Potassium Deficiency in Cotton After Bloom - The Symptoms
In 1982, a potassium (K) fertilization study was established by Arkansas Soil Testing and Research Lab personnel at the Cotton Branch Experiment Station in Marianna, Arkansas. The objectives of the study were to define soil test and petiole analysis calibrations for K fertilizer recommendations and critical K levels for petiole monitoring programs. In 1983, K deficiency symptoms began to appear on young leaves at the top of plants.
In 1988, leaf petiole K concentrations were taken to document the K deficiency symptoms that occurred at the top of the cotton plants. The following photographs/images were taken during the development of K deficiency in 1988. Unfortunately, K deficiency is still prevalent in much of the southern cotton belt. Farmers, Certified Crop Advisers, pest management consultants, fertilizer dealers, extension agents and others should become familiar with these symptoms and modify K management strategies to avoid these symptoms, which result in significant yield and profit losses.
Normal cotton in the second week of blooming. Rows on the right have received K fertilizer for seven years. At this time, on July 12, the K concentration in the leaf petiole (fourth leaf from the top) was 6.9%. Rows on the left received no K and had a leaf petiole concentration of 3.9% K.
First symptoms of K deficiency find the K deficient cotton plants turning a dark green color. Rows on the right are in the check plot. Note the dark green color. The top leaves then will become mottled with light green to gold mottling between the veins. The leaf petiole K concentration was 1.3%. Rows on the left received K and had a leaf petiole K concentration of 3.1%
This is an image of plants in the check plot of the K study during the sixth week of blooming. Top leaves continue to turn yellowish-green to gold and leaf edges are turning brown. Leaf petiole K concentration was 0.61%. Note that the bottom leaves appear normal.
An adjacent K plot received 150 lb K2O/A each year and had a leaf petiole K concentration of 3.42%. Plants in this K plot had a normal apearance.
Potassium deficiency symptoms advanced and were severe by the seventh week of blooming in the check plots. Leaf petiole K concentration was 0.19%. Top leaves are severely "rusted", reddish-brown in color, shriveled and curling. Most bottom leaves still appear normal ..... and adjacent 150 lb K2O/A plot had
a leaf petiole K concentration of 2.8%.
Top leaves are shed in the plot with no K applied. Leaf petiole K concentration is less than 0.10%. Bolls are poorly formed. Some normal leaves are still found at the bottom of plants.
Some have questioned whether K deficiency is actually Verticillium wilt. With Verticillium wilt, the vascular tissue of the stem is discolored and light to dark brown in color. To determine if Verticillium wilt is present, the stem
should be sliced with a knife and examined for vascular (xylem) discoloration.
The image below illustrates K deficiency in the absence of Verticillium wilt.
The image below illustrates leaf necrosis symptoms of Verticillium wilt in cotton (photo courtesy Dr. Terry Kirkpatrick, Plant Pathologist, University of Arkansas). Notice that the symptoms are not symmetric on the leaves.
To properly field diagnose Verticillium wilt, stems should be sliced and the tissue should be examined for vascular discoloration. The image below (courtesy Dr. Terry Kirkpatrick) illustrates the typical vascular discoloration caused by the Verticillium wilt disease organism. Field diagnoses should be confirmed by a reputable plant disease diagnostic lab.
Another disease can cause leaf symptoms which are frequently confused with Verticillium wilt and/or potassium deficiency. The image below (courtesy of Dr. Terry Kirkpatrick) shows leaf symptoms and stem tissue discoloration caused by Fusarium wilt. In this example, Fusarium wilt was associated with root knot nematode injury.
With K deficiency, the yellowing (chlorosis) of leaf margins is relatively uniform and extends symmetrically toward the leaf center. With Verticillium wilt, chlorosis and necrosis (tissue death) may occur only on certain leaf lobes. The image below is another illustration of K deficiency.
Any injury to roots can result in impaired nutrient and moisture uptake. Verticillium wilt and Fusarium wilt can aggravate K deficiency and result in complex symptoms. Cotton farmers and crop advisers are strongly encouraged to collect soil samples for fertility analyses and nematode analyses. Leaf blades can be collected from the uppermost mature leaves for nutrient analysis as soon as symptoms appear, and before the leaves become necrotic (brown). Entire plants, with the roots contained intact in a plastic bag (closed snugly around the base of the stem), can be rapidly delivered to a disease diagnostic or plant pathology laboratory for a disease assay.
The respective soil, plant tissue, and plant disease laboratories should be consulted in advance, to ensure that soil and plant tissue are collected and shipped properly. Many disease diagnostic laboratories prefer to have samples shipped overnight to help prevent spoilage, which could interfere with proper diagnoses. Plant tissue nutrient analysis laboratories prefer to receive samples which have been thoroughly air-dried so no mold risk is present during sample shipment.
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