Leek moth: major garlic pest
Temperatures are gradually rising and the snow is starting to melt. Spring is finally on its way! Garlic bulbs planted in the fall are starting to grow for this seasons harvest. Unfortunately, the milder spring weather brings worry about the emergence of a major garlic pest: the leek moth (Acrolepiopsis assectella).
Leek moth: portrait of a pest
The leek moth is an invasive species, native to Europe. It was spotted for the first time in eastern Ontario in 1993 and in Quebec in 2001. The caterpillars feed on plants from the Alliaceae family (leek, garlic, onions, chives, etc.), causing damage to the young leaves, flowers and cloves, resulting in a loss of yield.
Leek moth: life cycle
- The adults spend winter in plant debris.
- Adults become active at 9.5 °C.
- Females lay 2-6 days after breeding.
- Females lay 80 to 240 eggs.
- There are three generations of leek moths in Quebec.
Trichogramma wasps against leek moth
Trichogramma are tiny wasps that parasitize butterfly and moth eggs. In agriculture, they are mainly used to control corn borer (Ostrinia nubilalis), armyworms (Spodoptera sp.) and False looper (Trichoplusia sp.).
Trichogramma brassicae pupae are glued to cards and introduced in the field. Once set up, adult trichogramma will emerge after 5 to 7 days, depending on environmental conditions. Upon emergence, the female trichogramma wasp will actively search for moth eggs on the surface of the garlic leaves. Once detected, she lays inside them. The trichogramma larvae will grow inside the moth egg and feed on the future caterpillar. This will cancel the future generation of leek moth.
Biological control Trials by The University of Vermont
In 2019, researchers Scott Lewins and Vic Izzo of the Vermont Entomology and Participatory Action Researh team (VEPART), in collaboration with Anatis Bioprotection, tested the effectiveness of introducing the Trichogramma wasps (Trichogramma brassicae) for managing the Leek moth in onion crops. Preliminary data from their first field trials replicated across six Vermont farms are promising. The release of Trichogramma wasps significantly reduced the incidence of Leek moth larvae in onion leaves.
Follow these four steps to protect your garlic from leek moths
1 Scout by using pheromone lure traps
Releases should start as soon as moths are first detected (pheromone lure traps) or in early May (for Quebec and Ontario). If trichogramma wasps are not released before laying period, they can not prevent the development of larvae (= damage).
Scouting helps to determine the arrival of adults and the laying period. As soon as one leek moth is captured on the trap, it's time to introduce the trichogramma cards. Pheromone traps for leek moth are only available by reservation from March to April. For more information, please contact Anatis Bioprotection Sales representatives.
Monitoring for leek moth:
Leek moth adult (7 mm).©Anatis Bioprotection
To scout well, place 2 Delta 1 triangulat traps per field at the end of April (Quebec/Ontario). ©Anatis Bioprotection
Insert the sticky pad at the bottom of the trap. ©Anatis Bioprotection
Change sticky pads every 1 or 2 weeks (depending on the amount of pest and dirt on it). ©Anatis Bioprotection
Leek moth pheromone is distributed in the form of a small plastic cap. Use gloves when handling the cap. ©Anatis Bioprotection
Place the pheromone in the center of the trap. Keep unused pheromones in the refrigerator. ©Anatis Bioprotection
The Delta 1 trap must be horizontal and above the crop foliage. Place the trap at the edge of the field in a wind sheltered area. ©Anatis Bioprotection
From the first leek moth capture, it's time to order the trichogramma cards. ©Anatis Bioprotection
2Introduce the right number of cards
The introduction rates depends of the crop area. Trichogramma wasps must be uniformly distributed (by length and width). A bad distribution would cause unprotected areas.
The first card is placed 3 meters from the edge of the field and the other ones every 7 meters. For example, for plot of 30 meters by 20 meters :
30m wide / 7m = 4 introduction rows*
20m long / 7m = 3 cards per introduction row*
* Round to the nearest unit.
3Put in new cards every week
Each female leek moth lays up to a hundred eggs over a period of three to four weeks. That's why we need to release weekly new trichogramma wasps in the crop.
New cards must be introduced every 7 days, from the leek moth emergence to the appearance of the garlic flower. In general, 4 to 6 introductions are required to protect your crop against the 1st and the 2nd generation of the leek moth.
4Keep cards in the field
Depending on the temperature, trichogramma wasps will emerge from their cards after 2 to 7 days. By cooler temperatures, the emergence of trichogramma can be done over a longer period of time.
To prevent removal of non emerged trichogramma wasps, keep each card in the field for a minimum of 3 consecutive weeks.
Benefits and limitations
The use of trichogramma wasps provides many benefits:
- Simple to use;
- Quick to install (30 minutes/ha);
- Reduces ricks to the environment and human health
- Promotes natural enemies and insect pollinators.
Trichogramma are living organisms and their work may be affected by the following factors:
- Frost (= mortality);
- Excessive heat (32°C and above = mortality);
- Pesticides applications;
- Poor storage or handling conditions.
See the Tricho-Gard sheet