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Project description

Effects of Nitrogen Fertilization of Stone Fruits on Fruit Size and Quality, Brown Rot, Monilinia fructicola, and Peach Twig Borer, Anarsia lineatella. (91CC029)
Program UC IPM competitive research grants program
K.M. Daane, Biological Control, UC Berkeley/Kearney Agricultural Center
T.J. Michailides, Plant Pathology, UC Berkeley/Kearney Agricultural Center
R.S. Johnson, Pomology, UC Davis/Kearney Agricultural Center
N.J. Mills, Biological Control, UC Berkeley
Host/habitat Stone Fruits; Tree Crops; Nectarines
Pest Brown Rot Monilinia fructicola; Peach Twig Borer Anarsia lineatella
Disciplines Entomology, Plant Sciences, Plant Pathology
Cultural Controls
Start year (duration)  1991 (Two Years)
Objectives Evaluate the long-term effects of nitrogen rates on nectarine yield, fruit size and fruit quality and determine the potential for groundwater contamination by nitrates under these different nitrogen rates.

Determine the effects of nitrogen levels applied as fertilizers on the susceptibility of nectarines (or peaches) to brown rot fungus, Monilinia fructicola.

Study the effects of nitrogen levels on the susceptibility of shoots to the peach twig borer, Anarsia lineatella, and oriental fruit moth, Grapholita molesta.

Final report In stone fruits, annual applications of nitrogen are needed to maintain good productivity. However, excess amounts do not increase fruit size and generally produce only negative results such as excessive vegetative growth, environmental contamination, and reduced fruit quality. In an experimental orchard, fertilization rates from 100 to 325 lbs N/acre/year showed no difference in fruit size or yield. The lower rates of nitrogen have additional benefit as they induce more red coloration on the fruit, thus improving quality.

Excess nitrogen fertilization may also have deleterious effects on the tree's susceptibility to attack from pathogens and arthropod pests. The most important pathogen attacking stone fruits is brown rot, Monilinia fructicola. Control is with one or two applications of fungicide during bloom; however, there is increasing resistance to many fungicides currently used. Our work indicates that lower incidence of brown rot is correlated with lower levels of nitrogen fertilization. In contrast, nectarines collected from trees that received higher levels of nitrogen fertilization were severely infected.

In 1990 we observed that peach twig borer (PTB) preferred young, vigorously growing nectarine shoots. Orchards with high nitrogen fertilization had more shoot growth and observations indicated that more and better feeding sites allow for a greater number of moth pests. Field and laboratory studies found new shoot growth was correlated with increasing nitrogen fertilization and that PTB survival was higher in new shoots. Results of experiments conducted between 1991 and 1993 showed that fruit from trees that received high levels nitrogen fertilization (e.g., <250 lbs N/acre/year) had greater infestation levels of PTB, oriental fruit moth, and omnivorous leafroller than fruit with low to moderate fertilization rates.

From this study we conclude that in the 'Fantasia' nectarine block studied, the 100 lbs N/acre/year rate of fertilization resulted in leaf N levels of 2.8 to 3.0% N. which produced sufficient vegetative growth to maintain yields and fruit weights equivalent to higher fertilization rates. Applying higher rates of N fertilization produced no beneficial effects and would only reduce fruit red color and increase the possibility of leaching nitrates into the ground water. Potential water loss and cuticle thickness was influenced by N treatments, affecting postharvest storage potential and brown rot susceptibility. Nitrogen fertilization was positively correlated to increased levels of brown rot and lepidopteran pest damage.

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