How will the plant respond in cloudy weather? This blog from CottonInfo technical specialists Susan Maas and Sally Ceeney (with input from researchers Stephen Yeates, Michael Bange & Ian Rochestor) investigates...

Cloudy weather and rainy days can impact plant growth. Low temperatures can lead to establishment issues and unusually cloudy or rainy conditions can change the look of the plant - plants may produce bigger leaves in response to generally low radiation. Root development can also be affected, as root systems do not need to seek out moisture at depth.  

Low radiation can lead to some shedding of squares, as plants cannot produce the food (energy) to support them. Plants will compensate for shed squares when sunny conditions return. It is important to ensure the plants have sufficient nutrition and water at this time to compensate & that Pix is not over used as it can suppress the production of new fruiting sites. It is best to assume that if early squares are shed a good yield will only be achieved on a taller plant because new nodes are required to replace lost squares.

Some other key considerations:

Waterlogging: will generate additional physiological responses to those that are simply experiencing sustained warm, cloudy conditions, and in wet soil. Water logging is accentuated by rainfall after irrigation, cloudy conditions, and inadequate land preparation. Symptoms of waterlogged cotton include a general yellowing of the crop and stunted growth.

The major and immediate effect of waterlogging is blocking transfer of oxygen between the roots and the soil atmosphere. Plant roots may become so oxygen deficient that they cannot respire. As a consequence, root growth and absorption of nutrients is decreased leading to less overall plant growth. Waterlogging can increase sodium uptake which may then affect the uptake of other nutrients and the growth of the plant. 

In addition to the physiological impacts of waterlogging on the crop there are also significant impacts on nutrient availability and uptake. The availability of Nitrogen (N), Iron (Fe) and Zinc (Zn) (reduced) and Manganese (Mn) (increased) are directly affected by the decline in soil oxygen, and uptake of N, K and Fe by the roots is also impaired.

Nitrogen: denitrification of soil mineral N, may result in less N being available to crop even after water logging has ceased.  Foliar N is more effective in increasing the yields of waterlogged cotton when applied one day before irrigation under hot, sunny conditions. Application to a field that is water logged will not necessarily alleviate existing damage. Growers may be tempted to apply more N fertiliser to replace what may have been lost – leaf testing will indicate if this is necessary.

Recovery from waterlogging and fruit shedding is easier to manage on younger crops. Crops suffering from a combination of early shedding and reduced N uptake can cut-out prematurely that is the flower will reach the top of the plant with very few bolls set. Adding N in this situation can cause a second flowering & significantly delay maturity.

Phosphorus and potassium: Waterlogging is possibly involved in premature senescence of cotton. Under waterlogged conditions, uptake of P and K by the cotton crop may be reduced, predisposing the crop to the premature senescence syndrome.

Iron: The young leaves of iron deficient plants become yellow between the veins (chlorosis). The veins usually remain green, unless the deficiency is severe and the whole leaf may eventually turn white. Although the plant may contain high concentrations of iron, most of it is unavailable for chlorophyll production and the leaves lose their green colour. Foliar application of 200 g Fe/ha with a ferrous sulphate may return foliage to its normal colour within 2-3 days.

Nutrition monitoring and application: Petiole testing is not an option during cloudy, inclement weather. However, leaf tissue testing is the better option when weather conditions improve, to identify which nutrients may be lacking. NutriLOGIC  can help interpret results. Foliar fertiliser formulations that include N, P, Fe and Zn will probably be the most helpful, but best to wait until the sun shines. 

Irrigation management: As the plant, and in particular the root system has developed during a very wet period, when the weather warms up and soils dry out, irrigation scheduling will need to be responsive to the potential smaller root system, with shorter and more regular irrigations, particularly during periods of heat.  Use of probes for scheduling as well as responding to signs of stress in the plant is needed.

Vegetative growth management: Due to the indeterminate nature of the cotton plant the vegetative and reproductive growth occur in parallel and it is important to keep the reproductive and vegetative growth in balance. Crops that are too tall and rank are difficult to manage and pick and will not yield at potential, however short determinate crops may be limited in yield potential and can struggle to compensate if fruit loss occurs during future cloudy periods. 

It is important to closely monitoring vegetative growth rate (VGR), fruit retention & boll size. If excessive vegetative growth is detected, the use of mepiquat choride (PIX®) should be considered. Growth regulator applications combined with moisture stress can result in yield reductions.  Multiple small doses of Pix are usually better in these situations.