Crop Update
Fumigation Essentials – Part 1
Growing Forward: Food Safety and Traceability Program Information Session
Crop Update
Although conditions have not been favourable for rapid spread of Phytophthora over the past few days, symptoms continue to show up in ginseng fields. As a result, once favourable conditions return there is the continued potential for rapid spread and infection. Growers should continue to watch gardens closely for symptoms of Phytophthora and protect gardens as much as possible.
Botrytis has been the biggest issue over the past week due to damaged plant material and humid conditions last weekend (Figure 1). The risk of Botrytis will remain high until damaged plant material heals over or dries up. Alternaria leaf blight has also shown up in ginseng gardens. Closely monitor gardens for the development of both of these diseases, and protect the crop through a rotation of registered products.
Figure 1. Botrytis on a ginseng stem.
Fumigation Essentials – Part 1
Proper fumigation of ginseng fields is essential for long-lasting protection from root diseases, nematodes and weeds. If they are not applied properly, it does not matter what product is applied, it will not protect your garden from pests over the next few years. There are 7 main things to consider for maximum fumigation effectiveness: Timing, Land Preparation, Temperature and Moisture, Application Procedures, Preplant Land Preparation, Sanitation, and Product. This issue will focus on the first 6 things to consider. Part 2 of this article will focus on the products and will appear in next week’s issue.
Timing
Fumigation leaves the soil mostly free of disease-causing organisms (pathogens), but also free from many of the beneficial organisms that can keep the soil in balance and partially protect the crop from disease. With these organisms removed, the few pathogens that remain in the soil can begin to colonize the soil and gradually build up over time. Growers often fumigate early so that the land can be prepared for seeding when labour is available. However, early fumigation can allow more time for the pathogens to colonize the soil before the seedlings begin actively growing the following spring. Delaying fumigation and seeding as much as possible can delay this re-colonization and reduce or delay disease development.
Land Preparation
It is essential that cover crops and other organic matter sources are plowed down and allowed to decompose 4-6 weeks prior to fumigation. Organic matter in the soil will interfere with the dissipation of the fumigants by absorbing some of the chemical and restricting flow of the fumigant through the soil. Clods of soil will also restrict flow of the fumigant through the soil and should be broken up prior to fumigation.
Temperature and Moisture
Fumigants work best when soil temperatures at 15 cm depth are between 10 and 24oC. Since fumigation in ginseng fields occurs in the summer, most of the time the soil will be within this range.
Soil fumigants move 10,000 to 30,000 times faster in air than in water. As a result, the movement of the fumigant through the soil will be reduced if the soil is saturated. Only Vapam can move through the soil in soil water. On the other hand, soil that is too dry will allow the fumigant to move through the soil too quickly and will prevent the formation of an effective seal. An evenly moist, unsaturated soil is ideal for fumigation.
Application Procedures
It is very important to follow the label directions for all soil fumigants. All of the registered fumigants will require some type of seal to keep the fumigant in the soil and prevent its immediate dissipation into the air. For some fumigants, the best seal will be tarps to completely block this dissipation. For most fumigants registered on ginseng, rolling the soil or quick irrigation after fumigation will be sufficient to keep the fumigant in the soil. Consult the label for optimal sealing techniques.
The depth of injection is also important and will depend on the chemical used and the sealing method. Since most fumigants move upwards in the soil, the injection depth should exceed the desired area of control. Since bed formation often follows fumigation, ensure that any soil that will be turned up into the bed has been reached by the fumigant. Ideally, fumigation would occur after bed formation, but this would require specialized equipment for the application of the fumigant.
Preplant Land Preparation
Each product has specific requirements for the length of time the fumigant must be sealed in the soil, and the length of time the fumigant should be allowed to dissipate before seeding. Consult the label for specifics for each product. In most cases the soil will be sealed for a couple of days and then should be cultivated to aerate the soil and allow the fumigant to dissipate. Most fumigants require a minimum of 2 weeks of dissipation before seeding. Bed formation will also help with this dissipation. It is essential that un-fumigated soil is not brought up to the surface during the bed formation process. Pathogens in this un-fumigated soil will begin to re-colonize the soil in the bed and will drastically reduce the effectiveness of the fumigation process.
Sanitation
Because of the potential for re-colonization, take care to prevent contaminated soil from being carried into the field on machinery or field workers. Also ensure contaminated soil cannot be easily washed or blown into the field from neighbouring ginseng fields. Any pathogens that are re-introduced into the field will have no competition from beneficial organisms and can quickly colonize the soil.
Weeds will provide an indication of the effectiveness of fumigation. Most common weeds should be eliminated or greatly reduced by fumigation. If these common weeds begin sprouting immediately after fumigation it is a good indication of improper fumigation practices. However, certain weeds such as horsetail or nutsedge may not be controlled even with effective fumigation practices.
Growing Forward: Food Safety and Traceability Program Information Session
Date: Tuesday, June 9, 2009
Time: 5:00 pm – 8:00 pm
Place: Simcoe Research Station Auditorium, 1283 Blueline Road, Simcoe
Funding is available to help producers and processors adopt food-safety and traceability programs and practices on the farm. Ginseng growers interested in applying at the $20,000 level should attend this information session. Growers applying at the $5,000 level do not need to attend. Please bring your food-safety questions to the session.
**REGISTRATION IS REQUIRED. Space is limited and organizers need to know how many growers are attending to determine if a second session will be necessary. Call the Agricultural Information Contact Centre at 1-877-424-1300 to register.
Questions about ginseng can be directed to Sean Westerveld, OMAFRA’s Ginseng and Medicinal Herbs Specialist at 519-426-4323; E-mail: sean.westerveld@ontario.ca.
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