July 25, 2009

1 - Blossom end rot in New Mexico is due to hot, dry conditions.

Yard and Garden July 25, 2009


I have a healthy tomato plant. The fruits have black bottom areas as if rotten. Would this be caused by the current extreme heat we are having or am I watering too much?

- Steve G.



Your tomatoes have blossom end rot. This is a problem caused in New Mexico by heat, wind, and sun. A few weeks ago it was so hot and dry that the plants could not get water to all parts of the plant. Water carries calcium from the soil that is necessary for the proper development of the fruit, but on hot, windy days, the plants are unable to get water and calcium to the flowers and newly forming fruit. As the newly formed fruit enlarged, the damage (caused earlier by those hot days) became evident. Most books say to add calcium to the soil, but in our soil that is not necessary, we already have too much calcium in the soil, but on hot, dry, windy days the tomato plants cannot get it to the place where it is needed.

Pick off the damaged fruit and compost them. When the weather finally cools (and, hopefully, the monsoon comes) new fruit will form that do not have damaged blossom ends. Your fall crop of tomatoes should be OK. A friend reduced this problem by shading his garden with overhead slatted snow fence. The traditional Native American system of growing plants under clumps of corn plants also helps by shading and reducing wind around the other plants (they essentially grow shade over their tomatoes, chiles, beans, and squash).

2 - Tomato spotted wilt virus is a problem in New Mexico


Last week your garden column discussed curly top virus. As a Master Gardener in Sandoval County, I have seen a lot of problems this year. Curly top is one of the problems, but often plants were diagnosed to have tomato spotted wilt virus as well. Sometimes the plants had both viruses.

- Therese B.

Sandoval Co.


Your comments provide good information. Both viruses and some other tomato diseases are problems in New Mexico. You mentioned diagnosis. Proper diagnosis is important and can only be done in a properly equipped laboratory, such as the Plant Diagnostic Clinic at New Mexico State University. Local NMSU County Extension Service agents can send samples to the laboratory for gardeners who must know what is wrong. However, in the case of both viruses, the results are the same. The plants do not produce many tomatoes, if they even survive. In the case of tomato spotted wilt, the tomato fruits are usually not edible (not dangerous, but do not ripen properly). Tomato spotted wilt virus is spread by a different insect, but like the curly top virus, it must overwinter in a living plant. It is then transmitted to the garden vegetable by thrips insects. More information regarding this disease of tomatoes and other garden plants may be found in NMSU Extension Guide H-242 Tomato Spotted Wilt Virus.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.


For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook page.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!