Before planting parsnips, you should know about parsnip canker. Carrots, dill, parsley, and sunflowers may also get this disease.

Parsnip canker is an infection of Itersonilia perplexans and several other fungi that can reduce your crop by as much as 80%. But it is preventable.

Symptoms of parsnip canker

Like other cankers, symptoms include dark, mushy areas on parsnip crowns and shoulders. These areas may be black, brown, orange, or purple and typically have pale green halos. Lesions may also occur on the underside of young leaves.

Parsnip canker management

When growing parsnips, many gardeners mound soil over the crown as the plant grows in a practice known as hilling. Hilling in the UK has been shown to expose pathogens to predators, reducing the chance of infection. Unfortunately, this practice spread pathogens to neighboring plants in Australian gardens. I suspect it has something to do with temperature and humidity differences, but I am only guessing.

Other steps you can take to prevent parsnip canker include the following:

• Invest in certified disease-free seeds and seedlings.
• Plant seeds later in the season.
• Space plants no closer than two inches apart.
• Furrow irrigation reduces the chance that fungal spores will splash onto healthy plants.
• Employ crop rotation.
• Manage carrot rust flies whose larvae predispose plants to infection.
• Keep burdock, Chinese aster, and chrysanthemum away from susceptible crops, as they may carry the disease.
• Compost crop debris at the end of the growing season.

Foliar sprays of fixed copper may help treat the disease if applied early enough. And you can cut out the bad bits and enjoy the rest of the root.

Parsnips have a lot to offer, and they are easy to grow. The ones you might find in the grocery store are never as sweet and crisp as those you can grow in your yard.

​The first signs of infestation include withering and wilting. Close inspection of the crown at soil level may yield a small hole surrounded by frass that looks like sawdust. There are no biological or organic treatments against this pest. Commercial growers often use Diazinon to combat these pests, but that chemical is highly toxic to bees (and it probably isn’t good for us, either).

The more you know about raspberry crown borers, the better equipped you will be to prevent infestation.

Is it a moth or a wasp?

It all starts with what looks like a wasp. This type of clearwing moth has a one-inch wingspan. It is black with four or more stripes around the abdomen. The antennae are feathery and curled at the tips, the wings have longitudinal bars, and the legs are yellow. First-year larvae are one-half to one-inch long, while second-year larvae may reach an inch-and-a-half long.

Raspberry crown borer lifecycle

These fascinating (and destructive) parasites go through a two-year cycle that starts with females laying up to 140 rust-colored eggs on the underside of leaflets in late summer. Take a peek and extermigate any eggs you see. Larvae create tiny blistered hibernaculum (“winter tents”) in the base of the crown, where they are safe from winter weather and predators.

As temperatures rise, larvae burrow galleries throughout the crown, feeding as they go. In some cases, these larvae emerge as adults at the end of the summer. They often remain in these protected galleries through a second winter, causing even more damage.

Keeping plants healthy and monitoring for eggs and entry holes are the best preventative tools. Any plants infested with raspberry crown borers should be removed and destroyed.