Do you have a sad tiny plant that isn't producing much fruit and has misshapen odd leafs unlike any of your other tomato plants? There are more than 20 common viruses that can impact your plants health and harvest. The sad fact is you should really pull and destroy these plants immediately to prevent the virus from spreading. Chin up, there's always next year!
Avoid over-watering tomato plants; just because a plant is wilted doesn't mean it needs more water. Check the soil; if the soil is dry (does not stick to your finger) then water your plant concentrating the water at the base of the plant, not overhead.
PESTS (Caterpillars + Whitefly + Greenflly + Blackflly + Slugs)
Inspect your plant's leafs every few days for holes, bumps or bugs. Plant spearmint (in pots to prevent spreading), clover or daisies in proximity to your tomato plants to attract paper wasps, a natural predator of the horned caterpillar that rarely have stingers (next year to do list, check!). Feel free to manually remove pests at the end of a rough day with a big squish between your fingers (hey it's also organic). If you think you have slugs apply a thin layer of Diatomaceos Earth dust around the base of each tomato plant. An insecticidal soap picked up at your neighborhood garden center (we like Eggplant Urban Farm Supply) will also help fend off pests.
RED SPIDER MITES
Look for thin spiderwebs all over the plant or for the spider and eggs themselves on the underside of the leafs. Spray plants with a fine mist of water, twice daily, as the spider mite can only thrive in hot dry conditions. An insecticidal soap picked up at your neighborhood garden center (we like Eggplant Urban Farm Supply) will also help but should be sprayed every week.
You may start spotting the green unripened areas around the stem of the plant. Because this problem is caused by high heat and too much sun you really can only prevent this from happening by providing some shade for the plant (eg. a trellis, other taller plants or trees, we like giant sun flowers). Tomatoes with greenback are still edible, just cut the green sections off or allow them to ripen more in doors in a brown paper bag for a day or two.
This will first begin to appear as a white or yellow spotted area on the upper side of tomato that faces the sun. It's not really dangerous to the plant but long bouts of high heat can cause the fruit to blister then you might get fungal problems. Cages can help and a little extra nitrogen in the soil but rethink next year's planting spot. Give the plants a little shade provided by a fence or taller plants. If you know your growing space is susceptible to Sun Scorch plant tomato varieties that naturally have larger heavier foliage
Early tomato blight forms spots on the leaves, which then turn yellow and die. The spots may start out small and shrunken and as they get bigger they get longer. Spots which are on the stem near the ground can cause the stem to shrink.
Avoid overhead watering (do we sound like a broken record yet?) by watering at the base of the plant. Water your plants only in the mornings to give the leafs time to dry out. If you see anything that even remotely looks like blight, begin a spraying program of alternating organic copper spray, and Serenade biological fungicide, both of which are safe to use on edibles. If you have Late Blight (blue gray spots on the leafs and fruit that are turning brown) pull the effected plant immediately.
Real talk, I plant a few extra plants (spaced far apart to prevent overcrowding but also to prevent problems from spreading) and if any of my plants show any sign of blight I pull the plant. The earlier the better to prevent it from spreading to other healthier plants.
BLOSSEM END ROT
If you've spotted a dark, rotting spot on the bottom of your tomatoes the soil pH should be 6.5 to 6.8 to free more calcium in the soil chemistry. Test results will indicate the amount of lime to add. Even better, lime also contains calcium. Work the lime into the top 12 inches of soil. Use a lime labeled “fast-acting,” which is better than ground limestone unless you have weeks to wait for the lime to react in the soil. If the pH is already correct, the soil test will recommend a different calcium source, such as gypsum. Also, add crumbled egg shells to your compost or bury them in your garden over time to help maintain the calcium levels.
This is almost unavoidable during the end of a growing season, unless you are in a green house. Water regularly and fertilize the soil often to keep the plant happy and the soil around it healthy. We like Dr.Earth on our tomatoes.