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Bulletin #2443, Application Equipment for Potato Post-Harvest Disease Control

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Application Equipment for Potato Post-Harvest Disease Control

application equipment

Photo by Steven B. Johnson

Developed by Steven B. Johnson, Extension Crops Specialist

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Background

Late blight, caused by Phytophthora infestans (Mont.) de Bary, and pink rot, caused by Phytophthora erythroseptica Pethybr., are two devastating potato tuber diseases. These pathogens regularly cause storage losses in potato production systems. While these pathogens, especially P. infestans, spread rapidly in the field, there can also be substantial tuber-to-tuber spread during mechanical harvesting and tuber transfer procedures. With these diseases present in the field, storage losses well beyond what would be expected can occur based on the pathogen level in the field.

Phosphorus acid (phosphonate or phosphite) is the anionic metabolite of the systemic fungicide aluminum tris-O-ethyl phosphonate (fosetyl-Al). Phosphorous acid is effective in reducing tuber-to-tuber spread of P. infestans and P. erythroseptica during mechanical harvesting and tuber transfer in a situation where the diseases are present at harvest. The mode of action of phosphorous acid is not as a nutritional source but as systemic antifungal activity towards mycelial growth.

While there are effective post-harvest treatments to control these two pathogens, the application system is a weak link. Improper application of post-harvest treatments may result in poor disease control. It is essential to calibrate application equipment precisely and apply the correct rate of material in the proper volume of carrier. Improperly calibrated equipment can result in inadequate coverage, which can give the appearance that the treatment is ineffective, when in reality, the application method is responsible.

Applications with less than half the recommended material or less than half the recommended application volume failed to provide complete control of tuber-to-tuber late blight spread. Growers tend to have zero tolerance for tuber rot diseases in storage.

Phosphorous acid materials are generally applied at rates of 12.8 oz per ton. In Maine, growers are applying post-harvest phosphorous acid solutions ranging from 24 oz to 64 oz per ton. Unloading rates range from 15 cwt to 60 cwt per minute. With such a range in application and unloading rates, there is a need for adaptable application equipment. The equipment needs to stand up to the corrosive nature of post-harvest applied materials and be widely adaptable to varying unloading and application rates. The equipment should allow for additional nozzles and spray arms for increased flexibility.

Equipment

Growers typically use standard roller pumps, which corrode over time. The corroded pump becomes less efficient, forcing growers to recalibrate. The decaying pump also breaks down, causing both the screen and nozzle to plug. These issues cause improper applications. The use of coated roller pumps is essential, as these will last a great deal longer that the standard steel roller pumps.

Nozzle types described are TeeJet TX-2, TX-3, TX-4, or TX-6, with quick-release caps for ease of adaptability. These are brass hollow cone nozzles with an 80 degree spray pattern. The range of nozzles numbers is 3 or 4 per spray bar. Standard hydraulic couplers allow for use with any standard post-harvest applicator in use. A connector piece allows 6 or 8 nozzles to be used in higher volume situations. Nozzles need to be at a 45 degree angle, aimed forward and backward in alternating sequence. The ideal locations for spray bars are at transition points on the bin piler where potatoes are tumbling. Unloading booms in Maine are typically 24 or 30 inches wide. For a 24-inch boom, locate nozzles 6 inches above top of potatoes; for a 30-inch boom, locate nozzles 9 inches above top of potatoes. Having the bin piler belt damp enhances distribution of the phosphorous acid solution on the tubers.

Spray bar with 4 nozzles

Spray bar with 4 nozzles. Photo by Steven B. Johnson.

Spray bar with 3 nozzles

Spray bar with 3 nozzles. Photo by Steven B. Johnson.

Connector piece for 6 or 8 nozzles

Connector piece for 6 or 8 nozzles to be used in higher volume situations. Photo by Steven B. Johnson.

Forward and backward facing nozzles at 60 psi.

Forward and backward facing nozzles at 60 psi. Photo by Steven B. Johnson.

The calibration tables at the end of this bulletin provide phosphorous acid solution rates of 40, 48, and 64 ounces per ton, at 40 or 60 psi, for 3-, 4-, 6-, and 8-nozzle configurations. A three-nozzle 24 inch boom has a span of 12 inches; a four-nozzle 24 inch boom has a span of 15 inches; a four-nozzle 30 inch boom has a span of 19 inches. (Detailed plans and supply list.)

40 ounces of dyed solution (untreated potato in the center)

40 ounces of dyed solution (untreated potato in the center). Photo by Steven B. Johnson.

48 ounces of dyed solution (untreated potato in the center)

48 ounces of dyed solution (untreated potato in the center). Photo by Steven B. Johnson.

64 ounces of dyed solution (untreated potato in the center).

64 ounces of dyed solution (untreated potato in the center). Photo by Steven B. Johnson.

Procedure

  1. Determine the unloading rate. Timing the minutes it takes to unload a truck of known volume, and converting the truck volume into tons, will give the unloading rate in tons per minute. Convert the unloading rate in tons per minute to CWT per minute by dividing by 20. Tables 1, 2, and 3 below include unloading rates from 10 to 40 CWT per minute.
  2. Select the phosphorous acid solution rate. (Tables 1, 2, and 3 below include phosphorous acid solution rates of 40, 48, and 64 ounces per ton, respectively.)
  3. Select the application pressure. (Tables below include pressures of 40 or 60 psi.)
  4. Select the nozzle number on the spray bar. (Tables below include nozzle configurations of 3, 4, 6, and 8 nozzles.) Additional nozzles may be added or removed by hooking or unhooking the hydraulic connectors.
  5. Select the phosphorous acid rate. Consult the label of the product for the maximum rate.

Table 1. 40 ounces of solution per ton of potatoes

CWT per min PSI 3 nozzles 4 nozzles 6 nozzles 8 nozzles
10 40 TX3
10 60 TX2
15 40
15 60 TX4 TX3 TX2
20 40 TX3
20 60 TX6 TX4 TX3
25 40 TX6 TX4 TX3
25 60
30 40
30 60 TX6 TX4 TX3
35 40 TX6 TX4
35 60
40 40
40 60 TX4
24-inch boom: locate nozzles 6 inches above top of potatoes
30-inch boom: locate nozzles 9 inches above top of potatoes

Table 2. 48 ounces of solution per ton of potatoes

CWT per min PSI 3 nozzles 4 nozzles 6 nozzles 8 nozzles
10 40 TX4 TX3 TX2
10 60 TX3 TX2
15 40 TX6 TX4 TX3
15 60
20 40 TX6 TX4 TX3
20 60 TX6 TX3
25 40
25 60 TX6 TX4 TX3
30 40 TX6 TX4
30 60
35 40
35 60 TX4
40 40 TX6
40 60 TX6
24-inch boom: locate nozzles 6 inches above top of potatoes
30-inch boom: locate nozzles 9 inches above top of potatoes

Table 3. 64 ounces of solution per ton of potatoes

CWT per min PSI 3 nozzles 4 nozzles 6 nozzles 8 nozzles
10 40 TX4
10 60 TX4 TX3 TX2
15 40 TX6 TX4 TX3
15 60 TX6 TX3
20 40
20 60 TX6 TX4 TX3
25 40 TX6
25 60 TX4
30 40 TX6
30 60 TX6
35 40
35 60
40 40
40 60 TX6
24-inch boom: locate nozzles 6 inches above top of potatoes
30-inch boom: locate nozzles 9 inches above top of potatoes

The efforts of Jesse Clark and the financial support of NuFarm Americas are greatly appreciated.

References

Johnson, S. B. 2008. “Post-Harvest Applications of Phosphorous Acid Materials for Control of Phytophthora infestans and Phytophthora erythroseptica on Potatoes.” Plant Pathology Journal 7(1):50-53.

Johnson, S. B. 2010. “Post-Harvest Application of Phosphorous Acid for Control of Phytophthora infestans on Potatoes.” In: Schepers, H.T.A.M (editor): Proceedings of the Twelfth Workshop of an European Network for Development of an Integrated Control Strategy of Potato Late Blight (Arras, France, 3 – 6 May 2010). Special Report No. 14, Wageningen, the Netherlands, Applied Plant Research, Wageningen pp. 85-88.


Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

© 2013

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