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  • Author or Editor: John L. Jackson x
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The severe advective freeze of 23-26 Dec. 1989 killed most nonprotected trees in Florida's northern citrus region. Minimum temperatures reached - 8.3C with >43 hours below freezing. Microsprinklers elevated to a height of 0.6 or 0.9 m and placed inside the canopy of young `Hamlin' and navel orange trees [Citrus sinensis (L.) Osb.] provided excellent protection to heights well above 1 m. Initial survival height of trees with emitters elevated to 0.9 m was higher than has been reported for microsprinklers at a conventional 0.2-m height in earlier severe freezes. Trees rapidly approached prefreeze canopy size from regrowth of the protected scaffold branches. Six months after the freeze, trees protected by microsprinklers elevated to 0.6 m and delivering 26 or 47 liters·hour-1 had regrown to a height of 1.4 or 1.7 m, respectively. Trees with microsprinklers at a height of 0.9 m and delivering 101 liters·hour -1 had regrown to a height of 2.5 m. Trees with no microsprinkler irrigation were killed to the ground. Twelve months after the freeze, trees with elevated microsprinklers were still significantly taller and showed greater recovery than those with microsprinklers near the ground.

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The asian citrus psyllid [Diaphorina citri (Sternorrhyncha: Psyllidae)] is a detrimental pest to citrus (Citrus spp.) crops when it serves as a vector of the pathogen that causes greening (huanglongbing). Transmission of this disease causes mottling, chlorosis, dieback, and reductions in fruit size and quality. Citrus producers have found that many pesticides, when applied properly, are very effective at suppressing or eliminating asian citrus psyllids in groves. Due to the threat of greening, several pesticides have been granted Special Local Needs registration for use in the state of Florida if the product is sprayed with a volume median diameter of 90 μm or greater. A number of studies involving numerous citrus sprayers and a.i. were conducted to determine the droplet sizes generated by different sprayers operating under user-established settings and the adjustments required to those settings for the sprayers to meet the 90-μm requirement. In the sprayer tests, it was found that reductions in engine speed or increases in flow rate were required to increase droplet sizes to meet the product label-required droplet size. As the equipment tested here represent the most typical application equipment used in Florida for asian citrus psyllid control, these results will provide applicators, growers, and extension agents with general guidelines to ensure that spray systems are operated in a manner that complies with label restrictions.

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