Review of the 1998 Arizona Cotton Season

In 1998 250,000 acres were planted to Upland cotton (23% decrease from 1997) and 13,000 acres planted to American Pima cotton (41% decrease from 1997). Arizona has one of the highest proportions of the cotton crop planted to transgenic varieties. Approximately 80% of the 1998 AZ cotton acreage was planted to transgenic varieties. The transgenic acreages breakdown as follows as a percentage of the Upland acreage: 60% Bt, 10% Roundup Ready, 11% stacked gene (Bt + RR), with about 19% planted to conventional non-transgenic varieties. The latest USDA estimates indicate average 1998 yields for AZ at 1,137 and 768 lbs. lint/acre for Upland and Pima cotton, respectively. These yield estimates indicate a 10 and 8% decline in average yields from 1997. Cotton markets have been relatively poor, making profitability with cotton production in AZ very difficult. Strange as it may seem, I would anticipate a slight increase in cotton acreage in AZ in 1999.

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 a series of in-season bulletins (Cotton Comments), 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:

• 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 (early season)
  • Increased levels of risk and exposure to pests (e.g. insects and diseases)
• 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 rates of abortion for early squares
  • Due to wind, thrips, lygus, water stress, etc.
    • Causing poor retention of lower bolls on the plants, which delayed the crop even further
• Continuation of poor crop vigor in the pre-bloom and early bloom stages of development
  • A rapid transition to hot and dry conditions created more favorable growing conditions IF water was not limiting
• 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
    • Primarily affecting low elevation locations (<2,000 ft.)
      • Many fields in the Yuma area were at peak bloom at this time
        • With greatest susceptibility to heat and carbohydrate stress
      • Many fields in central Arizona were in very early bloom
        • FR, seed set, and boll size were negatively impacted, but fields may have been able to acclimate to some extent

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:

• With delayed planting (or replanting) conditions, a shift to more determinate varieties is imperative.
  • For many fields, crop management problems (high vigor/low FR) were compounded by the use of longer season, more indeterminate varieties that were planted too late to perform adequately.
  • Many of these fields were extremely late in maturity with a flush of late, green bolls at the top of the plant and there was too little time and too few HUs to mature and harvest them.
  • In general, more determinate varieties did rather well over a broad range of conditions.
• Planting cotton in close proximity to crops that are known to provide good harborage for lygus populations (or other pests) will require special consideration and management.
  • Crop and pest monitoring are very important.
• When the monsoon season arrives the beginning of the cotton fruiting cycle, many varieties commonly grown in Arizona can acclimate to some extent and maintain reasonable FR levels with proper management.
  • Yield potentials will likely be reduced due to heat-related crop stress, but fair yield potentials can still be maintained.
  • Water management, pest control, and crop nutrition will be extremely critical under this type of situation.
• The best general scenario for most Arizona fields still includes an early/optimal date of planting (provided adequate weather conditions) for promoting early fruiting, crop maturity, and good yields.