The 2019 growing season in Virginia is one that has been marked by a good planting window in early May resulting in a sizable portion of Virginia cotton planted in the first two weeks, followed by spotty rainfall events across the growing region with most areas receiving adequate rainfall throughout the season. Couple the early planting date with light overall insect pressure early during the reproductive period resulting in higher than normal fruit retention across Virginia. Yes, there have been pockets of high pressure from tarnished plant bugs, but for the most of Virginia pressure as been light through June and July. Cotton was flowering by July 4th in 2019 with early planting and entering week 5 or 6 of bloom by the first week in August. Data in Virginia show that nutrient concentrations in leaves and petiole decrease rapidly from the 1st to 4th weeks of bloom, indicating the plant is beginning to shut down in terms of nutrient uptake. After the 4th week of bloom nutrient concentrations level off at lower concentrations. With dropping petiole and leaf nitrate-N, sulfur, and potassium, fields will begin to show signs of nutrient deficiencies and overall yellowing or reddening. These areas will be more pronounced in sandier areas first then spread into heavier textured soils.
First, producers and/or crop consultants should evaluate nodes above white flowers (NAWF) to determine if cotton has reached “cutout”. Cutout has been described as the point at which NAWF < 4 or 5. Cotton that has fallen below this threshold and exhibiting overall yellowing or reddening will be at “cutout”. These symptoms usually occur towards the latter part of August in Virginia, but given higher fruit retention in 2019 coupled with an early planted crop and high heat unit accumulation these symptoms will occur sooner in 2019.
One may worry if your crop has low boll retention, also commonly referred to as “missing positions” and is exhibiting the symptoms of cutout. . Insect damage and other environmental conditions resulting in low fruit retention typically will delay maturity thus cotton will stay greener longer and exhibit a high level of vegetative growth. In this case, review rainfall data and nutrient management strategies as some environmental condition may have increased nutrient loss thus reducing crop uptake resulting in premature cutout. An example may be a large rainfall event leached a significant portion of nitrogen/sulfur/potassium thus cotton is running out of nutrients. There is no management strategy that will “make up yield” in this situation at this point in the season, however nutrient management strategies could be tweaked in future years to hedge potential losses in the future.
Earlier than normal cutout does not signify the need for higher rates or additional applications of nutrients, especially if boll retention is high and heat unit accumulation is appropriate for that growth stage of the crop. This is the natural senescence (entering dormancy) for cotton and is a positive when discussing defoliation and harvest aid applications. For Virginia, the last effective bloom date is around Aug. 25-31, so even though cotton has reached cutout early this does not mean it is no longer susceptible to insect pressure. Continue to scout and follow Dr. Sally Taylor’s recommendations to protect later bolls, which can represent around 10% of lint yield.
For further questions or concerns feel free to contact me at whframe@vt.edu and/or 757-807-6539.