Rose Report Understanding Japanese Beetles, the life cycle, and control options
O
ne of the most frequent questions I get about roses is how do I control the Japanese beetles. First and foremost I would say do not put up a Japanese beetle trap. This will attract more beetles to your garden. Understanding the life cycle To understand how to effectively control the beetle a basic understanding of the life cycle is needed. The adult beetles that you see in the garden will live for about two months and in our area that is mid to late June to about the first week in August, depending on the year. During this time their sole purpose is to mate. The female lays eggs in the first few inches of soil a total of 40 to 60 times during their short lives. An insecticide to kill the adults can be sprayed but you would need
to spray every day and in the process many beneficial insects would be killed making this an undesirable option. Hand picking them on a daily basis especially in the morning is best, especially as the females leave the plants in the afternoon to lay their eggs. A container of soapy water is best when picking off beetles, by simply dropping them into the soapy solution you will eliminate them without harming the beneficial insects. The grubs grow quickly and by August are almost full sized at one inch. Grubs feed on roots of turf grass doing best in well irrigated lawns. Mid-summer rainfall and adequate soil moisture are needed to keep eggs and newly hatched grubs from drying out, although grubs are relatively drought resistant and will move deeper into the soil if conditions are dry.
JUDY PENNER Expert Rosarian 8
September 2020 | kcgmag.com
Once the eggs are in the ground the developing grubs remain in the soil for the next 10 months. During the fall when the soil cools to about 60 degrees Fahrenheit the grubs move deeper into the soil. In the spring when the soil temperatures climb above 50 degrees they move up into the root zone following a feeding period of 4-6 weeks. The grubs pupate in an earthen cell and remain there until emerging as adults. Grub control requires properly timed applications of a soil insecticide to infested turf and flower beds. Control possibilities Two different strategies are available for controlling grubs with insecticides – Curative and Preventative, and regardless of the product, post treatment irrigation
should be applied to water the insecticide residues into the root zone. The Curative Control is applied in late summer after the eggs have hatched and grubs are present. Insecticides used for curative control have a relatively short residual effectiveness (two to three weeks or less). The best time to apply is early to mid August. A control can be used in late August or September but as the grubs grow larger they are more difficult to control. It’s best to get them when they’re young. The Preventative Control is applied as insurance before potential grub problems develop. Preventative Control requires the use of insecticides with long residual activity in the soil. Several such products are available and give excellent control of newly hatched white grubs when applied weeks or even two to three months before the grubs have hatched. These insecticides have a selective activity on target pests and pose little hazard to humans, pets and birds. Curative insecticides include but are not limited to Dylox and Bayer Advanced 24 hour grub control. Preventative insecticides include but are not limited to Merit and Bayer Advanced lawn and season long grub control. Applying your grub control at the proper time of the year will optimize the effectiveness of the grub treatment. Write it down with your other garden tasks for the month, as a reminder. It might make a difference. Remember to stop and smell the roses.
Judy Penner is Expert Rosarian at Loose Park, Kansas City, Missouri. You may reach her at judy.penner@kcmo.org.
