resulting in abnormal finiit growth and fixiit 

 cracking. 



Pruning to facilitate good air circulation 

 within trees helps to control peach scab. Fungi- 

 cides applied to control brown rot usually also 

 are efifective against peach scab. Peach scab 

 generally is more prevalent when warm, wet 

 weather occurs just after shuck split. 



Bacterial Spot 



Bacterial spot, caused by the bacterium 

 Xanthomonas pruni, can infect leaves, shoots, 

 and fruit of peaches, apricots, and nectarines. In 

 the spring, bacteria oozing out of overwintering 

 cankers are carried by water droplets to young 

 fruit leaves or shoots. Moisture in fog or dew is 

 sufficient to spread the bacteria. Heavy rain 

 spreads the disease even further. Frequent 

 rains accompanied by moderate temperatures 

 and high winds also encourage infections, espe- 

 cially during the months of June and July. 



Leaf lesions are small and angular, appear- 

 ing first as water-soaked spots and then turning 

 brown to black. Centers of these spots often fall 

 out, leaving reddish colored margins. Lesions 

 generally are more severe at the tips of leaves. 

 Leaves that are severely infected turn yellow 

 and drop. Early season infections on fruit de- 

 velop into cracks. Lesions are not confined to the 

 friait surface, but rather go deep into the frijit 

 flesh. 



Non-chemical controls for bacterial spot in- 

 clude the use of resistant cultivars such as 

 Redhaven, Loring, Sunhaven, Jefferson, and 

 Madison. Excessive use of nitrogen may aggra- 

 vate bacterial spot problems. 



to leaf tissue and infection then can occur. Leaf 

 curl is most severe during cool, wet weather, 

 particularly at temperatures between 50 and 

 70°F. Peach trees are susceptible only during 

 the short period of bud swell to bud opening. 

 Symptoms appear about two weeks after leaf 

 emergence. Small, reddish areas develop on 

 small leaves. As the disease infection 

 progresses, the leaf wrinkles and puckers in 

 small areas or along the entire leaf. The m^'or- 

 ity of infected leaves drop. The fungus produces 

 ascospores which spend the summer on the 

 peach tree, but then produce overwintering bud 

 conidia. 



Where leaf curl is severe, maintain tree vigor 

 by: 1) thinning fruit, 2) irrigating during periods 

 of drought, and 3) fertilizing by mid-June. A 

 dormant spray of a copper-containing fungicide 

 after leaf drop or before bud swell usually will 

 control leaf curl. 



A recent study conducted by L. Burkham 

 ("Alternatives for ControlHng Peach Leaf Curl" 

 appearing in Common Sense Pest Control Quar- 

 terly) found that organic growers in California 

 were able to control peach leaf curl by sprajdng 

 a seaweed fertiUzer once a month. Speculation 

 is that susceptibility to leaf curl may be related 

 to magnesium deficiency. Seaweed contains a 

 high level of this element. 



Also, numerous nectarine and peach culti- 

 vars have been evaluated for susceptibility to 

 leaf cin-1. (Scorza, R. 1992. Evaluation of foreign 

 peach and nectarine introductions. Fruit Variet- 

 ies Journal 46: 141-144). All of the North Ameri- 

 can cultivars mentioned in this study (Harbelle, 

 Elberta, Redhaven, ReUance, Loring, and Sun- 

 Ught) showed varying degrees of susceptibility. 



Peach Leaf Curl 



Peach leaf curl is caused by the fungus 

 Taphrina deformans. Spores of the leaf curl 

 fungus are very resistant to adverse weather 

 and can remain dormant on twig surfaces for 

 two years or longer. Overwintering spores are 

 washed to the surfaces of leaf buds by spring 

 rains. These spores then multiply during wet 

 weather until leaf bud scales open. Once bud 

 scales become loose, spores are carried by water 



X-disease 



X-disease is caused by a virus-like organism 

 known as a mycoplasma. Leafhoppers carry the 

 disease from infected chokecherries or peaches 

 to other peach, nectarine, or cherry trees. Once 

 in the trees, mycoplasmas live in phloem cells, a 

 type of vascular conducting cell. 



Symptoms of x-disease are leaf yellowing or 

 reddening with shot-holing appearing during 

 July and August. Affected leaves drop, leaving 



Fruit Notes, Winter, 1993 



