Application of Chemicals In-Season to Augment Pre-plant Fumigation

Authors: Gerik, James; KLOSE, SUSANNE - UNIVERSITY OF CALIFORNIA; GREENE, IAN - GOLDEN STATE BULB GROWERS

Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings
Publication Acceptance Date: 8/31/2007
Publication Date: 11/1/2007
Citation: Gerik, J.S., Klose, S., Greene, I.D. 2007. Application of Chemicals In-Season to Augment Pre-plant Fumigation. International Conference on Methyl Bromide Alternatives and Emissions Reductions.

Interpretive Summary: Fungicides applied through drip irrigation systems are typically used for calla lily production to control soil-borne diseases. Results from these fungicide applications have been disappointing; soil-borne diseases still cause large losses. We attempted to use low rates of methyl bromide alternative chemicals during the growing season hoping that these low molecular weight compounds would move in the soil better than the large molecular weight fungicides. Following pre-plant soil fumigation with methyl bromide:chloropicrin or iodomethane:chloropicrin, and planting, applications of the alternative chemicals were made during the summer while the crop was growing. The chemicals tested included 2-bromoethanol, dimethyl disulfide, furfural, and iodomethane, all at extremely low rates. No improvements in disease control or yield were obtained from these applications, and some indications of phytotoxicity were observed.

Technical Abstract: Hybrid calla lily (Zantedeschia spp.) is grown on the central coast of California for cut flowers for the wholesale flower market and rhizomes for propagators of potted flowering plants. The crop is direct-seeded in the spring and the rhizomes are harvested after approximately 18 months. The crop is severely affected by soil-borne plant pathogens including Pythium spp. which cause root rot, particularly during the second summer of the cropping cycle. Pre-plant soil fumigation with methyl bromide:chloropicrin (MB:Pic) is used in an effort to control these pathogens. Even with soil fumigation, fungicides are typically used during the second summer to attempt to control disease. We report here the results of using low dosages of methyl bromide alternatives during the cropping season in an attempt to improve disease control and rhizome yield. A field trial was established in May 2005 in Moss Landing, California on a ranch with an extensive history of calla lily production. The main plots were fumigated with either MB:Pic (50:50, 400 lb/acre), or Midas (50:50, 400 lb/acre) or water (control). The fumigants were applied in 1.5” of water using 5 irrigation tapes equally spaced over the bed width. The subplots were two plastic mulches with one half of each bed covered with high density polyethylene (HDPE) or a virtually impermeable film (VIF). The area under each half bed was further divided into five 50’ sub-sub plots. Each of these plots received two in-season treatments during each summer of the cropping cycle. These treatments consisted of either 2-bromoethanol, dimethyl disulfide, furfural, each at 25 lb/acre or iodomethane at 12 lb/acre, or water. The conclusion from this study is that the main fumigants applied by drip irrigation were sufficient in achieving a healthy calla lily stand, controlling Pythium spp. and Fusarium oxysporum and producing a crop value twice as high as in untreated soils. In this study and year, the type of film used made little difference, probably due to the high rates of the primary fumigants. The application of the low rate in-season fumigant treatments was not beneficial for the production of calla lilies. In the contrary, in-season pesticide treatments caused phytotoxicity on the calla crop with plants showing chlorosis and necrosis. However, even with the drip application of high rates of the primary fumigants MB/Pic and Midas, disease still adversely effected production of this crop. More work will be needed to find a method to curtail these losses.