Saturday, 9 May 2009

Tomato Troubleshooting

by Sadge, at Firesign Farm
Tomatoes are the most popular vegetables grown in home gardens. And no wonder - one plant bears many fruits over a long period of time, and there are varieties to fit every location from patio pots to trellises 15' high. Plus nothing beats the flavor of a vine-ripened tomato still warm from the sun, whether it's a tiny grape tomato popped right into your mouth or giant slices filling a sandwich.

More and more gardeners are returning to growing heirloom tomatoes. Growing heirlooms provides a much greater variety of flavors and colors, and allows the growers to select and save seeds according to individual tastes, uses, and climate. But in doing so, they also risk losing the disease protection bred into today's hybrids. Keeping a watchful eye on your tomato patch is especially necessary when growing heirloom tomatoes organically - to catch pests early and to remove diseased plants before the entire crop is infected.

But sometimes even the most attentive gardener will find something wrong in the tomato patch. Here are a few of the more common tomato problems and some solutions:

Blossom End Rot
Darkened area on blossom end of the fruit, that eventually becomes sunken, black and leathery. Caused by either inconsistent or uneven watering or a calcium deficiency (that's why I add the eggshells at planting time, or you can also use limestone). The fruit is still ok to eat after slicing off the damaged portion.

Fruits, especially the earliest ones, misshaped with darkened crevices and scars on the blossom end. Caused by environmental stress during bloom - usually temperatures below 55F (13C) or above 85F (30C), but also by drought, high winds, or fertilizers high in ammonia (such as insufficiently composted poultry manure). Wait to set out plants until weather has warmed sufficiently or provide protection such as row covers or Wall-o-waters.

Tomato skin cracks, either in concentric curves around the stem or by splitting radially from the stem. Caused by wide fluctuations in temperature or water (especially when a heavy rain follows hot, dry weather) during fruit growth. Excessive nitrogen can also cause cracking. Even watering and balanced fertilizer use lessens cracking.

White or light tan discoloration of the skin, especially on the top of the tomato. Caused by too much sunlight during hot weather - the tomato version of sunburn. If pruning tomato plants to a trellis, try leaving two stems instead of one to increase amount of foliage (plus, that can increase your yield too).

Tomatoes like between 1 and 1½ inches of water per week, and it's critical that the supply is on a regular and even basis. They're considered heavy feeders, so like both applications of compost or other slow-acting fertilizer in the spring at planting time, plus supplemental light side-dressing or foliar sprays periodically throughout the season. Besides the compost dug into their planting area before setting out my plants, I also add a heaping tablespoon of crushed eggshells, heaping teaspoon of Epsom salts, and a heaping tablespoon of my fertilizer mix - equal parts blood meal, bone meal, and greensand - to each planting hole (for my peppers and eggplants too). Tomatoes grow roots from stems buried at planting time, so I always dig my planting holes extra-deep and set the plants in so that only the top few leaves are above the soil line (removing any leaves below). The extra root area makes for much stronger plants later in the season, and better able to withstand our hot, dry summer weather.

Nitrogen Deficiency
Pale leaves, turning yellow, especially the lower leaves. Plants grow slowly and leaves are small. Flower buds turn yellow and drop off. For a quick remedy, spray your plants with a diluted fish emulsion or other liquid fertilizer.

Phosphorus Deficiency
Reddish, purple leaves, especially the underside veins and stems. Most often occurs in acid soil, and temporarily in cold, wet soils. Spray with diluted fish emulsion or liquid fertilizer, and add some wood ashes to the soil.

Potassium Deficiency
Slow growth and low yields. Leaves develop a yellowish-green color on the edges, bronze spots appear between the veins, that eventually turn brown and brittle. Spray with diluted fish emulsion or liquid fertilizer, and add some wood ashes to the soil.

Foliage curls, puckers, turns yellow
Aphids. Look for ants - they are a good sign that your plants have aphids. For light infestations, spray the plants vigorously in the early mornings every other day. For heavier infestations, spray with an insecticidal soap solution every few days until the aphids are under control.

Seedling Stems Severed at Soil Level
Cutworms - 1-inch dull-colored plump larvae that curl up when disturbed. They feed at night, and hide under the surface during the day. Protect individual plants with paper collars around stem at ground level and a bit below, or sprinkle cornmeal or bran around each plant.

Leaves Stippled Yellow
Mites. Spray plants forcefully with water, or a insecticidal soap solution, every few days until under control.

Large Holes in Leaves, or Leaves Completely Gone
Tomato Hornworm - a large (3 to 5-inch) caterpillar, green with white stripes and a pointed horn projecting from its rear. They start eating near the top of the plant, leaving entire stems without leaves. Also, look for dark colored droppings on the leaves below. Look for them alongside larger stems during the daytime (spraying the plant with water can make them thrash about, making them easier to see), and handpick from the plants (chickens just LOVE hornworms thrown into their pen - yum yum!). If you can't find the pests in the foliage, dust the plants with BT (Bacillus thuringiensis - a biological control that only affects caterpillars).

or Slugs. They work their way from the bottom of the plant up. Look for trails of slime on leaves or soil beneath plants. Handpick, create barriers with sand, ashes or hardware cloth, or make slug traps by creating shaded places under old boards, carpet pieces, cabbage leaves, grapefruit or melon rinds and then remove slugs daily.

Weakened Plants with Yellow Leaves
Whiteflies. When an infected plant is shaken, it looks like dandruff flying from the leaves. Honeydew secreted by the whiteflies encourages fungus and mold on the plant. Use insecticidal soap sprays to both prevent and treat whitefly infestations.

Damping Off - caused by a fungus in the soil. Seedlings with damping off just topple over at the soil line and die, cold soil can increase the potential for damping off. It can be prevented by using commercial potting soil to start seeds, or by heat-pasteurizing your own soil in an oven or under plastic in the sun before using. Using a fan for better air circulation around seedlings can both prevent damping off and make the stems grow stronger. I've found that watering just-sprouted tomato seedlings with a strong chamomile tea, and then bottom-watering after that can also stop damping off.

Most tomato diseases cannot be cured. If you think you have an infected plant, pull it out to prevent the disease from spreading to the rest of your plants. Wash hands and tools in a bleach solution before touching other plants. Better to lose the yield of just one plant than your entire crop. Many hybrids have been developed with resistance to some diseases - it may be better to buy seeds or plants and grow them instead of saving seeds from heirlooms if disease is common in your garden.

Curly Top - foliage yellows, curls, and twists to roll upward, exposing the undersides of the leaf. Veins in leaves turn purple and foliage becomes stiff and leathery. Plant growth stunted and fruit ripens prematurely.

Bacterial Wilt - plant wilts rapidly, and dies. Usually wilt from environmental problems occurs more slowly. If conditions in your garden are good and a plant wilts suddenly, remove it.

Fusarium Wilt - leaves yellow from base of plant upwards, sometimes only on one side of the plant or one half of the leaf. Leaves wilt noticeably before the plant dies.

Mosaic - Stunted, yellow, bushy plants with shoestring leaves. Aphids spread mosaic, so control aphids as soon as they appear, with strong water spray or insecticidal soap.

Many other diseases can be prevented by good fall clean-up practices in your garden, not working around the plants when they are wet, and keeping tobacco users away from your tomato plants. Your local garden center or Co-operative Extension office can tell you more about diseases and pests specific to your region. Once gardens in my area are up and growing, I'll try to add photos of specific problems to this post.