fumigants are needed. Biofumigants are a type of cover crop that, in addition to other soil benefits, have the ability to suppress soilborne pathogens including fungi or nematodes ( Kirkegaard et al., 1999 ). Biofumigation is a sustainable method of soil
Rachel E. Rudolph, Carl Sams, Robert Steiner, Stephen H. Thomas, Stephanie Walker and Mark E. Uchanski
Christina L. Pierson, Carl E. Sams, Dennis E. Deyton and Craig S. Charron
Biofumigation is an alternative to traditional methods of soil sterilization such as methyl bromide. Biofumigation utilizes volatile, pesticidal compounds in soil incorporated plant material from various Brassica species. Three experiments were conducted to study the degradation of allyl isothiocyanate (AITC) generated from the breakdown of glucosinolates present in Oriental mustard (Brassica juncea L. Czerniak). Mustard seed meal was incorporated into a sandy clay loam soil in all experiments. In the first experiment, samples were hydrated and then held in an incubator at 20 ± 0.2 °C. Samples were taken periodically for 7 days or until AITC was not detectable. For the second experiment, hydrated samples were removed from the incubator after 4 hours and 5 mL of ethyl acetate was added. The samples were then placed in a refrigerator at 4 ± 0.2 °C and samples were taken periodically over 77 days. For the third experiment, samples were taken from a strawberry plot experiment grown in a randomized complete block design. Samples were taken and 5 mL of ethyl acetate was added. Then samples were placed into a cooler until returning to the laboratory. The incubator experiment was repeated and showed that the highest concentration of AITC occurred between 2 and 8 hours after hydration. The storage experiment showed a stable relationship between time and AITC degradation. AITC was still present after 77 days. The strawberry plot experiment showed rapid AITC degradation similar to the incubator experiment. Future research will be done to confirm the effects of temperature and glucosinolate content on the amount of allyl isothiocyanate present.
Sanjeev K. Bangarwa, Jason K. Norsworthy, Ronald L. Rainey and Edward E. Gbur
the presence of soilborne insects, pathogens, or nematodes. Literature cited AMVAC Chemical Corp 2008 Vapam HL soil fumigant label AMVAC Chemical Corp Los Angeles, CA Angus, J. Gardner, P. Kirkegaard, J. Desmarchelier, J. 1994 Biofumigation
Andrew J. Price, Craig S. Charron, Arnold M. Saxton and Carl E. Sams
A study was conducted to quantify volatiles generated from Indian mustard (Brassica juncea L. Czerniak) tissue incorporated into soils under controlled conditions. Mustard residues were incorporated into noncovered and covered soils that varied by texture, temperature, moisture, pH, or sterility (autoclaved or nonautoclaved). Sandy loam soil had 38% more allyl isothiocyanate (AITC) than clay loam soil. AITC concentration in 45 °C soil was 81% higher than in soil at 15 °C, and 56% higher in covered compared to noncovered treatments. The microbial catabolism of AITC was suggested by the result that AITC concentration in autoclaved soils was over three times that measured in nonautoclaved soils. The highest AITC level detected (1.71 μmol·L–1) occurred in the autoclaved covered soil. Several factors also influenced CO2 evolution. At 30 or 45 °C, CO2 concentration was at least 64% higher than at 15°C. The covered soil had over twice the CO2 found in the noncovered soil, and the nonautoclaved soil treatment yielded twice the CO2 measured in the autoclaved soil. There were no main effect differences among soil moisture, soil pH, and soil texture treatments for CO2 concentrations. This information could be helpful in defining ideal soil conditions for field scale experiments. Additionally, this study demonstrates a sampling technique for testing fumigation potential of biofumigation and solarization systems that may have the potential to replace methyl bromide.
Ali A. Ramin, P. Gordon Braun, Robert K. Prange and John M. DeLong
Biofumigation by volatiles of Muscodor albus Worapong, Strobel & W.M. Hess, an endophytic fungus, was investigated for the biological control of three postharvest fungi, Botrytis cinerea Pers., Penicillium expansum Link, and Sclerotinia sclerotiorum (Lib) de Bary, and three bacteria, Erwinia carotovora pv. carotovora (Jones) Bergey et al., Pseudomonas fluorescens Migula (isolate A7B), and Escherichia coli (strain K12). Bacteria and fungi on artificial media in petri dishes were exposed to volatiles produced by M. albus mycelium growing on rye seeds in sealed glass 4-L jars with or without air circulation for up to 48 hours. The amount of dry M. albus–rye seed culture varied from 0.25 to 1.25 g·L–1 of jar volume. Fan circulation of volatiles in jars increased efficacy and 0.25 g·L–1 with fan circulation was sufficient to kill or suppress all fungi and bacteria after 24 and 48 hours, respectively. Two major volatiles of M. albus, isobutyric acid (IBA) and 2-methyl-1-butanol (MB), and one minor one, ethyl butyrate (EB), varied in their control of the same postharvest fungi and bacteria. Among the three fungi, IBA killed or suppressed S. sclerotiorum, B. cinerea, and P. expansum at 40, 25, and 45 μL·L –1, respectively. MB killed or suppressed S. sclerotiorum, B. cinerea, and P. expansum at 75, 100, and 100 μL·L –1, respectively. EB was only able to kill S. sclerotiorum at 100 μL·L –1. Among the three bacteria, IBA killed or suppressed E. coli (K12), E. carotovora pv. carotovora, and P. fluorescens at 5, 12.5, and 12.5 μL·L–1, respectively. MB killed or suppressed E. coli (K12), E. carotovora pv. carotovora, and P. fluorescens at 100, 75, and 100 μL·L–1, respectively. EB did not control growth of the three bacteria. This study demonstrates the need for air circulation in M. albus, MB, and IBA treatments to optimize the efficacy of these potential postharvest agents of disease control.
Steven Vaughn*, Terry Isbell, David Weisleder and Mark Berhow
Field pennycress (Thlaspi arvense L.) seedmeal was found to suppress seedling germination/emergence and biomass accumulation when added to a sandy loam soil containing wheat (Triticum aestivum L.), arugula [Eruca vesicaria (L.) Cav. subsp. sativa (Mill.) Thell.] and sicklepod (Senna obtusifolia (L.) H.S. Irwin & Barneby) seeds. Covering the pots with petri dishes containing the soil-seedmeal mixture increased phytotoxicity at the lowest application rate, suggesting that the some of the phytotoxins were volatile. Dichloromethane, methanol and water extracts of the wetted seedmeal were bioassayed against wheat and sicklepod radicle elongation. Only the dichloromethane extract was found to be strongly inhibitory to both species. Fractionation of the dichloromethane extract identified two major phytotoxins, identified by GC-MS and NMR analyses as 2-propen-1-yl (allyl) isothiocyanate (AITC) and allyl thiocyanate (ATC), which constituted 80.9 and 18.8%, respectively, of the active fraction. When seeds of wheat, arugula and sicklepod were exposed to volatilized AITC and ATC, the germination of all three species were completely inhibited by both compounds at concentrations of 5 ppm or less.
Victoria J. Ackroyd and Mathieu Ngouajio
. 21 437 444 Hoagland, L. Carpenter-Boggs, L. Reganold, J. Mazzola, M. 2008 Role of native soil biology in Brassicaceae seed meal induced weed suppression Soil Biol. Biochem. 40 689 1697 Kirkegaard, J.A. Sarwar, M. 1998 Biofumigation potential of
P. R. Johnstone, T. K. Hartz, E. M. Miyao and R. M. Davis
Mustard cover crop residue has been reported to have a “biofumigant” action when incorporated into the soil, potentially providing significant disease suppression and yield improvement for the succeeding crop. Such activity could be particularly useful in processing tomato rotations, where consecutive cropping invariably results in yield decline. Agronomic and environmental effects of growing over-winter mustard cover crops preceding tomato production were investigated in three field trials between 2002 and 2004. Two mustard cover crops [`Pacific Gold', a brown mustard (Brassica juncea), and `Caliente', a blend of brown and white mustard (Sinapis alba)] were compared to a legume cover crop mix, a fallow bed treatment (the standard grower practice in this region), and, in two of the three trials, a fumigation treatment using metam sodium. No suppression of soil populations of Verticillium dahliae or Fusarium spp. was observed with the mustard cover crops, nor was there any visual evidence of disease suppression on subsequent tomato crops. In these fields, the mustard either had no effect, or reduced tomato yield, when compared to the fallow treatment. At one of two sites, metam sodium fumigation significantly increased tomato yield. The presence of a cover crop, whether mustard or legume, reduced winter runoff by an average of 50% over two years of trials. No benefit of mustard cover cropping beyond this reduction in winter runoff was observed.
Craig S. Charron and Carl E. Sams
The U.S. Clean Air Act bans the use of methyl bromide after 2005. Consequently, the development of alternative methods for control of soilborne pathogens is imperative. One alternative is to exploit the pesticidal properties of Brassica L. species. Macerated leaves (10 g) from `Premium Crop' broccoli [B. oleracea L. (Botrytis Group)], `Charmant' cabbage [B. oleracea L. (Capitata Group)], `Michihili Jade Pagoda' Chinese cabbage [B. rapa L. (Pekinensis Group)], `Blue Scotch Curled' kale [B. oleracea L. (Acephala Group)], Indian mustard [B. juncea (L.) Czerniak, unknown cultivar] or `Florida Broadleaf' mustard [B. juncea (L.) Czerniak] were placed in 500-mL glass jars. Petri dishes with either Pythium ultimum Trow or Rhizoctonia solani Kühn plugs on potato-dextrose agar were placed over the jar mouths. Radial growth of both fungi was suppressed most by Indian mustard. Volatiles were collected by solid-phase microextraction (SPME) and analyzed by gas chromatography-mass spectrometry. Allyl isothiocyanate (AITC) comprised >90% of the volatiles measured from `Florida Broadleaf' mustard and Indian mustard whereas (Z)-3-hexenyl acetate was the predominant compound emitted by the other species. Isothiocyanates were not detected by SPME from `Premium Crop' broccoli and `Blue Scotch Curled' kale although glucosinolates were found in freeze-dried leaves of all species. When exposed to AITC standard, P. ultimum growth was partially suppressed by 1.1 μmol·L-1 (μmol AITC/headspace volume) and completely suppressed by 2.2 μmol·L-1 R. solani was partially suppressed by 1.1, 2.2, and 3.3 μmol·L-1 AITC. Use of Brassica species for control of fungal pathogens is promising; the presence of AITC in both lines of B. juncea suppressed P. ultimum and R. solani but some Brassicas were inhibitory even when isothiocyanates were not detected.
Sanjeev K. Bangarwa, Jason K. Norsworthy and Edward E. Gbur
Field trials were conducted in 2006 and 2007 to evaluate the performance of ‘Caliente’ mustard cover crop and herbicide combinations for weed control in polyethylene-mulched bell pepper (Capsicum annuum). ‘Caliente’ mustard is a blend of brown mustard (Brassica juncea) and white mustard (Sinapis alba). Herbicide treatments included 1/2× and 1× rates of two pre-emergence (PRE) and two postdirected (PD) herbicides. PRE herbicides were applied 1 week before transplanting, whereas PD herbicides were applied at 4 to 5 weeks after transplanting. ‘Caliente’ mustard did not supplement weed control or improve bell pepper yield in herbicide-treated plots. There was a significant herbicide selection by application rate interaction for large crabgrass (Digitaria sanguinalis) control and bell pepper yield, but only the main effect of herbicide selection and application rate affected the control of purple nutsedge (Cyperus rotundus), yellow nutsedge (Cyperus esculentus), and palmer amaranth (Amaranthus palmeri). Bell pepper injury was not more than 9% from all herbicides and application rates. Except for large crabgrass, control of all weed species improved by increasing the application rate from 1/2× to 1×. S-metolachlor PRE provided more broad-spectrum weed control than other herbicides. Halosulfuron applied PRE or PD was selective to purple nutsedge and yellow nutsedge, whereas trifloxysulfuron performed better than halosulfuron on palmer amaranth and large crabgrass. Plots treated with the 1× rate of S-metolachlor or trifloxysulfuron produced the highest marketable bell pepper yield among the herbicide treatments, but no herbicide treatment allowed for marketable yield equivalent to the weed-free treatment.