Publications - Faculty - Recently Submitted Faculty Publications 2008
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Spann - Proc. Florida State Horticultural Society
MANAGING CITRUS TREE GROWTH WITH HEDGING AND PLANT GROWTH REGULATORS: STRATEGIES FOR REDUCING PSYLLID FEEDING AND HUANGLONGBING INFECTION
Timothy M. Spann, Antonios E. Tsagkarakis and James P. Syvertsen
Abstract. Reducing excessive vegetative growth that is produced annually by citrus trees in Florida would reduce the opportunities for Asian citrus psyllid (Diaphorina citri Kuwayama) reproduction and thereby, the spread of Huanglongbing. Excess tree growth is routinely removed through hedging and branch re-growth can be reduced after hedging in the fall season under Florida conditions because of the onset of cool temperatures. Additionally, late-summer hedging may synchronize a final late-season flush and thus, reduce new flush leaves present during the winter to support over-wintering psyllids. We determined timing effects of fall and early winter hedging of ‘Hamlin’ orange trees on vegetative growth flush and subsequent yield during a two year period. None of the hedging times tested stimulated a growth flush or significantly affected yield by hedging time in either year.
The plant growth regulator prohexadione calcium (pro-cal) is routinely used in apple trees to control vegetative growth and also may have the potential to reduce insect pest populations in citrus either by reducing pest-required vegetative growth, increasing pesticide efficacy or by altering host plant metabolites or nutrition. Pro-cal reduced extension growth of shoots by more than 50% in greenhouse seedlings of ‘Carrizo’ citrange but less so in ‘Swingle’ citrumelo seedlings. Psyllid oviposition was also reduced by approximately 50% on pro-cal treated seedlings compared to untreated control plants, but variation was large and obscured statistical differences. Based on the current data we are confident that modifying hedging timing and/or the use of PGRs can be effective management tools to control excess vegetative growth of mature citrus trees in Florida. This will allow better management of the Asian citrus psyllid and thus, reduce the spread of HLB.
