Gardening Help FAQs

Here are answers to some of the most common questions we receive about garden plants. You will find concise information on general gardening techniques as well as plant selection and care. For detailed information on specific plant pests and problems refer to our Common Garden Pests and Problems page.

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Horticulture Questions and Answers

What problems do flowering crabapples commonly have?

The best way to avoid flowering crabapple tree problems is to select a cultivar that is resistant to the common diseases. Many of the new cultivars are resistant to or tolerant to scab, fireblight and rust. If you have an older, disease susceptible cultivar, you'll need to provide extra care to insure its health and beauty.

Scab is the most common crabapple disease, especially during a wet season. Leaves develop darkened spots which may look black or velvety, and then yellow and drop. Severely diseased trees often lose their leaves by mid to late summer. The trees will survive the attack, but become weakened after several years of losing their leaves. For more information on apple scab, listen to the Hortline message #372 "Controlling Scab on Flowering Crabapples".

Fireblight is another crabapple disease. It enters through wounds, flowers; and other openings during cool, wet weather. This bacteria, multiplies and blocks water and nutrient movement, causing twigs to turn black and die, giving diseased plants the appearance of having been scorched by fire. Fireblight may kill the tree.

Proper care can reduce the risk of fireblight. Avoid lawn mower and weed whip damage, along with other injuries that provide entry for the disease. Avoid excessive nitrogen fertilizer.

Control of fireblight is by pruning out diseased areas; make cuts 6" to 12" below the diseased area to insure removal of the entire diseased tissue. Prune when weather is dry and trees are dormant; the disease is not active at these times. Disinfect tools with bleach or alcohol solutions after each cut.

Rust is a third and less common crabapple disease. Infected leaves are covered with bright yellow to rusty-orange spots in early June. Leaves will fall off if the summer is dry and the disease is severe. Rust needs two different host plants to complete its life cycle. Certain juniper species serve as the alternative host. Like scab, rust rarely kills ornamental crabapples, but it can be unsightly.