We’ve just passed from spring into summer.This spring was relatively cool, and that was a blessing as the cool temperatures tended to suppress the development of insect problems in our gardens and landscapes. But as the daily temperatures rise, insect populations explode with many insects reproducing and growing as much as 10 percent faster with each daily average temperature increase of just 1 degree.
When left to her own devices, Mother Nature does a pretty good job of controlling insect populations. There are a number of phenomena that act to control the “bad” insects, from birds and mammals that feed on them to other predacious insects that eat and parasitize them.
You know all about the ladybug beetles whose larval stage, known as “aphid lions,” eat hundreds of aphids a day. And vegetable gardeners are familiar with the sight of a hornworm with tiny white projections along its spine chomping away on a tomato or eggplant. Those small white spots are the eggs of a parasitic wasp that will feed on the hornworm, and if left alone will kill it in just a couple of days. No pesticide needed.
But when we step in to control insects that we perceive as harming our plants, we often upset nature’s delicate balance and do more harm than good. So we need to tread lightly and consider the consequences of our sprays before we pull the trigger and let the sprays fly from our nozzles. A couple of great examples will highlight my point, then on to what we as gardeners can safely and thoughtfully do when insects truly threaten our vegetables, fruits and landscape plants.
We used to regularly get outbreaks or infestations of gypsy moth caterpillars that would routinely defoliate our oak trees. A panic would set in as the defoliation would cover blocks, then neighborhoods and even entire counties.
In the 1960s and 1970s, the solution was to get out the spray trucks, helicopters and airplanes and blanket the areas with pesticides to kill the caterpillars. But strangely, they returned year after year. It seemed that the more we sprayed the worse the infestations became in subsequent years. Sure, we had killed many of the caterpillars but we’d also killed the predators that fed on them.
After years of these controlled efforts, much of the money ran out for the spraying programs. Guess what? We and the oak trees not only survived but the gypsy moth caterpillar population seemed to resolve itself. They didn’t disappear, but they certainly dwindled.
But why? What changed?
Well, one year when there was little money for spraying we had a substantial caterpillar outbreak. All the alarms were sounded but nothing was done. Then it rained and it stayed cool for several weeks. The caterpillars died and fell from the trees.
Poison in the rain? Far from it. The rainy and cool weather promoted the growth of a naturally occurring fungus that kills the caterpillars. The more caterpillars that died, the more fungus spores became available and Mother Nature did what man couldn’t.
Since then, since we stopped using all the chemicals, in most areas the gypsy moth caterpillar has become a non-issue.
There was, and still is, a similar problem up in the Catskill Mountains. In some years leaf-eating caterpillars devour entire mountains and valleys of foliage. In some years, you could drive for several miles and where you’d expect to see lush green peaks all you’d see was brown.
Calls inevitably go out to the state and counties to spray and eradicate the caterpillars as they defoliate valuable timberland. But the caterpillars are also a threat to the valuable tourist economy as the caterpillars are dropping from local trees like rain along with their black, grainy droppings. Gross is a fitting description.
But a strange (okay, not) thing happened. One recent spring the caterpillars were set to do record damage. You could hear the munching, see the caterpillars falling on your car and on your picnic table. The droppings were everywhere.
Then it got rainy and it stayed damp and cool for several weeks. There was no spraying, but seemingly from nowhere something was killing all the caterpillars. Yup, you got it, another fungus among us. The following year, and for years since, the caterpillars have been under Mother Nature’s control.
However, the story is not so rosy for another problem out here on the East End.
A number of years ago, homeowners and landscapers on the South Fork began to notice that their beloved privets were dying. An examination of the suspect plants revealed that a long-known insect called “prunicola scale” was feeding on the privets and literally sucking the life out of them.
The scale, now known as the white prunicola scale or WPS, spread rapidly. As there was no known chemical control, all sorts of sprays were used on the privets in the hope that at least one of them would work.
The problem got worse and spread. Some chemicals were found that provided limited control, but as you may have noticed we’re still losing privet from Montauk to Speonk and beyond.
Some have had luck with chemical controls, but due to the very changeable weather conditions from one village to the next, the proper timing of the sprays and when they will be effective on the scale has become a crapshoot of sorts. But there’s more, and you knew that.
If you read the literature on WPS, one theme that’s repeated over and over (and as exemplified in a Cornell Extension publication), predators and parasites are abundant but not reliable for control.
“Why not?” we wonder.
Some suspect the wide range of pesticides used in attempts to control the WPS, added to the pesticides used locally to control the tick populations, have wiped out a substantial population of the predators and parasites that might have naturally controlled the scale. Then there’s also the issue of hundreds, if not thousands, of miles of privet planted out here, making it incredibly easy for the scale to overtake the privet.
Monocultures are the best places for insects and diseases to establish and take hold. Here on the East End, with miles and miles of privet, we have the perfect monoculture conditions.
Next week, we’ll focus on the chewers, suckers and raspers. We’ll also talk about how to find insect problems before they get out of control and how to treat them without killing every living thing, including us. As always, keep growing.