The 2017 growing season is thus far a decidedly wet one. Rainfall throughout the state (Alabama) was a welcome change from the previous dry spell, but excessive amounts have delayed cotton plantings or caused isolated replants. For cotton that is established and approaching squaring, the next critical management activity is application of PGRs.
Heavy rainfall years will require a change in PGR strategies, especially for dryland producers. No matter the strategy though, it is critical to get the first application out early – prior to 1st bloom or even early if excessive growth is present. This is crucial to managing growth later in the season. Growers cannot rely on late season applications alone. A lone high rate application late in the growing season may achieve early cutout, but will have missed the objective of early season boll retention and growth reduction.
There are several misconceptions of what PGR accomplish in the cotton plant. They do not stimulate flowering, boll production, or have any significant effect themselves on yield. The do improve boll retention especially in the lower canopy, manage excess canopy growth and there by allows better pesticide penetration, can reduce boll rot incidence, and reduce lodging. It is all of these things combined that contribute to the likelihood of increased yields.
The name of the game is 'Boll Retention,' especially early in the lower canopy. Retaining first position bolls boosts yield potential substantially. High square loss (25% or greater) trigger the plant to compensate with increased node production, greatly adding to excess vegetative growth. This growth is hard to control later in the season. In larger plants, it is difficult to get a high enough PGR concentration to have the desired effect of reducing growth. Early season PGR applications are extremely critical in wet years. The challenge is compounded by fewer chances to get the sprayer in the field. Therefore, it is imperative for growers to track and understand their cotton growth so timely applications are made.
DD60 = ((Max temp + Min temp)/2) - 60
Knowing the DD60 accumulation in a given field is important to effective plant growth monitoring. The table (below) gives a basic summary of DD60's required to reach flowing stage in cotton. During these critical stages measuring Height to Node Ratio (HNR), which is total plant height dived by the number of nodes present, can give a grower a good clue as to the type of growth the crop is having. If measurements are in the vegetative range, an aggressive PGR strategy would be advisable.
For some basic take home points, PGR application is justified when:
- Height: Cotton plant is 25-30 inches tall or greater during the 1st week of bloom.
- Nodes Above White Flower (NAWF): Plant has greater than 9-10 nodes above first white flower during 1st week of bloom, and optimum growing conditions look to continue.
- Square/Fruit Retention: Square retention is low (50-75% or less) at first bloom and soil moisture is high.
- Internode Distance: Is 3-5 inches between 4th and 5th node from terminal.
Cutts is the Alabama Cooperative Extension System cotton specialist.