DISEASES AFFECTING APPLES

By The Old House Web

DISEASES AFFECTING APPLES

List of files and visuals associated with this text.


There are many new practices to minimize the use of pesticides in treating diseases affecting apple crops. New specific pesticides are favored by the EPA over the older broad spectrum pesticides. These new pesticides have many merits: they are more effective, require less volume or number of sprays and are less likely to affect organisms other than the target pest.

However, these pesticides may also pose problems for home fruit growers. They may be packaged only in large quantities for larger commercial use, and may be difficult to obtain. It is unlikely that many labels will change as an entire approval process is required in order for a manufacturer to obtain a new label for homeowner use.

There are many more natural ways a grower can opt for in avoiding some of the diseases affecting apples. It is wise for a grower to plant in a good location-open, sunny and well-drained. Proper pruning and disposing of trimmed branches and dropped apples is also beneficial in warding off disease.

To assist in minimizing the reliance on pesticides, several new options have been developed. For example, many diseases can be avoided or minimized by the selection of less susceptable varieties. Although these resistant cultivars may require some chemical control, the number of sprays required is greatly reduced.

Some common diseases controlled by resistant cultivars include:

Apple Scab, the most common disease of apple trees. This disease is characterized by thick scabby growth which develops on the fruit, disfiguring it and lowering the quality. Apple Scab needs moisture to spread, and can occur all summer long, adding up to a lot of insecticide. Several management practices help to minimize spread, including proper pruning and the raking up of fallen leaves and scabby apples. In addition, several resistant cultivars have been developed.

Cedar Apple Rust is a fungal disease, most commonly found on crabapples. It spreads in winter months on juniper or cedar, then moves to the apple tree in spring. Its visual effect is much like scab, except it produces bright orange spots. Cedar Apple Rust could easily be avoided by planting cedars and junipers several hundred feet away and checking those already present. Resistant varieties include: Delicious, Jerseymac, Liberty, McIntosh, Priscilla, Tydeman and Redfree.

Fireblight is a serious disease, one that is potentially life endangering to the entire tree. A bacterial disease, it will blacken and wilt new shoots. Fireblight is most severe during warm humid weather, and passes winters in the infected wood. No variety of apple is totally resistant to fireblight, but a few have little problem with the disease. Fireblight can most easily be controlled by proper pruning and cutting of all infected limbs. It is important to disinfect the pruners after each cut.

Powdery Mildew is characterized by a white powder produced on leaves and new shoots. No apple variety is completely resistant to this disease, but some varieties are more resistant than others. Pruning annually and cutting off infected shoots is most helpful in offsetting powdery mildew. However, if spray becomes necessary, the most critical stage for application is from early spring until fall. The following table rates disease resistance in apple varieties:

Key to resistance rating: 1--very resistant; no control needed 2--resistant; control needed only under high disease pressure 3--susceptible; control usually needed where disease is prevalent 4--very susceptible; control always needed where disease is prevalent.

CEDAR APPLE APPLE FIRE POWDERY CULTIVAR SCAB RUST BLIGHT MILDEW ---------------------------------------------------------

Beacon 3 3 3 - Cortland 4 3 3 4 Delicious 3 1 2 2 Empire 4 2 2 3 Golden Delicious 3 4 2 3 Granny Smith 3 2 4 4 Gravenstein 3 2 3 3 Idared 3 3 4 3 Jerseymac 4 1 3 - Jonafree 1 2 2 - Jonagold 4 3 4 3 Jonamac 3 2 3 3 Jonathan 3 4 4 4 Liberty 1 1 2 3 Lodi 3 4 4 2 Macfree 1 3 2 - Macoun 4 2 3 3 McIntosh 4 1 2 3 Mollies 3 1 3 - Delicious Mutsu 4 3 4 4 Northern Spy 3 3 2 3 Paula Red 3 2 3 3 Prima 1 4 2 2 Priscilla 1 1 2 3 Redfree 1 1 2 2 R.I Greening 3 3 4 3 Rome Beauty 4 4 4 3 Spartan 3 2 3 2 Spigold 4 4 4 3 Stark Bounty 3 3 2 - Stark Splendor 3 3 2 - Starkspur 3 2 3 - Earlyblaze Stayman 4 3 2 3 Tydeman 3 1 3 2 Viking 3 2 2 - Wealthy 3 3 3 3

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REFERENCE:

Weed 'em and Reap February-March 1987 "Diseases on Apples" by Nancy J. Butler

Visuals associated with this text.

Visual title - Visual size Visual title - Visual size
Apple scab on overwintered leaf - 30K Apple scab, mummified fruit with scab - 24K
Apple scab, early summer defoliation - 81K Apple scab lesions on fruit - 15K
Fire blight on apple - 54K Fire blight canker - 38K
Fire blight canker on crabapple - 48K Fireblight on crabapple - 50K
Fireblight shepherds crook - 40K Fireblight, tree with many strikes - 58K
Fireblight, severe case - 53K Fireblight canker - 37K
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