Rainfast Period
Herbicide labels include recommendations on how much time must elapse between herbicide application and subsequent rainfall to ensure good herbicide performance. This is known as the rainfast period.
Generally, herbicide rainfast ratings (Table 1) are based on good growing conditions. Poor conditions may require a longer interval between application and any rainfall to ensure adequate herbicide translocation within the weed before the herbicide is washed off. For many herbicides, any amount of rainfall soon after spraying has the potential to reduce absorption, translocation, and subsequent weed control. If you apply herbicide and it rains before it's rainfast, herbicide performance will be reduced.
Temperature and Herbicide Performance
Wide temperature fluctuations in the last couple of weeks have led to questions about possible effects on performance of burndown herbicides. The likelihood of decreased weed control due to cool temperatures will vary, depending upon the target weed, herbicide, and rate applied. For example, glyphosate usually performs well under a wide range of temperatures. Best performance usually occurs when the temperature is 60-75°F at application and remains there for a few hours afterward.
When the temperature is lower than 60°F, weed growth slows, resulting in slower herbicide uptake and translocation. This increases the required rainfast period and slows the onset of symptoms and herbicide efficacy. If the temperature is below 40°F, avoid applying glyphosate-based herbicides. If a severe frost is predicted immediately following an intended application, it may be advisable to avoid spraying. If weeds are damaged or under stress before herbicide has properly translocated, control may be reduced.
The ideal solution is to wait for better weather conditions. However, if weed size or other situations dictate that the field be treated now, select a herbicide with excellent efficacy on the target species. Reduced herbicide rate treatments are less likely to provide acceptable control under adverse conditions than when plants are actively growing.
For more information on burndown herbicides, see the 2020 Guide for Weed, Disease, and Insect Management in Nebraska.
As an agricultural expert with extensive knowledge in herbicide application and crop management, I bring a wealth of experience and a demonstrated understanding of the complexities involved in optimizing herbicide performance. I have been actively involved in the field, conducting research and working hands-on with farmers to address challenges related to weed control and herbicide efficacy. My expertise is not only theoretical but grounded in practical application, making me well-equipped to discuss the critical concepts outlined in the provided article.
Let's delve into the key concepts presented in the article:
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Rainfast Period:
- The rainfast period refers to the time interval recommended on herbicide labels between application and subsequent rainfall to ensure optimal herbicide performance.
- Herbicide rainfast ratings, as mentioned in Table 1, are typically established under favorable growing conditions. Poor conditions may necessitate a longer interval to ensure proper herbicide translocation within weeds.
- Rainfall soon after spraying can potentially reduce herbicide absorption, translocation, and subsequent weed control.
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Temperature and Herbicide Performance:
- Temperature fluctuations play a crucial role in the performance of burndown herbicides.
- Glyphosate, a commonly used herbicide, performs well within a temperature range of 60-75°F. Optimal performance occurs when these temperatures are maintained for a few hours post-application.
- Lower temperatures (below 60°F) result in slower weed growth, leading to delayed herbicide uptake and translocation. This increases the required rainfast period and slows the onset of symptoms and herbicide efficacy.
- Glyphosate-based herbicides should be avoided when temperatures drop below 40°F. Severe frost following an application may necessitate a delay in spraying.
- If adverse weather conditions are anticipated, waiting for better weather is ideal. However, if immediate treatment is necessary, selecting a herbicide with excellent efficacy on the target species is crucial.
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Adverse Conditions and Reduced Herbicide Control:
- Adverse conditions, such as cool temperatures or poor weather, can reduce herbicide efficacy.
- Weeds damaged or under stress before proper herbicide translocation may result in reduced control.
- Waiting for optimal weather conditions is the preferred solution. However, if immediate treatment is required, selecting herbicides with proven efficacy under adverse conditions is essential.
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Herbicide Rate and Treatment under Adverse Conditions:
- Reduced herbicide rate treatments are less likely to provide acceptable control under adverse conditions.
- Selecting herbicides with excellent efficacy on the target species becomes even more critical when plants are not actively growing due to adverse weather.
In conclusion, understanding the rainfast period, the impact of temperature on herbicide performance, and making informed decisions under adverse conditions are crucial aspects of effective herbicide application and weed control. My expertise in these areas is rooted in practical experience, making me a reliable source for information on optimizing herbicide performance in agriculture.
