Kv Poster Feb. 2009

Comprehensive Evaluation of Pesticides K. M. Vaughn, C. Nansen, A. H. Gharalari, A. Sidumo Texas AgriLife Research, 1102 E FM 1294, Lubbock, TX 79403 Fig. 2a

Miticide Evaluation Results

Fig. 2c

Regarding complete coverage treatments, spider mite mortality was significantly higher on corn leaves treated with bifenazate and propargite compared to both controls, but there was no significant difference between the two chemicals (Fig. 5). However for both chemicals, spider mite mortality was significantly lower on partially treated leaves compared to complete coverage treatments. This suggests that both miticides may be repellent to spider mites, and that incomplete coverage may provide “refuges” for mites to recover and/or avoid treated leaf surfaces.

Mean (± SE) % mortality of spider mites

Introduction There are several methods to apply known and highly accurate dosages of pesticide formulations to plant leaves or other surfaces under laboratory conditions. However, most of these methods involve equipment that cannot be used under field conditions. A hand-held spraying device referred to as the “bottle sprayer” (Fig. 1) was designed to address this critical shortfall in applied research on use and performance of pesticides. Application of known formulation dosages of pesticides both under field and laboratory conditions allows us to address basic aspects of formulations, such as their: 1) repellency, 2) residual effect, 3) ability to withstand wash-off if a water event (irrigation or rain shower) occurs shortly after pesticide application. In addition, testing the efficacy of pesticides in field trials can be costly and labor intensive. With this in mind, we developed and evaluated a device that is easy to use, inexpensive, and provides a safe environment to screen pesticide formulations. Furthermore, it was important that this device can be used in a broad array of field crops.

Fig. 2b

Fig. 2d

Bottle Sprayer Structure and Calibration The bottle sprayer consists of a dual-action artist airbrush (Master MAS G22) mounted in a wooden frame to spray inside a 2-liter coke bottle (so we can apply formulation even under windy conditions) at a fixed distance of 20 cm. The device connects to a 5 lb. CO2 cylinder using a Chudnow 100 PSI (Pounds per Square Inch) regulator to deliver a constant pressure.

0.020 70 BPM & 10 PSI 80 BPM & 20 PSI

Fig. 3

Frequency Frequency

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color class (90-255) Color class8-bit (dark purple to bright yellow)

Bottle Bioassay for Miticide Evaluation

Analysis of spray droplet pattern

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Yellow water-sensitive spray cards (Fig. 2) turn blue or dark purple on exposure to water, and they were used to examine spray droplet patterns, while testing PSI and BPM ranging from 10 to 45 and 60 to 90, respectively. Comparing digitized cards sprayed at 70 PSI/10 BPM (Fig. 2a) to 80 PSI/20 BPM, (Fig. 2d), colors were converted into numbers between 1-255 with low numbers being equal to dark color (Fig. 3). The ideal spray droplet pattern (blue curve in Fig. 3) would be all pixels assigned to a narrow range of intermediate color classes. The wider the spread of color class distribution, the less uniformity of spray application. Fig. 2 and 3 show that 10 PSI provided a more uniform spray pattern. Importantly, do not to use a CO2 cylinder smaller than 5 lbs or set the PSI below 10, as it will be difficult to maintain a constant pressure.

Whole leaf segment Half leaf segment

80

Miticides were screened for efficacy against spider mites on corn using the bottle sprayer (10 PSI and 60 BPM). Corn leaf segments (6 x 6 cm) were treated and subsequently bioassayed in Petri dishes with spider mites (Fig. 4). To simulate incomplete coverage and examine possible repellency, we treated the entire area of the corn leaf segment or only half of the corn leaf segment. There were 4 treatments with 4 replications: 1) bifenazate at 1,120 grams/ha (Acramite®), 2) propargite at 3,360 grams/ha(Comite II®), 3) negative control – nothing sprayed on leaf , and 4) positive control – only water sprayed on leaf. Petri dishes were covered and kept at room temperature for 48 hours before mite mortality was recorded.

Fig. 4

negative control

propargite

positive control

From additional studies, we have shown that mortality rates of pests (from bioassays) can be predicted based on the proportion of dark purple pixels on spray cards (Fig. 6). This relationship is particularly important when pesticides are applied with conventional applicator s (i.e. airplane or ground rig). In other words, we can place spray cards in fields and use information from digitized spray cards to determine the performance of pesticide applications.

Mean % mortality rate

Fig. 1

The two main variables affecting pesticide application are gas pressure (in PSI) and length of spray time. Gas pressure is controlled with the gas regulator, and a metronome is used to standardize time of spray in units of beeps per minute (BPM).

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Fig. 6

y = 729.55x + 32.813 R² = 0.4089

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Proportion of purple pixels in the spray cards Discussion and Future Opportunities So far, the bottle sprayer has been used to successfully study the mortality, repellency, and longevity of insecticides to control adult potato psyllids on potatoes. We have tested dosage response and repellency of miticides to control spider mites on corn. We have conducted a study on residual effect of a miticide when simulating a water event at different time intervals after miticide application. Recently, we have purchased a video recording system to study behavioral responses of arthropods to insecticides. Insight into behavioral responses is critical for a complete understanding of how pesticides affect arthropods, as sub-lethal effects (i.e. sterilization and/or inhibition of feeding) may play major roles regarding modern pesticides. We welcome colleagues at research institutions and from ag-industries to contact us if you are interested in knowing more about our applied research on pesticide performance or related topics: http://www.pssc.ttu.edu/cnansen/Website.htm