Special table helps U of I study weed emergence

By John O’Connell

University of Idaho

MOSCOW – Scientists with the University of Idaho Kimberly Research and Extension Center have a new machine for studying how temperature affects weed emergence.  

Results of testing using the new thermogradient table will inform development of predictive models to help growers pinpoint when weeds are likely to emerge to time the application of herbicides.  

Researchers have been collecting weed seeds from throughout Idaho to grow within the stainless-steel table.

Weed seeds will be germinated either on specialized growing paper or in containers filled with sterilized soil, and the researchers will test how quickly weeds emerge when the table is set at various temperatures ranging from 35 degrees to 110 degrees. 

The table will also let the researchers test how different levels of soil moisture affect weed seed emergence and the activation of soil-applied herbicides. 

The model developed from the data will be posted on the Pacific Northwest Herbicide Resistance Initiative website, which is currently under development, where growers will input local temperature to determine how soon they’ll likely encounter emergence of various weed species and the percentage of weed seeds that will likely emerge at each temperature threshold.  

“Because of herbicide resistance, small grain growers are increasingly relying on soil-applied (preemergence) herbicides to control grassy weeds. Weeds that emerge before preemergence herbicides are applied won’t die,” said Albert Adjesiwor, a UI Extension weed specialist. “Being able to predict the best time to apply these herbicides will be very helpful to growers to maximize weed control.” 

Research using the table began in October. Adjesiwor’s doctoral student, Chandra Maki, will lead the study for her dissertation in weed science.  

“We know there are substantial differences in temperature … and moisture across the PNW,” Maki said. “We expect specific weeds from different conditions to behave a bit differently and this project would help us assess and map these differences.”

Maki is curious to see how regional differences may lead weed seeds from various parts of the state to emerge at different rates under the same conditions.

For the purpose of the model, emergence dates of weeds from throughout the state will be averaged together, recognizing equipment from one part of Idaho may be used for field work in another area of the state, introducing outside weeds.  

The thermogradient table will also help researchers understand how the soil temperature and moisture may affect herbicide activation. For example, when soil temperature is too high, certain herbicides may volatilize quickly and be rendered ineffective.  

The table was funded with roughly $24,000 from the Pacific Northwest Herbicide Resistance Initiative, a cooperative project under USDA’s Agricultural Research Service involving researchers in Idaho, Washington and Oregon.

Partners involved in weed research under the project in the three states have been sharing ideas and collaborating on various projects to maximize the benefit of this initiative to stakeholders and also to avoid duplication of effort.  

The Idaho Wheat Commission, Idaho Barley Commission and Idaho Grain Producers Association have supported this initiative.