Oct 23, 2026 · 23 min · 6 segments
In this edition: California orchard and vineyard trials separate johnsongrass timing effects from rainfall effects; New UC guidance explains redwood survival and working-forest recovery tradeoffs…
California orchard trials found substantially different Johnson grass suppression depending on application timing and rainfall.
In an October 13 report, University of California Cooperative Extension advisor Ryan Hill described the strongest results from early March through mid-April when adequate rain followed treatment.
It spreads through seeds and through perennial underground stems called rhizomes.
Reducing new seedlings and suppressing plants already established below ground are different measures of success.
Hill's October 2026 report moves beyond the question of whether rime-sulfuron treatments can suppress established Johnson grass.
Earlier research, reported in 2025, had shown suppression after early March applications.
The newer work compares application dates to investigate when that effect was strongest.
Researchers compared a mixture of glyphosate and rimesulfuron with reference treatments, then measured how much Johnson grass covered the plots.
That makes this a comparison of treatment results under particular field conditions, not a prescription for California farms.
Most trials use glyphosate alone as the reference, but two early applications on January 26 and February 6 had no emerged weeds to treat, so those trials used different reference treatments.
That distinction matters when comparing results across dates.
The baseline was not identical in every trial.
Researchers generally assessed coverage eight weeks after application.
The October summary also draws on applications made across 2024, 2025, and 2026, rather than one season's results alone.
For early March through mid-April applications with adequate rainfall, Hill reported a 76% to 98% improvement in control relative to the reference treatments.
Those figures describe the reduction in weed coverage compared with the reference plots.
they do not mean that treatments delivered that level of performance statewide, or that the same percentage of individual plants died.
At less effective timings, including late January, early February, and May, the October account described an improvement of roughly 35%.
Additional timing trials took place in olive and walnut orchards in Glynn, Tehama, and Shasta counties during 2026.
Each treatment was repeated four times.
That replication gave researchers several plots for each treatment, rather than relying on a single treated patch.
Coverage results were then compared with the reference treatments.
Most trials ran eight weeks.
California orchard trials found substantially different Johnson grass suppression depending on application timing and rainfall.
In an October 13 report, University of California Cooperative Extension advisor Ryan Hill described the strongest results from early March through mid-April when adequate rain followed treatment.
It spreads through seeds and through perennial underground stems called rhizomes.
Reducing new seedlings and suppressing plants already established below ground are different measures of success.
Hill's October 2026 report moves beyond the question of whether rime-sulfuron treatments can suppress established Johnson grass.
Earlier research, reported in 2025, had shown suppression after early March applications.
The newer work compares application dates to investigate when that effect was strongest.
Researchers compared a mixture of glyphosate and rimesulfuron with reference treatments, then measured how much Johnson grass covered the plots.
That makes this a comparison of treatment results under particular field conditions, not a prescription for California farms.
Most trials use glyphosate alone as the reference, but two early applications on January 26 and February 6 had no emerged weeds to treat, so those trials used different reference treatments.
That distinction matters when comparing results across dates.
The baseline was not identical in every trial.
Researchers generally assessed coverage eight weeks after application.
The October summary also draws on applications made across 2024, 2025, and 2026, rather than one season's results alone.
For early March through mid-April applications with adequate rainfall, Hill reported a 76% to 98% improvement in control relative to the reference treatments.
Those figures describe the reduction in weed coverage compared with the reference plots.
they do not mean that treatments delivered that level of performance statewide, or that the same percentage of individual plants died.
At less effective timings, including late January, early February, and May, the October account described an improvement of roughly 35%.
Additional timing trials took place in olive and walnut orchards in Glynn, Tehama, and Shasta counties during 2026.
Each treatment was repeated four times.
That replication gave researchers several plots for each treatment, rather than relying on a single treated patch.
Coverage results were then compared with the reference treatments.
Most trials ran eight weeks.
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