Carrot Diseases and Pests

Not all carrot diseases are obvious at first. Those affecting the top growth directly will be immediately apparent, but it can be very disheartening to see what looks like a healthy crop of carrots growing happily in the garden, and then dig them up and find the carrot root all riddled with tunnels.

"What's happened to my carrots?! And how could I have prevented it?"

Carrots can be affected by the following plant pests:

  • Aster Yellows Disease
    Aster yellows disease is caused by an odd type of organism  known as a phytoplasma. It's not-quite a bacteria, and it is carried by the aster leafhopper insect, similar to the way malaria is carried by mosquitos. The aster yellows disease causes leaf yellowing, stunting of the root, and top growth that gets short and bushy, called sometimes a "witches broom". It destroys the carrot's flavor, to the point of not being edible. The only way to control it organically is to prevent the aster leafhopper from landing on the carrots, which means growing carrots under row covers like Reemay.

  • Carrot Rust
    Carrot rust is caused by carrot rust flies that lay their eggs in the soil around the top of carrot plants. These eggs hatch into larva that burrow down into the soil, and into the carrot's roots. The larva proceed to munch rust-colored tunnels in the carrot, usually in the lower two-thirds of the root. 

  • Carrot Weevils
    Carrot weevils look more like a beetle than a fly, and also lay eggs in the soil around carrots. Like carrot rust larva, the larva burrow into carrots, but carrot weevil larva usually tunnel into the upper third of the carrot. 

  • Leaf Blight
    The most common carrot leaf blight is caused by Alternaria fungus, which also attacks tomatoes where it causes "Late Blight". Alternaria leaf blight causes yellow/brown spots, which can get so bad that they merge, eventually making the carrot tops look burned.   

  • Parsleyworms
    Parsleyworms are rather beautiful green caterpillars with alternating white bands and orange/black bands. They just chomp away at top growth in true, ravenous caterpillar fashion. 

  • Nematodes
    Both root-knot and needle nematodes are microscopic soil roundworms that can cause galls, malformed roots and root branching in carrots. They only grow if the soil is above about 55 degrees, so early plantings are rarely affectedl. 

  • Bacterial Soft Rot
    As its name implies, bacterial soft rot is a soil-borne bacteria that just sort of eats chunks of the carrot root into a mush.    

Control Measures for Carrot Diseases and Pests

Unfortunately, there are no good organic controls for these common carrot diseases, after the carrots are affected. Prevention is the best medicine if you are an organic gardener.

For insect-borne diseases or insect pests, growing your carrots under Reemay will prevent insects from laying eggs or chomping down your carrots.

For fungal and bacterial diseases, removing the affected plants and practicing good crop rotation and garden hygiene for the following year are your best choices.

For non-organic controls, visit the Cornell Plant MD site.

Related Articles:

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