By Ramdas Kanissery
Tackling herbicide tolerance in weeds is a critical aspect of effective weed control in citrus groves. It helps prevent both current and future weed management challenges.
Herbicide tolerance occurs when certain weed species naturally survive and reproduce after herbicide treatment. Unlike herbicide resistance, where genetic changes allow weeds to survive and spread, herbicide tolerance doesn’t involve any genetic alterations. In simple terms, these weeds are inherently less susceptible to specific herbicides or herbicide groups.
For instance, weeds like goatweed, lambsquarters and dayflower are naturally tolerant to post-emergence herbicides like glyphosate. As a result, standard herbicide treatments may not effectively control these weeds, making management more difficult.
Although herbicide resistance is not commonly reported in Florida citrus production, cases of herbicide tolerance have been observed in weeds like Spanish needles, goatweed and parthenium. This highlights the need to develop and implement strategies for effectively managing herbicide tolerance in citrus weed control.
ASSESS THE SITUATION
The first step in identifying whether herbicide tolerance is becoming an issue in your grove is to carefully evaluate the following factors to assess the situation.
Single weed species tolerance: If only one weed species appears to be tolerant, check if the other weeds listed on the herbicide label are still being effectively controlled. This can help you determine whether the issue is specific to that weed or if the herbicide is losing its overall effectiveness.
Multiple species survival: If several weed species have survived the herbicide application, it’s important to consider other factors that could be influencing control. Herbicide tolerance may not be the sole cause. Issues like weather conditions or application errors could also be contributing.
TAKE ACTION
If you suspect herbicide tolerance in the weeds in your grove, here are some proactive steps you can take to manage it:
Avoid under-dosing herbicides: Under-dosing can lead to incomplete weed control, allowing weeds to survive and possibly develop tolerance to the herbicide. For instance, Figure 1 shows how different rates of paraquat herbicide impact goatweed in citrus. Be sure to follow the product label recommendations when selecting herbicide application rates to ensure effective control.
Avoid repeated use of the same herbicide: Continuously using the same herbicide or herbicides from the same mode of action (MOA) group can encourage herbicide tolerance over time. Rotating herbicides with different MOAs helps prevent weeds from adapting to a single herbicide, reducing the chance of tolerance developing. To learn more about herbicide chemical families and MOA groups in citrus, check out Table 6 in the Weeds Chapter in the Florida Citrus Production Guide.
Use tank mixes: Combining herbicides with different MOAs can improve weed control effectiveness and lower the likelihood of weeds surviving and reproducing.
Use the right adjuvants: For weeds that are tolerant, use the adjuvants recommended on the herbicide label, such as surfactants, to boost the chance of effective control. You can find more information on this topic here.
Apply herbicides at the right time: Timing is crucial when applying post-emergent herbicides. Targeting weeds at the correct growth stage ensures maximum effectiveness and reduces the risk of tolerance.
Maintain your pre-emergent herbicide program: Regular use of pre-emergent herbicides can help prevent weed seeds from germinating, reducing the risk of herbicide tolerance issues. Additionally, when weed seeds break from long-term dormancy, they may contribute to tolerance issues if not managed properly.
Promote vegetation diversity in your groves: Encouraging a variety of vegetation species in your groves can prevent any one weed species from dominating and becoming tolerant. Practices like planting cover crops can help maintain a healthy soil ecosystem, reduce weed pressure and improve vegetation diversity in citrus groves.
Ramdas Kanissery is an assistant professor at the University of Florida Institute of Food and Agricultural Sciences Southwest Florida Research and Education Center in Immokalee.
Share this Post
Sponsored Content