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The BugDoc answers questions on season-long grub control

May 18, 2015 -  By

Grubs appreciate dense turf with organic matter. Photo: Alton N. Sparks, Jr., University of Georgia,

Editor’s Note: May 14, Dave “the BugDoc” Shetlar, Ph.D., addressed season-long grub control in a webinar presented by Landscape Management and sponsored by Nufarm. Here are some questions the audience had for the BugDoc and his answers.

Q: What is the ideal application timing for grubs in Florida?

BugDoc: It depends on where you are in Florida. The southern third of Florida has some species of white grubs that may be undergoing two generations in a season, while most of the others are doing the normal one-year life cycle. Southern White grubs are often regulated more by wet and dry seasons. Some species come out when the summer doldrums arrive, often emerging and laying eggs after a good rain, and others fly in late spring. If using products like Acelepryn, this should last for several months in the turf environment, so applications in May through July should hit most of the grubs that are present. Clothianidin has the longest residual activity of the neonics and it also should be effective for this time period. If using imidacloprid or thiamethoxam, the residual activities are probably no more than six weeks in Florida.

Q: Will you be covering warm season turf and the effect of drought on grub control?

BugDoc: Drought occurring at the time of white grub egg laying generally reduces the white grub populations. Drought, per se, shouldn’t reduce efficacy of grub insecticides unless you are applying liquid formulations that can be degraded by sunlight (especially imidacloprid). Granules also have to be moistened (irrigated or rained upon) in order to release their active ingredients.

grubchartQ: When is the best timeframe to treat for grubs and what chemicals are most effective during that timeframe?

BugDoc: Here is a chart that shows efficacy when insecticides are applied in May or June or July, first half of August and second half of August.

Q: What other insecticides are labeled for grubs, just like Arena, after grubs emerge? I work in California.

BugDoc: Virtually all the grub insecticides work well if you apply them when the grubs are in the first or second instars. Once you get into the third instars, they may not be feeding and it takes a lot more insecticide to kill them. At that time, only trichlorfon (Dylox), clothianidin (Arena) and carbaryl (Sevin) seem to have siginificant contact activity.

Q: What product have you found works best to control grubs and is safe for pets and vegetable gardens?

BugDoc: This is a leading question. Environmental Protection Agency (EPA) states that no insecticide can be claimed to be “safe” to people, pets or the environment. You can only state that they are less toxic (or in the case of some of the newer insecticides—practically non-toxic). None of the neonics or anthranilic diamides have been shown to have significant animal (meaning mammalian) toxicity. Vegetable gardens should not be an issue, as you are supposed to be applying grub control products to the lawn.

Q: There is much “buzz” about Heterorhabditis nematodes. Has the technology advanced enough to make it a viable alternative to neo-nic preventative treatments?

BugDoc: Insect parasitic nematodes in the genus Heterorhabditis have consistently performed better at killing soil-inhabiting insects, such as white grubs. I’m not sure this has changed, but the “buzz” has occurred because some states are prohibiting all pesticide applications to school grounds and municipal grounds. This leaves folks with the nematodes as being the only effective option. Even the new Bacillus thuringiensis (Bt) toxins are considered pesticides and are not allowed in these cases. The nematodes do not have any preventive action. They have to be applied when the grubs are actively feeding near the soil-thatch interface. The key to success is to get fresh nematodes and apply them immediately after receiving, and keep the treated turf irrigated for four to five days after the application.

Q: How can I “reteach” customers about spring applications of products, such as Acelypryn, after years of making mid-summer applications of neo-nics? Also, what are some other options to move away from the neo-nics, if for no other reason than public perception?

BugDoc: I don’t see customers as the real issue. The most common trouble is how a lawn care company should fit in an insecticide application at the time that the company has traditionally applied a broadleaf herbicide. Acelepryn works very well into mid-summer, but when you use it that way, you lose its effects on other insects, especially billbugs.

Q: Have you used cedarwood oil products for grub control?

BugDoc: None of the EPA Section 25(b) materials are effective at killing white grubs unless you drench the grubs (basically drown them).

Q: When is the best time to treat for grubs in lawns?

BugDoc: For cool-season zones, April into mid-August if using Acelepryn, May to mid-August if using clothianidin; June to mid-August if using imidacloprid or thiamethoxam.

Q: When is the best time to start applying a preventative grub treatment to lawns here in Southern California?

BugDoc: Like south Florida, the white grub biology in Southern California has not been well studied, but there is some evidence that the annual grub species are able to wait in the soil until rainfall events occur. They will then fly and lay eggs over a few days following such rains. I would think that May through June would be the best times.

Q: How often are applications of chemicals required to control grubs?

BugDoc: It depends on the area treated. For home lawns, the beetles can fly from one lawn to the next without trouble. So if the neighbor doesn’t treat, your customer is susceptible to getting white grubs every year. On golf courses, where superintendents have gone wall-to-wall, they can often skip a year, perhaps two.

Q: Do grubs have a circle so they come back every few years like other insects or viruses, or are grubs are a problem that comes back every year?

BugDoc: Most white grub population “booms or busts” are more related to the soil moisture present at the time the white grub species are laying eggs. Dry soils do not allow for white grub eggs to hydrate, and they quickly die. However, in irrigated turf, this never occurs. In short, when we get two or more years of “ideal” grub weather during egg lay, the grub populations can explode.

Q: What point in the life cycle is the most efficient for killing grubs?

BugDoc: All grub insecticides work best when they are present at the time that the first instar grubs arrive at the soil-thatch interface to feed.

Q: I need help with identification of grubs and treatment.

BugDoc: Most land grant universities have fact sheets, bulletins or websites that help identify the different white grub species. Just do a search for “white grub identification” or look for “grub raster patterns.”

Q: We know that spring and summer months see an increase in insect activity. Can grubs be a winter problem also?

BugDoc: Depends on where you are located. The European chafer is a true “cold season” grub species. It is the last to go down in the fall and first to surface in the spring, often as early as February. In Southern zones, there are some species that can resume feeding whenever the turf temperatures rise to 70 F or higher.

Q: What will be our options for grub control if neonicotinoids go away?

BugDoc: At present, antranilic diamides, like Acelepryn and Ference, but new Bt products are available.

Q: What is the most cost effective preventive insecticide available for grub worms?

BugDoc: At this point, generic imidacloprid is about the least expensive material that can be used as a preventive. Sevin is also available, but it is only effective as a curative treatment.

Q: What are the earliest signs of grub activity?

BugDoc: It depends on the type of turf, but slow growth and afternoon drought stress are early signs.

Q: What cultural practices can be used to help control an outbreak?

BugDoc: Keep turf dry to the point of dormancy at the time of beetle flight and egg lay. Keep thatch to a minimum.

Q: What’s the best post-treatment option for the Midwest?

BugDoc: Irrigation, of course, but without irrigation, use a granule that can last until a rainfall event occurs.

Q: What extra equipment will we need to address grub control?

BugDoc: You’ll only need good sprayers and/or spreaders.

Q: It seems most of the articles I have read tend to focus on ID once damage has already occurred, which usually leaves the technician digging into the soil at the location of the damage. Would it be best to pre-treat prior to the summer/fall months?

BugDoc: Early grub detection is difficult. Even entomologists have to wait until the grubs are second instars before they can be sampled. This means that mid-August turf sampling (taking a few cores and splitting them open) is the best option, but most don’t take the time to do this.

Q: Do grub control insecticides harm the bee population?

BugDoc: Neonics sprayed onto flowering weeds in turf pose a risk to pollinators. Neonics applied to turf without flowering weeds are no risk. Neonics applied as granulars do not end up in the nectar and pollen.

Q: For the past two to three years, Chafers have been a larger problem for us on the East Coast. Considering the life cycle and control products, how can I use one strategy to effectively control both chafers and white grubs?

BugDoc: I’m assuming that you are referring to European chafers, as there are five common native masked chafer species: Northern, Southern, Southeastern, Midwestern and Western. European chafers and masked chafers are white grubs. European chafers and the Oriental beetles have been more difficult to control because they seem to be slightly less susceptible to some of the neonics, especially imidacloprid and thiamethoxam. When dealing with the European chafer or Oriental beetle, you probably have an optimal window of four weeks rather than the normal six to eight weeks. So, make the application in July into early August rather than June or July into early August.

Q: My customers want permanent soil management, parasitic nematodes and milky spore solutions. They have heard of these ways to control and prevent grubs and are not interested in poisoning beneficial insects with the likes of pesticides. How do I serve my customers?

BugDoc: If they are willing to pay, the nematodes and new Bt products will probably satisfy their needs for grub control. The milky disease on the market only contains the strain that is active against Japanese beetles, not the other grub species. It has been well documented in the literature that applying milky disease does not increase the infection rate, which is usually in the range of 15 to 20 percent. Obviously, Acelepryn has the least non-target effects (killing beneficials) of the rest of the standard grub insecticides.

Q: Will getting rid of grubs help get rid of moles?

BugDoc: Nope! Moles’ primary food are earthworms, but they will “dine” on white grubs when they find them.

Q: What are the effects of grub control chemicals on earthworms, our best aerators, and the birds that eat them?

BugDoc: Virtually all the neonics and anthranilic diamides are harmless to earthworms. Carbaryl (Sevin), and some of the pyrethroids can lower earthworm populations.

Q: How do you check for a grub problem as early as possible?

BugDoc: Cup changer samples have been the easiest tool to use in our research.

Q: What are the best products for safety issues?

BugDoc: Safety to who or what? Obviously, anthranilic diamides (especially Acelepryn) get the “least toxic” designation for non-insects in the environment, and this is low in toxicity against most adult insects (like bees). Acelepryn is also the first insecticide to not need an EPA signal word on the label.

Q: What are the latest granular chemical control strategies?

BugDoc: Virtually all the common grub control products are available in granular formulations.



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About the Author:

Dave Shetlar, Ph.D., is associate professor of landscape entomology at Ohio State.

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