Regional Gardening Reports :: National Gardening Association

In the Garden:
Northern & Central Midwest
August, 2008
Regional Report

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Japanese beetles have voracious appetites.

Midsummer and Fall Insects

Most of us in the Midwest had a wonderfully wet and somewhat cool start to the summer. It's great for us, but it's also great for the bugs and diseases. Here are some things to watch out for as we crest summer and move toward fall.

I have seen scale insects on plants such as euonymus, lilac, magnolia, and maple. If there's a positive side to this, each type of plant has its own specific variety of scale, so maple scale doesn't infect magnolias. Scales are insects that suck plant juices and can stress a plant to the point that it succumbs to other diseases and insect attacks.

Controlling Scale
The insect is soft-bodied, but to protect itself it secretes a hard shell that is impervious to insecticides. Although you can use a systemic insecticide that the scale ingests when it sucks plant sap, they can also be controlled by plugging the breathing hole in the shell. Horticultural oil is a safe material that does just this, and it is available at most garden centers. Be sure to use it only as the label indicates to avoid plant damage.

Japanese Beetles
We've been hearing so much about Japanese beetles lately and I've seen pockets of damage throughout my garden. These shiny, green beetles turn leaves to lace by eating all the tissue between the leaf veins. In high numbers they can cause fairly extensive damage to ornamental plants. Their other nasty habit is chewing on turf roots, which can cause brown patches in the yard.

Controlling Beetles
The easiest way to control the adult beetles is to hand-pick and drop them into a container of soapy or oily water. There are no effective chemical controls that kill only the beetles and not a lot of other beneficial insects. Don't be tempted to use the traps that are available because they tend to bring in more beetles.

You can reduce Japanese beetle populations for next year by getting them when they are in the grub stage. The larvae burrow into the soil beneath turf, and while they are active in August and again in May, you can spread a bacterial disease called milky spore to kill the grubs before they emerge. Milky spore is specific to Japanese beetles so it will not kill other insects. There are also parasitic nematodes that you mix with water and spray on turf to control the grubs. Again, be sure to read and follow label directions carefully.

Fall Webworms
As we move into August, we will see Japanese beetles decline and fall webworms come on strong. These are the caterpillars that spin silken tents in all types of trees. They also feed on the tissue between the leaf veins. They don't usually do the amount of damage that spring tent caterpillars do, and are fairly easily controlled by clipping out the branch with the webs and destroying the caterpillars (stomping works quite well). Otherwise, you can spray into the web with a bacterial insecticide called Bacillus thuringiensis.

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