The Winter stem weevil (Ceutorhynchus picitarsis ) is a dreaded pest of rapeseed crops, capable of causing significant damage and reducing crop yields. Active mainly in autumn and spring, the larvae of this beetle attack the petioles of plants and the terminal bud. But how can you identify its damage? And what biological solutions can be applied to get rid of this rapeseed pest? Our explanations and advice.
How to identify the Winter stem weevil?
The adult measures between 2 and 3.5 mm in length. It presents sexual dimorphism : males are slightly smaller than females. Its coloration varies from dark brown to black, with a reddish head, antennae and legs. It is observed is the presence of a light spot on each elytron .
The larva of Ceutorhynchus picitarsis measures between 4.5 and 6.5 mm at its final stage of development. It has a stocky shape , without legs, and is white in colour with a black head capsule at the beginning of its development. Upon reaching maturity, the capsule takes on a yellowish hue. It is at this stage that the larvae cause the main damage to crops.
What are the host plants of Ceutorhynchus picitarsis?
Rapeseed ( Brassica napus ) is the main host plant of the terminal bud weevil. The pest can, however, attack other crops, although damage is generally more severe on rapeseed. Other host plants include:
- Dyeers’ pastel ( Isatis tinctoria ),
- Radish ( Raphanus sativus ),
- Chou
- The hub
- Other cruciferous vegetables
Development cycle of the Winter stem weevil
The Winter stem weevil has only one generation per year .
In the autumn, adults emerge from their summer diapause and migrate to the rapeseed fields. It is during this period that they lay their eggs in the petioles of the plants, a process that can take place between September and March.
The larvae that are born will develop inside the petioles , where they dig galleries and gradually migrate towards the terminal bud of the plant. This phase continues throughout the winter.
In spring , the larvae leave the plant and fall to the ground, where they pupate. This transformation is followed in May by the emergence of adults. These then feed on the flowers and pods of rapeseed before entering summer diapause again until the following autumn.
What damage is done to crops?
Bud weevil damage is particularly visible in spring. The presence of larvae inside the stems causes the following symptoms:
- Terminal bud destruction : This phenomenon leads to the development of secondary stems, and gives the rapeseed a bushy appearance. Affected plants have disturbed growth, leading to irregular bolting and flowering.
- Yield Reduction : Bud destruction and disordered plant growth results in reduced crop yield.
- Plant weakening : Affected plants become more susceptible to other pests such as stem weevils and pollen beetles. In severe cases, weevil attack can even lead to plant death.
In the absence of a precise risk threshold, any presence of weevil in rapeseed crops justifies intervention.
How to fight against the Winter stem weevil?
Control of the terminal bud weevil of rapeseed is mainly based on strategies aimed at eliminating adults before they lay eggs.
The use of traps is recommended to detect the presence of adults in the plots. These traps make it possible to monitor populations and determine the optimal time to intervene.
Agrobiotop solutions against the rapeseed bud weevil:
