Soil Scout Social - How to Use Soil Temperature Data for Effective Weed Control

Weeds are a major challenge for crop production, as they compete with crops for nutrients, water, light and space. They can also harbor pests and diseases, reduce crop quality and yield, and increase harvesting costs. Therefore, it is essential to implement effective weed control strategies to ensure optimal crop performance.

One of the key factors that affects weed control is soil temperature. Soil temperature influences germination for both crop and weeds, as well as their emergence. It also has a key role in the effectiveness of herbicides. In this blog post, we will discuss how to use soil temperature data to optimise the timing of weed control operations.

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Weed Control Timing

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To achieve optimal weed control, it is crucial to sow crops in soil that has the right temperature for quick germination and uniform growth to ensure the crop gets a vantage over weeds. Soil temperature also affects the efficacy of herbicides especially through correct timing.

Weed seeds, like crop seeds, need a certain soil temperature to germinate. This is called the base temperature. To get the best results from pre-emergent herbicides, you should apply them just before the soil reaches this temperature. For post-emergent herbicides, the optimal time to apply them is when the soil temperature has been well above the base temperature limit for a while and the weeds have emerged. It’s important to know the in-field variation of topsoil temperature, as factors such as shade, slope and crop residue thickness can result in zones staying cooler a bit longer, resulting in severe failure in weed control across those zones.

To effectively manage a specific weed problem, one needs to know soil temperature affects the problem weed's growth cycle and development, but of course also must have access to real-time soil temperature data to apply that knowledge on. Fortunately, there are many online sources that provide detailed information on the life cycles of most common weeds.

For example, poa annua (poa, annual bluegrass) is a common and persistent weed that is very difficult to manage. Soil temperature of 21°C (70°F) is the threshold below which poa seeds start to germinate in the fall and will continue to do so throughout the winter, resulting in multiple waves of emergence at any given location. To prevent poa from sprouting during the cold season, pre-emergent herbicides should be applied in late summer or early fall latest when the soil temperature drops below this critical level.

Below we provide a sample list of common weeds and the average base temperatures they need to germinate. However, some seeds can sprout even in less favourable temperatures. Moreover, other factors like soil moisture conditions also affect the germination process.

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