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In Poitou-Charentes, Vendée, and Centre-Val de Loire, rapeseed crops were subjected to heavy pressure from pollen beetles in late February and early March during their early growth stages. Dropping nighttime temperatures and morning frosts locally exacerbated damage to floral parts, resulting in the loss of buds and even flowers. Other crop issues were often already present: widespread infestation of large flea beetle larvae, and locally, of terminal bud weevil larvae; poor root development and/or a taproot degraded by winter waterlogging. This is unprecedented: such an extremely early growing season with flowering beginning on March 5–10.  With much shorter daylight hours than in April, we can assume impacts on plant function, including reduced light energy capture and lower mobilization of assimilates. Added to this are the consequences of delayed fertilizer applications for a crop that is ahead in development (waiting for the soil to dry out), sometimes resulting in a significant delay between application and utilization (waiting for the return of rain). High temperatures have also accelerated the development of rapeseed, which has not always been able to feed itself properly and at the right time: climatic stress was exceptionally high in March. The explanation for plots in difficulty is often multifactorial. These abnormally stressed rapeseed plants could rebound once favorable conditions return.

Today, flowering is impaired in many situations, and the timing of fungicide application requires careful consideration. Forecasted weather conditions are dry and cold, which is generally unfavorable for the development of Mycosphaerella in affected fields. Additionally, wind will reduce application windows and limit the number of petals adhering to leaves (a route of Sclerotinia contamination).

In this context, determining stage G1 is complicated, and consequently, the decision to apply the key fungicide is as well. As a reminder, stage G1 is commonly referred to as “the first petals falling,” but petals fall from the very start of flowering! Another definition of this key stage is possible and easier to grasp: it is the formation of the first siliques on the main stem.

Stage G1 reached: Schedule fungicide application	No siliques Stage G1 NOT reached Wait
March 26, 2026, Angliers (17)

Most rapeseed crops are currently at the E to F1 growth stages. Milder weather could reignite flea beetle activity, as the first flowers are now visible in nearly two-thirds of the fields.
Following an early and nearly widespread arrival of the pest in late February, threats persist in fields with slow growth or in sheltered areas (valleys, wooded edges). 
This year, flea beetle larvae are weakening the crop and reducing its resilience. Weevil pressure frequently exacerbates the situation.
Many fields have already been treated against weevils, but a follow-up treatment may be warranted as long as flowering has not clearly begun. Conversely, on healthy rapeseed that has passed the E-F1 stage, the risk of damage quickly becomes negligible, making insecticide treatment unnecessary.
At this time, treatments must remain strictly targeted at plots with confirmed risk, using solutions based on tau-fluvalinate or etofenprox. Apply under favorable conditions (sufficient humidity, limited wind, avoid hot hours) with a water volume > 200 L/ha and strictly outside foraging periods, in accordance with current regulations.

Jean Lieven - j.lieven@terresinovia.fr

With flower buds appearing very early this year, some farmers are wondering about the impact of late nitrogen application in the form of a nitrogen solution.  

The burns observed are mainly due to a contact effect: fertilizer droplets deposited on the plant parts become concentrated as the water evaporates. The increase in salt concentration can then cause dehydration and tissue necrosis. Recent leaves and especially flower buds, whose tissues are young and poorly protected by a cuticle, are particularly sensitive. In addition, the microcavities present in the buds can retain the droplets and prolong contact with the solution.

The risk increases when the buds are clearly visible and exposed on the inflorescences (progression from stage D1 to E), and as soon as the first flowers appear (stage F1). Sensitivity increases with the proportion of buds exposed to the droplets. Weather conditions also play an important role: hot, sunny, dry, or windy weather promotes rapid evaporation and increases the concentration of the solution.

In most situations, the impact on yield remains limited, unless the crop is already very fragile. Rapeseed has a strong compensatory capacity, thanks to the gradual development of its yield components (seeds/m² and TGW).

In practice, if no other form of fertilizer is available, it is preferable to apply nitrogen, even in liquid form, at a stage close to E-F1, rather than not applying any at all. Nitrogen solution should preferably be applied during rainfall, which will limit burning.

Jean Lieven - j.lieven@terresinovia.fr
Elodie Tourton - e.tourton@terresinovia.fr
Julien Charbonnaud - j.charbonnaud@terresinovia.fr
Thomas Mear - t.mear@terresinovia.fr