January 17, 2020
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The 5 pests that bugged Mainers most in 2019

Composite | BDN
Composite | BDN

As Maine’s farmers, gardeners and homesteaders reflect on this year and plan for the next, one thing strikes fear into even the most-practiced gardener’s heart: pests.

“People put so much time, effort and money into preparing their soil, adding amendments, creating usable compost, planting and raising their crops,” said Clay Kirby, insect diagnostician with University of Maine Cooperative Extension. “To then have insects come in and chew it all up is a downer of major proportions.”

Still, 2019 was a comparatively light year for pests in Maine.

“With the cold and wet spring, we actually didn’t have as many pests coming as early or in as high numbers as we have in the past few years,” said Caleb Goossen, organic crop and conservation specialist at the Maine Organic Farmers and Gardeners Association. “In some ways, farmers got a break.”

Even when growers get a much-earned “break,” pests can wreak havoc on hard-earned crops. The severity of the impact ranges from the frustration of the backyard gardener who had been anticipating their own home-grown vegetables to the working farmers who must produce crops to make a living.

Among the pests that Maine growers faced in 2019, here are the five that stood above the rest.

Swede midge

Courtesy of David Fuller
Courtesy of David Fuller
The tiny larva of the Swede midge can destroy cruciferous crops. It can prevent brussels sprouts from setting and forming.

In Maine’s pest world, 2019 may as well be known as the year that the swede midge arrived in Maine.

The swede midge — not “Swedish,” though they are an invasive pest from Europe, but “swede in reference to the European word for rutabaga — is a tiny fly similar in size to a fruit fly, the adult will lay eggs on brassica plants, such as broccoli, cabbage and cauliflower.

The maggots secrete digestive enzymes near the plants’ growth points that dissolve the critical, tender tissue.

“It causes complete disfiguration of the head of the plant,” said Kathy Murray, state integrated pest management entomologist and co-coordinator of the state’s Integrated Pest Management Council. “You can’t harvest it. It turns cabbage into a Brussel sprout.”

The midge was discovered in Franklin County on Aug. 26. Soon after it was confirmed hundreds of miles away in Aroostook County.

“There is no reason to think they won’t be found statewide,” said David Fuller, agriculture and non-timber forest products professional with the University of Maine Cooperative Extension. “They are here, and nothing I have read leads me to believe they can be eradicated [so] it is all about managing them now.”

Goossen said that because the swede midge was first found in Canada, Maine’s cold winters are unlikely to stop them, and the pest does not have many — if any — native predators. They are also difficult to detect.

“Because it’s so far into that growing point, you don’t see that happening, and the larvae get big enough that they drop off the plant and pupate in the soil,” Goossen said. “By the time you see the damage, it’s already been done and they’re off on the next generation of their life cycle.”

Swede midge are also hard to eradicate — especially for organic growers, but even for farmers open to using pesticides. Most larvae are so far in the plant that the pesticides cannot reach them very easily. Goossen said that one of the best ways to control swede midge is by using row cover to prevent female flies from laying their eggs and implementing a system of crop rotation.

“This is critical in that they overwinter in the soil, so getting as much distance from where you had brassicas the previous year as possible,” he said.

This past year was a landmark year for introducing this pest to the state, but subsequent years will be worse.

“Because they’re so new, the damage can be pretty bad when they build their populations up,” Goossen added. “It’s definitely going to need to be on people’s radar for next year.”

Leek moth

Courtesy of Maine Department of Agriculture, Conservation and Forestry
Courtesy of Maine Department of Agriculture, Conservation and Forestry
The leek moth (Acrolepiopsis assectella). Its larva feed on allium plants such as onions, leeks and garlic causing damage and economic loss.

In 2018, the Bangor Daily News predicted that leek moths would spread to Maine. That forecast came true.

“It’s a similar story to the swede midge,” Goossen said. “It was also introduced into Canada and has been spreading.”

Goossen said that leek moths feed on allium species, such as onions, garlic, shallots and — of course — its eponymous leeks.

“[The moths] lay their eggs on the crop and then the egg hatches and the larvae emerge,” Goossen said. “It’ll burrow inside that hollow leaf and eat the inside, leaving just the outside waxy skin, [like] windows in the onion leaves. Leeks and garlic don’t have hollow leaves, so they feed on the upper surface.”

To manage leek moths, Goossen suggested excluding adults using row cover so they cannot lay eggs.

“The moths only fly at night so if you wanted to weed things, you can leave your onions uncovered all day long and just make sure you put the cover back on before night,” he said.

Regardless, growers should expect more leek moths in the years to come.

“It seems like the leek moth maybe likes river valleys, may follow the rivers down through the state,” Goossen said. “There’s a progressive expansion of territory. For both [swede midge and leek moth], modeling of climate factors and what might be suitable habitat [show that] all of New England falls within suitable habitat and beyond.”

Browntail caterpillars and moths

Abigail Curtis | BDN
Abigail Curtis | BDN
The tell-tale red-orange dots on the back of browntail moth caterpillars make it easy to identify them.

Browntail caterpillars are an invasive species that have long plagued the coast in Maine, but experienced a comeback in 2019.

“Some of its natural enemies were introduced by government agencies a long time ago [that] suppressed them for a long time but for whatever reason has gone through a sudden resurgence,” Murray said. “It doesn’t show much sign of slowing down.”

Browntail caterpillars do moderate damage to crops — Goossen said they defoliate fruit trees, especially apple trees — but they are most irritating to the gardeners themselves because of their irritating hairs that cause a poison ivy-like rash.

“[The rash] lingers for weeks at a time,” Murray said. “It can cause respiratory problems [and] exacerbate asthma.”

Moreover, the browntail’s range continues to expand.

“It did sound like a lot of places are seeing browntails where they didn’t have it previously,” Goossen said. “It continues to spread.”

Goossen said row cover will help reduce browntail numbers, but the population will mostly depend on how many overwintering larvae were able to survive the winter and whether diseases will impact the population boom.

“There is a pathogen that kills it,” Murray added. “We were kind of hoping that this last year would be a little less because it was such a wet spring and summer, but it was not enough to make a difference.”

Spotted-wing drosophila

Courtesy of David Handley
Courtesy of David Handley
A spotted wing drosophila is pictured on a raspberry.

Spotted -wing drosophila is a pest that’s been causing damage to Maine fruit crops for close to a decade and one to keep an eye on in 2020, according to Kirby, the insect diagnostician with University of Maine Cooperative Extension.

The spotted-wing drosophila is different than the common fruit fly found in kitchens and pantries. This strain of fruit fly is native to northern Asia and was first seen in Maine in 2011. Common fruit flies feast and multiply on over-ripened fruit, but the spotted-wing drosophila targets soft-skinned fruits before they are ripe. In Maine, that’s bad news for late season fruits such as raspberries and strawberries.

“[It’s] a little more aggressive in that it can lay its eggs in fruit that haven’t started rotting,” Goossen said. “Fruit flies need a fruit to be decaying, but this one can puncture the skin and lay its eggs.”

Infestation can happen quickly, because one female fly can lay up to 400 eggs. The eggs only need between 10 and 14 days to become an egg-laying adult itself. It can take very little time for millions of the flies to be in a berry crop and begin feasting on the ripening flesh of the fruit.

Though this year’s strawberry season was shorter than usual, Murray said it continues to be a pest of berries, especially raspberries and late-season blueberries.

“It may be showing up more and more with a warmer climate,” Goossen said. “It takes a while for the population to build up enough to be a real problem. If it’s a warm spring, they will probably get a jumpstart and build up their numbers faster.”

Cutworms

Courtesy of Angela Yuriko Smith
Courtesy of Angela Yuriko Smith
The larval stage of a cutworm

Cutworms are a scourge for home gardeners and commercial farmers alike. The turnip moth larvae emerge in the spring, hiding under litter or soil during the day and sneaking out in the dark to feed. Though there are several different species of cutworms with different habits, the larva typically attacks the first part of the plant it encounters — often, the stem of a seedling.

“They [usually] cut plants off at the base,” Murray said. “You go out and all of a sudden see a bunch of plants laying on their sides.”

Goossen received more reports of cutworms in 2019 than usual, especially in Waldo County, but the distribution was scattered.

“A lot of people saw damage, [but] some people will not see any and other folks will see huge numbers of cutworms that take down everything they plant,” Goossen said.

Murray said that growers of certain crops had more problems with cutworms than others. There are several species of cutworms, she explained, and their prevalence can be spotty from year to year. One crop that particularly suffered was hemp.

“Hemp growers, one of our newest crops in Maine, had a real terrible time with cutworms,” Murray said. “It was not a cutworm that cuts the plant at base, but [one that] goes up in the flower in portions of the plant. It ruined the quality [of the hemp].”

When it comes to what growers can expect in the upcoming year, experts agree that predicting pests year to year is challenging because of the number of variables involved. Kirby said it’s difficult to predict the levels and range of these pests in Maine for the coming year, as populations depend on many variables, including weather conditions, pesticide applications, predators, parasitoids and diseases.

Goossen said gardeners should watch the winter to come — a tough winter with freezing a thawing and long cold spells without snow could kill overwintering pests — but even that is hit or miss.

“It’s always hit or miss,” Goossen said. “Sometimes you see the weather and you think you can make an assumption on that but it surprises you anyway.”

 



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