Trees were observed throughout the following grow- 

 ing season for symptom remission, yield, and wounding. In 

 September, 1987, every tree was rerated to determine any 

 change due to treatment or to progress of the disease. 



Results 



As indicated by the rating changes shown in Table 1, 

 most X-disease symptoms on the OTC-treated trees were 

 either absent or less severe. Untreated controls either 

 remained at the same disease level, or grew worse when 

 compared to the previous year's ratings. Of the untreated 

 trees with an initial rating of (healthy), 47% showed an 

 increase in X-disease symptoms. Trees with initial disease 

 ratings of 1 or 2 responded well to the OTC treatments, 

 often bearing as much fruit as healthy trees. The severely 

 diseased trees with ratings 3 and 4 gave variable results. 

 Many treated and untreated trees of the 3 and 4 rating 

 classes became worse or died. Even among those trees 

 responding to the treatment, most had only one or two live 

 scaffolds bearing fruit. 



Observations throughout the season showed that most 

 treated trees in rating classes to 2 had good fruit yields. 

 Untreated trees gave a wide range of yields dependent 

 mostly on the extent to which the crown was affected by X- 

 disease. 



Some trunk damage associated with the drilled holes 

 was evident a year after treatment. Over 60% of the holes 

 inspected had small cracks or gummosis associated with 

 the injection site. A few trees had extensive cracks (from 

 6 to 10 inches) and decay. Fourteen percent of the holes 

 had callused over after a year and a half. The injection 

 wound alone did not cause the cracks and gummosis; they 



were caused by the OTC treatment (Schieffer, unpublished 

 data). 



Discussion 



Mauget microinjection of OTC appears to be an 

 effective and simple technique for X-disease therapy de- 

 spite possible long-term drawbacks related to injection 

 wounds. Microinjection is not labor intensive and does not 

 require special equipment. Since most X-infected trees 

 decline quickly and eventually die, treatment of diseased 

 trees may at least prolong their productivity. However, 

 trees not more than half affected responded the most, 

 therefore, Mauget therapy appears to offer limited effec- 

 tiveness to trees in advanced stages of X-disease. Injections 

 will be most cost-effective where half of the tree or less is 

 affected by foliar symptoms at the time of treatment. 



Mauget microinjection may prove especially valuable 

 in delaying symptom development in asymptomatic trees 

 on sites where high disease pressure from infected choke- 

 cherries is present. Treatment of healthy trees, on the 

 other hand, may need to be considered carefully because of 

 the possible long-term wound effects from OTC injection. 



Research is continuing on the evaluation of risks vs. the 

 benefits of prophylactic use of this method in healthy trees, 

 and to determine how long treated trees remain in symp- 

 tom remission. 



References 



Lacy, G.H. 1982. Peach X-disease: Treatment site damage 

 and yield response following antibiotic infusion. Plant 

 Disease Reptr. 66:1129-1133. 



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