Dominus for cut flower production

Authors: Rosskopf, Erin; Hong, Jason; Burelle, Nancy; HOLZINGER, JOHN - Holzinger Flowers, Inc; BOOKER, BRAD - Pacific Ag Research, Inc; YATES-YARBROUGH, STEPHANIE - Pacific Ag Research, Inc; SANCES, FRANK - Pacific Ag Research, Inc

Submitted to: Proceedings of Methyl Bromide Alternatives Conference
Publication Type: Proceedings
Publication Acceptance Date: 9/25/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: Fumigation with methyl bromide was the principal method of soilborne pest control in cut flower production. Many cut flower growers in Florida have ceased production, but those that remain are restricted in the fumigants that they are able to utilize due to proximity to potable water sources and occupied structures. While all fumigants and non-chemical soil disinfestation practices have been evaluated for cut flowers, none have resulted in a readily-available, economically feasible alternative. One potential exception is a biofumigant with the active ingredient allylisothiocyanate, registered as the commercial product Dominus® (Isagro, USA). Initial experiments with Dominus resulted in nematode control that was comparable to that achieved with methyl bromide, but weed control has been variable. Although there are several herbicides labeled for control of broadleaf and annual grass weeds in field grown ornamentals, few have been tested in combination with fumigant materials. A series of experiments were performed to evaluate the effectiveness of Dominus, either applied alone or in combination with a limited number of herbicides. Experiments were conducted to compare Dominus directly to methyl bromide by pairing plots and growing several different floriculture crops. There were no significant differences between nematode and fungal plant pathogen control between the two fumigants. Yields were equivalent and weed control was similar with the exception of Carolina geranium, which was poorly controlled by both soil treatments and was slightly worse in Dominus. In a second set of experiments, Dominus and a combination of organic acids (SPK) were combined individually with three different herbicides. Herbicides had no effect on nematode or pathogen control, but two of the herbicides caused a high level of phytotoxicity in snapdragon, but not in sunflower. Although herbicides were labeled for snapdragon, testing of herbicides with the intended fumigant partner is needed in order to identify those that do not negatively impact crop production.

Technical Abstract: Fumigation with methyl bromide was the principal method of soilborne pest control in cut flower production. Many cut flower growers in Florida have ceased production, but those that remain are restricted in the fumigants that they are able to utilize due to proximity to potable water sources and occupied structures. While all fumigants and non-chemical soil disinfestation practices have been evaluated for cut flowers, none have resulted in a readily-available, economically feasible alternative. One potential exception is a biofumigant with the active ingredient allylisothiocyanate, registered as the commercial product Dominus® (Isagro, USA). Initial experiments with Dominus resulted in nematode control that was comparable to that achieved with methyl bromide, but weed control has been variable. Although there are several herbicides labeled for control of broadleaf and annual grass weeds in field grown ornamentals, few have been tested in combination with fumigant materials. A series of experiments were performed to evaluate the effectiveness of Dominus, either applied alone or in combination with a limited number of herbicides. In the first experiment, replicated strip applications were made by commercial applicator using paired plots of 100 ft long by 13 feet wide. The test was conducted on Oldsmar sand with methyl bromide shank applied at 400 lb/A under Klerk's virtually-impermeable film 1.2 mil. IRF-135 was applied at 40 gal/A, covered with the same film. Both materials were shank-applied to 8" depth. The field was separated into multiple planting areas after plastic removal 30-45 days after fumigation, depending upon the planting schedule for each variety. Cut flower crops included snapdragons, delphiniums, lupine, dianthus, and sunflowers. Weed, nematode, and fungal plant pathogen assessments were conducted throughout the season. In the second trial, Dominus (30 g/A) was compared to a combination of organic acids (SPK, 1714 g/A), both drip applied, and a non-treated check. The experiment was conducted as a split plot with four herbicide treatments: no herbicide, Dimension® 2EW (1qt/A), Showdown® (100lb/A), and Snapshot® 2.5GT (100lb/A). Sunflower (Procut Lemon) and snapdragon (Opus) were established by direct-seeding and transplanting respectively. Herbicides were applied when snapdragons were 12 inches tall and sunflowers were at the 3 true leaf growth stage. No root-knot nematode juveniles were detected in the post-treatment soil sampling of the first experiment. At mid-season of the first planting, there were no significant differences between any genera of plant parasitic or non-parasitic nematodes between Dominus and methyl bromide, with the numbers of all plant parasitic averaging fewer than 10 juveniles per g of soil. Disease was minimal and not significantly different between treatments with 1.5% incidence of wilt in snapdragons caused by Sclerotium rolfsii in Dominus-treated plots and 0.06% in the methyl bromide treatments. At first snapdragon harvest, there were no significant differences between root condition ratings and root galling. The roots from plants harvested from the Dominus treatment were significantly heavier than roots from methyl bromide (average of 6.96g/rt from Dominus vs. 5.99g/rt from methyl bromide). First larkspur harvest resulted in no differences between soil treatments. This was also the case for the first harvest of delphiniums, except for root galling in which the methyl bromide-treated plots had roots with slightly higher levels of galling (1.0 vs 0.04 p=0.0082). First harvest lupines had significantly larger stems (8.6 cm vs 7.2 cm; p=0.02) in the Dominus-treated plots. There were no significant differences between any plant parasitic nematodes extracted from roots from snapdragons, larkspur, delphiniums, and lupines from the first planting, nor the second. T