onspecialtycrops

By Melanie Filotas, Specialty Crops IPM Specialist, OMAFRA and Hannah Fraser, Entomology Program Lead – Horticulture, OMAFRA

With the dog days of summer upon us, it’s once again Japanese beetle season.  Adult beetles are active in much of southern Ontario.  In many horticultural crops, Japanese beetles can be controlled with insecticide sprays, however for some specialty crop growers, there are no registered products for this pest, or available products are very expensive.  At this time of year, we get a lot of questions about non-chemical management options for Japanese beetles.

In this case, it helps to have a basic understanding of the biology of this pest.  The adults you see now started to emerge from the soil in June, and will remain active into August, congregating on the leaves, flowers and fruit of over 300 plant species to feed and mate, often in large numbers.  They can fly considerable distances between host plants and egg laying sites, which are typically sunny areas with adequate soil moisture, moderate soil texture and short grass.  The eggs hatch into grubs (larvae) within 2 weeks and feed on roots in the soil into the fall, moving deeper into the soil as temperatures drop to overwinter.  Grubs move back up as temperatures rise in the spring and feed in the soil again for 1-2 months before pupating into adults.

The key points to take from this are (1) the adults and grubs feed on different food sources and are present at different times and (2) they are landscape-level pests, meaning that controls implemented on your land will only affect insects present there, so more beetles can continue to move in from other areas where controls were not implemented.  Both these factors influence control options.

Figure 1- Japanese beetles aggregating on hazelnut leaf

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