Steam disinfestation as a methyl bromide alternative in California cut flower nurseries

Authors: RAINBOLT, CHRISTINE - California State University; HANSON, BRADLEY - University Of California - Cooperative Extension Service; FENNIMORE, S. - University Of California; Gerik, James

Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings
Publication Acceptance Date: 9/1/2010
Publication Date: N/A
Citation: N/A

Interpretive Summary: Steam was applied by 2 methods to disinfest soil prior to planting cut flower crops in 3 trials. The trials were conducted in Nepomo and Oxnard, CA during 2009 and 2010. Steam was delivered by spikes pressed into the soil connected to a delivery hose, or by drain tiles buried in the soil. Soil was heated to at least 70 degrees C for at least 30 minutes. Steam treatments were compared to soil fumigation with methyl bromide and to untreated controls. Crops planted after treatment included snapdragon, lily, sunflower, and bupleurum. After treatment pest control efficacy was determined. Weed control was evaluated and populations of several soilborne plant pathogens were determined. In general, steam disinfestation using either spike hoses or drain tiles usually provided pest control statistically similar to hot-gas methyl bromide. No negative effects on crop growth could be observed in the steam treatments. The spike hose and drain tile techniques used here are an improvement over sheet steaming; however, additional gains in thermal efficiency (fuel efficiency and heat retention) and a more mechanized application system is needed before steam is used on a significant portion of California’s cut flower nursery acreage.

Technical Abstract: Steam may be an effective alternative to methyl bromide in cut flower production in California. Advantages of steam include broad spectrum pest control and a zero hour re-entry interval. The principle disadvantage of sheet steaming is cost effectiveness due to current energy prices and application efficiency. Testing and developing more efficient, bottom-up steam delivery methods may increase the viability of this non-chemical alternative to methyl bromide. To compare the effectiveness of two steam application methods to methyl bromide and an untreated control, three field trials were conducted in cut flower nurseries near Nipomo and Oxnard, CA in 2009 and 2010. Trials were conducted in commercial nurseries in three cut flower crops, snapdragon, Asiatic lily, and sunflower/bupleurum. Treatments were applied to pre-formed beds and included an untreated control, methyl bromide, and two steam treatments. Steam was applied through three or four rows of 3-inch drain tile buried 12-in deep in each bed or through four rows of 5-in polypropylene mesh hose with 8-in steel spikes spaced 10-in apart pressed into the top of the bed. Steam treated beds were heated to 70 C for at least 30 min. Data collection included crop emergence, weed counts, crop heights, and pathogen population quantification. Snapdragon Trial: The first trial was conducted in a hoop house near Oxnard, CA. No significant differences in weed control or Fusarium spp. among treatments were found. Asiatic Lily Trial: The lily trial was conducted in a greenhouse near Nipomo, CA. No significant differences were found among treatments for Fusarium spp. or Pythium spp. populations at 0 MAT or Pythium spp. at 4 MAT, weed counts at 1 or 2 MAT, crop emergence at 2 MAT, or crop heights. However, populations of Fusarium spp. were greater in untreated plots compared to both steam and methyl bromide treatments at the p<0.1 level by the conclusion of the experiment. In addition, fewer plants emerged in the untreated plots compared to other treatments at the p<0.05 level 1 MAT. Sunflower/Bupleurum Trial: The third trial was conducted in an open field near Oxnard, CA. Half of the plots (two replicates) were planted in bupleurum and half seeded to sunflower approximately one month after treatment. The spike hose application method provided significantly better control of weeds compared to the control. In addition, both steam treatments provided better control of Pythium spp. and Phytophthora spp. at the p<0.05 level and of Fusarium spp. at the p<0.1 level. No significant differences were found for Verticillium spp. control. The insulating pads used in this trial appeared to decrease the time required to reach the target temperature (70oC) and may have reduced pest control variability. In general, steam disinfestation using either spike hoses or drain tiles usually provided pest control statistically similar to hot-gas methyl bromide. However, high variability probably masked treatment differences in some cases. Although economic assessment of the treatments comparing flower yield and fuel cost estimates are still needed, steam disinfestation of soil in shallow-rooted crops like cut flowers appears to be a promising methyl bromide alternative.