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Weeds, Pests and Diseases

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Carrot Fly Control

If you had carrot fly (Latin name Psila rosae) in the past you’ll know that this little pest can completely ruin a lovely crop. Damage is caused by small white grubs which burrow into developing roots. These tunnels quickly turn brown and spoil the crop. They also make long-term storage impossible as roots will quickly rot. Carrots are not the only crop to be affected. Parsnips also suffer, as do other members of the same plant family; parsley and celery.

Until now, gardeners had to rely on cultural methods of carrot fly control such as completely covering growing plants using horticultural fleece, avoiding thinning of crops or by growing resistant varieties such as Flyaway, available from Unwins. But now there’s also a new, quick and easy spray treatment from Westland. Plant Rescue Fruit and Vegetable spray is available in either ready to use or concentrate versions.

Plant Rescue Fruit and Vegetable aims to kill adult flies before they can lay their eggs. Any adult flies sprayed directly will be killed as will any flies which land on treated foliage for up to 2 weeks after application. Carrots and parsnips can be safely harvested and eaten 14 days after being treated. Celery and parsley can be harvested in just 7 days from treatment.

Unfortunately, it isn’t easy to know when the adult flies are active and need to be sprayed. The black-bodied adults are only a few millimetres long and therefore difficult to spot. Carrot farmers decide when to treat their own crops by closely following the advice of horticultural scientists. These scientists predict when the adult flies are active by analysing data collected from special trapping sites combined with weather data, particularly temperature data. Amateur gardeners can also access this same data from The University of Warwick.

Generally speaking, carrot fly adults appear in 3 big waves every year, ready to lay their eggs. The last wave isn’t very important since it is too late in the year to affect our carrot crops. However, it is important to be ready for waves 1 and 2.
In the south, the first wave of adults hatches about mid May. In the north the first wave happens about mid-June due to cooler temperatures. Eggs will be laid about 2 weeks after these dates.The second wave of adults hatches about mid July in the south and then in August further north.

Adult flies are most active late afternoon and early evening, so sprays at these times will be most effective.

Plant Rescue Fruit and Vegetable Ready to Use and Plant Rescue Fruit and Vegetable Concentrate contain lambda-cyhalothrin. Always read the label. Use pesticides safely.