As warmer weather comes and fruit trees start to bud, it's key to think about using fungicides on trees that had a fungal disease last year. Apple and crabapple trees often get apple scab and cedar-apple rust. These diseases can make leaves look bad, turn them yellow, and cause them to fall early. They won't kill the tree, but they can lower fruit production and harm tree health. So, when should we spray apple trees for cedar rust, and why is it crucial?
Understanding Cedar-Apple Rust
Cedar-apple rust is a disease caused by fungi in the Gymnosporangium genus. It affects both apple trees and cedar trees. Both are needed for the fungus to complete its life cycle.
On apple trees, the disease shows as small greenish-yellow spots on the leaves. These spots grow and turn orange-yellow, surrounded by red rings. On the top of the leaf, black spots called spermogonia appear. On the underside, aecia form, with hairlike projections.
This disease can also harm immature apples, making them small and misshapen. Infected apples become useless for eating.
Cedar trees get infected by aeciospores in late fall to winter. The fungus grows galls on the trees, which swell in spring rains. These galls turn bright orange and produce spores that can infect apples.
| Characteristic | Cedar-Apple Rust on Apples | Cedar-Apple Rust on Cedars |
|---|---|---|
| Symptoms |
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| Infection Patterns |
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The Complex Disease Cycle
The disease cycle of cedar-apple rust is quite complex, lasting almost two years on cedar trees. Between June and September, cedar needles get infected by spores from apple leaves. These spores come from lesions on the leaves.
In the summer, small greenish-brown galls appear on the cedar. They don't fully mature until spring, growing up to two inches wide. These galls are often called "cedar apples."
After warm spring rains, the galls send out gelatinous tendrils. These tendrils have tiny spores called teliospores. These spores germinate, producing four spores called basidiospores. These spores can travel up to two or three miles by wind.
Some of these spores land on apple leaves or fruit, starting the infection cycle on the apple plant.
| Key Facts About the Cedar-Apple Rust Disease Cycle |
|---|
| - Cedar-apple rust affects apple trees, large fruiting crabapples, and hawthorns |
| - Eastern Redcedars can infect Malus plants up to a half mile away |
| - The gall formed on junipers is usually ½"-1" in size and brown |
| - Spores released from telial horns can travel far on wind currents to infect susceptible hosts |
| - Some apple varieties are more susceptible to cedar-apple rust than others |
| - Chinese junipers are less susceptible to cedar-apple rust compared to Eastern Redcedar |
The life cycle of the cedar-apple rust fungus is complex, with many stages and ways it moves between hosts. Understanding this cycle is key to managing this tough plant disease.
Control Measures for Cedar-Apple Rust
Controlling cedar-apple rust, a fungal disease, needs a multi-faceted approach. It's crucial to understand the fungus's life cycle and use strategic methods to manage it.
Separating apple and cedar trees is a key strategy. Cedar trees should be at least a quarter mile away from apple orchards, depending on the wind direction. This breaks the disease cycle and stops spores from spreading.
In yards, removing cedar-apple rust galls from cedar trees in late winter helps. This stops the fungus from infecting nearby apple trees.
For apple trees, using fungicide sprays can protect them. Apply these sprays from blossom time until cedar galls stop spreading spores. Fungicides like myclobutanil or fenarimol are effective.
Controlling the disease on cedar trees involves regular fungicide sprays. Spray every two weeks from June to September. This reduces spores that can infect apple trees.
Good sanitation is also crucial. Clean up debris and diseased leaves all year. This prevents the fungus from surviving and spreading.
By using physical separation, targeted fungicides, and sanitation, we can manage cedar-apple rust. This protects both apple and cedar trees.
When to Spray Apple Trees for Cedar Rust
Timing is key when fighting cedar-apple rust on apple trees. Experts say the best time to spray fungicides is when buds swell and green leaves appear, usually in April and May. This is when the fungi that cause the disease spread and infect the trees.
Spring fungicide treatments after an infection year can lessen disease severity. But timing is everything. If leaf spots are already there, fungicides won't help much. Start applying a fungicide like myclobutanil (Immunox) when buds swell. Then, spray again two to three times, every 7 to 10 days, as the label directs.
Apple, crabapple, and hawthorn trees need regular spraying to fight cedar-apple rust. Start spraying at the tight cluster or early pink bud stage. Sterol inhibitor fungicides (FRAC 3) are best for this disease. QoI (FRAC 11) and SDHI (FRAC 7) fungicides don't work as well.
| Fungicide Application Timing | Recommended Interval |
|---|---|
| Start at tight cluster or early pink bud stage | Repeat every 7-10 days |
By spraying at the right time and using the right fungicides, apple growers can control cedar-apple rust. This helps protect their crops from this harmful disease.
Variety Resistance and Tolerance
Choosing the right apple variety is key to fighting cedar-apple rust. Some apples are more resistant or tolerant to this disease. Knowing which ones can help growers make better choices and manage the disease better.
Popular Red Delicious, Liberty, McIntosh, and William's Pride apples are highly resistant. They stand strong against cedar-apple rust, making them a smart pick for orchards facing this issue.
Empire, Granny Smith, Jonagold, and Pink Lady are moderately resistant. They offer good protection but can still get the disease.
Braeburn, Golden Delicious, and Honey Crisp are more likely to get cedar-apple rust. They need closer watch and more care to stay healthy. Gold Rush, Jonathan, and Rome Beauty are very susceptible and best avoided in areas with the disease.
Crabapples also play a big part in cedar-apple rust, as they can host the fungus. Crabapple varieties resistant to cedar-apple rust can help stop the disease from spreading to apples.
By picking cedar-apple rust resistant apple varieties and using resistant crabapples, growers can make their orchards stronger. This way, they can use fewer fungicides, making their management more sustainable and eco-friendly.
Similar Rust Diseases
Cedar-apple rust is a well-known disease affecting apples and cedars. But, it's not the only one. Other rust diseases can hit hawthorns, quinces, pears, and serviceberries too.
Cedar-quince rust or quince rust is one such disease. It can infect quince, apple, pear, hawthorn, and other plants. On cedar trees, it causes cankers that stay active year-round unless the twig or branch dies.
On apples, quince rust makes the fruit pucker at the blossom end. It's about an inch big and has dark green spots on the surface.
Other Rust Diseases Affecting Apples and Cedars
- Hawthorn rust: Hits hawthorns and related plants like apples and crabapples.
- Pear rust: Affects pears and can also infect apples and hawthorns.
- Serviceberry rust: Targets serviceberry trees and can spread to apples and crabapples.
These rust diseases are less common than cedar-apple rust but still harmful. It's important to know how to spot and manage them to prevent damage.
Conclusion
Managing cedar-apple rust on apple trees requires understanding the disease cycle and spotting symptoms on both hosts. It's key to apply fungicides when tree buds swell in spring to stop infection. Removing galls from cedar trees and separating the hosts also helps break the disease cycle.
Choosing apple and crabapple varieties that resist the disease can also help. By using these strategies, growers can keep their orchards healthy and productive. This summary highlights the need for careful pest management for a good harvest.
A proactive approach is vital for apple growers. It helps increase crop yields and ensures high-quality fruit for consumers.
