Study and Control of Pseudomonas Syringae on Blueberry Plants

View the project final report

Commodities

• Fruits: berries (blueberries)

Practices

• Crop Production: food product quality/safety
• Education and Training: extension, farmer to farmer, networking, on-farm/ranch research, workshop
• Energy: wind power
• Farm Business Management: whole farm planning
• Pest Management: chemical control, prevention, weather monitoring
• Production Systems: general crop production
• Sustainable Communities: sustainability measures

Pseudomonas syringae is a naturally present environmental bacterium that causes bacterial leaf blight, twig blight and stem cankers on blueberry plants. Bacterial blight, caused by Pseudomonas syringae, is a serious blueberry disease in Washington State. Information in the public domain tends to focus mostly on frost-induced damage as the source of bacterial blight infections.

Standard cultural controls for the prevention and treatment of bacterial blight include frost protection measures (cover, heating/burning, irrigation), pruning diseased wood out before fall to remove the source of inoculum, and avoiding over-application of nitrogen after the first of July to prevent overly vigorous growth (which is very susceptible to frost damage and fall infection). Copper Oxychloride is also used to reduce the incidence of bacterial blight. Local blueberry growers applied these methods prior to the inception of this project, but the response has been less than acceptable.

Therefore, our goal is to investigate methods of reducing the incidence of bacterial blight infections. Two technological advancements will be sought:

1) Develop alternative preventative measures, specifically the use of wind machines, for controlling bacterial blight, and

2) Clarify the roles of contributing factors, i.e. environmental conditions, crop management practices, pests and pest management practices, blueberry cultivars, etc, in the development of bacterial blight.

With the use of wind machines, it is not known how starting temperature, dew point and relative humidity will impact frost damage in a blueberry field. Soil conditions and requirements for blueberries are different than for other crops. For example, organic mulches commonly used for blueberry are likely to influence heat transfer from the soil. It is also not known how varying exposures will affect bud break; the earlier the bud breaks, the higher the chances of tissue damage in the fruits.

The blueberry canopy is at various heights, and it is not known how these factors may impact the design (location, position) and any modification of the wind machines. It is also uncertain how the plants’ receptiveness to the disease and different moisture content of the berries and stems will impact the outcome of the experiment. This research project will be among the first that applies windmills for frost protection against bacterial blight.

Treatment and control areas will be delineated; the farms will be divided into blocks, each containing sub-blocks (50 x 50 feet experimental plots). For comparative reasons, one block will be located close to the wind machines, while the other blocks will be located at a different location from away from the wind machines.

Data collection and monitoring will continue, which will include manual temperature and relative humidity measurements; daily from March to May, weekly from June to August and twice a week from September to October. In addition, micro-weather stations (Onset Corp, Bourne MA) with temperature and leaf wetness sensors will be installed near the top of the canopy in the blocks with and without wind machines. These will provide a continuous record throughout the times that wind machines are used. Bud break conditions, especially bud frost damage, will be assessed in the early bloom time, and blight distribution surveys will be carried out across treatment and control areas. The cultivar susceptibility will also be considered as a potential source of variability in disease incidence.

Data with and without wind turbines will be collected and recorded for the different blocks and varieties. Blueberry plants will be assessed for tissue damage and bacterial blight infection by visually counting the number of blighted twigs on each blueberry plant in the study area. Pseudomonas counts will be carried out by an independent third-party laboratory. Average disease incidence will be calculated and compared between control and treatment areas. Comparative analysis of the current year’s results will be compared with the following years.

Further tests will be carried out to investigate the effects of using the wind machines as frost protection on the incidence, proliferation and distribution of other pathogens (such as bacteria, yeast and mold). Aerobic Plate Counts, Coliform counts and E. coli counts will be performed on field samples from all the experimental blocks.

To determine whether inoculum reduction by early pruning can reduce blight damage, aggressive pruning will be carried out in 50 x 50 feet experimental plots within experimental and control blocks during September and October. Infected stems will be collected and burnt to prevent any source of contamination and disease transfer. In regular practice, less aggressive pruning is carried out in the winter.

Relevance:

Use of wind machines for the prevention and control of bacteria blight (pseudomonas syringae) will minimize the use of pesticides and other chemicals, thereby improving environmental health.

With the reduced bacteria blight disease incidence, production is expected to increase, which will result in contributing towards economic profitability for the local farmers.

Findings of the proposed project will be used to educate local farmers, which will contribute to social and economic development for the local region.

Investigate methods of reducing the incidence of bacterial blight infections (June 2012 to May 2013).

Determine the causation and mitigating practices, two technological advancements will be sought: (March 2013)

A) to investigate the contributing factors, i.e. environmental conditions, crop management practices, pests and pest management practices, blueberry cultivars, etc, and their role in the outbreak of bacterial blight at this site; and

B) the development of alternative preventative measures, specifically the use of wind machines, for controlling bacterial blight.