Fight rape beetles gently and effectively

the essentials in brief

• In agriculture, pollen beetles are usually fought with pyrethroids. In the meantime, the sprays have proven to be ineffective.
• Before using chemical agents, the benefits should be weighed. Home remedies or beneficial insects are gentler and more effective.
• Green rapeseed beetles cause typical damage to oilseed rape. The damage threshold is an orientation value from which control measures should be initiated.
• The insects can be clearly recognized by their activity in typical habitats. Although they are increasingly spreading, they are harmless to humans.

How can I control pollen beetle?

The example of the pollen beetle has shown that chemical agents do not solve the problem of pest infestation but, in the worst case, are ineffective. You should therefore pay attention to the important information before you use sprays from the garden center.

also read

• Fight fig tree pests effectively
• Fight pests with insects
• Fight insects successfully, but biologically

spray

In the last 20 years, the rapeseed beetle has been controlled almost exclusively with pyrethroids. When the insects move in a sprayed crop, they come into direct contact with the insecticide. After a short time, the beetles show disoriented behavior. Your movements are no longer rhythmic, which is comparable to staggering. They eventually fall to the ground and perish.

Problems with using pyrethroids:

• Wash out by rain possible
• Active ingredient degrades with strong solar radiation
• work less well at temperatures below five and above 15 degrees
• Insecticide does not work selectively, it kills all insects

excursus:

In the past ten years, a decrease in the effectiveness of pyrethroids has been observed across Europe. The pollen beetle is increasingly unimpressed by the use of the pesticide. In laboratory tests, it was found that the beetles 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 increases so that the remedy becomes more and more ineffective.

Tips on handling chemical agents

The chemical club should only be used in an extreme emergency, because the toxic substances cause further problems. Not only do they have a negative impact on the environment, they can also be harmful to health. Your own garden should be a place to relax and provide safe food. Therefore, consider these tips before taking any control measures:

• Sit out : a bad weather period after a high automatically displaces the beetles
• Control : count beetles per plant daily in the morning to determine the effectiveness of the control
• Questioning : every use of insecticides should be checked for necessity

Pollen beetle - home remedies that help

In agriculture, further methods of control are being discussed that have so far received little practical use. Alternative means are the use of parasitic fungi, beneficial insects or trapping plants. In ecological cultivation and in private gardens, the beetle can be fought with gentle household remedies. Reflective substances such as milk of lime or straw are supposed to drive away the rapeseed beetle. In northern Germany, they are spread on the edges of fields, so that the immigration of beetles is delayed.

Youtube

Collecting

Beetle collecting machines are common on farms that fight pests biologically. In the home garden, collecting by hand has the same effect. With this measure, the infestation pressure can be reduced by about 30 percent, so that there is no further need for action for ornamental and useful plants.

Rock flour

Dusting substances are distributed on the oilseed rape plants before bud development begins. For the greatest possible success, you should use the agent for the first time when the temperature threshold of ten degrees Celsius is exceeded. Another application takes place after the appearance of the first flower buds. Rock flour (€ 14.95 at Amazon *) prevents the beetle from eating its way through the plant tissue. The infestation can be reduced by a third with timely application. 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 field edge, 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 the females of the pollen beetle are sensitive to lavender oil. It has a strong repellent effect on the insects.

Parasitic wasps

The insects prove to be useful pest fighters, which can reduce the larval populations of the rapeseed beetle by more than 50 percent. In order to encourage ichneumon wasps in your own garden, natural structures are essential. These generally ensure a higher biodiversity and ensure optimal living conditions for the natural enemies of rapeseed pests.

Habitat for ichneumon wasps:

• flower-filled hedges
• rotten tree trunks with retreat niches
• Species-rich walls in a sunny location
• Wildflower strips in the meadow

What damage do rapeseed beetles cause?

In the spring, pollen beetles go foraging for food. They feed on pollen that is inside the rapeseed buds. The insect pest causes visible traces of feeding, which in the case of severe infestation extend over the entire plant population. Small buds are completely eaten away, while larger buds show the typical drilling damage. Badly damaged buds show yellowing and slowly dry up until they fall off the stem. If the damage is minor, stunted flowers and misshapen or twisted pods develop.

Damage threshold

The control threshold is a value for orientation from when control makes sense. This value changes in the course of the vegetation period, as the plants cope better with feeding damage with increasing age. Therefore, the damage threshold at the beginning of the bud development is lower than shortly before the flower opens. Count the beetles on each plant to decide how to control it. The infestation is determined between March and April.

	harmless population	Combat makes sense
Buds are very small	one or two insects	three to four bugs
14 days before flowering	three to four insects	seven to eight bugs
Bud is about to open	five to six insects	more than eight bugs

Are rapeseed beetles dangerous?

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 humans do not have to fear a sting or bite from the pollen beetle. They only eat their way through plant tissue to get the coveted pollen.

If you ride your bike when the weather is nice and don't want to attract bugs, you should pay attention to dark clothing. Light-colored shirts and trousers are attractive to the insects. They mistake yellow clothes for a radiant bloom.

Although rapeseed beetles can be a nuisance in summer, they pose no threat to humans.

Spread in recent years

In recent years the weather has favored the spread of the small black insects. The pollen beetle found optimal living conditions in 2018, as the temperatures rose to the optimal range early in the year. In windless and sunny conditions, a particularly large number of insects can hatch at the same time, so that a plague can quickly occur.

The pollen 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 reduce the build-up of resistance. Since spring 2019, new agents have been approved for the control of the rapeseed beetle.

Recognize rapeseed beetle

The insect has the scientific name Brassicogethes aeneus. Its English name common pollen beetle indicates its preferred food. Rape beetles belong to the gloss beetle family, of which 140 to 150 species are known in Central Europe.

Appearance

The beetles reach a size between 1.5 and 2.5 millimeters. They have a shell made of chitin, which is usually colored black and has a metallic sheen. Occasionally, specimens with blue, green, or purple base tones can be observed. Legs and antennae stand out in color from the oval-shaped body. They appear in dark brown tones. The short antennae resemble a club due to their thickened shape. If you take a closer look, you can see small hairs on the wing covers.

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 the forest in order 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 are around 14 months old.

Tips

Unfavorable weather conditions can increase the death rate. Wait for rains and depressions. Wind also drives away the pests.

Habitat and way of life

Green rapeseed beetles specialize in the color yellow. In years with favorable weather conditions, they can spread en masse despite their natural enemies. Birds will find a protein-rich treat in the little black beetles. The main enemies of the beetles are parasites.

activity

Green rapeseed 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 diurnal and prefer to fly on rapeseed fields.

Since they do not only feed on rapeseed, pollen beetles also appear on other plants with yellow petals. They feed on pollen and can also destroy the pistils and ovaries of the flowers. If the flowers are not yet open, the beetles will eat their way through the bud leaves to the inside. Their larvae only feed on pollen and do not destroy any flower organs.

Occurrence

Green rapeseed beetles are not only found in Europe but also in North Africa, Asia and North America. You will 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 the flowers and buds of rapeseed plants and fly to yellow-flowered cruciferous vegetables or plants from other families such as nasturtiums. If the bugs appear in the apartment or house, there is nothing to worry about. You have lost your way through open windows and doors.

Tips

Green rapeseed beetles don't seem to like the smell of lemongrass. Fresh lemongrass stalks are ideal for putting them off.

frequently asked Questions

How can I prevent the rapeseed beetle from spreading?

Create optimal growth conditions for your plants and prevent waterlogging or soil compaction. Coordinated fertilization and gentle tillage promote rapid flowering. The beetles migrate from the edge into the fields. Create large and compact beds instead of small, narrow strips to keep eating damage to a minimum.

The administration of liquid manure can also reduce the damage caused by feeding if it is applied in dry weather. Avoid growing summer rapeseed and choose early flowering rapeseed instead. Due to their faster flower development, these varieties are less damaged.

How do rapeseed beetles develop?

The females drill a hole in vigorously developed buds from below in order to deposit their eggs near the stamens. A few days later the larvae hatch and find good feeding conditions. They feed on pollen and do no harm to the plant.

The larvae molt several times and drop to the ground in the last larval stage. They live in the substrate for the next three to four weeks to pupate. The new generation of beetles hatches when the rape is in bloom. The air temperature can drop to nine degrees Celsius.

How do the pollen beetles hibernate?

When temperatures gradually drop from the end of August and the food supply dwindles, the beetles of this year's generation swarm out. They fly to protected hedges and forest edges and start looking for suitable winter quarters. You will find this in a loosened soil with coarse material. They leave their hiding place next spring when the air temperature rises above ten degrees Celsius.

Are there effective attractants that attract pollen beetles?

Since pollen beetles do not only fly on rapeseed but generally on yellow-flowering cruciferous vegetables, other cultivated plants can serve as attractants. The diurnal beetles colonize a rapeseed field by penetrating inwards over the edges. A six to twelve meter wide border strip with turnips or early flowering cruciferous vegetables, which 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 way of life, rapeseed should be grown in large and compact plots. This reduces the damage caused by feeding.