Grub Watch: What golf course superintendents should look for this fall. (E0016TURF)

There are typically two species of grubs that can cause damage on golf courses in Michigan.

There are typically two species of grubs that can cause damage on golf courses in Michigan. In general, the Japanese beetle is more common in irrigated turf and the European chafer in dry rough, but frequent rain in July and early August can make the rough look pretty good to female Japanese beetles when they are laying eggs. Consequently, golf courses can have more Japanese beetle grubs than usual in the rough plus the usual numbers of European chafer grubs. Signs that Japanese beetle or European chafer is active on your golf course may include skunk damage and some patches of dead turf that die during late summer and early fall droughty periods. Check around damaged areas for the presence of white grubs by pulling back some turf near any dead patches and counting the number of grubs per square foot.

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Scouting is a critical step in evaluating pest thresholds.

Turf damage may begin to occur any time after Labor Day. Usually damage from Japanes beetle will not occur on irrigated areas unless there are very high numbers of grubs, because present as healthy, well maintained turf will tolerate up to 15 grubs per square foot. Watch for damage over the next four weeks where more than five grubs per square foot are found in dry turf, and where more than 15 per square foot are found in irrigated turf.

  • This fall. Spot treat damaged areas and heavily infested turf with either Dylox (triclorfon) or Sevin (carbaryl). Dylox and Sevin do not last very long when the pH is 7.8 or higher. Sprayable formulations will not work well unless they are watered-in immediately after application. Granulars are more stable after application but must be watered-in with 1/2 inch of irrigation or rain before they affect grubs. Check treated areas about three weeks after application to see how well the insecticide worked.  
    Use a map of the golf course to mark portions of fairways and rough where grub damage is observed. This map can be used to apply a preventive grub control compound next summer.
  • Reseeding. If grubs are present, an insecticide should be applied before reseeding. Grubs can eat grass seed and the roots of new grass plants.
  • Next spring. Dead patches of turf may develop in the spring. Watch for the first signs of grub damage, sample for grubs and treat hot spots with Dylox or Sevin if grubs are found.
    Merit (imidacloprid), Arena (clothianidin), Meridian (thiamethoxam), Acelepryn (chlorantraniliprole), Mach2 (halfenozide), Allectus (imidacloprid plus bifenthrin), and Aloft (clothianidin plus bifentrhin) are preventive compounds and will not kill grubs when applied in the fall or spring.

Preventive compounds are highly effective against young grubs for the first month after egg hatch and therefore should be applied between late May and August 15th.

Battle plan for next year

Although the hot spots for grub damage move about somewhat from year to year, depending on adult beetle activity, there is a tendency for the same areas to be hit repeatedly.

  1. Apply Arena, Meridian, Mach2, Acelepryn, Aloft, Merit, or Alectus between late May and August 15th.
    Refer to your fall grub damage map and treat the most heavily damaged areas. Treating all the fairways is usually unnecessary.
  2. Watch for the first signs of grub injury in September and October, and spot treat where needed.
    Follow the directions in the first and second paragraphs.