Photo by Betsy Martin
Citrus rust mite (CRM) populations in Texas often reach peak levels from late spring through early fall, researchers with Texas A&M University-Kingsville Citrus Center reported. The researchers, Tolulope Agunbiade and Mamoudou Sétamou, offered background on CRM and management practices in “Citrus Rust Mite, Tiny but Mighty for the Texas Citrus Industry,” an article in the first edition of the university’s Citrisphere newsletter.
The article notes that CRM has been the most economically important arthropod pest of Texas citrus since the inception of the industry. Heavy CRM damage can contribute to increased fruit and leaf drop and reduced fruit size. CRM-damaged fruit may be smaller in size than unaffected fruit.
Management practices suggested include:
MONITORING
Effective management begins with regular monitoring, about once every two weeks during the active growing season. Check four leaves and/or four fruit from each randomly selected tree. Sample at least 20 trees in a 10-acre block. A threshold of 10% of fruit or 20% of leaves infested, or an average of four CRM per leaf or two CRM per fruit, should trigger the implementation of control measures.
CULTURAL CONTROL
Maintain proper irrigation practices that will minimize canopy humidity while maintaining optimal soil moisture. Skirt trees to improve grove aeration.
CHEMICAL CONTROL
The most effective management approach in Texas often involves proactive application of miticides. A suggested timing of chemical control based on citrus phenology includes:
Pre-bloom (January to February): Mite populations are generally low during this time. An early proactive treatment is recommended that can drive populations even lower. This reduces the risks of infestation on the first flush of the year.
Post-bloom (April): A post-bloom spray may be warranted if the mite threshold is reached.
Late spring (May to June): This period coincides with the beginning of rapid CRM population buildup. Control measures should be implemented to prevent early fruit infestation and damage.
Summer (July to August): Due to higher temperature, a rapid increase of CRM populations is observed. Thus, timely application of miticides must be made when infestation thresholds are reached to prevent fruit damage.
Late summer (August to September): Climatic conditions continue to be favorable for CRM development and population increases, thus making citrus fruit vulnerable to infestation and damage. A timely action is necessary.
Fall: Monitoring should inform whether control action is necessary to avoid late-season fruit damage.
To ensure effective and residual control in case of heavy infestations, combine a miticide and an insect growth regulator. As an important precaution, ensure an interval of four weeks between sulfur and oil sprays.
RESISTANCE MANAGEMENT
Because citrus rust mites can develop resistance to miticides, it is important to rotate between different modes of action throughout the growing season.
Source: Texas A&M University-Kingsville Citrus Center
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