Late-Season Crop Condition and Management

by Jeffrey C. Silvertooth,
Extension Agronomist - Cotton

The 1998 Arizona cotton crop continues to be a very challenging experience. It seems that the season has been a continual process of encountering and dealing with one major obstacle after another. Normally by the first of August, we would have many fields that have completed, or were very near completion of the primary fruiting cycle. But true to form for this unusual season, we are still notably late in crop development and maturity in many areas. Poor fruit retention (FR) and high vigor conditions are common in many low elevation areas. However, there is a great deal of variability in crop condition, even within a given area. There are also some fields and regions that are in relatively good condition. For example, the higher elevation areas (e.g. Safford Valley) are still in good condition and progressing close to normal.

The late maturity, poor FR, and excessive crop vigor conditions that presently exist are a result of a number of factors or events, including:

• An exceptionally cool and wet spring planting season, which resulted in
• Delayed planting dates and a high rate of replanting in many areas
• Poor seedling vigor
• A continuing pattern of storms and cool weather in the spring
• Followed by slow plant (root and shoot) development
• Persistent winds and in some cases high thrips pressure
• Contributing to an exceptionally high rate of terminal loss
• Resulting in further delays in crop development
• Late formation of the first fruiting branch (mainstem nodes eight and higher)
• High rate of abortion for early squares
• Continuation of poor crop vigor in the pre-bloom and early bloom stages of development
• Heavy and persistent lygus bug infestations
• Contributing in many cases to substantial square damage and abortion
• The beginning of monsoon weather conditions in early July
• Resulting in a high rate of abortion of young (one to three day old) bolls
• This pertains primarily to low elevation locations (<2,000 ft.)

So here we are in early August, approaching the later stages of the fruiting cycle with many fields supporting an inadequate boll load. In most years, I would recommend terminating the crop once the bolls set up to cut-out reach maturity (for many fields) in an effort to realize optimum agronomic and economic efficiency. This still might be the recommended course of action for many fields this season. But the end of the first fruiting cycle will likely be later, and many fields will not be carrying a sufficient boll load to pay the bills at cut-out. As a result, many fields could very likely warrant later season production in an attempt to develop higher yields, during the more favorable late summer (post monsoon) weather. Therefore, it is extremely important at this stage in the season to make a very thorough and objective assessment of crop conditions in an effort to decide on how long the crop should be carried.

The bottom line on this level of management is going to come down to economics. Many fields have a lot of money invested in them already. The question basically becomes "What is the probability of being able to develop a significant yield late in the season while offsetting any additional costs?". More time in the field can result in higher yields but more costs as well. Key to tilting this equation in your favor depends on consideration of the following factors:

• Current boll load and FR (refer to UA baselines)
• An estimate of current yield; 15 to 20 bolls / foot of row (36 to 40 in. row spacings) equate approximately to one bale of yield / acre
• Crop vigor (height:node ratio, HNR)
• Insect pest populations
• Variety (late season and back-fruiting potential)
• Fruiting branches currently available on the plant
• Incidence of any plant disease problems
• Late season fertility needs (particularly N)
• Irrigation costs
• Land rotational needs
• Elevation and probable length of the available crop producing season
• Your best weather forecast, and
• Budget

Even more factors may need to be considered and certainly each field will need to be evaluated on a case by case basis. Make a careful evaluation of all fields and consider production potentials and constraints. Some useful guidelines concerning crop development are listed in Table 1.

As the monsoon-type weather conditions continue, and plants try to set some bolls, appropriate management is important. Avoid water stress (be careful not to over-irrigate as well), be very conservative with fertilizer N, try to control vegetative crop growth with appropriate PIX_™ (mepiquat chloride) applications, and control insect pest populations. With PIX_™ applications, consider both FR and HNR levels together (refer to UA baselines). If FR is dropping or low (relative to baselines) and HNR levels are high and/or increasing, PIX_™ applications may be needed (see UA PIX_™ use guidelines). If so, minimum application rates of about 1.0 pt. PIX™/acre would probably be appropriate in most cases. Recognize that PIX™ applications will impact crop growth for about one to two weeks, or the period required to produce about three to six mainstem nodes.

Monitor the crop routinely and be flexible in terms of the management steps that crop conditions may indicate. If the weather were to change to hot and dry conditions once again, some fields could still have the potential to set additional bolls if carried into the fall. However, a timely conversion in weather conditions and a warm open fall will be critical to the prospect of recovering a profitable late season crop.

Table1. Important growth stages for cotton development.

Full Disclaimers

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.

The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.

Any products, services, or organizations that are mentioned, shown, or indirectly implied in this web document do not imply endorsement by The University of Arizona.