A drastic change in weather pattern has brought cooler temperatures and rainfall into the forecast for the remaining days of July. Recent calls have questioned how we might need to change our approach to plant growth regulation and fungicides, given this abnormal forecast. In this blog, I highlight a couple of things to consider as we move into next week.
I think it best to begin this discussion by recognizing that it is fairly difficult to describe the ‘average’ TN cotton acre. There are clearly ‘early’ and ‘late’ acres, with considerable range within the ‘late’ classification. We also have areas which have received almost perfect rainfall amounts through the end of June into July, which are contrasted with areas which have missed most all rainfall events up til the rainfall events which fell earlier this week. Best management within these scenarios will be quite different, and while the extremes I will describe will directly apply to some acres, many will find themselves in-between.
I also want to point out that while cotton ‘likes it hot’, cotton physiologists have long considered the ideal night and daytime temperatures for cotton to be 68F and 86F, respectively (Oosterhuis et al., 2017). The temperatures forecast for the next 10 days represent as near to perfect temperatures as I’ve seen in July. I’ll also point out that cotton is not typically grown in more northern latitudes because the period of time in which temperatures reach or exceed this range in more northern states is typically too short to produce a productive cotton crop – not because more northern latitudes only occasionally break 100F.
One last point, before we move into management decisions. Prolonged periods of cloudy and/or rainy weather can reduce fruit retention; periods of low light intensity are recognized by the plant and as a response young fruiting bodies are often shed. As more resources are invested in a fruiting body (and it becomes older), the less likely the plant will choose to abort the fruiting body. Fortunately, we typically do not see fruit abortion associated with short-term periods of clouds, and if our forecast holds, I would be very surprised for the events of next week to generate any noticeable abortion.
PGRs
Now, to management. First, plant growth regulation in our latest planted cotton will soon likely need to be aggressive. Most of these areas are flowering now. The recent rainfall events will have likely moved more nitrogen into the effective rooting zone and further spurred growth. As the internode between the fourth and fifth nodes begins to expand beyond 2.5-3”, I would consider responding with between 0.5 – 1.0 ounce per node per acre of a 4.2% mepiquat chloride product, depending on variety and growth potential of the acre. A follow-up application should be planned within 10 days of the first, should excessive internode elongation continue.
Moving forward, the regulation of our earlier planted acres will likely be easier than our later planted acres, as reproductive growth in these acres has already begun to regulate vegetative growth. Many I have visited with in the past few days have mentioned NAWF near or beyond 5. If the internode between the fourth and fifth node begins to expand beyond 2.5-3” on these acres, I would consider a 16 oz application of a 4.2% product to be followed by another application within 10 days, should excessive elongation continue. On the most aggressive varieties and acres, you may consider adding 2 oz Stance to the pint application of a 4.2% product.
On acres which NAWF counts have crashed due to excessive drought, you will likely see the plant attempt to re-enter a predominately vegetative stage of growth before beginning to add more fruiting bodies. This second try at setting fruit is slow and we do not always see these bolls make the basket, but I think our chances at making this second crop may be better this year, given rainfall resumed relatively early in the season. I would not be terribly aggressive with PGRs on these plants, unless you do not want to give the plant a chance to make the second crop. I’ll add here that in a small portion of Australia, a similar two crops on the same stalk production system has become more common.
Fungicides
There has been some discussion about applying fungicides proactively in this crop. I would urge you to consider fungicides in cotton to be responsive, not pro-active, especially in a market where margins are this thin. There are scenarios where foliar fungicides in cotton can provide a return on investment, but certain things must be present for this to occur. At the moment, I have not seen or heard of a single TN field which has enough Target Spot incidence or severity to warrant an application. If other leaf spots from the ‘leaf spot complex’ are present, keep in mind that while a foliar fungicide will prevent these leaf spots from spreading, they do not typically increase yields.
I will be working closely with Dr. Heather Kelly over the coming weeks to track Target Spot incidence and severity and we will be updating the blog with information should conditions change. Expect a blog article from Dr. Kelly next week concerning fungicide use in this crop.
