fungicide

Evaluation of Potential New Insecticides and Fungicides for Honey Bee Repellency in Seed Carrots

Series/Report number: 
COARC2016
Abstract: 
To insure honey bee safety during crop pollination, potential new products were screened for bee repellency. This research was conducted in a carrot steckling field at the Central Oregon Agricultural Research Center (COARC). Bee visits were counted beginning one day after bees were brought into the field and continued for a total of four counts. There was no statistical difference between treated and untreated plots, indicating no detrimental effect on bee activity from these products.

Evaluation of Disinfectant Seed Treatments to Reduce Xanthomonas hortorum pv. carotae in Carrot Seed Lots

Bacterial blight of carrot, caused by the plant pathogenic bacterium Xanthomonas hortorum pv. carotae (Xhc), is a common disease of carrot wherever the crop is grown. The disease can affect carrot foliage, stems, umbels, and roots and can be seed-borne. Symptoms of bacterial blight include small, irregular, chlorotic areas on leaves that can manifest into water-soaked, necrotic lesions. Lesions can also occur on stems and petioles. Floral infections can result in blighted umbels, reduced seed yield, and reduced germination rates of harvested seed. Once established, Xhc is difficult to control and disease prevention is challenging because Xhc is seedborne and seed treatments with hot water or disinfectants may not entirely eradicate the pathogen. The seed-borne nature of Xhc makes it a major concern not only to the hybrid carrot seed industry in the Pacific Northwest but also to regions that import carrot seed for root production. Epiphytic populations can reach high levels on plants in the field, resulting in seed that is infected or infested by the pathogen. Seed lots that are highly infested with Xhc (>105 CFU/g seed) necessitate seed treatment to reduce the risk of bacterial blight occurring in commercial root crop production. Seed treatments are usually in the form of hot water treatment (52°C for 25 minutes) which can be effective but can reduce germination and/or shelf life of seed lots. Germination can be reduced further if seed lots need to be treated multiple times to reduce infestation levels below the 105 CFU/g threshold that was established for carrot seed planted in the Central Valley of California. Chemical seed treatments, which can remove bacterial pathogens that are borne on the seed surface, may provide alternative or additional methods for reducing Xhc in carrot seed lots. The objective of this project was to evaluate chemical disinfectants as seed treatments to reduce Xhc levels in carrot seed lots.
Series/Report number: 
COARC2016

Evaluation of ManKocide Alternatives for Bacterial Blight Control in Steckling-to-Seed Carrot Seed Crops

Series/Report number: 
COARC2016
Abstract: 
Management of bacterial blight in carrot seed crops can be difficult and begins with the planting of healthy or treated seed. However, planting healthy or treated seed may not prevent the disease in biennial seed production fields because new plantings are often located adjacent to or in close proximity to the previous years’ plantings. The pathogen, Xanthomonas hortorum pv. carotae (Xhc), is readily disseminated by contaminated irrigation water, wind-blown rain, insects, soil or carrot refuse and newly emerged seedlings of the next biennial season can become infected from nearby fields of the previous biennial season that already harbor Xhc. The disease has even been observed in isolated plantings, suggesting long distance dissemination of the pathogen on aerosolized seed crop residues or introduction of the pathogen on seedborne inoculum. In addition to infested seed, infected carrot stecklings may be a source of inoculum for carrot seed producers. A previous study detected Xhc in 4 of 12 steckling crops that were sampled directly from shipping crates (du Toit et al. 2005). The use of disease-free stecklings is an important component of an integrated disease management program to reduce the impact of bacterial blight on harvested seed. However, there is a lack of effective control options for infected stecklings. Carrot seed producers would like to reduce Xhc populations on harvested seed in order to minimize the need for hot water treatment and lessen the impact of bacterial blight on subsequent root crops in California, Washington, and other carrot-producing states and countries. Copper-based bactericides such as ManKocide (mancozeb + copper hydroxide) are applied multiple times each season to manage bacterial blight and increase seed quality, and are currently a primary control measure for bacterial blight in carrot seed crops. However, copper-based bactericides are most effective when used as preventative treatments and have limited ability to reduce Xhc populations once the pathogen becomes established in a seed crop (du Toit and Derie 2008).
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