Gazette Gardener: Nipping problems in the bud

PHOTOGRAPHER: Natalie Walsh

These rose blossoms have been ravaged by beetles. Gardeners are facing a number of problems with their plants this year.

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This has been quite the season. I’ve heard from you that you are having troubles in the garden from insect pests to fungal diseases.

This column identifies some of the problems and explains what you can do to remedy the situation.

There are a number of beetle pests on ornamental plants this year. The beetles causing the most concern are the Japanese beetle, the Oriental beetle and the Viburnum Leaf beetle.

The Japanese beetle and the Oriental beetle are related. Most people recognize the Japanese beetle for its distinctive shiny metallic green color. The Oriental beetle is about the same size but its color varies from a light brown straw color with dark markings to an all black beetle.

The adults of both beetles feed on the leaves, flowers and fruit. Unfortunately, the adult beetles visible on plants will be depositing eggs this month that will hatch into grubs that feed on grass roots. The Oriental beetle also feasts on the roots of woody shrubs.

Right now, hand-picking is effective, as the adult beetles are often grouped together when feeding.

You can go into the garden with a can of soapy water and flick the beetles into the can.

There are insecticidal sprays that can limit the damage of feeding adults, but the real problem occurs in the larval stage when the grubs of these beetles hatch and damage the lawn. Before you reach for a grub- control chemical, check that you really have a problem. The rule of thumb is to dig up a 3-inch-deep square foot of turf and if there are more than 8 grubs present, treat the soil. The time to treat is mid-August to September with Dylox (trichlorfon). Wet the soil before applying Dylox and water in after application as per the label instructions. This recommendation also works for Oriental beetle grubs.

I know some readers are trying Milky disease spore powder, a bacteria that kills Japanese beetles grubs. However, Cornell University scientists have determined that the temperatures in upstate New York are too cool and the bacteria is “not very effective north of Westchester County.”

Viburnum leaf beetle

I spotted the damage of the viburnum leaf beetle (VLB) while on a garden tour. Take a look at the second photo in the above photo gallery. The viburnum leaves had been skeletonized and on the bark of a slender branch I saw the telltale line of brown caps where an adult female deposited her eggs.

VLB is an invasive, nonnative beetle that has steadily spread since it first appeared in New York state in 1996. It can completely defoliate viburnum shrubs. And in northern New York, we use a lot of viburnums in our landscapes and have many in our woodlands. After two or three years of infestation, the shrubs die.

How do you know if this is what is chewing on your viburnum leaves? Look for a series of small holes on a twig, most likely on the current season’s growth. Adult females lay eggs all summer until the first killing frost. They have a distinct pattern of making a hole, laying eggs inside and sealing the hole with chewed bark and excrement. If you spot a series of brown caps, you know the culprit is VLB.

On the Cornell University Web site, the following is recommended:

“Pruning and destroying infested twigs after egg laying has ceased in the fall, anytime from October to April, is the most effective means of control for small scale plantings.

“When pruning is not practical, pesticides may be effective in controlling larvae or adults. Home gardeners may use spinosad or acephate, if the product is labeled for leaf beetles. Spray when larvae first appear in early May for best results. If damage from adults is excessive, a second application in mid- to late summer may be helpful. Insecticidal soap is not effective against adults.”

For a list of viburnums that are less susceptible to damage, go to www.hort.cornell.edu/vlb/suscept.html.

Blossom end rot

The third photo in the photo gallery shows blossom end rot on a tomato but it can occur on peppers and eggplants, too. Gardeners usually notice a dark sunken area on the blossom end — opposite the stem — of the fruit. In short time, the lesion turns black. On peppers, the lesion is light brown.

There are several possible causes from a low supply of calcium, too much nitrogen and fluctuations in soil moisture. My guess this year would be improper watering.

I know we have had a lot of rain, but it is still wise to turn over a shovel full of earth in the garden to see if that afternoon storm really seeped down to water the roots. In my own garden, the skies have been gray but the actual rainfall has often not adequately watered the vegetables.

Powdery mildew

The fourth photo in the gallery shows powdery mildew on a zucchini leaf. You probably have seen it on lilacs, fruit trees, bee balm, phlox and many others this year. Houseplants such as African violets and begonias are also susceptible.

It looks like a dusty gray to white coating on the leaves. It’s a fungal disease that thrives in wet seasons with high humidity, like the one we have been having.

The seriousness of the problem depends on the plant. Lilacs seem to weather the fungus while begonias often succumb to the disease.

What can you do? Your best bets are to buy resistant varieties when available and keep your plants well spaced to promote air flow, which discourages the fungus.

You can also help the garden by buying healthy plants. If there are any visible signs of spotting, yellowing or wilting — even if the plant is priced half off — it’s no bargain.

And, grow each plant in the environment they need to succeed. Vegetables and herbs prefer full sun. You don’t want to stress or overcrowd your plants as this weakens them and makes them more susceptible to problems.

Another tip would be to avoid overhead watering and choose soaker hoses or drip irrigation instead. This will help keep diseases from moving from one plant to another.

As you enjoy your garden, look over your plants. Problems spotted early are usually easier to manage.

If you are having trouble with tomatoes, e-mail me a digital image and I’ll help identify what is going on, the likely cause and the remedy.

Happy Gardening.