Fear of moths (mottephobia) runs in our family both my mother and my aunts were deathly afraid of the menacing- miller. As a young boy I scored points for tracking down moths and killing them when they ventured inside.
How does this relate to cutworms? Cutworms are the larvae of miller moths.
The Pale Western Cutworm is the cutworm most common in Alberta.
An excellent resource on insect – pests and their control is “Insect Pests of the Prairies” published by the University of Alberta. The information that follows is based on material in that text and personal experience as related to glads and dahlias in particular.
1. Delaying cultivation of the ground in August and September
The adult female prefers to lay her eggs in loose soil. If the crust which normally forms over the soil in summer is left in place the females are more likely to seek a more suitable site to lay her eggs.
2. Watering -The eggs of the moth do not hatch until spring (March to May) depending of soil temperature.
Once the eggs hatch into larvae (April to June) if there is a period of 12 consecutive days of 6 mm of precipitation in a row cutworm populations are drastically depleted. Gardeners could insure that such an event as this occurs.
When cut worm damage is observed, you can usually locate the cutworm alongside the shoot (stem) that is damaged. Simply, dig with your finger around the stalk and you will often locate cutworm – which you can dispose of. This is best done in the morning. Note- cutworms are rather well camouflaged and you usually have some difficulty seeing them. That they are generally moving once dug up helps.
Occasionally, with glads the cutworm will be right in the stem just above the bulb and squeezing the stem will kill it. Usually however the cutworm will stay close to stem its food source rather than in it.
Note – if the stem or stalk is not cut off it will survive the damage. With dahlias in particular, the stem is likely to be completely cut through – New shoots will develop but the blooming date will be delayed.
Trying to find the cutworm is important as it spends a rather long time in the soil and will move on to new plants or the new shoots as they develop.
Chemical Control –
1. Dusting glad bulbs with bulb dust at the time of planting is effective in controlling cutworms on glad bulbs and would probably work for dahlia tubers too.
2. Spraying with a systemic insecticide will help control the cutworms
3. Contact chemicals will work as well –both sprays and dusts. Although the cutworm spends most of the time underground; when feeding it comes to the surface cuts off what it wants and pulls it beneath the surface to continue its consumption. If the infestation is not wide spread, you may wish to target the particular plants showing damage or a particular area where the cutworms seem more active rather than generally spraying or dusting everything. As the cutworm feeds through the night and early morning it is generally most effective to spray (dust) in the evening.
Control of adults-
Once the larvae pupate – further control is probably not practical until the adult moth emerges. Natural- predators of the moth such as bats and birds are your best bet at control the adult stage. Bat boxes can be purchased which provide shelter for the bats.
But, if you have family members afraid of millers, knowing that you are rearing bats in your yard is unlikely to encourage visitors.
One of our cats used to love moth hunts when she was alive. I would take her outside and hold her close to where the moths were flying by the door light. She would catch the moths against the wall and proceed to eat them. Our vet assured us that they were a good source of protein though they were too crunchy for my taste