Late Season Fungicide Applications – Vegetable Crops Hotline

Late Season Fungicide Applications

Recent heavy rains have caused an increase in foliar disease in many vegetable fields. A sudden increase in foliar disease may lead some growers to purchase expensive fungicides to take care of the problem. However, there are several considerations before one applies the most expensive fungicide.

  1. The optimum time to apply a very effective, and perhaps expensive fungicide, is right before or at the time of intense disease pressure. This is because an effective fungicide on the leaf surface just as spores arrive may help to halt or at least significantly slow disease progress. Using a disease-forecasting system such as MELCAST for cucurbit growers should help to time such applications.
  2. An effective fungicide applied after infection may enter into the leaf and halt some infections, but such an application will not be as effective as one applied right at or before infection.
  3. When looking at a field that one wants to rescue, note that no fungicide will bring back green tissue. No amount of ‘kick-back’ that a fungicide may have will cause brown tissue to turn green.  The most one can hope for is that plants that have had an effective fungicide application will begin to produce healthy new growth.
  4. Unfortunately, the amount of diseased tissue that one observes in a field is almost certainly worse than can be observed with the eye. This is because initial infections can’t be seen with the naked eye until 7-10 days after infection.
  5. Make sure that the symptoms you observe are really an infectious disease and not physical injury or a nutritional problem.
  6. Check the Pre-Harvest Interval of the fungicide you intend to use.

The message here is that the best time to apply effective and potentially expensive fungicide applications is earlier in the season—right before or early in the disease cycle. Be realistic about late season fungicide applications!

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