Disease Forecasting Discussion Group

Potato Late Blight On-line Workshop
Late Blight Management
Discussion Forums

Disease Forecasting / Fungicide Application Technology

More than 50 individuals attended the Disease Forecasting / Fungicide Application Technology session at the North American Potato Late Blight Workshop in Tucson, Arizona, representing the interests and concerns of research and extension personnel, agribusiness supporters, and producers. After considerable discussion and deliberation, the following priorities were submitted by the group to the Workshop organizers for distribution to the national and international community for their input.

Priority I. Late Blight disease forecasting models need baseline research to more accurately incorporate the following abiotic components: environmental monitoring at the microclimatic and macroclimatic levels, weather forecasts, environmental systems (i.e., irrigated, rainfed), fungicide efficacy and timing, fungicide resistance/sensitivity, fungicide weathering.

Priority II. Late Blight disease forecasting models need baseline research to more accurately incorporate the following biotic components: initial inoculum from various origins (seed, cull, volunteer, oospore), pathogen dispersal, host and pathogen genotypic variability, host phenology.

Priority III. Late Blight disease management with fungicides needs baseline research on effects, costs/benefits and risk assessment of varying fungicide rates, intervals, chemistry and application technology method (equipment, water volume, air speed, nozzles) on the host, pathogen and environment.

Priority IV. Late Blight disease forecasting and surveys need to incorporate local, regional and national geospatial relationships and technology based upon Global Positioning System (GPS) and Geographical Information System (GIS) tools, in addition to standardized disease assessment methodology.

Priority V. Late Blight disease forecasting needs access to and support from more comprehensive and timely environmental monitoring, weather forecasting and technology transfer networks at state, regional and national scales.

General Statement: Encourage the USDA to provide ample and sustained funding for these research initiatives on a multi-year renewable basis. In addition, encourage the USDA to establish a special pool of Collaborative Funds as seed money for innovative ventures between the USDA + States + Commodity Groups + Private Enterprise to address Potato Late Blight priorities identified by this workshop and its participants.

Howard F. Schwartz - 11:10am Feb 25, 1997
Environmental monitoring and disease forecasting models have relied upon a variety of instrumentation such as hygrothermographs, Campbell Scientific (CS) units among others. Our research in Colorado has relied upon CS units for regional monitoring and disease forecasting efforts for our potato industry, and recently we investigated the value of a new in-field electronic unit (I call this an electronic hygrothermograph since we can download temperature, humidity, rainfall, wind data via a notebook computer) produced by Spectrum Technologies (ST). Both systems can be connected to cellular telephone + modem systems for easier access with a total price tag for equipment + telecommunications of approximately $ 6000 for CS and $ 2250 for ST.

Both the regional (Campbell Scientific at 801-753-2342) and the in-field (Spectrum Technology at 800-248-8873) environmental monitoring stations have been useful for research with foliar pathogens such as early blight and late blight. Are there other environmental monitoring systems available with which potato researchers have had good experiences?

Blair Geisel - 06:43am Mar 4, 1997
Until recently, growers in Manitoba have relied on aircraft to apply fungicides for the control of early blight and since 1994, for the control of late blight. It has become apparent that aerial applications of fungicide for the control of late blight may not be adequate, so many growers are switching to ground application. We understand that high water volume and pressure are required, but what types of spray nozzles will provide the best coverage?

David Anderson - 12:53am Mar 12, 1997
Abbotsford BC. Ca. Our sprayer is configured with one row top nozzle, and a "hill elevation" nozzle on each side of the row. each tilted up 10 degrees from horizontal and alternating 10 degrees ahead of and behind the spray boom to create a "mini cyclone" within each plants foliage as the sprayer passes. I use a John Bean pump at 150 psi. and prefer morning spraying when the dew is still on the plants and the foliage will suffer least breakage due to the turbulence. My goal is to cover all the undersides of all the leaves in the canopy as well as to fog the moist soil under it.

Philip Hamm - 12:52am Mar 14, 1997
Blair:
I would not automaticly discount the use of fixed wing aircraft for applying fungicides for late blight control. This method of application can achieve control if the following conditions are met: (1) first application is done at least 2 weeks prior to exposure to late blight;(2) weekly applications are followed with "reasonable" kinds of products; (3) factors during application are correct (proper distance to the canopy, no wind, droplet size to allow drop to the canopy, humitity and height to canopy okay, pressure, etc); and (4) and most importantly, there are no application skips. The later can be control by proper wind conditions during application and the use of flags, GPS etc.

While data from our testing would indicate that more material is deposited during ground application (others in North Dakota have found the same), plane is second, and chemigation third, plane application will be adaquate if the above conditions are met. All three methods do have drawbacks.

Gary Barten - 08:13pm Mar 14, 1997
Philip Hamm:
Some additional comments in addition to my previous message. I read your paper on "Efficacy of Application Method for Depositing Fungicide in a Potato Canopy" in the June/July 1996 edition of Potato Country. I have some questions in reference to that paper. 1)Were final yields recorded? Are there any suggestions that chemigation would yield less than another application method?

I am an Assistant Farm Manager on an irrigated potato and vegetable farm in the Central Sands of Wisconsin. We are looking at chemigation but have concerns when reading your research results.

Philip Hamm - 10:51am Mar 18, 1997
Gary:
In answer to your question about the efficacy of chemigation for applying fungicide for late blight control, I would say probably. In our tests and those done in North Dakota, chemigation always deposited less total material in the canopy than did air or ground application. We assume that was due to the amount of water used during chemigation, usually around .2inch/A or about 5-6,000 GPA. The material is just washing off. Interestingly, in contrast to ground and air application, chemigation deposited about an equal amount of material throughout the canopy. Plane deposited much more in the upper canopy, ground was somewhat mixed, putting more in the upper and mid canopy regions.

We know that chemigation works, however, to control late blight. I have Infra red photographs of chemigation skips. This is where the fungicide injection pump has plugged and instead of backing the pivot up to ensure complete coverage, the pivot was allowed to continue forward. Without fungicide, a wedge formed with late blight in these fields. Having said all that, I believe where we lose control is on the end of the application cycle. By seven days, given the amount of water we apply to fields in the Columbia Basin, and the reduced amount applied because of wash-off, the level of fungicide in areas of the canopy has been reduced to levels no longer able to control late blight infections. Possibly a reduced frequency of application, say 3-5 days would be a more adaquate way of using chemigation while providing adaquate disease control. This would be particularly true under high late blight pressure with favorable late blight weather.

As for when chemigation would be the perferred method of application, never at this time. I am working with Dennis Johnson and Brad Geary at WSU on chemigation aspects using far less GPA than has been done in the past. This past summer we compared what is called a detached boom arrangement (a boom mounted below the pivot) that applied Bravo using about 73 GPA of water. It deposited 3 times the amount of Bravo than .1 inches of water. If water rates can be reduced to levels like that, than I would suggest that chemigation does have a reasonable place. We are also looking at other reduced water application aspects this summer.

We did not yield our plots but I have no reason to suspect that chemigation will reduce yields. Work done by Mike Thorton of University of Idaho this past summer, however, indicated about a 1% yield reduction due to using ground applicators. Apparently soil compaction in the wheel tracks reduced yield. This amount of reduction would vary based on the width of the booms = less tracks in the field less yield reduction.