Late tomato blight

(Question)

From having read one of your questions concerning late tomato blight, I believe that is what I have. I have planted about 200 plants for the last 40 years and have never had this before. Can you please tell me what I can do next year to prevent this…thank you so much.
The blight forms in blotches about the size of a quarter on the tomato. Eventually the whole tomato is consumed by the blight and eventual rot. Usually blight wrecks the plant but not the tomato. This blight destroys everything.
Thank you so much for your help. I really appreciate it.

(Answer)

It is terribly disheartening when this happens after nursing the plants through the whole summer.

Blight spores thrive in periods of wet weather and high humidity, and there is really nothing you can do once it has taken hold.  One of the best ways to control blight is to ensure that you thoroughly remove and destroy all affected plant matter, as well as other plants that you grow in your garden that are of the “deadly nightshade” family.(e.g. Petunias or Nicotiana ) as bits of these plants left in the soil can overwinter the spores.

Unfortunately there are mixed reviews about blight resistant tomato varieties.  One idea might be to grow early ripening varieties as they will ripen before late blight sets in.

The government of BC has a very good website (I have included the link at the bottom of this message) but here are some of their suggestions:

  1. Grow plants in a warm, dry, sunny area. If you have had blight previously, move to a different area if possible, or replace the upper soil layer since “oospores” will carryover in soil.
  2. Water only underneath the plants, not the foliage. Drip irrigation is preferable to watering with a hose, to reduce water splash. Don’t over fertilize or over water.
  3. Grow on a light sandy soil if possible or cover soil with a white plastic mulch to increase soil and air temperatures around the plants and reduce humidity.
  4. Growing plants under an overhang or a clear plastic shelter will help prevent spores from being deposited on plants by wind and rain. But plants must be covered before infection has occurred. Covering the plants after they are infected may raise humidity and make the disease worse.
  5. Grow the tomatoes on raised beds with well-spaced trellises or in containers off the ground. Tomatoes grown on balconies or roof-tops rarely develop late blight, probably because the environment is warmer and drier.
  6. Remove all of last year’s tomato or potato debris to prevent carryover of disease.
  7. Remove diseased leaves, shoots and plants that are severely diseased, immediately. Bury them, or seal them in a plastic bag and take to a landfill. Do not compost diseased plants. If “oospores” are present, they will survive in compost.
  8. Destroy any volunteer potato or tomato plants in the garden.
  9. Destroy any nightshade weeds in and near the garden. Nightshade is related to tomato and potato and is also a good host for late blight.
  10. Apply copper sprays or other home garden fungicides recommended for late blight at least once a week when weather is favourable for disease. READ THE LABEL. Copper, which is accepted by most organic producers, should be applied for prevention more than cure, that is, before the disease has become established.
  11. Gardeners who are unable or choose not to follow a regular fungicide spray program for late blight are strongly urged to destroy (bag or bury) all infected tomato or potato garden plants or plant parts as soon as the disease is observed. If in doubt whether it is late blight, take a sample to a local garden centre or Master Gardener for identification.

Good luck with your tomatoes in the future!

https://www.agf.gov.bc.ca/cropprot/lateblighthg.htm

For more in depth information on tomato blights and other diseases, this may also be of interest:

https://vegetablemdonline.ppath.cornell.edu/cropindex.htm