Biofumigation is practiced to control soilborne pests and weeds in agronomic fields. The objectives of this research were to assess the dose response of weed seeds to Indian mustard biofumigation and associate responses to seed dormancy state, initial dormancy, and seed parameters. A petri dish biofumigation methodology was developed to expose seeds of common lambsquarters, bird vetch, wild carrot, common ragweed, green foxtail, velvetleaf, hairy galinsoga, and red clover to allelochemicals produced after rehydrating 0 (control), 1.94, 2.90, 5.81, 11.61, and 17.41 mg cm-2 of dried mustard powder. Weed species expressed specific dose responses, estimated ED50, LD50, and maximal mortality. Hairy galinsoga and wild carrot were consistently the most affected by biofumigation, with maximal mortality reaching 97% and 95%, ED50 values for germination were 1.91 and 2.68 mg cm-2, and LD50 values were 3.31 and 3.69 mg cm-2 of dried mustard tissue, respectively. Initial dormancy was assessed by germination and tetrazolium tests. Seed parameters such as testa thickness, relative weight of the testa, and seed size were measured directly by manual dissection, weighing seed structures, and stereomicroscopic imaging software measurements. Linear regression analyses revealed initial dormancy to be positively related to ED50 and LD50 values with a significant interaction with seed surface and seed width, respectively. Exposure to 5.81 mg cm-2 of dried mustard powder increased common ragweed seed mortality for after-ripened seeds by 293% and by 58% for primary dormant seeds compared with untreated seeds. Mortality of common lambsquarters secondary and primary dormant seeds increased by 730% and 106%, respectively, and for wild carrot by 1,193 and 156%, respectively. Results underline the potential to incorporate biofumigation into weed management programs for repression of susceptible weed species.
Nomenclature: Indian mustard, Brassica juncea (L.) Czern. ‘cv. Caliente 199’; velvetleaf, Abutilon theophrasti Medik. ABUTH; bird vetch, Vicia cracca L. VICCR; common lambsquarters, Chenopodium album L. CHEAL; common ragweed, Ambrosia artemisiifolia L. AMBEL; green foxtail, Setaria viridis (L.) Beauv. SETVI; hairy galinsoga, Galinsoga quadriradiata Cav. GASCI; red clover, Trifolium pratense L. TRFPR; wild carrot, Daucus carota L. DAUCA.
ED50: estimated half maximal effective dose of dry mustard biomass that decrease germination;
LD50: lethal dose of dry mustard biomass that kills 50% of viable seeds.