PHOTO: Mark Levisay/Flickr
We’ve all been there. Your prize-winning tomatoes are coming along beautifully, when all of a sudden, the leaves start to yellow and the fruit turns black. Or your butternut squash is growing a tremendous vine with the signs of fruiting, when all of a sudden it starts to wither, only giving you one or two squash. The unfortunate reality is that our favorite garden vegetables aren’t native plants, and as such, they’re susceptible to a multitude of diseases and pests.
An impressive industry has developed around breeding disease-resistant crop varieties to hold up against common bacterial and viral diseases encountered in vegetable gardens. While many of us may choose to grow time-tested heirlooms that have some of these inherent qualities, sometimes we make the decision to grow disease-resistant varieties when a particular disease becomes a problem. Using disease-resistant plants in conjunction with other planting strategies can provide vigor to your vegetable garden.
As you go about seeking disease-resistant crop varieties, first understand what diseases are present in your area. Look through your garden notes to see what diseases you’ve battled in the past, and talk to your local extension agent about what’ diseases and pests are common in your area. Once you know your enemy, finding the right crop variety will be that much easier. Here are some of our recommended varieties of your favorite crops to help you get started.
The most common tomato diseases you might encounter in your garden are fusarium wilt, verticillium wilt, nematodes and tobacco mosaic virus. All of these diseases will kill your plants for the season and have the potential to linger in the soil, affecting future plantings. When purchasing tomato starts and seeds, look for varieties that list their resistance to these problems. You will see the following codes on the tag that correspond to the diseases to which the tomato is resistant:
- F: fusarium wilt
- V: verticillium wilt
- N: nematodes
- TMV: tobacco mosaic virus
Two tried and true resistant tomato varieties:
- Big Beef (V,F,N, TMV)
- Celebrity (V,F, TMV)
These are also All American Selections winners with high yield and good flavor.
Much like tomatoes, eggplants are also susceptible to wilts, including fusarium and verticillium. Resistant varieties include:
- Diamond (F, V), which is often available as organic seeds and starts
- Black Pride (V)
- Nadia (V)
In dry climates where peppers thrive, most damage to both the plant and fruit come from insect and sun damage. However, in wetter climates, peppers are susceptible to cucumber mosaic virus, which can be transmitted by aphids. Resistant varieties include:
- Ace/New Ace (bell)
- Sweet Chocolate (bell)
- Italian Sweet (sweet)
- Anaheim Chile (hot)
- Hungarian Wax (hot)
With all nightshades, good crop rotation is one of the best methods to fight soil-borne diseases, such as verticillium wilt. In areas where wilt and other diseases are common, a four- to five-year rotation is recommended. In between these seasons, plant vegetables from other families outside of the nightshade family.
Both summer and winter varieties of squash are commonly susceptible to powdery mildew and, in some climates, mosaic viruses. In drier climates, powdery mildew usually attacks late in the season after most of the fruit has set but can be overcome. However, in wet climates, an early onset of powdery mildew can stunt plant growth and greatly reduce yields.
Summer squash varieties that are resistant to powdery mildew include:
- Multipik (yellow straight neck)
- Revenue (zucchini)
Winter squash varieties include:
- Bugle (butternut)
- Honey Bear (acorn)
- Japanese Kabocha
Cucumbers are far more resistant to disease than other plants in the cucurbit family (melons, squash, etc.), but they’re still susceptible to powdery and downy mildew, bacterial wilt, angular leaf spot, and cucumber mosaic virus. Bacterial wilt can be spread by insects, so it can be helpful to tent or cover cucumber plants up until they set flowers.
The best disease-resistant slicing varieties are:
- Marketmore 76 and 80
- Straight Eight
- Dasher II
For pickling cucumbers, try:
Gardening Against Disease
In addition to planting disease-resistant crop varieties, a number of gardening techniques can be implemented to offer additional aid to your plants.
Grafting is a strategy used to create disease resistance in tomatoes and other vegetables. A desirable tomato, such as an heirloom, is grafted onto disease-resistant stock and can be purchased at nurseries or through catalogues. Often times, the strong rootstock also produces more vigorous plants with higher yields. Grafting is a common practice in the industry for tomatoes, cucumbers, eggplants and melons. While these varieties are more commonly sold in areas with high incidence of soil-borne diseases, they are now available and grown all over the country.
Good watering practices are key to growing healthy plants, which in turn will help the plant fight off disease, whether it be caused by environmental factors, pest, bacteria or virus. Set a schedule that emphasizes less frequent deep watering instead of frequent shallow watering; this will force root growth deeper into the soil leading to stronger, larger plants.
Plants need adequate airflow to fight off disease. Some diseases are spread by moisture, so it is important that the soil and the plant has time to dry out between each watering. Good air flow is maintained by appropriate plant spacing, thinning plants as they grow and cleaning up all dead plant debris. The latter is especially important at the end of the season to prevent overwintering of plant pests.
When a bacterial or viral infection is suspected, it is very important to remove the infected plant as soon as possible. Leaving a plant in the ground in the hopes that it will recover can allow the disease to spread to unaffected plants.
Between seasons, it is always a good idea to rotate crops through your vegetable beds. In general, plants from the same family should not be grown in the same bed from one year to the next. Instead, try rotating the plants to other beds and not returning to the original for at least three seasons. This allows time for any lingering pests or diseases to die out in the soil.
Gardening is a practice of trial and error. Even with all the best disease-mitigating techniques put into place, there’s a chance you’ll lose a plant every now and then. But with some careful observation and tweaking of your garden strategy, you’ll be able to find a happy balance, where you keep diseases at bay and enjoy the harvest for yourself.