Renewable Farming

Concerned about a dry summer? These “endophytes” help crops tolerate stress

This season, Renewable Farming offers farmers one of the most intriguing biological innovations we’ve seen in years. They’re beneficial bacteria and fungi called endophytes. These microbes live inside your crops, helping them withstand stress from drought, heat, cold or excess moisture. 

February 17, 2021 These natural organisms were first discovered in one of the world’s highest-stress zones: Yellowstone National Park’s geothermal zones, where temperatures swing from below freezing to 150 F., and rainfall is erratic. In the mid-1990s, Dr. Rusty Rodriguez and his wife noticed that common plant species in these high-stress areas had an uncommon tolerance to weather extremes. 

Rusty and his company co-founder, Regina Redman, isolated a wide array of fungal and bacterial organisms which enable their host plants to thrive through weather extremes. The concept has proven sound — and profitable for growers — through more than a decade of lab and field experience. Their company, Adaptive Symbiotic Technologies, has gained worldwide recognition in dozens of press reports and scientific articles.  AST keeps searching globally for additional endophytic organisms to enrich their products for growers.

Greater drought stress, greater yield gain over untreated

At Renewable Farming, we appreciate biological firms which back up their products with careful field results under a wide array of farming conditions over several seasons. That’s what the AST team has done. In 15 field evaluations with corn, BioEnsure alone averaged a 26% yield increase. Compared with untreated corn the greatest weather stress generated the largest yield gains with AST endophytes.

Data from an even larger assembly of 327 trials — most in low-stress conditions — showed an average 4.9% yield gain. We concluded that even a modest amount of stress, like two or three weeks of hot, dry summer weather, would generate enough extra yield to pay for the products. AST now recommends blending two microbe mixes: the original BioEnsure (packaged as a liquid) and their new BioTango (packaged as a dry soluble powder).  

For corn, the most economical application is seed treatment, at a retail cost of $4.29 per acre (at a population of 35,000 seeds per acre). A planter-box treatment with BioEnsure and BioTango blended with a special talc lubricant is $6.74 for 35,000 seeds. In-furrow and foliar treatment takes more product, at a cost of $9.80 per acre. A practical feature of foliar treatment is that you can buy some “yield insurance” with a foliar spray if the season starts looking dry. 

Even though AST has conducted years of research and on-farm tests, we couldn’t resist testing some corn in our greenhouse this winter. Our trials are simple, but they help us see firsthand how the endophytic organisms perform. We were surprised to learn that the microbes multiply within corn seedlings in just a few days. 


These two greenhouse photos show our simulation of a June-August Midwest weather scenario like this: You get an inch of rain in mid-June, then nothing until mid-July when a storm sweeps through with a 1.5-inch cloudburst. After that, August turns hot and dry. What we did in the greenhouse was to speed up that stress sequence, starting with V2 corn in small pots of soil.

These photos show the result of forcing the four corn plants in the front two rows to endure two successive dry stretches, where a moisture meter showed a totally dry soil. Trays with the young corn were kept on warming mats (the kind used for greenhouse germination) to speed drydown. 

The back row of four corn plants was seed treated with BioEnsure and BioTango, then kept at normal moisture to simulate what happens under good growing conditions.

The middle row of four plants was also seed-treated with BioEnsure and BioTango. Front row was our untreated control.

Bottom line: After the second ‘dry spell’ of several days had wilted both the treated and untreated rows, the untreated control row had suffered so severely that it didn’t recover when watered. Corn seed-treated with BioEnsure and BioTango bounced back. 

We intend to conduct several more observations, including some root mass measurements of treated vs. untreated corn. Stay tuned… this is a developing report.


Update February 18:  We also tested foliar BE/BT on corn, spraying seedlings at the V2 stage while leaving a row of four plants untreated, like in the tray above. Results were similar to seed treatment. After two “drought” episodes, the untreated corn gave up and failed to fully recover after watering.

With this experiment complete, we compared root structures on the four treated plants, vs. the untreated four. The bottom photo shows the difference. Total weight of the treated plants and roots was more than twice the untreated set. When we removed roots from the small pots, it was clear that the treated roots were more profuse, and showed more root hairs which had soil clinging to the roots. This indicates an abundance of mycorrhizal fungi, which add greatly to the plant’s ability to absorb soil moisture and dissolve nutrients.