Disease, Temperature Extremes Can Cause Tomato Problems

Aug 13, 2013
Tomatoes are subject to a number of problems. 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 to which that particular tomato is resistant).
 
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 degrees and 70 degrees Fahrenheit 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 degrees or above 80 degrees, 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 degrees and 80 degrees. However, during hot weather above 90 degrees, 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 that 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 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. Maintaining proper calcium levels in the soil can also be helpful.
 
Of the diseases, tomato anthracnose is the most common. Caused by a fungal pathogen, the disease infects lower leaves and makes them wither, turn brown and collapse.
 
It also infects fruit, 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 that repeat the disease on new leaves and fruit. Avoid overhead watering, as this spreads the disease, and remove infected leaves from the plant.
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