Insects and Dahlias
Traps have proven quite effective in controlling these insects when your dahlias are outside. You can use many different objects as traps; rubber tubes, damp cloths, rolled-up newspaper - all are desireable hiding places for these determined insects. Place these in locations that you see high densities of earwigs, or near the plants you wish to protect.
Another trap can be made by burying a tin can in the ground with the edge at ground level, containing a small amount of fish, tuna or sardines, and more vegetable oil or fish. Think about where you are, however, we wouldn't want to attract skunks or raccoons to dig out your flower beds.
To discourage many intruders from attacking your plants, you can try the following: mix 5 ml of dish soap (or baby shampoo) in 500ml of water and spray the plant, especially the emerging leaves and shoots. If this is done regularly, the soapy residue left on the plant should discourage many insects.
Since cutworms (caterpillars) only come out at night, their damage is often difficult to diagnose at first. They attack most plants at their base; grasses, vegetables, and some ornamentals such as dahlias are often attacked by these voracious pests. Cutworms are active usually in mid-May to late June.
In order to catch these insects, you can scratch the surface (3-5cm) delicately around the plant - they can ususally be found in this layer. You can also wait until night and use a flashlight.
For slugs, research has shown that using coffee is effective at repelling them. A typical cup of instant coffee, containing a solution of .05% caffeine, can be used to soak the ground around the affected area.
Another approach : Place a small pot (like yogurt) at the foot of a plant, half filled with beer. Slugs are attracted to beer and will drown. Change these every 2 days. Spraying the plant with a mixture of water and garlic once a week can also help.
The corn rootworm (a pale, green beetle) attacks both the buds and petals which cause flower deformation. Adults start to become a apparent in July - preferring white or paler type flowers to feed on. If you are near a cornfield in july or august, chances are you will run across this rather abundant critter.
Tarnished plant bug
The tarnished plant bug (TPB) attacks plants at their growth points and at the flower buds. Equipped with "piercing-sucking" mouth parts, it damages the tissues of plants by introducing digestive enzymes. These enzymes can lead to stunting, leaf deformation, flower deformation and abortion of the flower bud.
Flea beetles feed mainly on leaves, riddling them with holes. In our flower beds, we mostly have the black ones and red ones which can often been seen feeding during a hot, sunny afternoon.
For rootworms, plant bugs and flea beetles you can use an insecticide containing rotenone and pyrethryn.