Can companion planting reduce allium leaf miner?
The Experiment 🔗
This experiment was developed with consultation through Garden Organic’s citizen science action group. The topic, the pest and the plants were selected through suggestions from gardeners through an online workshop and virtual noticeboard.
• Allium leaf miner was selected as a topic as it is becoming an increasing challenge in the UK, but there are few effective non-chemical ways of managing it apart from covering the crop.
• Two companion plants were tested: chard as a taller plant and clover as lower growing plant. Growing crops next to other plants has been known to reduce infestation by pests. As the pest is searching where to lay eggs, if it lands on an alternative plant more than a few times, it will give up and go somewhere else. This theory (‘inappropriate/appropriate landing’) has been tested extensively in brassicas but not with alliums.
• The leeks, chard and clover all established well, but the chard was clearly competing against the leeks from July onwards.
• There were visible signs of damage from allium leaf miner from September onwards leading to extensive losses by November.
• There was a consistent trend for chard intercropping to reduce the infestation from allium leaf miner although this was not statistically significant. The low growing clover had very little effect.
• Using chard as a companion plant significantly reduced marketable yield by 69% - the competitive effects far outweighed any balance of reducing pest damage.
• Companion planting has the potential to reduce damage by allium leaf miner, but a balance must be sought between reducing pest damage and losing yield. Since allium leaf miner can cause extensive damage, growers would be likely to tolerate a moderate reduction in yield if companion planting could salvage their crop.
