September 2013 Web Extra: More grub talk

September 3, 2013 -  By

Editor’s note: In July, Dave “the BugDoc” Shetlar, Ph.D., addressed preventive and curative grub control in a webinar presented by Landscape Management and sponsored by Valent Professional Products. We ran some of the Q&A in the September issue. Here’s a bit more Q&A between Shetlar and participants on this hot topic.

Q: What do you think would be the best way to fix a turf where there are more than two types of grass there? Also, this situation arises when the neighboring turf is different. —Florida

BugDoc: Since you are likely in St. Augustinegrass, Bahia, centipede or even Bermudagrass, this really depends on the dominant type of turf present. Obviously, it would be difficult to seed any of these species, so sod replacement is the only real option. Ouch! That’s expensive. Consultation with the customer to see what he/she wants is the key to making the decision. If you have to sod, then be sure to check with your local supplier to find the best St. Aug cultivar that seems to be resistant to chinch bugs and billbugs. Also, consider some of the newer zoysiagrass cultivars as a replacement for Bermudagrass, even St. Aug.
Q: Is there such a time as being too late or too early to treat for grubs? —North Carolina

BugDoc: Most of the white grub species stop feeding in the fall, after they have developed to a certain point. As an example, Japanese beetle grubs in Lexington, Ky., usually stop feeding in the third or fourth week of September, but they will continue feeding until the second week of October in Columbus, Ohio. Basically, if the grub has taken on a distinctive yellowish look, it has stopped feeding for the season. Since most of our insecticides work best by ingestion, if the grub is not feeding, control will be poor. However, trichlorfon (=Dylox) does have pretty strong contact toxicity. If the grubs are at the surface and you can immediately irrigate in a Dylox treatment with ½-inch of water, you may still get 50 percent to 70 percent control of grubs. The “too early” question is more difficult as it relates to when the beetles are laying eggs in your particular area. If you have grub adults active in late May and early June, then an early May application would be correct. But, as mentioned in the webinar, Wisconsin applications may be best applied in July and early August.

We also have to realize that all the insecticides are different in their effective residual periods. Acelepryn seems to have the longest activity. We have put it down at the medium to high rate in April and killed the new crop of grubs that arrive in July and early August. On the other hand, if you go down at the lowest rate, the April application will run out of effective residues by August. Imidacloprid and thiamethoxam, when applied in the first three weeks of May, seem to lose effective residues by August, but June applications hold in. Clothianidin seems to have longer residual effects with May applications holding strong into August. Dylox only lasts for three to five days and Carbaryl seems to last for 10 to 14 days, if the soil is not active in degrading this molecule.

Q: Is the larval stage the optimum time to treat for grubs or are there more effective treatment times in earlier life stages? —Virginia

BugDoc: Virginia is experiencing an invasion of new grub species. Where you used to be dominated by Japanese beetle and masked chafers, Oriental beetles, Asiatic garden beetles and even some European chafers could be in your working area. Learning which of the grubs are present and their life cycles is the key to success. With that said, the “target” of any grub treatment should be the first instar grub. It is the smallest stage and most susceptible to insecticide residues (and even biological controls). What I wanted you to understand is that, if you match up the effective residual period of your insecticide so that it is in the soil-thatch zone when the first instar grub surfaces to feed, you will get excellent grub control. I know of golf course superintendents that have tried to kill adult Japanese beetles in the hopes of reducing grub populations and we see no correlations between adult control and resulting grub populations. In some zones, grub adults, like masked chafers, don’t feed as adults, so adult control would be impossible anyway.

Q: I’m interested in switching to Acelepryn, but in our own trials we did not have good success with the granular version. Sprayable was good. But we generally start our spray around about May 1 and finish in late June. Can we expect good results spraying during this time frame? And what about mixing with broadleaf and preemergent materials? —Kansas

BugDoc: Obviously, Acelepryn has an environmental footprint that is pretty attractive and it doesn’t come with the “pollinator” baggage that the neonics have been branded with. What has me concerned is the attempt to keep lowering the rate of Acelepryn in order to make it more cost effective. Basically, it will never reach the cost of imidacloprid (Merit and generics), but the cost of the raw material is not the only factor to be considered. As you suggest, Acelepryn may result in callbacks if not applied at the correct time and/or rate. Call-backs are the economic killer in the lawn care industry, so reducing this is a plus. My thoughts are that the 8 oz rate (0.1 lbai/A) is the lowest rate that I would consider and the full 16 oz rate (0.2 lbai/A) would be the best for early (like April) applications. I am looking at 4 oz rates (0.05 lbai/A), applied in July and early August to see if we can still kill grubs with this low rate by making the application at the time that eggs are being laid and first instar grubs are appearing. DuPont didn’t want to go here in the past, but Syngenta wants to now. In all the studies published, we haven’t seen any major difference in performance between granules and liquid sprays, so I’m a bit mystified by your statement that the granules didn’t work as well as you expected. Could this have been a rate issue?

When DuPont had Acelepryn, it was looking at combining it with preemergent herbicides and saw no interference between the chemistries. Golf course superintendents often apply Acelepryn with herbicides, fertilizers and/or growth regulators without issue.

Finally, have you identified the primary grub species you are dealing with? It should be southern or western masked chafers, but May/June beetles have been on the increase. The problem is with the western masked chafer that may delay flight until late July through August. If you are working with this pest, then a later application would certainly be recommended.

Q: In St. Augustinegrass, do the grubs leave white traces (like a fungus) in the soil, approx. 2 inches under what is left of the turf? —Texas

BugDoc: I have never seen this situation though I’ve seen lots of grub damage to St. Aug, especially in the Tampa Bay area. I would suspect that there might be a fungus that is helping decay the organic matter that remains in the soil and the path of least resistance would be a grub or mole cricket burrow.

Q: How do you tell if there is a grub problem, and how do you tell that it’s grubs and not ground pearls? —North Carolina

BugDoc: I hate to be flippant, but you have to get out of your truck and look! Grubs generally eat in the soil-thatch zone and sever the roots in the process. This leaves the turf like a loose carpet, which can be pulled back to reveal the grubs. Classic ground pearl damage appears in irregular circles, often resembling fairy ring, but the affected grass is dead or dying, not greener.

I keep a digging knife with me and I pull up a core of the underlying soil where the dead and live turf adjoin. If ground pearls are present, they should be in the top 2 inches to 3 inches of soil. So, in this case, grubs will be easy to find, but you will have to dig a bit to find the ground pearls. Unfortunately, we still don’t have a good cure for ground pearl infestations, but I would like some folks to try dinotefuran treatments (Zylam) applied in early to mid-May (right after the ground pearl females surface, mate and return to the soil to lay eggs).

Q: We’ve been dealing with 3rd instar June beetles on a very large property we just took over that destroyed about 75 percent of a roughly 10-acre facility at anywhere from 5 sq ft to 10/sq ft. We have hit them hard with Duocide 1 time per month since April and reseeded and things are improving. What type of preventive measures are required from here on out? They don’t have irrigation and soil is very sandy. —Iowa

BugDoc: It has been my experience that native May/June beetles are on the rise in several Midwestern zones. We are not sure why, but my suspicion is that some of the older, long-residual insecticides (like Chlordane) are finally disappearing from the environment. I would recommend contacting your local entomologist or extension person to see if they can put a name to your particular May/June beetle. Most books state that these grubs take two to five years to complete their life cycles, but there are species that can complete their cycles in one to two years. If this is the case, then an application of any of the regular grub insecticides in June or early July should hit the current year’s crop of small grubs. This will have to be repeated the following year to catch any larvae that come from adults that emerge (from the second year). In your zone, applying a granular formulation will also help when no irrigation is possible.

Q: Is it necessary to put preventive applications down yearly and what is the best time frame to do the application? What is the best product that is reasonable for my customers? —New Jersey

BugDoc: If you had all the time in the world, kept records and did some sampling, you could probably reduce the need for grub treatments by 50 percent to 60 percent. But, who would pay for this time and effort? There are “grub” neighborhoods and “chinch bug” neighborhoods (sometimes both). If you know where these hot spots are, these should receive yearly preventive treatments. If you don’t experience grub issues in a particular neighborhood, then curative treatments may be a better option. I covered the efficacy of the grub insecticides in my webinar, so you will have to check the prices for these products.

Q: How long in the soil does Arena last? —California

BugDoc: This is a simple question, but there is no simple answer. First, there is a vast difference between detectible residues of an insecticide and effective residues. I’ve seen reports of detectible residues of clothianidin that are over 200 days. However, it has been my experience that applications of clothianidin applied in early May have sufficient residues in soil to kill new grubs that arrive in early August–basically 90 days. I find it interesting that Aloft’s (contains clothianidin plus bifenthrin) manufacturer, Arysta, guarantees applications of Aloft for grub control if you make the application in May, June or July. I suspect they are looking at the same data that I’m looking at. LOL! It is also my experience that the systemic action of clothianidin is probably only in the 20 to 30 day range (for chinch bugs and billbugs), so the soil/thatch residual action is very different from the surface residual action.

About the Author:

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

Comments are currently closed.