Controlling Grubs

This package containing 50 million beneficial nematodes arrived by express delivery last week. There are thousands of species of nematodes, worm-like microscopic organisms; and, while some can damage plants by feeding on their roots and foliage others,are considered "beneficial" because they they will attack and feed upon lawn and garden pests.  Beneficial nematodes can attack a wide variety of soil dwelling pests releasing a bacteria that will multiply and eventually kill their host. The nematodes will then exit the insect body and look for a new victim to infect. I have been using them for years to keep lawn grubs under control.  It is important to select the right kind of nematode to address the particular pest(s) of concern. For lawn grubs the recommended type is of the Hb (Heterorhabditis bacteriophora) variety. These nematodes will seek out relatively stationary pests such as grubs. Another variety Steinernema carpocapsae will attack more mobile pests such as fleas and army ants. Because nematodes are alive they need to be refrigerated upon arrival and applied under the right conditions to survive. Ideally the soil should be warm and moist as water facilitates the distribution of the nematodes in the soil. Also, the target pests need to be present at the time of application, or the nematodes will die. To address lawn grubs, late summer, after new beetle larvae have hatched and are actively feeding is the ideal time. They can also be applied in the spring, but the grubs will be larger and more difficult to kill. Also, in the spring, the soil temperature may not be warm enough for the nematodes to thrive.

I selected Saturday for the first application as the forecast was for rain showers in the afternoon. As soon as it started sprinkling, I divided the package into the number of applications needed to cover our yard, mixed in water and applied with a watering can. Unfortunately, the soaking rain I was looking for never arrived. I then spent the next few hours moving lawns sprinklers around the yard hoping that this was adequate for them to survive. Since the nematodes I purchased arrived in a powder format and are not visible to the naked eye, there is some trust involved that they are living creatures and will do their job.

Having had infestations of grubs in the past, it is fairly easy to recognize the tell-tale signs of lawn damage from grubs. The grass will turn yellow in patches and becomes very easy to pull up by the roots. I prefer to be proactive and treat at the first signs of damage. There is no need to panic, however, if you find a few grubs in your lawn. A healthy lawn should be able to handle several grubs per square foot. If you dig up the grass and find more than ten grubs per square foot, or if you see evidence of damage, along with confirmations that grubs are in the soil, then treatment may be needed. 

I have found that the best approach is multi-faceted. If you have a problem with Japanese Beetle grubs then Milky Spore powder is a terrific organic approach to use as well. It is easy to obtain at local feed stores, and if you purchase the concentrated powder, one application can last up to fifteen years. Once infected with milky spore, the infected grubs will die. When they do, additional spores will be released that can infect other grubs. It is important to note that Milky Spore only affects Japanese Beetle grubs, other beetle larvae will not be impacted. Another approach available to control grubs is a botanical pesticide called Azadirachtin which is derived from the fruits and seeds of the Neem tree. I have tried two products. The first is AzaSol, which is a concentrated powder that has to be  mixed with water prior to application. This is available from Arborjet http://www.azasol.com/. The second product  is  Safer Brand Grub Killer. The later was very easy to use as it comes ready to apply in a liquid form complete with a hose adapter. Since any type of pesticide can also harm nematodes in addition to the target pests, you should not apply them within several weeks of each other. I apply milky spore no more often than every ten years; and, if necessary, azadirachtin in the spring and nematodes in late summer.

Every year the number of beetles (e.g. Japanese, European Chafer, June Bug) will vary, If it is a particularly bad year for beetles in your yard, you will most likely have a problem with grubs later in the summer and fall.  Grubs are part of the food web, being eaten by birds and small mammels. However this web has been disrupted by the introduction of so many non-native species. As their names imply Japanese beetles and European chafer beetles are not native to the United States and Mother Nature may therefore need a little extra help in keeping their populations in check. However, under no circumstances should pesticides containing neonicotinoids (found in many synthetic pesticides) be used. This class of chemicals has been linked to the population decline of bees and other pollinators. Although the U.S. EPA is not set to complete their review of these chemicals until 2019, their use has been severely restricted by a partial ban from the European Union in 2013.