Keeping mole crickets in check
Of all the pest challenges facing turf, the soil insect pests can be the most challenging to diagnose and treat. There are a number of reasons for this difficulty in attaining effective control. The mere fact that the insects are hidden and somewhat protected by the soil in which they live is a major factor.
Several turf insect pests live in or near the soil surface, including various white grub species and mole crickets. White grubs are certainly the most common turf insect problem in North America, but mole crickets represent the most serious soil insect pest of turfgrass in the South. The damage and cost of control of this pest is measured in terms of tens of millions of dollars in many states and hundreds of millions of dollars in Florida. Mole crickets range as a serious pest from North Carolina down to Florida and across into Texas. A few isolated outbreaks have occurred in Arizona and California as well.
The most important species, the tawny mole cricket and the southern mole cricket, are pests introduced (accidentally!) from South America. A native species, the northern mole cricket occasionally causes problems in the South and other parts of the country. In South Florida, another introduced species, the short-winged mole cricket, causes serious problems, but its inability to fly has limited its geographic spread.
In most locations, the tawny and southern mole crickets have one generation per year. However, some areas of southern Florida may see two generations.
Why are they so hard to control?
Mole crickets are unique creatures that are well-adapted to their subterranean environment. Their extensive tunneling and aggressive behavior make them destructive and demand attention. The lack of above-ground symptoms while the crickets are small (and easier to control) makes them difficult to detect in a timely manner.
But the challenges of managing mole crickets go far beyond the fact that they live below the soil surface and avoid our detection. Recent research has shown that mole crickets are capable of holding their own against our best efforts. The best way to understand why is to review their life cycle and behavior.
To reiterate, mole crickets typically have one generation per year. Adults fly, mate and lay eggs in the spring. Egg laying usually takes place in areas of sufficient soil moisture to ensure good egg survival. Once the eggs hatch (in about three weeks), the small nymphs begin to feed. This is generally in early summer. At this time of year, warm-season turf, such as bermudagrass, should be entering its stage of rapid growth. No one would ever suspect what is occurring beneath the soil surface.
In just a few weeks, the cricket will have grown to a half-inch in length or more. At this size they are suddenly causing a lot of visible damage, but they are also more difficult to control. The longer you allow them to feed and grow, the more difficult the task of managing them. Large mole crickets require a more potent dose of insecticide for effective control.
In addition, the larger the cricket, the greater its ability to tunnel deep into the soil. This useful ability allows it to avoid contact with many control agents including conventional pesticides and some biological control products as well. As you might guess, this is bad news for anyone who waits too long to initiate control strategies. Waiting until you see obvious damage may mean you've waited too long.
What's the best approach?
There are several approaches for effective mole cricket control. All of these approaches seek to control the crickets before they get large. Baits can be relatively effective against larger crickets, but even with baits, it's not by design that you allow the crickets to get large prior to initiating control.
- Preventive controls
A preventive approach would include a long-residual product such as fipronil (Chipco Choice) or imidacloprid (Merit). The residual activity of Chipco Choice is such that it can be applied well before egg laying and will still control the nymphs as they hatch. Fipronil may be a little slower acting than some other products, but it does get the job done. A new formulation of fipronil (Top Choice) will be available for fire ant control, and the slower action of this product lends itself well as a fire ant bait. The label indicates that mole cricket suppression will also be obtained with this formulation, and my experience is that, applied as a surface broadcast, it is quite effective against mole crickets. Whether you use fipronil or imidacloprid, the main point is not to wait until the crickets get too large before you initiate control.
You can apply imidacloprid early, but not too far in advance of egg laying. Applying at early egg hatch is a good target. As the eggs continue to hatch, the residual activity of imidacloprid is so sufficient that it will continue to kill the small nymphs. Timing is critical for acceptable control. If you apply the product too early, its residual activity wears off before all the eggs hatch. If you apply it too late, it has difficulty controlling large nymphs.
Applying imidacloprid for mole crickets may also result in good control of white grubs. However, there may be exceptions, such as when the resident grub population consists of May/June beetles and a portion of the population is in its second year.
An important point about fipronil is that, contrary to some reports, this product does not create white grub problems. But it does exhibit only limited effectiveness against grubs. It's possible that after controlling mole crickets with fipronil, any grubs that are present might become more noticeable due to the lack of mole cricket damage.
- Curative controls
Other approaches to controlling mole crickets include products such as the pyrethroids and acephate. Just as with imidacloprid and fipronil, application timing is critical. The residual activity of these products is relatively short and they must be applied just as the bulk of the mole crickets have hatched.
My general rule of thumb is to begin treatments (with short-residual products) 2 to 3 weeks after you begin seeing hatch. While spring hatch is influenced by how warm or cool it has been, rainfall also has an influence. Above-normal rainfall can move up the timing for egg hatch, while drier conditions can delay it.
Soil moisture can also play a significant role in influencing the level of control you obtain. When the soil is hot and dry, don't expect any product to work too well. The product may have a greater tendency to bind tightly to organic matter and soil. Also, under drier soil conditions, the crickets have a tendency to reside deeper in the soil as well. These factors reduce the likelihood of obtaining good control.
My research has shown that, if soil is dry, you should take steps to improve soil moisture in the days preceding treatment. If you are going to put a lot of water on, put it on prior to the application of the product. Start several days before you plan to treat.
Additionally, remember that too much water following treatment can be detrimental. A light irrigation is usually sufficient to water-in the control product. In the case of acephate, no post-treatment irrigation is necessary.
Baits can be effective, particularly against larger crickets. Using the product requires good soil moisture to make sure the crickets are working near the surface. Do not apply baits prior to irrigating or when rain is forecast. I believe that applying any product late in the day will aid effectiveness, but this is particularly true of baits.
Again, I must reinforce the point that timing is critically important for mole cricket control. Large crickets are more difficult to kill. More importantly, large crickets are more capable of avoiding pesticides by tunneling, and the larger the cricket, the longer they can avoid contact. In some instances, their ability to avoid contact with the insecticide may last longer than the residual of the product. This may explain why we sometimes observe an initial reduction in the amount of surface tunneling following a treatment, only to see it dramatically increase a few weeks later.
The key is in understanding pest biology to ensure accurate timing and good record keeping so that you can map and monitor high-risk locations. With this information at hand, you can cost-effectively manage this troublesome pest.
DID YOU KNOW?
The male mole cricket's mating call is usually louder if it is made from a tunnel in moist soil. This helps ensure that the female is attracted to an area with good soil moisture to lay eggs.
MONITORING FOR MOLE CRICKETS
You can monitor for mole crickets with a 2 percent soap solution used as a flushing agent. Pour a gallon of this per square yard and observe the area closely for 3 to 5 minutes. Keep good records and build a database over the years to help you understand the timing of the egg hatches and the duration of egg hatch (how long a period of time you keep flushing up very small crickets).
Dr. Rick L. Brandenburg is professor and extension turfgrass entomologist at North Carolina State University (Raleigh, N.C.).
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