Abstract
Imidacloprid (IM) is used to control the Asian Citrus Psyllid (ACP) and citrus leafminer (CLM), which are related to the spread of huanglongbing (HLB or citrus greening) and citrus canker diseases, respectively. In Florida citrus, imidacloprid is mainly soil-drenched around the trees for proper root uptake and translocation into plant canopy to impact ACP and CLM. The objective of this study was to determine the effect of imidacloprid rate, and irrigate amount on concentration of imidacloprid in the soil following drench application to citrus trees in three age classes. The plots were established at the Southwest Florida Research and Education Center, Immokalee, using a randomized complete-block design for three age classes of trees: one-year-old trees (B1), three to five-year-old trees (B2), and eight-year-old trees (B3). The treatments were a combination of two rates each of imidacloprid (1D, 2D) and micro-sprinkling irrigation (1I, 2I). Imidacloprid and bromide (Br-) used as tracer were applied simultaneously. Soil moisture and concentrations of imidacloprid and Br were monitored using soil cores from hand held augers. Soil moisture content (θV) did not differ under two irrigation rates at any given observation day or depth, except following heavy rainfall events. Br- was lost from the observation depths (0–45 cm) about two weeks after soil-drench. Contrarily, imidacloprid persisted for a much longer time (4–8 weeks) at all soil depths, regardless of treatment combinations. The higher retardation of imidacloprid was related to the predominantly unsaturated conditions of the soil (which in turn reduced soil hydraulic conductivities by orders of magnitude), the imidacloprid sorption on soil organic matter, and the citrus root uptake.Findings of this study are important for citrus growers coping with the citrus greening and citrus canker diseases because they suggest that imidacloprid soil drenches can still be an effective control measure of ACP and CLM, and the potential for imidacloprid leaching to groundwater is minimal.
Highlights
Imidacloprid (IM) is a systemic insecticide commonly used in home lawns, gardens, pets, and many agricultural commodities such as citrus, tomatoes, grapes, potatoes, and lettuce, just to name a few [1]
In Florida, imidacloprid use in citrus is common for the control of Asian citrus psyllid (ACP) which vectors Candidatus Liberibacter asiaticus (CLas) putative pathogens of “huanglongbing” (HLB) or citrus greening disease, as well as citrus leafminer (CLM) Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae) which exacerbates the spread of citrus canker. [2,3,4]
This study was conducted at the University of Florida, Institute of Food and Agricultural Sciences (UF-IFAS) Southwest Florida Research and Education Center (SWFREC), Immokalee (Lat. 26 ̊ 27.75’ N; Long. 81 ̊ 26.83’ W), where the dominant soil series is Immokalee fine sand (IFS), which is a flatwoods Spodosol commonly found in south Florida [30]
Summary
Imidacloprid (IM) is a systemic insecticide commonly used in home lawns, gardens, pets, and many agricultural commodities such as citrus, tomatoes, grapes, potatoes, and lettuce, just to name a few [1]. HLB is the most devastating disease of citrus [4,5]. HLB originated in China [5,6], and has spread to most citrus producing areas of the world including the United States, South America, Central America, South Africa, South Korea, and Brazil [7]. The disease was first confirmed in Florida’s Miami-Dade County in 2005, and has spread as far north as Putnam County at the northern edge of the Florida citrus industry. By February of 2009, the disease had spread to 33 out of 64 Florida counties including most commercial citrus production areas [8]
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