Phone calls indicate that grubs are already causing turf damage

A recent grub question I had reflects many emails and phone calls this week about lawns, athletic fields and golf courses.

Roger’s question is typical of many questions I received this week. The unusually warm spring followed by a hot and dry July has caused Japanese beetles, European chafers and June beetles to emerge earlier than usual, deposit eggs early, and grubs to develop rapidly in the warm soil. Consequently, we are seeing grub damage to lawns, athletic fields and golf courses more than a month earlier than we do in most years. Adding to the problem is that many lawns have a thin root system because of the extremely hot and dry conditions in July and early August.

Turf with a poor root system is highly susceptible to grubs because it doesn’t take very many grubs (maybe five or so per square foot) to devour all of the roots, which will cause the turf to turn brown and die quickly if the soil is dry. If you have enough grubs, even moist turf can die in patches. The grub problem is even being found in some irrigated lawns where just enough irrigation was applied to attract Japanese beetles to deposit eggs, but not enough irrigation to keep the turf actively growing. So, we are seeing lots of European chafer grubs and turf damage on dry lawns, and on poorly or minimally irrigated lawns and athletic fields, and we are seeing lots of Japanese beetle grubs on turf that had enough moisture in July and early August to attract the females for laying eggs. I am hearing reports of anywhere from five to 40 grubs per square foot. Even five grubs per square foot can cause damage to a stressed lawn with a poor root system. Unfortunately, after this summer, most of our lawns meet these conditions.

Grub damage
Grub damage in a Michigan home lawn.

If five or more grubs per square foot are found in stressed lawns, you may want to begin irrigation immediately and treat the lawn with Arena or Aloft now. Athough these two products and other nicotinoid insecticides work best when applied from June to early August, they have also worked well in many efficacy tests conducted in September and early October. They may not work very well later in October when soil temperatures cool to below 60 degrees Fahrenheit.

An alternative is to apply Sevin (carbaryl) or Dylox (trichlorfon) at the labeled rate for grub control. Sevin and Dylox usually give 50 to 75 percent grub control when applied in September. They will not work as well in late October. One problem is that Sevin and Dylox degrade rapidly in soil with a high pH (above 7.8). For lawns, athletic fields or roughs with a high pH soil, a second application of Sevin or Dylox may be needed twoweeks after the initial application. Arena and Aloft work in soils with a wide range of pH.

Other nicotinoid insecticides (Merit, Allectus, Meridian and others) may also work at this time, but have been less consistent in tests when they were applied in September or October. One thing is clear: Sprayable formulations of insecticides applied for grub control work best when applied to moist turf and when they are watered-in immediately after application with 0.25 to 0.5 inch of irrigation. Granular formulations are more stable, but should be watered-in or rained-in within a week of application. We have consistently seen reduced levels of grub control when insecticides are not watered-in.

Dr. Smitley's work is funded in part by MSU's AgBioResearch.

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