The Truth About Grub Damage/Repair and Control

Forward

With the launch of the new web page, it was decided that I should do a blog to communicate my knowledge of our horticultural practices and to keep our client base informed and educated on what we are doing. I must admit it has been a while since I wrote in any real way: this will be a an educational and challenging process for me that I will quite enjoy. (I hope) So with that being said, here is my first blog… Dan

 

The problem

The most common call we get in the spring and fall about lawns is to look at damage caused by something digging in the lawns. 99% of the time this means white grubs. In Southern Ontario, white grubs are the larval stages of 3 different beetles: European chafer, Japanese beetle and May/June bugs. For years European chafer has been the main problem, but in many areas, the Japanese beetle can be considered just as large a problem. The grubs themselves do cause some damage. They eat the roots of your lawn, causing brown patches where the lawn can be pulled out in clumps. However, in a healthy lawn, this can sometimes go unnoticed, as the grass keeps pace with the feeding. The main damage caused by grubs is their ability to attract skunks and raccoons, who dig up the turf in order to eat them. This can devastate lawns, leaving behind a mangled mess of turned up soil and dead grass, a homeowner’s worst nightmare.

Treatments

 

As with most lawn problems, the best way to avoid a grub problem is to maintain a high level of turf health. This can be done by proper mowing, watering and fertility, but that is an entirely different subject.

For preventative and curative treatments that specifically target the grubs, the options are limited. Under the Ontario Cosmetic Pesticide ban the old chemical treatments for grubs, which were extremely effective, are no longer available. The one option we do have available for us is beneficial nematodes.

As with many currently available lawn care alternatives, when dealing with nematodes it is best to approach the situation with realistic goals in mind. With a nematode application chances are you are not going to solve the entire problem, but reduce the population of grubs. In the early days of the ban, many products listed their efficacy at around 67-75%, although with practice and further research, the number that we seem to be settling on is 40-50%, and this is only if you follow the directions exactly.

Perhaps it is best to back up and explain what beneficial nematodes are. Nematodes are a phylum of tiny organisms that can best be described as round worms. There are over 28,000 species of nematodes, but when it comes to grub control, we are speaking of a very small number of species. The species of nematodes that are applied to lawns cause a parasitic infection in white grubs that result in illness, then death.

The problem then becomes that 1) with nematodes we are dealing with a living organism and 2) we are dealing with an infection.

Let’s address problem 1 first. Nematodes are a living organism. This means that before they make it to a lawn, first the supplier, then the retail outlet, then the applicator and finally the homeowner, must ensure that they stay alive. Nematodes  a) are temperature sensitive, b) live in water, c) are UV sensitive, d) need food and e) can be killed by mechanical means.

a)      When you purchase nematodes they are in a dormant state, usually on a sponge. To keep them in this dormant state, they must be refrigerated. If they have not been refrigerated, the heat will have awakened them and then, without the proper environment, they will have died. This can happen from improper storage at the store, or during transport (which includes bringing them home in the car without a cooler). Also, to survive and do their job, nematodes must be applied when soil temperatures are between 15 and 30 degrees Celsius. 

b)      Beneficial nematodes live in water. If they dry out, they will die. This means that they are mixed with water prior to application and that the environment to which they are going must have water. So before applying beneficial nematodes, the lawn area must be thoroughly watered to a moist but not wet state. About an hour with a standard fan sprinkler. Immediately after an application, the area should be watered again to wash the nematodes into the soil. In order for the nematodes to survive long enough to work, the lawn area should be kept from completely drying out for a couple of weeks after the application.

c)      Nematodes are very sensitive to UV radiation. For this reason, it is best to apply nematodes in the early morning or late at night to avoid direct exposure to the sun’s rays. Long periods of time in an exposed tank will also cause the nematodes to be killed by UV rays.

d)      As living organisms, nematodes need food to survive. In their case, the food supply is the grubs. This is the reason the preventative applications do not always work. If there is no food in the soil when they are applied, or even if they do not reach their food source in time, the nematodes will starve to death. 

e)      Although nematodes are invisible to the naked eye, they are large enough to get caught in sprayer filters. Small filters will shred the nematodes, so you must remove screens and filters before application.

All of these things must be kept in mind when applying nematodes. If any of their needs are not met, just like people, they will not survive for long and thus not have the desired effect.

The second major issue is that nematodes are an infection. For an infection to be a successful means of control, the parasite (nematodes) must a) reach its host, b) infect its host and c) do enough damage to the host in order to kill it.

a)      Nematodes travel through water, so the only way for them to reach the grubs is to move through the water in their environment. This is another reason the pre water, apply in water and post water are very important.

b)      Though there is little in our control that can affect this step, there are some things that can help. The most important one is timing. Grubs are most accessible when they are feeding and closer to the surface. During the winter and early spring, grubs are hibernating well beneath the ground and in the early summer, they have emerged as beetles or are still just eggs. So, applications during these times are rarely effective.

c)      This is another issue of timing. Like humans, the older a grub is, the better it is able to fight off infection. The two most common white grubs, European chafer and Japanese beetle, follow a similar life cycle. They are born from eggs in the mid summer (early August give or take a couple of weeks each season) and begin feeding. It is then, when they are young and vulnerable in late August, that it is best to apply nematodes. The grubs then mature through the fall, hibernate through winter, and emerge in the spring much tougher. In spring, nematodes can still infect and kill grubs, but the success rate will be much lower since the more mature grubs are more successful fighting off the infection. Then, in mid-May, they go into a pupal form, where nematodes are completely ineffective. Shortly thereafter they emerge as adult beetles and begin the cycle again by laying eggs. As there are no grubs in the soil, early summer applications are also not useful. The one exception to these rules are May/June bugs, who follow a two year cycle. If you have May/June bugs, then a spring application may be more successful as the grubs in the first year are still vulnerable. You must also keep in mind, that like humans, not all grubs will succumb to the disease no matter what is done.

As you can see, the application of nematodes to control white grubs leaves many areas in which to err and thus reduce the effectiveness of the application. That is why, even when using a professional service, you must follow all directions precisely in order to achieve some degree of success.

Lawn Repair

This article has run on much longer than I expected, so I will defer this topic to the next entry. I look forward to writing my next post!

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