When good vegetables go bad

You started seeds in spring and watched as they sprouted, then watered, fertilized and even staked plants as they grew, while visions of summer salads, grilled vegetables and homemade pickles danced in your head.

Then one day, black blotches, yellow-spotted leaves and mushy bottoms showed up, and your dreams turned to nightmares.

Many home gardeners lovingly tend their plants only to find them ravaged by unknown forces before harvest time.

But fear not: Here are some tips for identifying and treating five of the most common ailments that threaten your crops.

Anthracnose

A fungal disease that affects beans, cucumbers, eggplants, melons, peas, peppers, tomatoes, pumpkins and spinach. Anthracnose presents as small leaf spots with yellow halos that gradually darken and spread to cover entire leaves. On cucumber plants, foliage may drop, and entire vines may die. Tomatoes and peppers exhibit dark, sunken spots that become more apparent as fruit matures. Pea pods become marred with dark lesions. Round, sunken, yellow spots appear on melons, darkening to brown and then black.

To prevent this, try rotating crops, amending soil with compost before planting and applying mulch afterward. Seek out resistant plant varieties, when available. Avoid overhead watering, which wets foliage and encourages fungal growth. And keep the soil clear of infected plant parts and fallen fruit.

Treat infected plants with a fungicide containing chlorothalonil or copper, carefully following the instructions and safety precautions on the package.

Blossom end rot

Caused by a calcium deficiency that mainly affects tomatoes, eggplant and peppers. Characterized by dark, mushy spots on fruit bottoms, the disorder typically results from inconsistent watering, improper soil pH, injured roots or excess nitrogen.

Prevention measures include testing the soil’s pH before planting. If results are lower than 6.3, incorporate dolomitic lime into beds according to label directions.

Avoid damaging the roots by installing stakes and cages around tomatoes at planting time, instead of when plants — and roots — are larger. And don’t plant a vegetable garden in or near a lawn that receives fertilizer, which can raise the nitrogen level of the surrounding soil.

Treat affected plants by drenching leaves with a calcium spray until the product drips off. Fruit produced after treatment is usually symptom-free, although sometimes a second application is necessary.

Wilt diseases

Verticillium and fusarium wilt are soil-borne fungal diseases caused by different pathogens that result in similar symptoms.

Primarily affecting eggplants, peppers, potatoes, pumpkins and tomatoes, the diseases ravage roots, resulting in curled, yellow and wilted foliage, brown xylem tissue inside stems and overall stunting. Eventually, entire plants wilt and die.

This is one instance where a good offense is the only defense: Avoid infection by planting resistant varieties (check plant tags for V, F, VF or VFN, resistance indicators for verticillium wilt, fusarium wilt and nematodes). Rotate crops by keeping infected beds free of susceptible plant species for three or four years, essentially starving the disease of a host to clear the pathogen from the soil. And regularly clean up fallen leaves, fruit and plant debris.

Squash vine borer

Zucchini, squash, cucumber and muskmelon plants die quickly after blooming, without so much as a goodbye. But if you look closely, you’ll see the small puncture holes in the bottoms of stalks and stems caused by these pests, which start life as moths that lay eggs at the base of plants. Inch-long white caterpillars follow and bore into stalks, killing plants as they chew their way around and out. And just when you think the damage is done, they cocoon in the soil until the following year, armed and ready to repeat the carnage.

Prevent damage by monitoring susceptible plants closely. Watch for red, flat, oval eggs early in the season and pick them off by hand. Keep hunting every week.

And if you find signs of damage like punctures and frass, their sawdust-like excrement, use a razor blade to slice affected stems open near the holes and manually pick out the borers. Cover the slits with mounded soil to encourage new root growth.

If necessary, treat plants with Bacillus thuringiensis, or Bt, a bacterial insecticide (several versions are available; seek the one labeled as a control against squash vine borer).

Slugs

Jagged holes, typically in leaf centers rather than edges, indicate slug damage. The nocturnal gastropods feast on basil, cabbage, cucumbers, lettuce, tomatoes, peppers, and ornamental plants like hostas, leaving a telltale slimy trail behind.

Get ahead of the slithering miscreants with a spring cleanup that clears leaves, plant debris and slug eggs from the soil surface, and keep mulch no deeper than 3 inches to avoid creating a haven.

Sink a small can or jar into the soil around affected plants, leaving about an inch exposed above ground, then fill it halfway with beer. Slugs will crawl in for a drink and drown. Alternately, if you aren’t squeamish, you might go into the garden at feeding time (overnight) and sprinkle a bit of salt on each of your little visitors. As their bodies attempt to dilute the irritant, slugs will dehydrate and die. But don’t be tempted to sprinkle salt around plants. Doing so would risk damaging the soil.