Target spot and boll drop – the knowns and unknowns

Authored by Heather M. Kelly, Extension Plant Pathologist and Tyson Raper, Cotton and Small Grains Specialist, University of Tennessee

This is a repost from the UT Crops News blog. Since it has general information, I thought I would include it in our regional blog.

The abnormally warm and wet conditions in the Mid-South during August have contributed to the highest level of target spot-driven defoliation in commercial fields to date. Still, the majority of Tennessee’s cotton will not see a yield penalty from the disease due to a late onset and very low levels of defoliation.  However, the warm and wet conditions during August in conjunction with excessive rates of nitrogen, high planting rates, narrow rows, and/or rank growth have resulted in defoliation in excess of 50% on a limited number of acres.    Within confined areas of a small percentage of these fields, large boll drop has been confirmed (see images below).  This boll abortion phenomenon appears to be caused by a lack of supporting resources for developing bolls low in the canopy as a result of excessive defoliation caused by target spot.  Aborting bolls are typically:

  1. Second position fruit
  2. Located on first or second fruiting branch (nodes 6-9)
  3. Vary in size from a quarter to slightly larger
  4. Are immature at the time of abortion (estimated at 14-20 days of age; no seed coat color, still have jelly in seed, are easy to cut with a sharp knife).
  5. Are a minimum of 5 nodes away from the nearest leaf (either subtending or mainstem) remaining on the plant.

Please go to the UT Crops News blog for the entire post.

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