The rapeseed beetle does not have a good reputation. It can turn beautiful summer months into torture. Anyone cycling past rapeseed fields often attracts hundreds of insects. To combat the beetle in your own garden, simple home remedies are usually sufficient.
How can I combat rapeseed beetle?
To effectively combat rapeseed beetles, home remedies such as rock dust, vegetable oils and the promotion of natural enemies such as parasitic wasps can be used. Chemical agents should only be used in emergencies as they can also kill other insects and harm the environment.
How can I combat rapeseed beetle?
The example of the rapeseed beetle has shown that chemical agents do not solve the problem of pest infestation and, in the worst case, are ineffective. Therefore, please note important information before resorting to sprays from the garden center.
Sprays
Pyrethroids also kill all other insects
In the last 20 years, the rapeseed beetle has been controlled almost exclusively with pyrethroids. As the insects move around a sprayed crop, they come into direct contact with the insecticide. After a short time, the beetles show disoriented behavior. Their movements are no longer rhythmic, which is comparable to staggering. They eventually fall to the ground and die.
Problems when using pyrethroids:
- Washout by rain possible
- Active ingredient breaks down in strong sunlight
- work less well at temperatures below five and above 15 degrees
- Insecticide does not act selectively, but kills all insects
excursus:In the past ten years, a decreasing effectiveness of pyrethroids has been observed throughout Europe. The rapeseed beetle is becoming increasingly unimpressed by the use of the spray. In laboratory studies it was found that the beetles had developed an enzyme to break down the toxin.
The main reason for this development is the fact that in the past only pyrethroids were used. If the mechanism of action is always the same, the beetles that are less susceptible survive. The proportion of insensitive insects is increasing, so that the product is becoming less and less effective.
Tips for dealing with chemical agents
The chemical club should only be used in extreme emergencies, as the toxic substances cause further problems. Not only do they have a negative impact on the environment, but they can also affect he alth. Your own garden should be a space for relaxation and provide safe food. Therefore, consider these instructions before taking any control measure:
- Sit it out: a period of bad weather after a high automatically drives out the beetles
- Control: count beetles per plant every morning to determine the effectiveness of the control
- Question: every use of insecticides should be checked to see if it is necessary
Rape beetle – home remedies that help
In agriculture, other control methods are being discussed that have so far received little attention in practice. Alternative means include the use of parasitic fungi, beneficial insects or trapping plants. In organic cultivation and in private gardens, the beetle can be controlled with gentle home remedies. Reflective materials such as lime milk or straw are intended to drive away the rapeseed beetle. In northern Germany they are spread on the edges of fields so that the immigration of the beetles is delayed.
Collect
Beetle collection machines are common on farms that control pests biologically. In your home garden, collecting them by hand has the same effect. With this measure, the infestation pressure can be reduced by around 30 percent, so that there is no further need for action for ornamental and useful plants.
Rock flour
Dusting substances are distributed on the rapeseed plants before bud development begins. For the greatest possible success, you should first use the product when the temperature threshold of ten degrees Celsius is exceeded. Another application takes place after the first flower buds appear. Rock dust prevents the beetle from eating its way through the plant tissue. If used early, the infestation can be reduced by a third. You can either sprinkle the flour by hand or mix it with water and spray.
Vegetable oils
In order to reduce the immigration of beetles from the edge of the field, the edge areas are sprayed with rapeseed or sunflower oil. The solubility of unformulated vegetable oils is increased by adding a neutral soap. In English laboratory tests it was found that female rapeseed beetles react sensitively to lavender oil. It has a strong repellent effect on insects.
Parasitic wasps
Parasitic wasps are very helpful in the fight against rapeseed beetles
The insects prove to be useful pest controllers that can reduce the larval population of the rapeseed beetle by more than 50 percent. In order to promote parasitic wasps in your own garden, natural structures are essential. These generally ensure greater biodiversity and ensure optimal living conditions for the rapeseed pests' natural enemies.
Habitat for parasitic wasps:
- flowery hedges
- rotten tree trunks with retreat niches
- species-rich walls in a sunny location
- Wildflower stripes on the meadow
What damage do rapeseed beetles leave behind?
In spring, rapeseed beetles go looking for food. They feed on pollen that is inside the rape buds. The insect pest causes visible feeding marks that extend over the entire plant population in severe infestations. Small buds are completely eaten away, while larger buds show the typical bore damage. Severely damaged buds show yellowing and slowly dry out until they fall off the stem. If the feeding damage is minor, stunted flowers and misshapen or twisted pods will develop.
Damage threshold
The control threshold is a value for orientation as to when control makes sense. This value changes over the course of the growing season because the plants get better at dealing with feeding damage as they get older. Therefore, the damage threshold at the beginning of bud development is lower than shortly before the flower opens. Count the beetles on each plant to decide on possible control. The infestation is determined between March and April.
| non-hazardous population | Combat makes sense with | |
|---|---|---|
| Buds are very small | one or two insects | three to four beetles |
| 14 days before flowering | three to four insects | seven to eight beetles |
| Bud is about to open | five to six insects | more than eight beetles |
Are rapeseed beetles dangerous?
Rape beetles only bite flowers, not human skin
The crop pests are widespread in the summer months. They settle on light-colored clothing and bath towels and become a nuisance when cycling. The insects bite - but people do not have to fear a sting or bite from the rapeseed beetle. They only eat through plant tissue to get the coveted pollen.
If you're cycling in nice weather and don't want to attract bugs, you should wear dark clothing. Light-colored shirts and pants are attractive to insects. They confuse yellow clothes with a bright flower.
Although rapeseed beetles can be a nuisance in summer, they do not pose a danger to humans.
Spread in recent years
In recent years, the weather has favored the spread of the small black insects. The rapeseed beetle found optimal living conditions in 2018 as temperatures rose to the optimal range early in the year. In calm and sunny conditions, a particularly large number of insects can hatch at the same time, quickly becoming a plague.
The rapeseed beetle was a much-discussed insect in 2019. Due to the numerous reports of increasing resistance to pyrethroids, new insecticide strategies have been developed. They should weaken the development of resistance. Since spring 2019, new agents have been approved for combating the rapeseed beetle.
Identify rapeseed beetle
The little beetles look really cute
The insect has the scientific name Brassicogethes aeneus. Its English name common pollen beetle indicates its preferred food. Rapeseed beetles belong to the family of beetles, of which 140 to 150 species are known in Central Europe.
Appearance
The beetles reach a size of between 1.5 and 2.5 millimeters. They have a shell made of chitin, which is usually black in color and has a metallic sheen. Occasionally specimens with blue, green or violet basic tones can be observed. The colors of the legs and antennae contrast with the oval-shaped body. They appear in dark brown tones. The short antennae resemble a club due to their thickened shape. If you look closely, you can see small hairs on the wing coverts.
Lifespan
After the beetles hatch in the year they lay their eggs, they spend the rest of the year looking for food. From the end of August, the insects fly near the edges of forests to look for suitable winter quarters. They overwinter in the loose humus layer in forests or hedges. When the sun warms the ground next spring, the insects leave their hiding place. They live around 14 months.
Tip
Adverse weather conditions can increase the mortality rate. Wait for rain and low pressure areas. Wind also drives away the pests.
Living space and way of life
Rape beetles like yellow
Rape beetles have specialized in the color yellow. In years with favorable weather conditions, they can spread en masse despite their natural enemies. Birds find the little black beetles a protein-rich treat. The main enemies of beetles are parasites.
Activity
Rape beetles fly at temperatures between ten and 15 degrees Celsius. They prefer sunny conditions and calm conditions. Mild weather can encourage the beetles to spread particularly early. The insects are active during the day and prefer to fly to rapeseed fields.
Since they do not feed exclusively on rapeseed, rapeseed beetles also appear on other plants with yellow petals. They feed on pollen and can also destroy the pistils and ovaries of flowers. If the flowers are not yet open, the beetles eat their way through the bud leaves and into the interior. Their larvae feed exclusively on pollen and do not destroy any flower organs.
Occurrences
Rape beetles are found not only in Europe but also in North Africa, Asia and North America. They find optimal living conditions in open and bushy landscapes. Since the beetles prefer to fly to yellow flowering plants, they can also be observed in the garden or on the balcony. They settle on flowers and buds of rapeseed plants and fly to yellow-flowering cruciferous plants or plants from other families such as nasturtiums. If the beetles appear in the apartment or house, there is no need to worry. You got lost through open windows and doors.
Tip
Rape beetles don't seem to like the smell of lemongrass. Fresh lemongrass stalks are ideal for scaring away.
Frequently asked questions
How can I prevent the rapeseed beetle from spreading?
Create optimal growing conditions for your plants and prevent waterlogging or soil compaction. Coordinated fertilization and gentle soil cultivation promote rapid flowering. The beetles migrate into the fields from the edge. Create large, compact beds instead of small, narrow strips to keep feeding damage to a minimum.
The administration of manure can also reduce feeding damage if it is applied in dry weather. Avoid growing summer rapeseed and instead choose early-flowering rapeseed varieties. Due to their faster flower development, these varieties are less damaged.
How do rapeseed beetles develop?
The females drill a hole into strongly developed buds from below in order to lay their eggs near the stamens. A few days later the larvae hatch and find good feeding conditions. They feed on pollen and do no damage to the plant.
The larvae shed their skin several times and fall to the ground in the last instar. They live in the substrate for the next three to four weeks to pupate. At the time of rapeseed flowering, the new generation of beetles hatch. The air temperature can drop to nine degrees Celsius.
How do rapeseed beetles overwinter?
When the temperatures gradually drop from the end of August and the food supply dwindles, this year's generation of beetles swarm out. They fly to sheltered hedges and forest edges and start looking for suitable winter quarters. You will find this in loosened soil with coarse material. Next spring they leave their hiding place when the air temperature rises above ten degrees Celsius.
Are there effective attractants that attract rapeseed beetles?
Since rapeseed beetles do not only fly on rapeseed but generally on yellow-flowering cruciferous plants, other crops can serve as attractants. The diurnal beetles colonize a rapeseed field by moving inward over the edges. A six to twelve meter wide edge strip with turnips or early-flowering cruciferous vegetables that runs around the entire field distracts the beetles from the main crop.
In this way, the rapeseed is protected during the critical development phase. Because of the beetle's lifestyle, rapeseed should be grown in large, compact plots. This reduces feeding damage.
