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What are the most common problems of tomatoes in this area?
Tomatoes are subject to a number of problems. Of these, some are related to cultural practices and weather conditions while others are caused by fungal plant pathogens. Always choose tomato varieties that are disease resistant. Look for tomatoes with several initials after their names (i.e. VFN--each initial represents a disease that this particular tomato is resistant to).
Tomatoes dropping their blossoms and not setting fruit is common here. If your tomatoes are doing the same, then you have good company. The fact is that conditions for tomato fruit set are quite narrow. Night temperatures between 60 and 70 F are ideal. Low or high temperatures present more of a problem with successful pollination and set. Frequently, gardeners will attempt to stimulate setting of fruit by making an application of "blossom set". The active ingredient in this material is a hormone that improves the chances of successful pollination. During periods when the night temperatures are below 60 F or above 80 F, this hormone, as it naturally occurs in the plant, becomes depleted. An application of hormone can overcome this problem but is only worth the effort when the problem is cool weather. Improved set may occur at temperatures between 70 and 80. However, during hot weather above 90 F, it is not effective. The ultimate sacrifice is when tomato plants abort their blossoms, a problem also due to temperature extremes. Again, there is no real solution to the problem and no cultivars exist which seem better than others.
If your vines did not seem to produce any or small numbers of fruit, they may have been watered and fertilized too aggressively. Excessive amounts of nitrogen in the initial stages of growth will promote growth of leaves and stems and suppress flower formation. This can be corrected by pinching the terminal growth and root pruning. The latter is done by inserting a spade into the ground around the periphery of the plant root system in about three places. Do not completely circle the plant as this will lead to some die back.
Another disorder of the fruit you may have noticed is called blossom end rot. At an early stage of development you will see a small water-soaked spot at the blossom end of the fruit. This will continue to develop until it consumes about half the size of the fruit and looks brown to black, circular and somewhat leathery. The symptoms appear after a particularly moist early growing period followed by a drought spell. If watering schedules are not uniform and plants are growing in high clay soils where moisture is sure to fluctuate, blossom end rot is more common. Mulching ensures that the moisture levels remain more uniform. A consistent watering schedule will help to avoid moisture level extremes promoting this problem. If you have had a high frequency of fruit with end rot, for next season, work more compost or peat moss into the soil to buffer the moisture levels.
Of the diseases, tomato anthracnose is the most common. Caused by a fungal pathogen, this disease infects lower leaves and makes them wither, turn brown and collapse. It also infects fruits, ripe or unripe and appears as numerous circular, water-soaked, slightly discolored lesions anywhere on the fruit. A semi-soft decay will occur and make the fruit unattractive. Extreme decay will lead to complete loss. Control by non-chemical means requires removal of infected lower leaves and fruit as soon as you notice discoloration. The lesions contain spores which repeat the disease on new leaves and fruit. Avoid overhead watering, as this serves to spread the disease. Rotating next years crop to another garden area is also good practice. Infected leaves which were not cleared out would be the source of inoculum for next years crop. It takes about three years before infested leaves decay and the fungus is destroyed.