Making the cotton replant decision

Adverse conditions experienced during or after cotton planting can negatively impact cotton seedlings and result in seedling death. If severe, stresses can reduce stands to unprofitable yield potentials. Unfortunately, cool nights, excessive rainfall and marginal seed quality from some seed lots have increased reports of failed stands. Determining whether to accept or replant a marginal stand of cotton is a particularly challenging decision since many factors must be considered. The purpose of this post is to highlight a few factors to consider while making the replant decision.

Factors to Consider:

Calendar date. In Tennessee, the recommended cotton planting window falls between April 20^th and May 10^th. While profitable yields may still be possible at later planting dates, later planting dates delay boll development into periods associated with greater insect pressure and less rainfall and increase the likelihood of exposing the later developing bolls to an early freeze (Table 1). Subsequently, a stand that may be considered poor on May 1^st may be acceptable on May 25^th. Recent evaluations of planting dates and populations clearly display this trend (Fig. 1); as planting date moves later in May, the relative yield potential of the stand declines at a rapid pace. Establishing a uniform stand prior to May 25^th is crucial to ensure ample time is available to accumulate enough heat units to finish the crop.

Table 1: Date and probability of a fall freeze by location.

Figure 1: Predicted lint yield potential based on planting date graphed by plant population. Model generated from five populations across seven planting dates in Mississippi, Missouri and Tennessee. Populations are reported in plants per acre.

Plant population. Research evaluating the influence of plant population on cotton yield consistently suggests uniform stands of as low as 1 plant per foot may produce a profitable crop and limited yield increases are associated with populations in excess of 20,000-30,000 plants per acre (Fig. 1). It is critical, however, that the stand is uniform; while cotton can compensate for low populations and variable distances between plants, skips greater than 3 row feet will negatively impact yields. Fields that possess a large number of skips greater than 3 feet in length will likely warrant a replant.

Table 2. Plant populations at various row spacings.

Evaluating the existing stand. The most common approach to assessing stands is the 1/1000^th method, which consists of counting the number of plants within a certain distance of row based upon row spacing (Table 3). The number of plants in the corresponding distance is then multiplied by 1,000 to provide an estimate of the number of plants per acre. In order to account for field variability, this process must be repeated in a randomized pattern approximately 10 times. Other parameters should also be noted while evaluating plant population. Note the number and spatial density of skip lengths longer than 3 row feet. Also understanding the cause of poor emergence is important. Was the stress caused by soil crusting, herbicide damage, limited moisture, or disease? Determining the cause will provide guidance to cultural practices that may save the existing stand and/or corrections that should be made prior to replanting. Examine plant terminals to determine if new growth is emerging or if severe injury has occurred. Occasionally, only small areas of impacted fields require replanting. A partial replant will likely be less expensive but will result in different maturity ranges within the same field. If a spot-replant is selected, replant with a variety with a similar growth habit and maturity.

Table 3. Length of row needed for 1/1000th method

Costs, cultural practices, and other points. In some scenarios, replanting to cotton or planting to an alternate crop is not an option. Verify spray records to identify if products with long replant intervals to soybeans have been used, as these virtually lock you into replanting cotton. Also, contracts with the gin or land owner may require cotton to be produce on those acres. Has a crop specific fertilizer been applied? What will seed or technology fees cost in a replant scenario? Will replanting cotton be more profitable than planting another crop or properly managing the currently emerged crop? The upcoming weather forecast must also be considered. Do the next 5 to 7 days like more conducive to plant growth or rapid germination and emergence? Also consider the variety planted and availability of seed for the replant. Determinate, early maturing varieties will likely be more affected by reduced numbers of plants.

Figure 2: Accepting thin stands may be acceptable if there are few skips larger than three ft in length and the field generally has a minimum of one plant per row ft.

Managing a replant or poor stand

The first step in managing a replant or marginal stand is to develop a realistic yield goal. Considering the financial aspects of each in-season input will be necessary to properly select timings and rates and guarantee a profit is realized at the end of the year. In both scenarios, managing for earliness and aggressively protecting first and second position fruiting bodies will be very important. For more information on managing for earliness refer to Guide to Earliness Management in Short-season Cotton Production (PB1830).

If replanting, the original stand should be killed through mechanical or chemical means. In Tennessee, it will almost always be necessary to select an early maturing variety for the replant. Particular attention should be placed on plant growth of the replant. Often, an aggressive mindset must be taken to eliminate the chance of delayed maturity from excessive plant growth. Closely monitor internode elongation, especially in the event a mid-maturing variety is planted. Additionally, a slight reduction in nitrogen rate will reduce input costs and help to manage earliness with a negligible impact on yield potential.

Keep in mind that later planting dates will delay boll development into periods associated with increased levels of insect pressure. Many of these pests will have to be managed later than an earlier planted crop. Furthermore, sole reliance on Bt traits may lead to failure of the technology. An application of a late season bollworm product may be warranted in the event of late planting.

Cotton is forgiving and it should be noted that the general rule of thumb among most cotton Extension specialists is ,’if the decision to replant is difficult, then there are probably enough plants to keep the stand.’ Once you make this decision, stick to it, and if managed properly, you will likely be pleasantly surprised by the results.