Control
Because apples are the economically important crop, control is usually focused there. Interruption of the disease cycle is the only effective method for control of the cedar apple rust. The recommended method of control is to “remove cedars located within a 1-mile radius” of the apples to interrupt the disease cycle, though this method is seldom practical. For those doing bonsai, it is common to have the trees within feet of each other and on the central eastern seaboard of the United States, Eastern Red Cedar is a common first-growth conifer along roadsides.
There are differences in the susceptibility of various apple varieties. Jonathan, Rome Beauty, Wealthy and York Imperial are susceptible. Grimes Golden, Red Delicious, Winesap, Staymans, Redfree, Jonafree and Priscilla are resistant. Crabapples are generally more susceptible than apples. Resistant crabapples include Adams, Beverly, Candied Apple, Dolgo, Donald Wyman, Eleyi, Inglis, Indian Summer, Liset, Mt. Arbor, Narangasett, Periscifolia, Red Jewel, Robinson, Robusta, Royalty, Sargent cv., Tina, Snowdrift, and Special Radiant. Resistant Crataegus (Hawthorn) include crus-galli, Intricate, laevigata, Autumn Glory, phaenopyrum, pruinosa, viridis, and Winter King. The resistant varieties are less susceptible to attack, but that does not mean that they are free from an aggressive attack.
Fungicide sprays applied in a timely manner are highly effective against the rust diseases during the apple cycle. Most sprays are applied four times at 7- to 10-day intervals, starting with pink bud on crabapples. These applications are to protect the apples from spores being released from the cedar host in mid-spring. If cedar apple rust disease is diagnosed on apple fruits and leaves it is far too late to spray. Systemic fungicides are available.
Fungicides listed for use on apples can be used in July and August on the cedars to reduce infection. Application of fungicides to the junipers before and while they are in the infectious orange gelatinous state seems to reduce the severity of the outbreak.
Read more about this topic: Gymnosporangium Juniperi-virginianae
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—Lawrence Balter (20th century)
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—Jane Alpert (b. 1947)