The majority of oilseed rape crops are approaching stem extension, with some in warmer areas already showing flower buds above the canopy. This leaves a narrow timeframe to apply the final herbicides –clopyralid or clopyralid and halauxifen-methyl – to manage thistles, mayweed, crane’s-bill, poppies, and cleavers. Any weeds left after this window closes will persist until harvest desiccation.
Ollie Johnson, head of farming systems and agronomy at AHDB, offers this advice to growers.
Pest control
Pollen beetle activity is currently under scrutiny. Typically, these pests emerge from mid-March to mid-May, especially during daytime temperatures surpassing 15°C. Delays in bud formation prolong the period of susceptibility.
The monitoring of pest populations is crucial. The AHDB’s treatment-threshold guidelines are based on the number of beetles per plant during the green-to-yellow bud stage and the plant population density.
Treatment Thresholds:
Fewer than 30 plants/m2 = 25 beetles per plant
30–50 plants/m2 = 18 beetles per plant
50–70 plants/m2 = 11 beetles per plant
More than 70 plants/m2 = 7 beetles per plant
If beetle numbers fall below these thresholds, spraying is not economically viable. Avoiding unnecessary sprays helps preserve beneficial insect populations and slows the spread of insecticide resistance, which is prevalent in this pest (pyrethroid resistance).
Pollen beetles exhibit a unique behaviour: they can transition from being a pest to beneficial in a short time span. This is because they are eager to access pollen and may bore through buds, causing damage to developing flowers. Once flowers bloom, beetle activity can aid in crop pollination.
Nutrient and disease management
During flower development, oilseed rape requires sufficient sulphur and boron. As some of these nutrients are prone to leaching, especially in wet weather, preventing deficiencies before symptoms (and flower development) emerge becomes critical. Tissue testing can identify potential deficiencies. Swift corrective action, ideally through foliar treatment, is essential during this period.
With rising temperatures, symptoms of light leaf spot become apparent. The pathogen’s polycyclic nature often results in the presence of all life cycle stages simultaneously, making complete control challenging.
In areas of high risk or where symptoms are observed, fungicide treatment should be considered. Both azoles and non-azoles are effective against light leaf spot, aiding in fungicide resistance management. The annual reports from our fungicide-performance project offer valuable insights into balancing chemical and non-chemical control methods for light leaf spot and phoma.
Light leaf spot
During flowering, attention should be paid to sclerotinia stem rot. Despite the pathogen’s complex infection cycle, understanding the main risk factors – presence of inoculum (spores), weather conditions (warm and humid), and flowering crops – can aid in targeted control efforts.
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