disease-resistant plants

Disease-Resistant Vegetables and How to Find Them

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I mentioned in my post last month that many of the pepper plants I grew from seed this year were infected by bacterial leaf spot. I did my best to remove diseased material from the garden, but undoubtedly some of it still lingers in the soil and might survive to infect plants next year, so I will plan to grow varieties that are resistant to this disease.

Pepper leaves infected by bacterial leaf spot. Photo from HGIC.

And no, I don’t just have a list of these varieties in my head. I’ll have to do some research. Maybe you’ve faced this problem too, when all or some of your tomatoes or squash or some other vegetable succumbed to a disease you managed to get identified—and your friendly Master Gardener or Extension specialist advised you to plant resistant varieties. How do you go about finding them?

First, check out Cornell Cooperative Extension’s Disease Resistant Vegetable Varieties page. Here you can find a list for each of many common vegetables of available varieties and the diseases to which they’re resistant. For example, if you have a problem with fusarium wilt in tomatoes, click on Tomato and then skim down the list to note all the varieties with fusarium wilt resistance. (Lucky you; there are lots.) You can also download the information in spreadsheet form for easy reference.

If you have favorite seed catalogs, they can be another good source. Most seed catalogs will add codes to each variety listing that represent disease resistance; for example, fusarium wilt is coded as “F” and if you see “F1-2” that means it’s resistant to both races 1 and 2 of fusarium. (The more resistance, the better, since you probably don’t know which race infected your plants.) Somewhere in the catalog section for each vegetable there will be a list of codes and what they mean.

If you don’t grow your own plants from seed, use these resources anyway. Make a list of resistant varieties, find a garden center or other plant source with a wide selection, and pick out the plants that meet your criteria. Make sure the plants you select look healthy!

Here are some other things to keep in mind:

  • Hybrid varieties are more likely than heirloom or other open-pollinated varieties to have demonstrated disease resistance. If you have anecdotal evidence that an heirloom is pretty resistant, try it out, but you might want to grow it separately from your bed of resistant types. Same goes with that variety you just have to grow because you can’t do without it, but you suspect it may come down with the bug—grow it away from the others.
  • “Disease resistant” does not mean “can’t possibly get the disease.” If the pathogen is present, it will probably still infect plants, but the resistant plants will stay healthy much longer—maybe until the very end of the season, if you’re lucky.
  • Know the source of your pathogen: is it present in the soil, or will it reappear blown in on the wind, or is it more likely to come from infected seed or plant material? Knowing a bit about how transmission works will help you strategize to keep plants healthy. The HGIC website is a good source for information about plant diseases and how they spread (hint: look at the entry for the vegetable and it will list relevant diseases).
  • There may be other methods available to keep disease away, such as treating seeds with bleach or hot water, using fungicides, and most importantly keeping soil around plants covered with mulch to prevent splashing onto leaves. Also try to avoid overhead watering; water at the base of the plant. You can also remove and destroy infected plant parts when you spot them. Using these methods in combination with planting resistant varieties will increase your odds of success.

Do your research and have a bountiful, disease-free growing season next year!

By Erica Smith, Montgomery County Master Gardener. Read more posts by Erica.

Be Proactive to Prevent Vegetable Diseases

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When it comes to vegetable diseases, an ounce of prevention is worth a pound of cure. Many diseases can be stopped before they start with smart garden practices.

Spring rains cause spots, dots, and fuzzy blots to pop up in everyone’s vegetable patch. That’s fungi having fun. But whether our weather is wet or dry, fungi, bacteria and viruses stand ready to harm plants. 

So, how do you keep them at bay? Be informed and watchful. Look at your plants often to spot small problems before they get big and use the following tips to prevent disease problems.

If you have repeat offenders – diseases that show up year after year – look for disease-resistant varieties. For example, there are varieties of tomatoes labeled as resistant to both verticillium and fusarium wilt. 

Early blight is a common disease of tomatoes. Photo:  J. Traunfeld, UME

Some plants are available in certified, disease-free starts. Choose potato tubers, garlic bulbs, and asparagus and rhubarb crowns that are certified and disease-free. 

Vegetables hate soggy soil. If your garden area is wet, consider creating a raised bed to improve drainage. Or, grow in containers or move the garden to an area that drains well.

You’ve heard me preach the gospel of compost time and again. But did you know that compost actually discourages some plant diseases? Garden smart by adding compost every year. 

Help prevent disease by spacing your plants properly to encourage good air circulation. Plant labels often give spacing tips as do garden books and websites.

Warm, humid weather invites powdery mildew on squash. 
Photo: UME Home & Garden Information Center

Rain can spread soil-borne diseases, splashing infected soil up on plants’ leaves. So keep your soil covered with an organic mulch such as untreated grass clippings or newspaper covered with straw.

Fungi love wet leaves, so water wisely. Water at the base of the plant using soaker hoses or drip irrigation. And water in the morning, not the evening, so leaves dry before nightfall. 

Practice tough love. Remove infected leaves or pull entire plants if they become badly infected. It’s better to lose one bad plant than the whole row. Don’t compost sick plants: bag and trash them.

Overripe vegetables invite disease organisms. So, harvest your vegetables before they get mushy. 

A thorough cleaning of your vegetable bed at the end of the season is crucial since many diseases can overwinter in the soil. Again, if anything had a serious disease issue, bag and trash it.

If you spot a problem, e-mail your local Extension horticulturist a photo or bring them a sample to identify. Here’s a list of our county offices. We can usually get back to you in a day or two with advice.

For other growing tips and diagnostic help, visit our Home & Garden Information Center website. It has photos, management tools, and a wealth of resources. There’s even an Ask Extension link to submit gardening questions to certified horticulturists.

Enjoy your vegetable garden this year. A few seeds and transplants, some rain, sun, and a watchful eye will have you enjoying fresh, healthy homegrown food all season long.

By Annette Cormany, Principal Agent Associate and Master Gardener Coordinator, Washington County, University of Maryland Extension. This article was previously published by Herald-Mail Media. Read more by Annette.