Rotating commercial crops of organically-grown strawberries with broccoli helps dispel a lethal wilt disease that turns berries to mush.
To some extent a few other vegetable crops rotated with the berries have had a similar effect. Strawberry growers who produce organic crops without agricultural chemicals, notably pre-plant soil fumigation, seem convinced that crop rotation is worth the loss of their strawberry income every fourth year or so.
It’s all part of a study conducted by the University of California Cooperative Extension Service (UCCE). It has taken four years to develop data that positively credits the crop rotation process for holding the pervasive wilt disease at bay. Broccoli is minimally affected by wilt, sometimes not at all.
A full report on the project is part of the July-August issue of ARE Update, the bi-monthly newsletter of the Agricultural and Resource Economics Department of the University of California. The article was prepared by four agricultural scientists who conducted the research.
The authors include Aleksandr Michuda, a Ph.D. candidate; Rachael Goodhue, UC Davis professor and Agricultural and Resource Economics Department chair; UC associate researcher Joji Muramoto; and professor Carol Sherman, Environmental Studies Department at UC Santa Cruz.
The study was conducted on a plot of ground at UC Santa Cruz maintained as an organic host property for 40 years. The researchers were mindful that organic strawberries are a very high-value crop and that rotating with other crops can significantly reduce net revenues.
UCCE cost-return studies indicate that revenues for organic strawberries in their fourth year average $61,000 per acre, contrasted to returns for organically grown broccoli of $10,000 per acre. Replacing such a high-value crop to obtain control of wilt becomes an economic issue for growers.
One of the illustrative charts included in the article indicates that rotating strawberries with broccoli every fourth year allows returns near average prices, even slightly above in a case or two. But rotating every two years cuts revenues sharply to less than half the average in some cases.
Broccoli was the most persistent wilt resistant crop rotated with the strawberries, but lettuce and a few other moderately wilt resistant crops were used as well. Whatever crop a strawberry grower chooses they are left with the responsibility of guessing what the value of the alternate crop will be at the time the market is ready for it.
Also among the considerations a grower must make are seed costs, revisions of the irrigation system, shaping and cultivating beds, and harvest costs which accounted for the majority of expenses with all crops tested.
The authors of the report conclude that crop rotation in organic production systems can be commercially viable although more time is needed to evaluate how rotations affect the incidence of disease over multiple repetitions.
This was a long term and somewhat complicated research project. When the UC and other entities consider undertaking projects of this kind they know their outcome will be something of a gamble. Growers in California can be grateful that institutions exist that are willing to take the chance.