Excessive Moisture and Field Variability

Heavy rainfall throughout the region has led to flooded fields, nutrient losses, increases in early-season disease, and growth stage variability within the same field. Application of plant growth regulators can help balance vegetative and reproductive growth for fields previously under saturated soil conditions.

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Yellow Cotton

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Fields with heavy clay soils may not been able to drain excess moisture, leading to anaerobic (oxygen-deprived) conditions. In anaerobic soil conditions, plant root respiration is limited, as well as nutrient uptake. In these conditions, cotton plants can begin to show symptoms of nutrient deficiency, as indicated by yellow cotton plants in water-logged areas of the field. Because extended rainfall corresponded with squaring, Dr. Gaylon Morgan, AgriLife Extension state cotton specialist stated that “the cotton plants have a tremendous nutrient uptake demand, and simultaneously poor conditions for nutrient uptake into the roots,�? and “in the majority of the fields, the upper cotton canopy is yellow while the lower canopy is green.�?1 This is a result of plant mobile nutrients like nitrogen, phosphorous, potassium, and magnesium moving from older leaves to younger leaves. Younger leaves of nutrient-stressed plants can be collected and sent to a laboratory to help determine nutrient status, and if a foliar fertilizer application is needed. As favorable conditions return, and soil dries out, plants should be able to resume nutrient uptake.2 For more information about cotton nutrient deficiency symptoms, visit the International Plant Nutrition Institute website: http://www.ipni.net/.

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Wet Weather Blight

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Figure 1

Figure 1. Symptoms of Wet Weather Blight on a cotton leaf. Source: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org.

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This disease is caused by the fungus, Ascochyta gossypii, and often occurs after continued rainfall. This fungus can appears on leaves, stems, and branches of cotton plants. Symptoms begin near the petioles of the leaves as small, round, red to brown lesions with dark margins. As the disease progresses, the middle of the spots turn grey and the tissue may die (Figure 1). Lesions can continue to grow and merge together, leading to defoliation. Cankers can form on plant stems and branches, which can eventually girdle the stem or branch, killing the tissue above.

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Wet Weather Blight is usually sporadic and plants may recover once warm, dry weather returns.3 Dr. Thomas Isakeit, AgriLife Extension plant pathologist, stated that “it appears that with warm, dry weather, the cotton plant outgrows the fungus. In one field, I did a fungicide application on some rows and after seven days, I did not see any difference between the treated and untreated rows.�?

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Managing Variability in the Field

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With large variability in cotton plant growth within the same field, it can become difficult to determine when to apply a plant growth regulator (PGR). There are several factors to consider when determining when to make a PGR application, including growth stage, fruit load, the size of the plants, and the likelihood that the cotton variety planted will continue to grow vigorously. The goal is to find balance between decreasing internode length of larger plants in the field, without slowing the growth of smaller plants. Decisions regarding PGR applications should be made on a field-by-field basis to help create a balanced PGR application rate for fields with extreme variability.

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PGR application should be avoided or minimal until the soil dries out and plants are no longer under stress. Saturated soil conditions, coupled with a high rate of PGR, can push cotton into the cut-out stage early, reducing yield potential. A PGR application is recommended for cotton plants that are no longer experiencing stress from saturated conditions, are past early bloom, and have an average (top 5 nodes) internode length of over 2.25 inches. A conservative PGR rate, like 8 oz/acre of mepiquat chloride, can help gauge the condition of the crop.4

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Growth Management of Deltapine® Cotton Varieties

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It is important to understand the growth habit of a particular variety in order to manage vegetative growth. Certain varieties maintain an aggressive growth pattern when compared to other varieties, and mepiquat rates and timing must be managed accordingly.

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Deltapine® cotton varieties may each respond a little differently to applications of mepiquat. The projected response of each variety is provided in Table 1. DP 1212 B2RF, DP 1518 B2XF, DP 1612 B2XF, and DP 1614 B2XF have shown the highest response to mepiquat, which may result in lower rates or fewer applications needed. DP 1219 B2RF, and DP 1359 B2RF have shown the lowest response to mepiquat, so timely early-season applications at higher rates or multiple applications may be needed to control vegetative growth. Although local soil and management issues may impact PGR applications, consider the following guidelines: for cotton varieties in the moderately and least responsive categories, growers should plan to aggressively apply mepiquat if there is a history of rank growth, or was rotated behind corn or another crop where a high nitrogen rate was applied. Mismanagement of mepiquat or other PGRs can have a negative effect on yield potential, especially when applied to stressed cotton, or when applied to a determinant cotton variety.

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Table 1. Deltapine® variety response to growth management with mepiquat.
Very ResponsiveResponsiveModerately ResponsiveLeast Responsive
DP 1518 B2XFDP 1522 B2XFDP 1646 B2XFDP 1359 B2RF
DP 1410 B2RFDP 1555 B2XFDP 1219 B2RF
DP 1321 B2RFDP 1553 B2XFDP 1549 B2XF
DP 1044 B2RFDP 1252 B2RF
Note: Dicamba is not yet approved for in-crop use.
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Mepiquat and other PGRs should be considered management tools used to maintain ideal cotton height and fruiting retention. In-season cotton-plant monitoring, provides the best information to determine application rate and timing of growth control measures. Every cotton field is under different conditions so growth management strategies should be tailored to each field situation.