Sampling Methods for Estimating Cotton Lint Stickiness
Steve Naranjo, Eric Hequet
The accurate determination of cotton lint stickiness in the field could greatly aid management and research efforts. Field sampling of stickiness could augment pest monitoring techniques and improve overall decision-making for pest suppression. Field sampling could also identify unacceptable levels of stickiness at harvest that may require some remedial action such as the use of enzyme treatment systems that are currently being investigated. Our research targets the development of standard methodologies for collecting lint samples from fields to ensure statistically precise estimates of stickiness. Two assay systems were investigated, the manual thermodetector (SCT) and the high speed (automated) sticky cotton thermodetector (H2SD).
The newest H2SD system consistently detects more thermodetector spots than the SCT and the relationship between the platforms appears to be nonlinear, at least for field-collected samples encompassing a very wide range of stickiness levels. The distribution of sticky lint in the field is random regardless of which platform is used to assay the lint. Examination of many different sizes of field sample units suggest that smaller sample units (e.g. all lint from 1 plant or lint from 20 bolls collected at random) are more cost-efficient than larger sample units. The assay system (SCT or H2SD) used is critical to the development of a final field sampling plan; however, there is considerable flux in the industry relative to a standard platform for stickiness testing. Given this uncertainty, we have developed sampling plans for both platforms. Reasonably precise estimates of stickiness can be achieved with a sample size of about 15 on either platform using the 1-plant sample unit. Even fewer samples would be required using a 20-boll unit. Sample sizes as high as 41 or 82 would be required for estimates with very high precision on the H2SD or SCT platform, respectively. Overall sampling costs are much lower for the H2SD because of the speed with which samples can be assayed. Sampling efficiency could be further improved with sequential sampling strategies or with sample plans focused on categorizing (non-sticky vs. sticky) rather than estimating actual levels of stickiness. These sampling applications await further research to define critical levels of stickiness and/or the implementation of wide-scale testing where any time savings would be at a premium. (PDF)
A New Sampling Technique for Assessing the Density of Natural Enemies in Cotton
Allen Knutson, Mark Muegge, Ted Wilson (Texas A&M), Steve Naranjo
The cost-reliability of five sampling methods (visual search, drop cloth, beat bucket, shake bucket and sweep net) was determined for four groups of predatory arthropods on cotton plants in Texas. The beat bucket sample method was the most cost-reliable sampling method for Orius adults and the beat bucket and drop cloth were the most cost-reliable methods for Orius nymphs. The drop cloth and beat bucket were the most cost-reliable methods for sampling spiders. For sampling adult Coccinellidae, the sweep net and the beat bucket were the most cost-reliable. The visual sample method was the least cost-reliable method for Orius adults and nymphs and spiders. No one sampling method was identified as the optimum method for all four predator groups. However, the relative cost-reliability of the beat bucket method ranked first or second among the five sampling methods and this method was chosen for further evaluation in field studies in Texas and Arizona. The relative cost-reliability of 1-, 3-, 5- and 10-plants per beat bucket sample varied with predator group, but multiple plant sample units were equal to or more cost-reliable than the one plant sample unit. Fixed sample plans for the beat bucket method were developed for Orius adults, Orius nymphs, spiders, and adult Coccinellidae and the sum of these groups using the 3-, 5- and 10-plant sample unit sizes. The greater cost-reliability of the beat bucket sampling method and its ease of use is of particular advantage in assessing predator densities in a commercial cotton field monitoring program.
The contribution of conservation biological control to integrated control of Bemisia tabaci in cotton
Steve Naranjo, Peter Ellsworth (UA)
Integrated control systems are based on the complimentary contribution of chemical and biological control fostered by conservation of natural enemies. Yet, in the 50 years since the integrated control concept [ICC] (Stern et al., 1959) was introduced there are few operational programs and even fewer attempts to analyze the mechanisms that allow chemical and biological control to act in concert. The dearth of demonstrable evidence for the ICC has eroded the credibility of biological control and its usage in operational IPM plans. We used in situ life tables within an experimental design to measure and compare the contribution and interaction of biological control and insecticides as tactical components within three pest management systems for Bemisia tabaci (Gennadius) in cotton. Insecticides were the key factor immediately following applications of broad-spectrum materials or one of two selective insect growth regulators (IGRs), and this mortality replaced that provided by natural enemies. Two-6 wks later, however, mortality from natural enemies, primarily predation, in the IGR regimes rebounded to the high levels observed in untreated controls and became the key factor. Mortality from natural enemies remained depressed in the broad-spectrum insecticide regime. Single IGR applications were sufficient to suppress B. tabaci populations throughout the season, while up to five broad-spectrum applications were needed to achieve comparable control. The chemical residual of IGRs was limited to several weeks, demonstrating a key role for mortality from conserved natural enemies that extended the control interval. This “bioresidual” allows for long-term, commercially acceptable pest suppression following the use of selective insecticides. We provide a rare experimental illustration of integrated control, where chemical and biological controls “augment one another”. Our approach and methodology could be applied to demonstrate and validate integrated control in many other systems, addressing a critical need for implementation of biological control in practicing IPM systems. (PDF)
50 years of the Integrated Control concept
Steve Naranjo, Peter Ellsworth (UA)
Fifty years ago Stern, Smith, van den Bosch and Hagan outlined a simple but sophisticated idea of pest control predicated on the complementary action of chemical and biological control. This Integrated Control Concept has since been a driving force and conceptual foundation for all IPM programs. The four basic elements include thresholds for determining the need for control, sampling to determine critical densities, understanding and conserving the biological control capacity in the system, and the use of selective insecticides or selective application methods, when needed, to augment biological control. Here we detail the development, evolution, validation and implementation of an Integrated Control (IC) program for whitefly, Bemisia tabaci, in the Arizona cotton system that provides a rare example of the vision of Stern and his colleagues. Economic thresholds derived from research-based economic injury levels were developed and integrated with rapid and accurate sampling plans into validated decision tools widely adopted by consultants and growers. Extensive research that measured the interplay among pest population dynamics, biological control by indigenous natural enemies, and selective insecticides using community ordination methods, predator:prey ratios, predator exclusion and demography validated the critical complementary roles played by chemical and biological control. The term “bioresidual” was coined to describe the extended environmental resistance from biological control and other forces possible when selective insecticides are deployed. The tangible benefits have been a 70% reduction in foliar insecticides, a >$200 million savings in control costs and yield along with enhanced utilization of ecosystem services over the last 14 years. (PDF)