Crop rotation can keep you a step ahead of fusarium wilt

Peas in the pod (photo by Lee Reich)

In some gardening circles, a gardener’s worth is measured by how well he or she grows peas: how soon the first pea gets to the table, the crop’s abundance and, of course, the flavor. Sad to say, I haven’t been able to grow peas well for about ten years.

Peas require a humusy, moisture-retentive soil and early planting, all of which I provide. But about ten years ago, just as the crop was coming on strong, vines began to turn yellow, leaves would flag and plants would die. The probable cause was fusarium wilt disease (caused by Fusarium oxysporum). This soilborne fungus invades plant roots and then clogs up the vascular system.

You may have heard of fusarium wilt of tomatoes and other vegetables. Fear not spread of fusarium among these vegetables, because different vegetables have their own fusarium subspecies. Cucumbers have F. oxysporum f.sp. cucumerinum, cantaloupes have F. oxysporum f.sp. cubense and peas have F. oxysporum f.sp. pisi. How cozy.

Fusarium wilt probably never made it past my garden gate. It was probably already in my soil at some low level. Over the years, I’m guessing that it built up to a critical mass and was inadvertently spread – by me – on trowels, boots and trellising. That leads to one way to keep the disease in check: Clean trowels before planting peas; clean hoes before hoeing peas; and clean or torch the chickenwire trellises and metal support posts that keep the vines off the ground.

Some pea varieties are resistant to fusarium disease. But there are a few races of the disease. A variety resistant to one race may be susceptible to another race. Planting a resistant variety one year did not ratchet up my “good gardener rating.” The plants succumbed to the disease as in other years, and understandably so, since I did not know which fusarium race I was up against, and variety descriptions for wilt-resistant peas don’t always specify to which wilt race the variety is resistant.

This year I’m back in the game again with peas – and an excellent harvest it is: abundant, early and flavorful! (These are shelling peas, which take longer to mature than snap peas or snow peas, but also taste better, even if they do need shelling.)

One thing that I did this spring – the thing that I’m touting as responsible for my good crop – was to plant the pea seeds in my south vegetable garden, where I haven’t grown peas for the past six years. My wan efforts over the years have been plantings in my north vegetable garden, and they have been consistent failures.

    F. oxysporum f.sp. pisi survives from year to year in the soil as spores – very hardy spores, so hardy that the recommendation is frequently made not to plant peas again, ever again, in tainted soil. Other recommendations are to wait five or ten years before replanting. In either case, of course, it’s necessary to be very careful about spreading the disease again on tools, boots or trellises. And again, the ideal would be to plant disease resistant varieties.

People sometimes ask me if I rotate my crops each year. Crop rotation does not involve twirling plants; it’s moving certain plants – be they in a botanical family or part eaten – to different parts of the garden each year.

In the case of plant families, it’s a way to reduce pest problems, because family members may host the same pest (clubroot disease of broccoli, cabbage, turnips and radishes, for example). A pest that overwinters in the ground will eventually starve if a suitable host is not on hand on which to feed. A pest that flies or that shoots spores far and wide can travel some distance to find a host; but that, fortunately, is beyond the capacity of many pests.

In the case of rotating by part eaten, such as leaf, fruit or root, the idea is to balance nutrient uptake. Leafy vegetables are hungry for nitrogen, root vegetables for potassium and fruiting vegetables for phosphorus.

It’s generally safe to rotate vegetables on a three-year cycle – that is, not to return a vegetable in the same family or with the same part eaten to the same place sooner than within three years. Planting in beds makes this easy because, once the garden is planned out, you just move the crop to the next bed, or two beds away for further distance, each year.

Do I rotate my crops? You betcha. With peas, I’ll try the three-year rotation in the south vegetable garden. And I’ll wait at least another five years before planting them again in the north vegetable garden, then giving the south garden a “rest” from them. It’s good to be unzipping green pods again and scooping out the sweet peas within.

Drip irrigation saves water, makes for healthier plants and less weeds and is easily automated to eliminate watering chores. I will be holding a Drip Irrigation Workshop on July 19 from 2 to 5:30 p.m. where I’ll cover the benefits of drip irrigation, how to design a system and where to source components. This workshop includes a hands-on installation of a complete drip system in an existing vegetable garden and berry planting. Preregistration is a must; for information/registration, contact me at (845) 255-0417 or [email protected].

Any gardening questions? E-mail Lee at [email protected] and he’ll try answering them directly or in his Almanac Weekly column. To read Lee’s previous “Gardener’s Notebook” columns, visit our Almanac Weekly website at HudsonValleyAlmanacWeekly.com. You can also visit Lee’s garden at https://www.leereich.blogspot.com.

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