Carol O’Meara is a horticultural entomologist and an extension agent in Colorado, but she grew up on the East Coast. When she and her siblings got into trouble, her family had chores for each kid. Carol’s job was picking Japanese beetles from the roses. “I spent a LOT of time picking off Japanese beetles,” Carol said in her talk at the Denver SymROSEium on April 1st. “I was a very willful child.” On the plus side, the chore may have started her on her career path. “I do think Japanese beetles are absolutely spectacular,” she said. “They are gorgeous scarab beetles.”
JAPANESE BEETLE DAMAGE: Japanese beetles are gregarious, polyphagous feeders. Polyphagous means eating a lot of different plants. Gregarious means that they are a bit like humans on Thanksgiving. The beetles send out an aggregation pheromone, that “tells the other Japanese beetles that the party is all here.” They gather in masses and feed together and the plant becomes skeletonized, with just the plant’s veins left behind.
Japanese beetle larvae, the grubs, are among the most damaging turf grass insects in the US. “The single most effective things we can do to eradicate the Japanese beetle,” Carol said, “is to make the soil dry enough so they do not support the grub’s life.” The beetles are very briefly on our landscape as adults, but are in the soils for almost a year. With golf courses, sports fields, school yards, and public parks, Colorado’s front range is keeping its turf grass and soil at a moisture level that is comfortable for the grubs. They will feed on the root system and sever the roots to the extent that the turf can actually be lifted up.
Japanese beetles are insects of regulatory concern. Carol explained that if an insect is economically impactful, regulations come into place. “For Colorado, what this meant was an impact on our nursery industry. We can bring plant material in from other states, but now, unless nurseries are treating in a certain way and can prove that they are Japanese beetle free, they can no longer ship out to non-Japanese beetle states.” Because Japanese beetles are not borers, the risk comes from plants that have soil around the roots. Bare-root plants are fine. The issue of introducing Japanese beetles into new areas is also a problem for home gardeners. “How many of you,” Carol asked, “will dig up and share a plant or two that has gotten a little out of control? With roots, soil and all, you run the risk of spreading this insect, just like the nurseries run that risk.”
UNDERSTANDING THE LIFE CYCLE: In spring, the grubs are moving upward in the soil. They feed heavily in April and May on the turf grass roots, or roots of other plants in the landscape. From the end of May and into July, the adults are active and are feeding on plants. Unfortunately, “our particular season is about twenty days ahead of itself this year.” That means that this year, the insects will be active earlier.
The females dig a hole a couple of inches deep into the turf grass, and lay a few eggs, then emerge and resume feeding. In all, one female can lay forty to sixty eggs in her lifetime. The larvae will hatch and will begin to feed on the roots. Carol remarked that “the larvae are at the surface, and at their most exposed point for biological controls at this stage, in August and September. For rose growers who want to introduce biological controls into their landscape, this is the timeframe to do it.”
CONTROL THROUGHOUT THE SEASONS: In terms of the fight against Japanese beetles, Carol emphasized that there is no product that will allow you to spray your landscape once and be done. “I wish I could give you the magic formula,” she said. “The reality is that this insect has been a problem in the United States for a hundred years. I urge you to change your approaches as you go through the season so that you don’t rely on one thing as the miracle cure. I can’t give you that.”
What Carol did give the Rose Symposium attendees was an arsenal of controls to use at various times throughout the year. There are insecticides, parasitic nematodes and possibly natural enemies that call all be used in the fight against Japanese beetles. Carol cautioned that the insecticide class known as neonicotinoids (including imidacloprid, acetamiprid, clothianidin, dinotefuran, nithiazine, thiacloprid and thiamethoxam) affects the central nervous system of insects – and bees are insects. Neonicotinoids are toxic to bees. If used, they must only be applied where there are NO blooming plants. And that, Carol stressed, is blooming plants “whether you want them there or not—so that includes dandelions.”
LONG TERM: The most effective control for Japanese beetles will be to eliminate the larval food supply. This means making the soil dry enough so it does not support life. For many gardeners, this may mean changing from turf grasses to xeric grasses, and letting those xeric grasses go through a period of drought in the late summer.
SPRING (Anthrinilic diamides): Measures taken in spring target the late larval grub stage of the Japanese beetles, just before the final instar, or molt, into their adult form. Carol explained that there is now a new class of pesticide called anthrinilic diamides. These work by opening the calcium pathways inside cells. This leads to muscle paralysis and the death. On product labels, the compound name listed as the active ingredient is Chlorantraniliprole.
One of the great things about this product, Carol commented, is that “the insects that it targets have a sensitivity that is three to four thousand times greater than mammals, birds, fish and other insects. It is incredibly low toxicity.” However, even though the product is low toxicity, it should still be applied with long-sleeved shirt and pants and shoes. “This is not a flip-flop moment,” Carol laughed. “But the label specifically addresses bees. It is not toxic to bees.” It is available commercially as Acelepryn® and Scotts Grub-Ex®. It should be applied when the grubs are returning to the surface, from early April through the end of May, with early April being best.
SUMMER (Hand-picking and Foliar Sprays): In summer, control measures are targeted at the adult beetles. Traps are not recommended, because while they are very good as a monitoring device, they will attract more Japanese beetles to your yard. Hand-picking is effective against the adult beetles, although it must be done several times a day. “The natural response of this insect, when it feels threatened, is to play dead,” Carol said. “It will release the plant and drop to the ground. You need something big enough to catch it in that will kill it, and soapy water is effective.”
Foliar sprays are another option against adult beetles. Acelepryn® is available in a spray form. Another option is products derived out of the Neem tree, an Indian lilac. Carol commented that many of the Neem oil products have had azadirachtin removed. “This is a shame,” she explained, “because azadirachtin is a compound that is also produced by the Neem tree and it is a very effective insecticide.” It is a feeding disruptor that interferes with the ability of the insect to molt. BioNEEM® has azadirachtin left in it.
One problem with BioNEEM® is that it must be re-applied about every three days. The much larger problem is that it should not be applied when bees are visiting. This would be when plants are blooming or near bloom.
Another product Carol discussed was Bacillus thuringiensis galleriae. There are many varieties of BT, and each affects radically different insects, depending on the strain. For Japanese beetles, Btg is needed. “We spray this on the plant, and the Japanese beetles must feed on it. Crystalline proteins develop in the central stomach and literally tear the stomach apart. So they get a killer belly-ache,” Carol said, “but it takes three to five days to get the satisfaction of seeing dead beetles. It is a really sustainable choice.”
One of the challenges is to find these products. Carol warned that they will fly off the shelves, and suggest that we start shopping now. Bacillus thuringiensis must be stored in a climate-controlled area, because it can be damaged by heat. It should not be stored in a shed or garage.
LATE SUMMER (Parasitic nematodes and Milky Spore Bacteria): One biological control for Japanese beetles is parasitic nematodes or microscopic worms. The parasitic nematodes Heterorhabditis is effective against white grubs, in a soil system that is kept moist. The moisture is important. “There has been real hesitation,” Carol noted, “to recommend parasitic nematodes being introduced into our landscapes in Colorado because we are routinely dry. But a turf grass situation, where the female chooses to lay her eggs, is generally kept moist enough to support these parasitic nematodes.” The grub is vulnerable to nematodes just after egg hatch. Therefore the Heterorhabditis must be applied in August, on a cloudy day or in the evening, without much sun. “You have to give the nematodes a bit of a chance to get into the soil and not burn up.”
Another option for Japanese beetle control is Paenibacillus popilliae, or Milky Spore. “You pour this on your soil, and the grub ingests it. The spores will hatch inside, and they colonize the body of the grub. I think we should be applying this to our soils, but expect it to take about seven years or longer for it to build up in our soils to a level that is helpful to us.”
Carol warned that none of the measures she discussed will be completely effective against Japanese beetles. Even if the larvae can be completely controlled, it may have no impact on the number of adults, because the adult are strong flyers. DRS members will need to use multiple approaches. As Carol said, “it is a labor of patience.” And that’s a lot like rose-growing itself.
This article first appeared in the May 2017 issue of “The Rose Window,” the on-line publication of the Denver Rose Society.