In this decade we have experienced a number of very challenging cotton seasons in Arizona. Beginning in 1990 we had the infamous pink bollworm year and a strong monsoon season. The 1992 season was marked by the devastation that hit many fields as a result of whitefly problems. Both 1995 and 1998 were affected by cool, wet spring planting seasons and heavy monsoons. At the closure of the 1998 season, statewide yields are generally low (at present, the USDA is estimating 1,137 and 768 lbs. lint/acre for Upland and Pima cotton in Arizona). The crop has been very late in development, maturity, and harvest in many areas. Poor fruit retention (FR) and high vigor conditions mid- to late-season were common problems in many low elevation areas this past season. We also experienced a great deal of variability in crop growth patterns and yields, even within a given area. However, some fields and regions in Arizona have done fairly well. For example, the higher elevation areas (e.g. Safford Valley) had a crop that progressed close to normal all season and resulted in rather good yields. In earlier bulletins in this series, I provided updates of statewide crop conditions and assessments of problems that were encountered over the course of the 1998 season in Arizona. Here, I intend to review the 1998 cotton season, with its challenges and perhaps some lessons to be learned.
The poor FR, excessive crop vigor, and late maturity conditions that impacted many fields, particularly in the lower elevations (< 2,000 ft.), were the result of a number of factors or events, including:
The difficulties in FR that many fields have experienced commonly stem from four basic factors: 1) delayed planting, 2) abortion of many early squares, 3) lygus bug damage, and 4) heat-related stress. The monsoon weather patterns began the first of July for most cotton producing areas of the state, and many cotton fields responded to the heat and humidity with characteristic drops in FR (primarily in lower elevations). Upon review of many cotton fields across the state we found a good relationship between the categories of weather-related stress (Levels 1 and 2 as defined by Dr. Paul Brown) and FR levels. We also commonly found a higher proportion of malformed bolls (parrot-beaked bolls) resulting from poor pollination in blooms that were apparently malformed during the square stage of development as a result of Level 2 stress conditions. The monsoon conditions persisted for over eight weeks and exacted some toll on the fruit load in many fields. Heat-related damage was also greater in fields that were subjected to water stress during the primary fruiting cycle.
I believe the negative impacts on the crop due to heat, while serious, was relatively minor in relation to the damage that was caused by lygus bugs in some areas of the state. In central Arizona, the monsoon season began in early July coincident with early bloom in many fields. There is evidence that the crop apparently was able to acclimate to some extent and maintain fair yield potentials (see Cotton Comments, 14 November 1998). When the problems associated with a delayed crop were compounded by the damage from lygus bugs that were encountered in some areas this season (in addition to the heat), many fields were unable to develop an adequate fruit load and had correspondingly poor yields.
The problems encountered this season with lygus bugs and their management in cotton, remind us that we need to consider the overall crop ecology of our production systems. With the current agricultural economy, growers are responding to markets by diversifying the crops produced in many areas of Arizona. Crop diversification brings with it many positive factors (agronomically and economically). However, changes in the cropping system can present special challenges to crop managers. For example, pest dynamics change with changes in the proportions of various crops grown, and these pets may require special attention and management. This may be a moot point for some parts of Arizona this season. However, many farmers and crop managers (e.g. PCAs) that were trying to grow cotton in close proximity to safflower or seed-alfalfa this season would probably agree that this aspect of crop ecology is an important issue. Crop ecology can be complex but is an area where farmers, PCAs, entomologists, weed scientists, plant pathologists, economists, agronomists, etc. need to plan ahead and try to anticipate the various problems that a given cropping system or combination of crops may pose. We need to address this in the continuing development of cropping systems in Arizona and increasing crop diversification.
Based on the experiences from the 1998 season, there are several positive points (or lessons) as we look ahead to planning for future seasons:
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.
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Information provided by Jeffrey C. Silvertooth, email@example.com
Extension Agronomist - Cotton, College of Agriculture, The University of Arizona.
Material written 12 December 1998.