

Labate, Joanne A., Larry D. Robertson, Angela M. Baldo, and Thomas Björkman. 2006. Inflorescence identity-gene alleles are poor predictors of inflorescence type in broccoli and cauliflower.  J. Amer. Soc. Hortic. Sci. 131: 667-673

Björkman, T. 2004. Effect of Trichoderma colonization on auxin-mediated regulation of root elongation. Plant Growth Regulation 43: 89-92 doi:10.1023/B:GROW.0000038260.85276.82

Altomare, C., Norvell, W.A., Björkman, T. and Harman, G. E. 1999, Solubilization of phosphates and micronutrients by the plant-growth promoting and biocontrol fungus Trichoderma harzianum Rifai strain1295-22.  Appl. Environ. Microbiol. 65: 2926-2933.

Garner, L. C. and T. Björkman. 1999. Field performance of tomato transplants treated with mechanical conditioning. HortScience 34:848-851

Björkman, T. 1999. Dose and timing of brushing to control excessive hypocotyl elongation in cucumber transplants. HortTechnology 9:224-226.

Björkman, T. 1998. Mechanical conditioning for controlling excessive elongation in transplants. J. Japan Soc. Hort. Sci. 67:1121-1123

Harman, G.E. and T. Björkman. 1998. Potential and existing uses of Trichoderma and Gliocladium for plant disease control and plant growth enhancement. In: G.E. Harman and C. P. Kubicek (eds.), Trichoderma and Gliocladium. Vol .2. Enzymes, biological control and commercial applications. Taylor and Francis: London. pp. 229-266

Björkman, T. and K.J. Pearson. 1998. High temperature arrest of inflorescence development in broccoli (Brassica oleracea var. italica L.) Journal of Experimental Botany: 49:101-106

Björkman, T., L.M. Blanchard. and G.E. Harman. 1998. Growth enhancement of shrunken-2(sh2) sweet corn by Trichoderma harzianum 1295-22: Effect of environmental stress. Journal of the American Society for Horticultural Science 123: 35-40

Garner, L. C. and T. Björkman. 1997. Using impedance for mechanical conditioning of tomato transplants to control excessive stem elongation. HortScience 32:227-229

Björkman, T. 1997. Root colonization and growth responses to an improved biocontrol fungus. In: H.E. Flores, J.P. Lynch and D. Eissenstat (eds.) Radical biology: advances and perspectives on the function of plant roots. American Society of Plant Physiologists. pp. 532-534

Garner, L. C., F.A. Langton and T. Björkman. 1997. Commercial adaptations of mechanical stimulation for the control of transplant growth. Acta Horticulturae 435: 219-226

Samimy, C., T. Björkman, D. Siritunga and L. Blanchard. 1996. Overcoming the barrier to interspecific hybridization of Fagopyrum esculentum with F. tataricum.Euphytica 91: 323-330

Garner, L. C. and T. Björkman. 1996. Mechanical conditioning for controlling excessive elongation in tomato transplants: sensitivity to dose, frequency and timing of brushing. Journal of the American Society for Horticultural Science 121: 894-900

Björkman, T. 1995. The Role of Honeybees (Order: Hymenoptera) in the Pollination of Buckwheat (Family: Polygonaceae) Journal of Economic Entomology 88:1739-1745

Björkman, T. 1995. The effectiveness of heterostyly in preventing illegitimate pollination in dish-shaped flowers. Sexual Plant Reproduction 8:143-146

Björkman, T. 1995. The effect of pollen load and pollen grain competition in fertilization success and progeny performance in Fagopyrum esculentum. Euphytica 83: 47-52

Björkman, T., C. Samimy and K. Pearson. 1995. Variation in pollen performance among plants of Fagopyrum esculentum. Euphytica 82: 235-240

Björkman, T. 1994. Pollen competition in buckwheat. In: A. Stephenson and T-h. Kao (Eds). Pollen-pistil interactions and pollen tube growth. American Society of Plant Physiologists. pp. 280-283

Björkman, T. 1992. Perception of gravity by plants. Advances in Space Research 12:195-201

Björkman, T. and R.E. Cleland. 1991. Extracellular calcium in root gravitropism. Planta 185:379-385

Björkman, T. and R.E. Cleland. 1991. Root growth is not regulated by epidermis. Planta 185:34-37

Cleland, R.E., S.S. Virk, D. Taylor and T. Björkman. 1990. Calcium, cell walls and growth. In: Calcium in plant growth and development (R.T. Leonard and P.K. Hepler, eds.) Amer. Soc. Plant Physiologists: Rockville, MD pp. 9-16.

Björkman, T. 1988. Perception of Gravity by Plants Advances in Botanical Research 15:1-42

Björkman, T. and A.C. Leopold. 1987. An electric current associated withgravity sensing in maize roots. doi: http:/?/?dx.?doi.?org/?10.?1104/?pp.?84.?3.?841 Plant Physiology 84: 841-846.

Björkman, T. and A.C. Leopold. 1987. Effect of inhibitors of auxin transport and calmodulin on a gravisensing electric current. doi:10.1104/pp.84.3.847 Plant Physiology 84: 847-850.

Back to Thomas Björkman's main page

Conference abstracts

Björkman, T., J.W. Shail, D.C. Brainard, C. Lowry, J.B. Masiunas, D. Anderson. 2013, Effect of Late Summer Cover Crops on Weed Management in Organic Vegetables in the Great Lakes Region, Hortscience 43:S357. American Society for Horticultural Sciences.

Lowry, C., J.W. Shail, D.C. Brainard, T.Björkman. 2013. Late The optimal time to establish late-summer cover crops in the Great Lakes Region, Hortscience 43:S410. American Society for Horticultural Sciences.

Björkman, T. 2007. Avoiding volunteer seedlings after a buckwheat cover crop. American Society for Horticultural Sciences.

Duclos, D. and T. Björkman. 2007. Gibberellins’ effect on the reproductive development of Brassica oleracea. American Society for Horticultural Sciences.

Björkman, T. 2007. The use of buckwheat as a precise weed control tool. New England Vegetable and Fruit Conference.

Björkman, T. 2006. Establishment of buckwheat as a summer cover crop after early vegetables. American Society for Horticultural Sciences.

Duclos, D. and T. Björkman. 2005. Temperature effects on meristem identity genes controlling the reproductive development of cauliflower (Brassica oleracea var. botrytis) and broccoli (Brassica oleracea var. italica). American Society for Horticultural Sciences.

Duclos, D. and T. Björkman. 2004. Detecting Genes Expressed at Different Stages of Reproductive Arrest in Brassica oleracea. American Society for Horticultural Sciences.

Labate, J., Larry Robertson and Thomas Björkman. 2003. Genotypes at the BoCAL-a Locus in B. oleracea do not predict Broccoli, Cauliflower, and Purple Cauliflower phenotype. American Society for Horticultural Sciences.

Sheffer, Susan M., Joanne Labate, Thomas Björkman, Larry Robertson, and Angela Baldo. 2002. BoGSL-ELONG as a candidate diagnostic marker in phenotypically diverse brassica populations. Molecular Evolution.

Björkman, T. 2002. Many shades of black: cabbage storage disorders. New York State Vegetable Conference.

Björkman, T. 2001. How to mine starter P from the soil instead of adding to it. New York State Vegetable Conference.

Björkman, T. 2001. Increasing spring phosphorus availability without starter fertilizer. American Society for Horticultural Sciences.

Björkman, T. 2001. Causes of poor stand establishment after heavy rains. VII International Symposium on buckwheat.


Björkman, T., Blanchard, L.M. and G.E. Harman. 1999 Selection of fungi for high rhizosphere colonization in vitro, and subsequent ability to colonize roots in the field. Plant Physiology.

Björkman, T., Blanchard, L.M. and G.E. Harman. 1998 The effect of rhizosphere competence on colonization of sweet corn by biocontol fungi. HortScience 33:525.

Björkman, T. and Garner, L.C. 1998 Tomatoes remember being brushed. HortScience 33:471

Björkman, T. and L.C. Garner. 1997. Temporal integration of touch stimuli in reducing stem elongation of tomato seedlings. Plant Physiology 114:S-285 (American Society of Plant Physiologists annual meeting, Vancouver, BC)

Hayes, C.K., T. Björkman and G.E. Harman. 1997. Results of field trials using a commercial biofungicide. (American Phytopathological Society annual meeting, Rochester, NY).

Blanchard, L.M. and T. Björkman. 1996. The role of auxin in enhanced root growth of Trichoderma-colonized sweet corn. HortScience 31: 688

Altomare, C., T. Björkman, W.A. Norvell and G.E. Harman. 1996. Solubilization of manganese dioxide by the biocontrol fungus Trichoderma harzianum.

Björkman, T., G.E. Harman, and L. Blanchard. 1995. Root development of sweet corn inoculated with the biocontrol fungus Trichoderma harzianum HortScience 30: 810

Björkman, T. and K. Pearson. 1995. Sensitivity of broccoli infloresence development to high temperature. HortScience 30: 885

Garner, L.C. and Björkman, T. 1995. The effects of mechanical conditioning on tomato transplant growth and field performance. HortScience 30:776

Björkman, T., H.C. Price, G.E. Harman, J. Ballerstein, and P. Nielsen. 1994. Improved performance of shrunken-2 sweet corn using Trichoderma harzianum as a bioprotectant. HortScience 29:471

Björkman, T. G.E. Harman and H.C. Price. 1994 Effects of the biocontrol fungus Trichoderma harzianum on root development in Zea mays. Plant Physiology 105:S-44.

Björkman, T. 1993. Mechanical height control for tomato plug transplants: effects on yield. HortScience 28: 554

Björkman, T. 1993. Pollen competition in buckwheat (Fagopyrum esculentum). XV International Botanical Congress Abstracts: p. 289

Björkman, T. and R.E. Cleland. 1993. Extracellular calcium in root gravitropism. XV International Botanical Congress Abstracts: p. 490

Björkman, T. and Rathbun, K. T. 1992. Progressive increase in sterility can prevent plant maturation in buckwheat. Plant Physiol. 99:S-53 (Amer. Soc. Plant Physiol., 1992)

Björkman, T. and C.S. Samimy. 1991. Effect if developing flower buds on embryo abortion in buckwheat. HortScience 26:736 (Amer. Soc. Hortic. Sci., 1991)

Björkman, T. and R.E. Cleland. 1990. The necessity for apoplastic gradients across the root cap for gravitropic curvature in maize roots. ASGSB Bulletin 4: 97 (Amer. Soc. Gravit. Space Biol., 1990).

Virk, S.S., Björkman, T. and R.E. Cleland. 1990. The relationship between wall-bound calcium, free apoplastic calcium and the apoplastic pH of soybean hypocotyl tissues. ASGSB Bulletin 4: 21 (Amer. Soc. Gravit. Space Biol., 1990).

Björkman, T. and R.E. Cleland. 1990. Is the epidermis essential for root growth control? Plant Physiology (Amer. Soc. Plant Physiol., 1990).

Björkman, T. and R.E. Cleland. 1990. Changes in calcium activity during gravity sensing in maize roots Plant Physiology (Amer. Soc. Plant Physiol., 1990).

Extension Publications

Cover photoBjörkman, T., R.R. Bellinder, R.R. Hahn and J.W.Shail. 2008. Buckwheat Cover Crop Handbook. Cornell University. 18 pp.

Björkman, T. 2008. Organic fertility recommendations. In: Organic University; Advanced Row Crop Management. Midwest Organic Sustainable Education Service, pp. 65-80



Back to Thomas Björkman's main page

In the cool and humid climate of the northeastern United States, vegetation is typically maintained between the rows of wine grape (Vitis vinifera) vineyards, but the area directly beneath vines is conventionally kept bare using herbicides or cultivation, to reduce competition for water and nutrients. Yet with rising concerns of herbicide resistance, environmental contamination, and soil erosion, alternatives to maintaining bare ground in vineyards should be considered. In warmer and more arid climates, using cover crops as an alternative to bare soil has sometimes resulted in reduced vine growth and yields. In cooler and more humid climates, like in the northeastern United States, conditions can promote excessive vine growth. We tested whether replacing bare soil with under-vine cover crops improved vine growth characteristics and fruit quality by reducing excessive vigor. This study compared three annual under-vine cover crops of resident vegetation (RES), buckwheat (BW) (Fagopyrum esculentum), and annual ryegrass (ARG) (Lolium multiflorum), planted in the 1-m-wide strip directly under vines at the start of each growing season, against the conventional weed-free under-vine row maintained with glyphosate. The experiment was established in 2011 and repeated in 2012 and 2013 in a 20-year-old block of ‘Riesling’ wine grapes (clone 198 on S04 rootstock) in a commercial vineyard in the Finger Lakes region of New York State. Harvested grapes were fermented in duplicate using standard white wine procedures. Among the four under-vine treatments, no significant differences were found in measures of vegetative growth, yield, petiole nutrient concentrations at veraison, or predawn and midday stem water potentials. Under-vine treatments were not found to significantly affect soil organic matter, aggregate stability, and nutrient concentrations. Juice characteristics were also not significantly different among treatments. In this study, the mature vines in this rain-fed ‘Riesling’ vineyard likely had a well-developed and extensive rooting system that was able to overcome any competition effects for water or nutrients from the comparatively shallow root systems of the annually established cover crops. Without any induced competition in the conditions of this study, under-vine cover crops had no effects on vine growth, yield, or juice characteristics when compared with conventional herbicide use in the under-vine row. When multidimensional scaling (MDS) analysis was used to determine differences in aroma among wine treatment replicates, treatments were found to significantly impact the perceived aromatic properties of the wines, even though no measures of growth or juice characteristics were affected. Using under-vine vegetation may be a viable alternative to conventional herbicide use for vineyard floor management in mature wine grape vineyards in cool and humid climates.
Starter phosphorus (P) is often recommended for warm-season vegetables sown in cool soil, even if soil P index levels are already high. The cost and environmental risk associated with excessive P fertilization justify re-examination of the practice. The objective of the study was to confirm that performance of early plantings of snap bean (Phaseolus vulgaris L.) is improved by starter P application and to test whether solubilizing soil P with potassium bicarbonate (KHCO3) can serve as an alternative in western New York soils. Addition of starter fertilizer at either recommended (15 kg/ha) or supraoptimal (35 kg/ha) P rates did not generally improve seedling tissue P concentration, early growth (biomass at flowering), or pod yield. Starter P application increased tissue P in only two of 11 experiments, and it never increased yield. Application of 6 kg/ha KHCO3 to release soil-bound phosphate was not phytotoxic to snap beans. In the two experiments in which starter P increased tissue P, KHCO3 application had a smaller effect in one and no effect in the other. KHCO3 application did not increase yield in any of the six experiments where it was tested. A direct test of the contribution of P limitation to the poorer performance of early plantings showed that neither starter P nor KHCO3 application increased yield at early planting. Seasonal differences in crop performance could not be attributed to mineralization of soil phosphate after soil warmed. Water-extractable soil P was not lower in the spring than in summer, remaining constant at all 11 bean fields that were sampled from mid-April through mid-July. In these trials, P was likely not growth-limiting in the cool soils tested. Because starter P may not be necessary in vegetable soils testing high or very high for P, vegetables would also not likely benefit from bicarbonate application under high P conditions.
Cauliflower (Brassica oleracea var. botrytis) and broccoli (B. oleracea var. italica) differ in the developmental stage of the reproductive meristem at harvest. A cauliflower head is formed by arrest at the inflorescence meristem stage and broccoli at the flower bud stage, and the horticultural value of the crop depends on synchronous development across the head. In other plant species, gibberellin (GA) can promote floral development and is therefore a candidate for providing the early developmental cues that shape the curd morphology. This research investigated the effect of GAs on the two horticulturally important transitions of the reproductive meristem: initiation of the inflorescence meristem and initiation of floral primordia on the proliferated inflorescence meristems. GA is known to affect the former in many species, but effects on the latter have not been determined. It is also not known whether one or both active forms produced by the two GA biosynthetic pathways is involved in the reproductive transitions in this crop. GAs from the early-13 hydroxylation pathway (GA3) and the non-13 hydroxylation pathway (GA4+7) were applied to the shoot apical meristems of cauliflower and broccoli at three developmental stages: adult-vegetative, curd initiation, and curd enlargement. GAs applied during the adult vegetative stage caused the curd to form faster and after fewer additional nodes in both cauliflower and broccoli. GAs applied to the inflorescence meristem did not cause floral primordia to form nor did the expression of transition-associated genes change. Integrator genes BoLFY and SOC1 had constant expression over 24 hours, and meristem-identity genes BoAP1-a and BoAP1-c remained undetectable. However, GAs applied early during the reproductive phase increased bract development in cauliflower curds. This study shows that GAs from both pathways can trigger the vegetative-to-reproductive transition in both cauliflower and broccoli, resulting in earlier curd formation. However, GAs did not advance the inflorescence-meristem-to-floral-primordium transition; on the contrary, they increased bract incidence in cauliflower, a sign of reversion toward the vegetative stage, suggesting that another pathway is responsible for this second transition in cauliflower and broccoli.
Short-season cover cropping can be an important weed management tool. To optimize the use of mustard in the Great Lakes region, we assessed planting time effects, mustard biomass production, and weed suppression during mustard growth and after incorporation. The study was conducted in Illinois, Michigan, and New York for spring and fall from 2010 to 2012. Mustard was sown every ~10 d from mid-March to early June for spring plantings and from early August to mid-September for fall plantings. Spring mustard biomass, weed density, community composition, and dry biomass were collected at mustard flowering. Fall mustard biomass, weed density, and dry biomass were collected at season end. Spring mustard biomass ranged from less than 0.5 to 4 t/ha. Early fall biomass ranged from 3 to 5.5 t/ha, and was related to growing degree days according to a logistic function. Weed biomass during mustard growth was reduced by at least 50% in 9 of 10 site-years (90%) for fall-planted mustard but only 15 of 31 site-years (48%) in spring plantings. Weed suppression was independent of mustard biomass. The total number of weed seedlings emerging after mustard incorporation was not significantly reduced, but there was a species-specific response, with a decrease in common lambsquarters and grass emergence. The results permit a location-specific recommendation to plant mustard cover crops 13 to 23 August in the southern Great Lakes Region, and no later than 1 to 10 September for adequate biomass production.
For organic growers, planting a cover crop after vegetable harvests is an important tool for weed management and soil building. In the Great Lakes region, there is often not sufficient time for a second vegetable, but there is enough growing season left for weeds to become a serious problem. Cover crops are only effective at producing these results if they are sown at the right time of the season. We identified the optimal planting date range for sudangrass and mustards, developing a degree-day model that allows growers to estimate the best time in their location. In order for the model to be applicable across the region, we did sequential plantings in two states: Michigan and New York. Sudangrass required a minimum of 700 growing degree days with a 50°F base temperature (DD) before frost to produce meaningful biomass and suppress weeds. 'Idagold' and 'Tilney' mustard required 1700 to 2200 DD32 before a hard frost to produce sufficient biomass. The biomass increased sharply with DD within that range, so a few days delay in planting can substantially reduce the cover crop value. The crucifer-planting window is approximately 2 weeks long, occurring in early-mid August in the cooler parts of the region, and late August in the warmer parts. When mustards were sown earlier (> 2200 DD32) they produced no more biomass, but they did produce seeds. Those seeds create a high risk for volunteer mustard, that is a difficult weed problem. Tests of other crucifer cover crops (albeit not on organic ground) show that the response of cover-crop radish, brown mustard, forage rapeseed, forage turnip, and winter canola have exactly the same optimal plant- ing window. All have a tendency to bolt and go to seed in the fall sown later than ideal, and a tendency to overwinter and go to seed in spring if sown too soon.
Organic vegetable growers rely on cover crops to contribute to their weed management by reducing weed seed rain and increasing weed seed mortality. We investigated whether late-summer planting of cover crops in the Great Lakes region would reduce fall weed escapes and subsequent weed growth in the following year's crop. We also investigated whether the effect of a late-summer cover crop is different if it is allowed to decompose over winter with the roots undisturbed or incorporated in the fall so that it is thoroughly decomposed. Furthermore, untreated bean seed is susceptible to many rot pathogens whose abundance might be affected differently by the various cover crop species, and by how recently and rapidly the decomposition occurred. To obtain results applicable to the broader Great Lakes region, we performed the experiment in New York, Michigan, and Illinois using organic practices. While fall tillage resulted in a substantially lower stands of beans, that effect was the same whether there was a cover crop present or not. In spring-incorporated plots the stand was slightly better following sudangrass, with the other cover crops being equivalent to no cover crop. Fall weeds, and therefore, weed seed rain, were strongly suppressed by cover crops. The weed biomass was less than 20% of the unmanaged plots. Sudangrass was effective when it emerged quickly, but when drought delayed its emergence, sudangrass failed to suppress weed establishment. Buckwheat, which was terminated in September, allowed some cool-season grasses to establish afterward. Weed pressure in the bean crop was measured in several ways relevant to a growers' weed management: initial flush of seedlings, post-cultivation emergence, and time required to hand weed after mechanical cultivation. There was no consistent effect of any cover crop on the subsequent weed pressure. At an individual site and year, there were sometimes large effects that may indicate a suppression mechanism that would be useable if it could be identified. While these cover crops were effective for reducing the weed seed production, and would therefore be valuable in long-term weed minimization, the benefit was not consistently detectable in the subsequent year.
Vegetable growers can suppress late summer weeds by planting buckwheat as a cover crop following vegetable harvest. In the northeastern U.S., the window of opportunity is short, so timing is critical. We determined the tillage and timing of sowing buckwheat that yield the best chance of success. Planting buckwheat only one week after crop incorporation of early vegetables is sufficient and better than waiting the traditional two weeks. However, buckwheat must be sown when there are at least 700 growing degree days (GDD50remaining in the season.
Vegetable growers in the northeastern U.S. often have soils with phosphorus levels so high that fertilizer applications have environmentally detrimental effects. However, growers raise crops that require phosphate fertilizer in cool soils regardless of soil P levels. A method to increase bioavailable P to vegetable seedlings in cool soils would have great value. Bicarbonate is a safe and inexpensive material that solubilizes some pools of adsorbed phosphate. Incubation of 50 µmol potassium bicarbonate gram-1 of soil increased water-extractable phosphate three- to eight-fold in soils characteristic of P-impacted vegetable soils in the northeastern U.S. A banded treatment at this rate is equivalent to 28 kg ha-1. Multivariate analysis of soil characteristics revealed that the most responsive soils were those high in sand content. The response increased linearly with sand content above 50%. A bicarbonate application technique would therefore have particular promise on sandy, high-P soils such as those found on the Atlantic seaboard.