Some years in spring mature willow plantations can become infested with willow beetles (Chrysomelidae):

• Brassy or green (Phratora vitellinae)
• Blue (Phratora vulgatissima)
• Brown (Galerucella lineola) This can check growth of the willow due to leaf defoliation and can also be a nuisance to neighbours. Outbreaks can be as a result of:
• Lack of clonal diversity in the varieties planted in a mixed clonal population or poor mixing or varieties.
• Mild winters without frosts that mean that not enough over wintering beetles or their larvae are killed. Combined together this can result in a population explosion in early spring with willow beetle numbers proliferating and spreading across the whole plantation and surrounding areas. This is often followed by a population crash and the cycle is repeated every few years.

In such circumstances there are a number of options A crop that is ready to be harvested: Harvest the crop as soon as possible and spray the targeted pesticide Hallmark, once straight after harvest then a second spray a month or two later. This will not affect willow growth if applied as per the label. (Please note you should seek agronomist advice before applying any pesticides)

• A crop that is NOT ready to be harvested: If population numbers are large, they can be reduced by target spraying the borders of the plantation with insecticide when the beetles are re-colonising the plantation from their overwintering sites in early spring. However, this is a one-off operation and routine spraying is NOT recommended for both economic and ecological reasons.
• Non chemical option 1: Harvest the crop as soon as possible. It is likely that a residual population will remain and perhaps cause problems again in the near future. To avoid this it might be necessary to grub out some rows completely and replant with a better mixture - there are some suitable hybrid varieties (European/Chinese heritage) that are less prone to beetles (e.g. Endurance, Terra Nova, Esther). This is relatively expensive but is a good long term strategy.
• Non chemical option 2: willow beetles over winter on the bark of mature trees or similar niches (e.g. fence posts). It’s impossible and ecologically irresponsible to try and modify this. However, it might be possible to break the life-cycle by removing any fallen trees from areas adjacent to the willow plantation.
• No intervention allowing it to take its course this time. This is not a very good long term option as the problem will return periodically, lead to reduced yields and cause complaints from neighbours. Some growers have removed crops due to persistent beetle issues. This is very expensive.

You can find out more about the reason for planting mixtures by reading the https://envirocrops.com/resource/short-rotation-coppice-willow-best-practice-guidelines You can find out more about which currently available varieties should be used to create a robust mixture at: https://www.rothamsted.ac.uk/sites/default/files/Project_files/SRC%20Willow%20Variety%20Selection.pdf)