For the past four days the leaves on our sycamore tree have been falling like it's autumn, and they're covering the whole yard.

Some are healthy green, others are brown with holes. We cleaned them up this morning, the wind came up and it is like we did nothing.

Could the tree have a disease?

— Barbara

Your sycamore tree has a fungal disease called anthracnose. The disease infects newly emerging leaves in the spring.

The fungus forms brown, irregular spots on the leaf that follow along the larger veins. As the disease progresses, these individual lesions merge and can involve the entire leaf.

Infected leaves will curl and fall from the tree, littering the ground. This leaf drop isn't all that bad in and of itself; the tree will push out new growth in the next several weeks, and the tree will look pretty good this summer.

However, the fungus will infect the small twigs the leaves are attached to. Often these dead twigs form a bushy "witches broom" that is a characteristic of this disease. As time progresses, the fungus will eventually move into larger and larger branches, then it forms dead sunken areas in the stem called cankers.

These cankers grow slowly from year to year, restricting water and nutrient movement in the stem, causing yellowing, thinning, leaf scorching and die-back on that stem.

We don't see sycamore anthracnose every year as the disease needs certain weather conditions to become a problem in western Colorado. It needs temperatures below 60 degrees with cloudy, damp weather. Those conditions aren't all that common in the desert, but that's what we've had this spring.

So, what to do about it? It's important to understand that anthracnose can't be effectively controlled during the current season. It is something you have to prevent in the future.

Control involves several things. First, make sure the tree is as happy and healthy as you can make it. Strengthening the tree enables it to better withstand the infection and to heal damage.

Make sure the tree is watered deeply but infrequently. It also is helpful to lightly fertilize the tree to stimulate regrowth later this spring and summer.

You also should prune any infected or cankered stems. This may have to wait until later this summer or even early next spring so you can tell what is infected and what is not. If you leave the cankers, they can grow and continue to damage the tree as well as produce spores that spread the infection.

When pruning, it's a good idea to disinfect your pruners in a 10 percent bleach solution between cuts to reduce the chance of spreading the disease on contaminated pruners.

You also should to be sure to pick up any fallen leaves and dispose of them in the trash — don't compost them. These leaves are a prime source of reinfection, and most backyard compost piles don't get hot enough to kill the spores.

Finally, you can spray the tree with a fungicide. The fungicides available are preventative in nature, and they won't cure existing infections. Because of this, fungicide sprays should be applied at bud break and repeated one or two more times at 10– to 14-day intervals. The best sprays to use are copper sprays or Fertilome Systemic Fungicide.

Since sycamore trees get pretty big, they quickly outgrow your ability to spray them, requiring you to hire a spray company to do the job. Because this is expensive, many people choose to remove the tree and plant something less troublesome.

However, before you scratch sycamore off your list of trees to plant, it's important to know that sycamore anthracnose is pretty much only a problem on American sycamore.

The American sycamore was planted commonly years ago, but is pretty rare today. London plane sycamore is the common one sold today, and Bloodgood, the common variety sold, is extremely resistant to the disease.

It's still sad to see big old American sycamores around town and to watch them shrink year to year.

Dennis Hill is the nursery manager at Bookcliff Gardens, bookcliffgardens.com. Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506, or email info@bookcliffgardens.com.

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