Spurred by hot, dry weather conditions, spidermite numbers are rapidly increasing across the UK in many protected and outdoor horticultural crops, including soft fruit, ornamentals and for the first time, top fruit.
Selchuk Kurtev, IPM manager, advises growers to implement an integrated strategy to reduce spidermite populations, before they get out of control.
Spidermites populate the underside of leaves and feed by sucking nutrients out of the leaf cells, producing speckling damage visible on the upper side.
If high numbers are present they can form webbing at leaf tips, which they can use to climb up canopies, moving on to and desiccating, other plants.
At the point of visible webbing, flower and fruit yields are significantly reduced, due to interference with chemical and macrobiological control effectiveness. This can result in severe profit loss for growers.
Introducing macrobiologicals can be an effective control method for spidermite. But, it’s important to get the ratio of predatory mites to the number of pests correct to ensure success.
Spidermites have a shorter lifecycle (five to six days) compared to predatory mites, so they can reproduce at a quicker rate. They also thrive in hot, dry conditions, whereas predatory mites prefer humidity.
Therefore, it is recommended to increase the ratio of predatory mites to spidermites to 1:5 in the current climate.
Monitoring the underside of leaves for spidermites daily is key to enable growers to act fast with macrobiological introductions.
Applying insecticide treatments can compliment the use of beneficial insects. However, it’s important to ensure compatibility with treatments for other pests and diseases as part of a wider IPM strategy.
Alternating actives, such as Eradicoat/Majestik or Botanigard, which has recently been granted an EAMU for cane and bush fruit, can also help to reduce resistance.