Problem 1: Basil, lettuce, or spinach leaves are skeletonized

Diagnosis: Slugs

Treatment: Handpick slugs; set out baits or traps

One minute it seems as if the leafy greens in your garden are fine, and then, seemingly overnight, you dis­cover that they have been decimated. Despite their small size, slugs can practically annihilate a plant in one meal. The first act of defense should be diligent monitoring of your plants. Usually you’ll see a few Swiss cheese–like holes in the leaves before the entire plant goes down; that’s because slugs send out scouting parties that test out a potential dining site before committing to a 12-hour dinner reservation. When you detect these holes, go outside with a flashlight in the early evening (when slugs are active) and pick the slugs off the plants and dispose of them. A few nights of doing this should reduce the local population. Another option is to use organic slug baits or traps—just be sure to place them away from susceptible plants.

Problem 2: Rotting black spots are appearing on peppers

Diagnosis: Sunscald, followed by rain

Treatment: Stake properly; avoid pruning

Although sunscald is most commonly associated with tomatoes, it can be a big problem with peppers and eggplants as well. In these crops, the sun burns a hole in the skin of the fruit and then, when moisture gathers on the wounded portion, it rots the damaged area. This ruins the fruit. Leaf cover is essential for avoiding sunscald, and problems usually arise when eggplants or pepper plants have tipped over or when large branches have broken off, exposing the fruit. Strong staking is the best way to avoid compromised plants. Eggplants and peppers, in fact, are perfect candidates for tomato-cage supports. While many tomatoes get too big to be ade­quately contained by these metal enclosures, smaller eggplants and pepper plants are the perfect size for these small containment structures. Also, remember that there is no need to prune eggplants or pepper plants (as you do with tomatoes). The only reason you should ever remove foliage is because it is damaged or diseased; otherwise, leave it alone. Cutting off the foliage is only asking for sunscald trouble. For areas of the country prone to hot, humid summers (ideal conditions for sunscald), plant thick-skinned varieties, like ‘Poblano’ peppers and ‘Ghostbuster’ eggplants.

Problem 3: The top of your radish or carrot is rotten

Diagnosis: Boron deficiency

Treatment: Adjust soil pH; amend with compost

Boron deficiency in veggies tends to be triggered by drought stress; low organic matter in the soil or soil that is highly alkaline will also exacerbate boron deficiency. If this problem arises in your garden, get a soil test. This inexpensive laboratory analysis will reveal how much boron (available at garden centers) to use as a soil amendment so that you’ll have healthier crops in the future. A test reading of less than 0.14 mg/kg indicates a deficiency. As organic-matter decomposition occurs, boron is released, so amending your soil with compost can be helpful as well. Too much boron, though, is toxic to plants, so be conservative in your application—regardless of which amendment you choose.

Problem 4: Tomato plants are dying from the leaf tips inward

Diagnosis: Verticillium wilt

Treatment: Plant resistant varieties in the future

Although blight has gotten a lot of press lately, a more common and devastating problem for tomatoes is verticillium wilt, a soilborne fungus. This pathogen is sensitive to soil moisture and temperature. Tomatoes (as well as potatoes) are usually subjected to at least a day of saturated soil before infection occurs, so you’ll often see your plants start to decline after a significant rainfall. Plants might survive long enough to produce a small crop, but they gener­ally die off before any sub­stantial fruit can be harvested. Unlike blight, plants with verticillium wilt always start to die from the leaf tips. Do not plant susceptible crops in infected soil for four to five years. The best defense is to plant resistant varieties, like ‘Rutgers’, ‘Jet Star’, and ‘Supersonic’.

Problem 5: Eggplant leaves have hundreds of pinholes in them

Diagnosis: Flea beetles

Treatment: Use floating row covers

If you discover pinholes in eggplant leaves, look closely: You’ll probably see small black bugs, or flea beetles, next to those pinholes. These tiny marauders suck the juices out of the foliage, leaving behind pockmarked plants. After transplanting, spread a floating row cover (a type of light fabric, sometimes sold under the brand name Ree­may) over your plants. This physical barrier allows light and moisture through but keeps pests out. The beetles are the biggest problem in spring, so you can generally remove the cover when the plants reach 1 to 2 feet tall. At this point, even if a few stray flea beetles do attack, the plant is big enough to survive. The best defense against flea beetles is a strong, healthy plant.

Problem 6: Rough brown wrinkles are showing up on ripe peppers

Diagnosis: Cuticle cracking caused by irregular moisture

Treatment: Water consistently

When prolonged dry conditions are followed by an excessive amount of moisture, the cuticle (or skin) of many veggies will show some strain. The fruit first becomes dry and hard and then, when the plant starts taking up water (which makes the fruit swell), it splits. This same occurrence can happen to tomatoes, eggplants, and even peaches and plums. The cracking will appear different on each fruit or vegetable. Consistent watering throughout the season is the best way to avoid this condition, but the weather sometimes makes that impossible. Rest assured, though, that this cracking does not affect the edibility or taste of the fruit.

Problem 7: Onion foliage is yellowing and dying off

Diagnosis: Pink root disease

Treatment: Use soil solarization; plant resistant varieties

Pink root disease, a common soil fungus, is difficult to diagnose accurately without pulling up a growing plant because, as the name indicates, you need to pull up the plant to see if the roots are pink. Aboveground, though, the foliage will start to yellow and die off, leaving the plant no means to feed and sustain the bulbs belowground. This kind of damage is seen when plants are stressed by climatic conditions or poor drainage; a wet spot in a garden may show symptoms while the rest of the crop appears unaffected. Infected plants cannot be salvaged, although they may last long enough to produce a decent crop. Soil solarization (laying a clear plastic tarp atop garden soil to “cook” it) can be effective in killing off the soilborne disease for the following year, but it will kill off the good microbes as well, so you’ll need to amend liberally the following season before planting. Or you can simply plant resistant varieties, like ‘Candy’ and ‘Red River’. Pink root disease, unfortunately, also affects garlic.

Problem 8: Striped bugs are causing burn spots on potato plants

Diagnosis: Colorado potato beetle

Treatment: Apply Bt, neem oil, or spinosad

Congratulations—you’ve caught the Colorado potato beetle in the act! Although this little guy looks like a relative of the much-loved ladybug, it is not beneficial in any way. Adult beetles and larvae nibble leaf edges, which then die back, causing what look like burn spots. An effective control is the daily hand­picking of adults and larvae and squashing the bright yellow-orange egg clusters on the underside of leaves. This is time-consuming, however, and it’s nearly impossible to get rid of all pests. So you might want to consider applying an organic insecticide. The most effective is Bt (Bacillus thuringiensis), which can control the larvae; neem oil and spinosad are also quite effective if applied regularly.

Peter Garnham is a commercial grower of herbs and vegetables in East Hampton, New York.

Photos, except where noted: Danielle Sherry