Soil Fumigation Naturally

June 19, 2023

Soil-borne diseases such as phytophthora, rhizoctonia, pythium, verticillium, fusarium, and others can cause significant challenges and yield loss in crop production. In some cases, maybe all, they cause the plants vascular system to decline, thus reducing water and nutrient uptake.

It should be obvious that nutrition is a huge factor in preventing proliferation of these diseases. After all, why are some plants affected while others are not?

Then there is fumigation. Soil can be fumigated to help prevent these diseases, which is often done in a conventional situation. For those looking for an effective natural treatment, consider the mustard cover crop. A mustard cover crop can substantially reduce proliferation of these soil-borne diseases if the cover crop is left to bloom for about 5-7 days.  During this time, the mustard sends out chemical compounds that have a bio-fumigant effect on these soil-borne pathogens, as well as on root rot nematodes. Terminate and incorporate 2 weeks before planting the next crop.

Mustard is generally easy to establish. It will winter kill, so a general rule of thumb is to sow no later than 1 month before a killing frost. When winter-killed, it leaves a mellow bed that is very easy to plant into the next spring. Seeding rates are 10-15 pounds per acre, although I go heavier if not in a mix. It can also be sowed in spring and summer if adequate moisture is present.

Let’s dig into some examples of what mustard can do:

I already mentioned phytophthora, which travels with water and thus is especially prevalent in wetter years. In this specific example, a local grower had trouble with this disease in watermelon. After evaluation of the actual farm and the management practices used, the recommendation was to subsoil, apply the Rejuvenate program, then sow a cover crop mix of oats, mustard, and peas, which the grower did for fields that he wanted to grow watermelon in the following year.

The following year was a wet year – wet enough that phytophthora damage would have been easy had the conditions been right. But the grower reported almost zero phytophthora. Thus encouraged, he did the same thing that fall as the year previous, except no mustard was put into the cover crop mix because the seed was in short supply.

The next year, it was much drier. Dry enough that you would not expect significant phytophthora pressure. But the grower reported much more phytophthora pressure that the year before even though it was much drier.

Obviously, it is hard to say that a practice prevented disease. But it seemed obvious, given other experiences and the general information, that the mustard cover crop had an impact.

Another example is of the grower who tried a treated versus control strip on strawberries. There was a night and day difference! The rows where the mustard cover crop was grown had significantly less disease pressure than the row that had no mustard in the cover crop.

The bottom line is that mustard is an inexpensive help to producing a healthier crop. It’s easy to grow. Our advice it to get this cover crop into the rotation ahead of high impact crops, like tomatoes and strawberries. It’s still time to sow mustard where strawberries are being planted in mid-August.