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A second kind of spore is released over a larger part of the 

 growing season. These spores are called pycnospores and they are 

 borne in another type of fruiting body called a pycnidium. Pycnidia 

 appear as tiny black pustules in the old infections. As with the 

 ascospores, the pycnospores mature over the winter and are ready 

 for release during the next season. Pycnospores are mature and 

 may be released from March to October. However, the bulk of the 

 pycnospores appear to be released from June to mid-August. It is 

 during this period that most new infections occur, indicating the 

 importance of these spores in the disease process. 



Once released, both types of spores are wind-carried to the 

 leaves and buds of canes. Senescent tissue is most susceptible. 

 One theory states that the lower leaves are preferentially infected 

 because they begin to senesce in June. The infection then travels 

 down the leaf stem and infects the node. Others feel that buds and 

 laterals in the lower part of the planting provide relatively moist 

 niches for fungus development. 



Once the spores have germinated they infect and injure or kill 

 an area around the leaf petiole and its base. There is little in- 

 formation as to what stimulates pycnidial formation versus perithecial 

 formation. The fungus overwinters in the infected tissue producing 

 pycnidia and perithecia. The next spring these structures release 

 spores which infect new plants. The life cycle is shown in Figure 1. 



Management 



The first decision a grower should make is whether there is a 

 serious spur blight problem in a planting. As mentioned, serious 

 outbreaks can reduce yields by 301. If the problem is causing eco- 

 nomic damage, there are a number of steps which can help manage the 

 disease. When growing summer-bearing raspberries in the narrow 

 hedge-row system, cut out old canes immediately after harvest. Also 

 remove weak and diseased canes, and thin the rows. The rows sliould 

 be no more than 1 ft. wide at ground level. There should be about 

 25 canes growing in every 10 feet of row. Good weed control is 

 also essential for maintaining good aeration and spur blight control. 



1. Insure proper ventilation in the planting. This is important 

 in managing other fungus diseases, particularly fruit and cane blight 

 ( Botrytis ) and anthracnose ( Gloeosporium ) . Too dense a row inhibits 

 drying and spray penetration, and encourages fungal development. 



2. Do not overfertilize, or push growth too fast. Raspberries 

 are a vigorous plant and respond well to fertilization. However, 

 too much growth causes dense foliage (see 1. above) and increases 

 senescence in the lower leaves. This increased number of senescent 

 leaves increases the number of places where infection can occur. 

 There is a practice which advocates applying a controlled amount 



of contact herbicide to the first flush of cane growth in spring to 

 reduce overall growth and promote cane health through the rest of 

 the year. This practice is still experimental, but illustrates how 



