60 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 46 



tained by fungicidal sprays. There are two periods when juni- 

 pers may be sprayed for control of rust. One period is in April 

 or early May, when the orange spore-horns appear on the cedar 

 galls or cedar apples. The other is in July or August, when spores 

 produced on diseased leaves of apple or crab apple are carried to 

 junipers. Cycloheximide (Table 1) applied during the first pe- 

 riod, after the spore-horns have appeared and before they become 

 gelatinous, will kill the horns and prevent spore production. Fer- 

 bam (Table 1) applied during the second period will protect juni- 

 pers from spores produced on the foliage of apple or crab apple. 



Cedar-Hawthorn Rust. — This disease, caused by the fungus 

 Gymnosporangium globosum, produces galls on juniper and leaf 

 rust on apple, crab apple, hawthorn, mountain ash, pear, and 

 serviceberry. It does not produce visible symptoms on the fruit. 

 The galls on juniper are small, reddish-brown, and spherical to 

 irregular in shape but similar in texture to the galls produced by 

 cedar-apple rust. The galls of the cedar-hawi;horn rust, most of 

 them less than an inch in diameter, usually originate on young 

 stems, but they may originate on leaves. They persist and pro- 

 duce spores for 3 to 5 years. Only a few brown, wedge-shaped, 

 spore-horns are produced on each gall. During rainy periods, 

 they expand into orange-colored, gelatinous, tongue-shaped 

 structures (Fig. 56). Spores produced on these spore-horns in 

 April and May cause leaf rust on hawthorn and other deciduous 

 hosts. On hawthorn, the disease appears as yellow to orange- 

 colored spots on the upper surfaces of the leaves and as raised 

 orange to brown spots, with tubelike appendages in the centers, 

 on the under surfaces (Fig. 57). These tubelike growths do not 

 split open and curl outward and backward as do the cylindrical 

 tubes produced by cedar-apple rust. If, in late summer, the spores 

 produced in the tubelike growths from the spots on hav^horn 

 leaves are carried by wind to leaves of juniper, they produce 

 brown galls on the juniper. 



Because this rust requires both juniper and hawthorn or 

 other pomaceous hosts in its life cycle, the fungus cannot perpet- 

 uate itself if the hosts are separated by distances greater than 

 the distance spores are carried by wind. Adequate protection 

 usually is given by distances of a mile or more. Whenever possi- 

 ble, species or varieties of juniper resistant to rust should be 

 planted. A list of these may be obtained from the Illinois Natural 

 History Survey. Spraying as recommended for cedar-apple rust 

 will control cedar-hawthorn rust. 



