Pear tree rust spreading on Long Island, natural remedies for powdery mildew

DEAR JESSICA: I have a question about your column of Aug. 19, where you mention that the fungus that causes rust disease can be cured by getting rid of junipers, which host the fungus. I have two ornamental pear trees that have the disease, and it’s getting worse and worse, to the point where I’m this close to taking down the trees. I’d be happy to remove the two junipers on my property to restore the health of the trees, which are now about 15 years old. However I have my doubts about being successful with that approach. The town of Massapequa where I live uses ornamental pears as street trees, so they are quite plentiful in my neighborhood, and I have yet to see a single healthy tree. Are the spores capable of traveling great distances? Because not all folks appear to have junipers, but all folks who have these trees seem to have the disease. What do you think is the likelihood of my trees returning to health if I remove the junipers on my property?

— Jim Wipper,

Massapequa

DEAR JIM: The pear street trees surrounding your property aren’t infecting your pears, but they could be infecting your junipers, which in turn are infecting your pears. Pear rust disease, caused by the fungus Gymnosporangium, G. sabinae, follows a transmission route of alternate hosts: Spores from junipers only infect pears, and spores from pears only infect junipers.

The juniper culprit in this case is the cultivar Robusta Green, according to Margery Daughtrey, senior extension associate and plant pathologist with Cornell University, who is based in Riverhead. So “it would be advisable to avoid planting J. chinensis Robusta Green near pear,” she said.

The biggest danger of infection is among plants within 100 yards of each other. “There can be wind spread over longer distances, but usually so few leaves are affected that it is not a very noticeable infection.”

There are no absolute, 100-percent guarantees that removing your junipers will save your pear, because your neighbors might have infected junipers that you’re unaware of, and spores from those could infect your trees. But if you can confirm that neighbors within 100 yards don’t have junipers, it’s a safe enough gamble that removing yours will alleviate your pear problem. Regardless, the disease is not lethal. Infected trees can look really bad, so a lot of people remove them, but they aren’t actually dying.

Ornamental pear trees, notably Callery Bradford pears, have been used extensively as street trees on Long Island for many years. They proved to be a poor choice, however, mainly because their branch structure makes them weak, and they break and split easily in harsh weather. But because of their overuse, disease has become another reason to avoid planting them.

Pear rust has been prevalent on Long Island since about 2009, but it escalated this year due to heavy rains, which created the perfect conditions for the fungus to thrive and multiply, Daughtrey said.

In New York, the fungus’ spores are released from around October through December, or until there is a killing frost, according to Daughtrey. “This spore-release timing is very late,” she said. “With cedar-apple rust, we expect juniper infection in August. Pear trellis rust spores take longer to mature and have a long release period, making control of the disease by using fungicides on junipers difficult to impossible.”

DEAR JESSICA: Mildew is killing my honeysuckle vine. I don’t want to spray poison due to the bees and birds. Should I plant a different vine?

— Peg Rissier,

Kings Park

DEAR PEG: Powdery mildew is the most common affliction of honeysuckles, and the best way to combat any mildew, whether in your shower or on your plants, is to maximize air circulation and keep things as dry as possible.

For your vine, this means ensuring it receives as much sun as possible, which might entail cutting back surrounding plants and trees that are casting shade, and thinning the plant by removing crowded stems. This will help counter the toll of humidity. To that end, also avoid overhead watering, as from in-ground sprinkler systems, which will dampen foliage, and instead direct water only to the roots.

Rake leaves around the plant now and clean up thoroughly, disposing of diseased plant parts and debris in the trash.

Next spring, before leaves emerge, spray the plant with a fungicide and repeat a few times during spring and summer.

Here are two pollinator-friendly recipes to try: Combine two tablespoons of light horticultural or vegetable oil and four teaspoons of baking soda in a gallon of water, or mix one part whole milk and two parts water in a spray bottle.