When it comes to application of crop insecticides to row crops, getting the most for your money often boils down to finding the answers to the right questions, said a Texas AgriLife Research expert.

Dr. Christian Nansen, AgriLife Research entomologist at Lubbock, said success often hinges on knowing how long a treatment will last (its residual effect), if adjuvants (substances that enhance effectiveness) will make the treatment last longer and whether or not the spray placement and penetration deep into the crop canopy is important.

“Controlled uniform applications are key aspects of finding answers in insecticide performance research,” Nansen said. “When doing experimental work with insecticides in the laboratory or in field plots, we need to be able to apply known and accurate insecticide dosages to individual crop leaves to determine their optimum effectiveness against target pests.”

Until now, Nansen said finding those answers under field conditions has been something of a logistical nightmare due to Lubbock's frequent windy and dusty conditions and because they have not had the proper equipment for field testing of insecticide applications.

He and his research team solved the problem by developing a simple, inexpensive device they call the “bottle sprayer.” The invention consists of a two-liter plastic soda bottle with the bottom removed and an artist's airbrush mounted inside the top. The bottle is attached to a simple wooden frame and a small compressed carbon dioxide air cylinder operates the airbrush.

The entire unit costs less than $400. They have calibrated the device to know how much formulation is being delivered under different air pressure conditions to simulate what is being applied under commercial applications.

“The airbrush acts as a miniature spray nozzle while the bottle keeps the resulting spray pattern confined within a small measured area,” Nansen said. “The whole unit is portable and great for field use. And with the soda bottle protecting the spray pattern, it doesn't matter if the wind is blowing or if there's dust in the air.”

Nansen said the bottle sprayer is ideal for testing a number of pesticides quickly which is critical when producers are faced with a new little-known pest or need rapid screening of a series of insecticides.

A good example is his work with the potato psyllid, an insect implicated in zebra chip disease, caused by Candidatus Liberibacter bacteria. Producers can't sell infected potatoes because when the tubers are fried consumers find the resulting dark discoloration unappealing. The disease has cost Texas producers millions of dollars in lost revenue, according to Nansen.

Using the bottle sprayer under both laboratory and field conditions, Nansen has found one insecticide, Agrimek, to be very effective in controlling adult potato psyllids. His research team used the bottle sprayer in field test plots to apply Agrimek to individual potato leaves at different positions within the canopy.

By using the bottle sprayer, Nansen was quickly able to show that Agrimek lost its efficiency within a few days after application due to the sun's ultraviolet rays breaking down the insecticide. These findings strongly suggest that there is a great need to look into how the insecticide can be applied so that it penetrates deep into the crop canopy and thereby is protected from sunlight degradation.

Ultimately, the goal is to develop application methods for the insecticide to be applied to the underside of crop leaves in order to increase residual effect, and psyllid mortality, as the psyllids tend to feed and lay eggs underneath potato leaves.

By using the bottle sprayer, Nansen and his colleagues were able to determine that the application method was the main constraint regarding effective use of Agrimek. So the trick in this instance, is to apply the insecticide under the leaves and out of direct sunlight.

“Many insecticides like Agrimek are expensive and farmers want to know whether they work or not, so it's important to not only ask, but to be able to answer all their questions,” Nansen said. “As researchers, we want to help farmers, agency personnel and chemical companies with in-depth performance analysis so they can save money, develop more efficient application strategies and reduce the risk of pesticide-resistant insects while protecting the environment from unnecessary spraying."

“The bottle sprayer lets us do all that by helping us find the answers to those key questions quickly and cheaply," he said. "It's a luxury we've not had before.”