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Pests & Diseases

How to Protect Cabbages and Carrots from 2 Common Pests

Carrot seedling

Baby carrot header

Firstly, thank you to anyone who replied to last week’s mail expressing interest in information on plant feed for container growing. I am a bit tight for time this week and there is a lot to go through so I will have an article for you in next week’s email. For this week, I would like to briefly cover protecting plants from pests as we are at the point in the year where we need to take some preventative measures.

There are a wide range of pests or diseases that could be a problem in your garden but, if you have a nutrient rich organic soil that grows healthy plants, you will likely avoid most of them. I have been growing for many years now and generally encounter very few issues but unfortunately there are a couple like carrot root fly, cabbage root fly and potato bight that are almost inevitable.

Carrot root fly damage carrot roots

If you are growing organically, your pest control regime mostly revolves around keeping pests out rather than trying to kill them. The two most common issues at this time of year are carrot root fly and cabbage root fly, both of which lay eggs around your plants that hatch into maggots and eat carrot or cabbage roots.

Carrot root fly
In the case of carrot root fly (resulting damage above), the larvae don’t kill the plant but tunnel into the roots which is annoying in mild cases and makes the crops unusable when severe. There are 2 generations of the root fly which are at large from May to mid June and August to October. We can be wily in our sowing times to avoid the worst, I sow my maincrop carrots in late May as they take 2 weeks to germinate so will be coming up as the first generation of root fly dies off.

Mainframe crop protection mesh

The most effective way of keeping root fly off your crops is to use an insect mesh with a fine weave small enough to keep the adult fly out. The mesh is normally branded as either ‘enviromesh’ or ‘micromesh’ and is either laid directly on top of the crop or supported by hoops or a frame structure. Above, you can see my maincrop carrot bed last year using our aluminium ‘Mainframe’ system to create a neat box frame which gives the carrots plenty of room to grow.

Micromesh carrot root fly protection

One of the reasons I like the mainframe is that it comes with little sprung plastic clips to hold the mesh to the poles making it very easy to remove the cover for thinning or harvesting crops. By the way, carrot roof fly are attracted to the smell of bruised carrot foliage so thinning you crop will attract them in droves. My advice is to always thin in one go rather then over a period of time to reduce the ‘attraction window’ and to thin when the carrots are as small as possible as it is much quicker and there is less foliage deal with (that creates the attractive smell). It is also better to thin carrots in the evening as there will be fewer flies about.

For the benefit of new growers, thinning carrots refers to the practice of removing carrot seedlings to leave the required 3-4cm space between each one. The reason they can’t be sown at the correct spacing is carrot seeds are very small so are impossible to sow accurately.

Cabbage root fly maggots

Cabbage Root Fly
Cabbage root fly larvae eat the roots of brassica (cabbage family) plants including cabbage, cauliflower, Brussels sprouts, kale and turnip although some suffer less than others. With kale, for example, I find Italian kale is a problem while Russian or curly kale usually emerges unscathed.

Root fly can be an issue at any time of the season but it is more of a problem in spring and early summer when cabbage family plants are young. Older plants usually survive an attack because they have developed large root systems so can afford to loose a few but young seedlings will almost certainly succumb. The tell tale signs of a problem are blueish wilted leaves; if you tug the plant it will easily pull free of the soil revealing very few fine roots and the little white maggots pictured above.

Cabbage collar root fly protection

Cabbage root fly can also be effectively controlled using a mesh, again laid directly or on a support. As cabbage family plants tend to have sturdy leaves, the mesh is better suited to laying on the crop than carrots (which have very light foliage) so can simply be weighed down around the edges with stones or bricks. The reason, by the way, that you can’t just use the fleece you used earlier in the year to protect from frost is it traps too much heat in summer while the mesh provides ventilation.

The other alternative is to use a cabbage collar (above) either supplied in packs or home made from roofing felt or another suitable material. The idea here is that the root fly can’t find suitable terrain around the root to lay eggs and, if she does, they can’t burrow through the material down to the roots. I find mesh more effective than collars but collars do work very well if weighed down with stones as they have a tendency to blow off in windy weather.

Mini polytunnel root fly protection

Mini Polytunnels
If you are growing in raised beds or a smaller area you might find our mini polytunnels a useful solution as they can be covered with either fleece, polythene or insect mesh. This is a product we manufacture ourselves which consists of a timber frame, connecting brackets and tubing. You can either purchase a kit or the component parts separately, the tiimber frame is designed to fit a 2×2 timber while the tubing used is standard blue water pipe.

The mini polytunnel kits had been out of stock for a while as we had some manufacturing issues but we are delighted to be offer the full range again as of today. The kits can be made to fit most bed sizes (within reason) so it is a very versatile solution. You can see yours truly demonstrating the covers in the video above.

Kinked baby carrot

Kinky Carrots
The trick to carrot growing is having a nice light, preferably sandy, soil with no stones or other obstructions. It is the only way to grow long straight roots. As my garden soil is fairly heavy (clay based) I have created a number of dedicated carrot beds using a sandy soil mix so I can grow uniform roots.

I thought I would finish up today with a carrot I pulled from one of my polytunnel carrot beds to see how they were coming along. The 14 inch high bed was part filled with soil and a 30% mix of sand followed by a layer of 50/50 soil/sand mix. You can see the immature carrot is straight as an arrow to begin with but then kinks at the point it encountered the heaver mix, all the carrots in the bed have the same shape. I just thought that was interesting. It also means if anyone steals my carrots I should be able to identify the stolen goods as they all kink at exactly the same point. Carrot thieves take note.

That’s it for today, I will see you next week

Andrew

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