Changing Face Of Fumigation For Strawberry Growers
November 15, 2011 The last five years have introduced a lot of uncertainty for strawberry growers with regard to fumigation, due to the progressive decrease of methyl bromide supplies and the new fumigant labels. Many growers have experimented with alternative fumigants to methyl bromide + chloropicrin formulations. Numerous growers have converted their system to these alternatives after experimenting on smaller sections of their strawberry land.
Overall, most growers have had success making the alternatives work well. Each alternative has limitations, though. More precise management is needed with regard to soil preparation, ideal soil moisture requirements, application methods, and plant-back intervals. The best product or combination of products depends on the history of known problems on each farm.
Farming Without Fumigants
Many growers are uncertain about the future use of fumigants on their farms, particularly on farms surrounded by houses or other live-in structures. Thus, there has been an increased interest in growing strawberries without the use of annual fumigation.
When considering strawberry production without fumigants, there are many considerations. In most cases, such a decision requires a farming systems management plan that integrates best management practices (BMP) and integrated pest management principles (IPM). Most farms have problems with weeds and soilborne diseases. The main disease problem is black root rot (BRR). BRR can result in up to 20% to 40% loss of yield on land with a history of strawberry production. Regional experiments and grower experience indicate that the benefit of fumigation decreases from the east to the west in North Carolina. For example, several experiments in the mountains of western North Carolina showed limited advantage with fumigation, whereas there is typically a high benefit to fumigation in the eastern coastal plain region. Northern production regions may benefit less from fumigation compared to southern states.
A key farming-systems decision in farming without fumigants is the capacity to include crop rotation. The pathogens and weeds associated with strawberries build up with year-after-year use of the land for strawberries, but crop rotation will break the biological cycle of many pests. A two- to four-year rotation is ideal. Crop rotation has been successfully complemented with the use of compost.
Another beneficial practice is to use summer cover crops prior to planting strawberries. In general, a legume/grass mixture suited to the region is ideal. The cover crop can suppress weeds and higher organic matter content can be suppressive to BRR problems. In addition, cover crops and other organic amendments enhance the soil’s physical and chemical properties that are beneficial compared to continuous production of strawberries. Cover crops can been grown and managed without excess plant residue problems when it is time to form the beds.
We have been doing considerable work evaluating the use of registered fungicides and herbicides (in cooperation with weed scientists) to determine the level of success that can be achieved with well-timed soil applications of these products compared to fumigation. Some very promising results have been achieved, but further research is needed. To date, the overall body of data suggests this approach will offer modest benefit — better than not fumigating at all but not as good as a broad-spectrum fumigant product(s).
Weeds can be managed by applying registered herbicides, minimizing the size of the planting hole (especially if bare root plants are grown), and hand weeding. If nematodes are a problem, some new products are coming to market that can be drip applied. Thus, for growers not able to fumigate, a series of products may offer some advantages to help manage soilborne diseases and weeds as part of an overall IPM plan.
Several growers have already found ways to effectively grow strawberries without fumigants. However, future progress will require the cooperative efforts of growers, Extension, researchers, consultants, private industry, and other stakeholders to advance the productivity and profitability of strawberry production systems.
Other Approaches
Research in a method known as biological soil disinfestation (BSD) or anaerobic soil disinfestation (ASD), first done in Japan, then the Netherlands, California, and Florida, now has preliminary results in North Carolina. Briefly, soil organic matter is added in the form of green manure or other highly digestible organic matter (some have had good success with molasses). The organic matter is incorporated into the beds and the beds are covered with plastic (usually VIF) and then flooded for a period of time. Soil bacteria begin to digest the organic matter and then with the high moisture content, the soil conditions become anaerobic. This creates a condition where various fermentation products are made and these toxins and the low oxygen content kills weed seeds and many types of pathogens. After a certain time (three to six weeks depending on the temperatures), the plastic can be punched to allow aeration and strawberry plants can be field set. Preliminary data in strawberry production systems has shown high promise and more work is underway.
Work has also been done using mustard meal (MM). The meal is incorporated into the beds and then the beds are watered to activate the MM resulting in gases that directly kill pathogens and weed seeds. In addition, the MM seems to encourage certain types of soil microorganisms that further suppress soilborne problem.
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