(Under the direction of Dr. Mark Hoffmann, Chair)

Location (Hybrid): 121 Kilgore Hall / Zoom
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Meeting ID: 926 8547 0010
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Abstract:
Methyl bromide was phased out as a reliable pre-plant fumigant throughout the United States in 2005. In its place, pre-plant chemical fumigants like dazomet, chloropicrin, 1,3-dichloropropene, and metam sodium have been utilized to control soilborne pests, pathogens, and weeds, in annual strawberry plasticulture systems. However, these chemicals can be difficult to use due to cost and government regulations. Alternative soil disinfestation practices, such as field-based steam application and biofumigation, have been studied and utilized to control soilborne pests, pathogens, and weeds. Steam application can control soilborne pests and pathogens through exposure to high temperatures. Steam has been utilized as a non-chemical alternative in greenhouse production settings for decades. However, disinfecting large volumes of soil through field-scale steam application is limited by time, labor, and cost.

Biofumigation utilizes crops or seed meals from the Brassicaceae family to release isothiocyanates, which are linked to fungal, oomycotal, weed, and pest suppression. Synthetically produced isothiocyanates, such as Dominus® (allyl isothiocyanate; AITC), are commercially available and can be used for pre-plant fumigation. However, this product has shown inconsistent efficacy as a sole pre-plant fumigant.

Two studies were conducted to improve the efficacy and efficiency of field-based steam application and biofumigation. Study 1 analyzed soilborne pathogen control through the application of steam and two exothermic substances, quicklime (CaO) and sodium peroxide (Na2O2), in a microplot study. Exothermic substances activated by water have the potential to increase soil temperatures more rapidly than steam by itself. It was hypothesized that soil-applied steam, in combination with exothermic substances, will lead to improved pathogen and weed control, compared to steam alone. Six treatments were established in a randomized complete block design with 4 replicates per treatment in Clayton, NC:  1) Non-treated control; 2) Steam for 30 min; 3) Sodium peroxide; 4) Sodium peroxide + steam for 30 min; 5) Quicklime; and 6) Quicklime + steam for 30 min. Steam + quicklime killed Pythium sp. at the 2.5 cm and 12.5 cm distances from the steam injection point, but steam alone and quicklime alone did not. Steam + sodium peroxide did not increase Pythium sp. control efficacy. The combination of quicklime and steam is a viable method to improve steam application efficiency in the field.

Study 2 investigated pathogen and weed control of AITC co-applied with steam in strawberry plasticulture settings in Clayton and Castle Hayne, NC. It was hypothesized that heat application through steam would increase the efficacy AITC, making it a more effective soil disinfectant. Nine treatments were applied and replicated 4 times each: 1) Non-treated control; 2) chloropicrin + 1,3-dichloropropene (60:40); 3) AITC; 4) AITC + 60-min steam application; 5) AITC + 30-min steam application; 6) AITC + 10-min steam application; 7) 60-min steam application; 8) 30-min steam application; 9) 10-min steam application. Pythium sp. and weed control, as well as strawberry yield, were analyzed. Weeds and Pythium sp. were controlled by AITC alone as effectively as 1,3-dichloropropene + chloropicrin. Steam alone did not effectively control weeds or Pythium sp. Yields were similar between AITC alone and 1,3-dichloropropene + chloropicrin. These results show the potential for shank-applied AITC to work as a pre-plant fumigant alternative in NC strawberry production.