Sugar Producer

14 Sugar Producer JUNE/JULY 2020 Friend Foe? or Water is an essential part of life; it is necessary for plants to thrive during the growing season, and it is the mainframe through which nutrients are transported. That said, irrigation, although necessary, represents challenges such as the vulnerability to weed, disease and insect pressure. Can water be a grower's worst enemy? In some regions, many aspects of irrigation are outside a grower's control. In areas such as the Dakotas, Michigan and Minnesota, beet growers rely on rain to irrigate their crops, giving them less control over the amount of water they use and possibly putting them at a higher risk for soil-borne disease and other pathogens. In fact, instead of adding water, efforts are often concentrated on getting rid of excess water in their crops. In places like the West, where water can be controlled with more accuracy, careful consideration should be placed on how irrigation is managed. For a majority of Western states, growers use river and ground water and have the ability to control how much and when water is applied. The timing of irrigation is critical not only for the yield and development of a crop, but for disease, insect and weed pressure, and even for a successful harvest. Effects of Water on Diseases Finding an ideal balance of irrigation can be difficult. Over-irrigating can cause nutrients to be leached, potentially reducing yield. Further, sugarbeets in continuously wet environments are more vulnerable to root diseases. Saturating the soil without letting it dry out can result in an increase of root pathogens like Rhizoctonia, and Aphanomyces, as well as those affecting leaf tissue such as Cercospora or powdery mildew. The literature tells us that Cercospora thrives in 90 to 100 percent humidity with temperatures ranging from 77 to 95 degrees Fahrenheit during the day with nighttime temperatures of around 60 degrees. Rhizoctonia and Aphanomyces are both soil-borne fungi that can live in the soil for years. Infection from these pathogens typically occurs when soil temperatures reach 72 to 77 degrees under saturated conditions. On the other end of the spectrum, being too dry can increase insect and other pest pressure such as spider mites, which thrive in hot and dry conditions. During the past several years, noticeable effects from wildfires in the West have also made it challenging to control the amounts and timings of growers' irrigations due to changes in temperature and humidity from constant cloud or smoke cover. Lower temperatures and increased humidity can cause large swings in disease dynamics and increase the ability of fungi to grow. These types of effects have been observed in other non-crop systems like forests as well. In Western sugarbeet-growing areas, these effects, combined with the natural tendency for growers to over-water during this time of year, exacerbate the situation and can often cause perfect conditions for fungi to thrive in a sugarbeet crop. Of course, one way to help mediate disease pressure using irrigation is to Excess water can lead to the advancement of root diseases such as Rhizoctonia and Aphanomyces. Photo by Oliver Neher, manager of sugarbeet quality improvement and plant health, Amalgamated Sugar Company

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