| North Dakota
Agricultural Research North Dakota State University, Fargo, ND 58105
A Portable
Aerial Spore Collecting System (continued) |
Abstract |
Sampler operation was tested near Prosper, ND in a wheat field that was being harvested from windrows. For three samples, test flight parameters ranged from 150 to 750 yards downwind of the combines, from 16 to 75 feet elevation, and three to six combine passes. Collection heads were disassembled and surfaces examined under a microscope. Three conidia of Bipolaris sorokiniana were found in the sample taken at 50 ft. above the ground and 300 yards downwind from the harvested windrow. This fungus causes common root rot and spot blotch of wheat leaves. Test results suggested that spores of a wheat pathogen can be detected with this sampling methodology. Wind produced the most difficulty for balloon stability. According to North Dakota Agricultural Weather Network (NDAWN) records from the station closest to the sampler trials, average wind speeds at 10 ft. during testing ranged from 6 to 11 mph with gusts up to 17 mph. During gusts, the balloon was forced down so that sampling at a specific altitude could not be maintained. To maintain sampling within predetermined limits, the sampler must be turned off as it moves below the accepted sampling height and turned back on when the altitude increases again. The problem of collection at a specific altitude was addressed after the field trials. The push on/push off switch was replaced with a push on/release off switch (Table 1) that would turn the collector on when the switch was compressed and off when decompressed. The same hinge and spring setup was used and a 1 lb. (0.45 kg) weight was added to the end of the string that is attached to the switch mechanism. The weight was attached at the length of the desired elevation. When the weight comes off the ground the switch is compressed and the collector starts to spin. When the weight comes in contact with the ground it puts slack in the string and the switch decompresses, shutting off the device. This collecting system is portable and can be transferred from field to field and from site to site within a field. The balloon was transported in the back of a full-sized pickup truck (Figure 4) (53KB color jpg photo). A poly-type tarp was put under the balloon to prevent punctures. Another tarp was placed on top of the balloon and was tied down to the corners of the truck to secure it. Both tarps were tied to the corners and middle of the truck box. This allowed transport at normal highway speeds. The performance of the sampler could be improved, but ideas were excluded to reduce costs. A lightweight radio-controlled servo-mechanism to turn the sampler on and off could be purchased for around $200. This improvement would eliminate the need for an extra person and the string controlling the switch. An enclosed 7 ft. wide trailer would allow for faster transport by eliminating time for tie down and concern about accidental release. The trailer would also eliminate concern for puncture in transport and allow for faster travel. Finally, a second sampler would allow measurement of spores upwind of the field under study to determine background levels of air spora. The sampler has several advantages over other systems. Any crop and growth stage can be sampled due to the portability of this system. The sampler is useful in remote areas where fixed towers or buildings are not available to measure spore dispersal height. The balloon can reach an elevation of 150 ft., unlike portable towers that are limited to a length of about 30 ft. As height increases, so does the frequency of laminar air flow; therefore, the accuracy of the sample is affected less by nonlaminar air flow caused by ground obstructions such as buildings or trees. Cost of materials is less than $1,000; some volumetric samplers cost more than $4,000. The major disadvantage of a helium balloon sampler is the dependance on clement weather with low wind. We are particularly interested in the liberation and subsequent dispersal of wheat fungal pathogens during harvest in the southern Great Plains. Our hypothesis is that newly important pathogens are part of the air spora being transported long distances across the Great Plains. This device can give us sample data to test this theory.
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