When Will This Cotton Start Growing? (Collins & Edmisten)

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Several calls have come in over the past few days with folks expressing frustrations regarding how this cotton crop is not growing. It’s no surprise that this stagnant growth is the result of cooler weather, and it is clearly exacerbating the issues we are seeing with heavy thrips pressure across much of the state. Rapid growth can offset some of the issues we are seeing with thrips, but when can we expect to see this crop turn the corner and begin to grow.

Most every year has it’s cool spells, and 2023 is no different. The chart below illustrates heat unit accumulation at Rocky Mount from May 1st to June 4th over the past two years. It may not be fair to compare last year to this year, in that we’ve experienced both extremes during these two years, with 2022 being warmer than normal, and 2023 being cooler than normal. When observing heat unit accumulation for the last two years, take not of where the “plateaus” occur which indicate a period of low or negative heat unit accumulation. The more obvious cool spells occurred during May 6th-12th in 2022, and a very short spell around May 24th-25th, with very rapid heat unit accumulation both before and after each of these cool spells. In 2023, cool weather prevailed during the first week of May, in which little cotton was planted during that time, but also during May 18-19th and May 24th-28th. Aside from these “obvious” periods, heat unit accumulation was simply slower even during the times we’ve had a little heat. We cant say that it’s been “cold” per se, simply because stands have been very good across much of the state, but growth has been noticeably slower, simply as a result of slower heat unit accumulation.

Heat unit accumulation

So when can we expect this to change? It is very difficult to say how many heat units are required to develop a new node or true leaf, especially when growth is expected to be slow, such as during the early season. Furthermore, heat units also need to be accompanied by adequate soil moisture and sunny weather in order to be able to predict growth. Most areas have had decent soil moisture, but we have had cloudy weather. Cloudy weather, thrips pressure, seedling disease, herbicide injury, etc. can complicate the ability of heat units to predict future growth as well. However, we can say that 10 or more DD-60’s per day for several days would likely lead to more rapid growth. To achieve this, we need daily highs to exceed 80 degrees, and nighttime lows to exceed 60 degrees. In the absence of herbicide injury, seedling disease, cloudy weather, etc, we could expect to see a new node or true leaf every 3 to 4 days under these conditions.

In the chart above, the predicted heat unit accumulation for the next week at Rocky Mount can be seen to the right of the green line, and this is based on the current forecast. The next day or two are expected to bring decent temperatures, and again during the latter part of the week or weekend, as indicated by the sharp change in slope of the line. With that said, assuming the forecast holds true, we would expect to see growth noticeably accelerate by this weekend into early next week, which would obviously help the current situation with battling thrips. Check your local forecast to observe more local temperature forecasts.