This article appears in the June/July 2020 issue of Sugar Producer as part of our recognition of Smart Irrigation Month in July.

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 simply reduce the amount of water applied. For Cercospora, letting the canopy dry out during the night, especially when it is 60 degrees or warmer, helps deter the development of disease. Additionally, allowing the top part of the soil profile to dry for several days helps slow the development of root diseases.

In December 2019, during the University of Idaho Sugarbeet Conference in Burley, Idaho, a panel of growers discussed strategies for controlling pests and diseases. A grower from the western part of the growing area described how irrigation plays a key role in his management decisions. He described some of the challenges of over-irrigating, citing one of his fields as an example. Disease pressure showed up in this grower’s field, ultimately resulting in lost yield. Improved water management, including altering his irrigation schedule, made all the difference for this grower. He observed an overall decrease in disease pressure and an increase in yield—by as much as 10 tons per acre.

During the 2019 growing season, several Amalgamated Sugar crop consultants conducted an irrigation study. The objective of the study was to gather data on how much water growers were actually applying to their sugarbeet crop, and to see if there was, in fact, excessive watering. Rain gauges were placed in fields and measured three times per week. The data was then entered into an irrigation scheduler program (Washington State University’s Irrigation Scheduler), which would then plot irrigation patterns on a graph. The results concluded that the majority of growers tested by the consultants were over-watering—that is, constantly keeping the soil at field capacity. The general idea is not to do this; rather, a grower would ideally allow periods of drying between irrigations. These drying periods help build robust root structure, keep humidity down, and slow the development of root pathogens.

Growers may also download and use this tool on their own smartphones by visiting www.weather.wsu.edu/is or by searching for it on their device’s app store. Amalgamated Sugar crop consultants can also provide more information to growers interested in learning more ways to manage irrigation.

Effects of Water on Harvest

Balancing weather and irrigation during harvest operations can also be a challenge. An abundance of water during harvest, whether supplied through irrigation or a weather event, can lead to compaction, mud plugging up equipment, higher tare, and potentially a delay in harvest operations. Not enough water in the soil can result in the breakage of sugarbeet tails and an overall loss of yield.

Overall, growers in the West are pretty lucky. Managing irrigation is one of the most cost-effective disease and insect management strategies available in the region. Water does not have to be sugar producers’ enemy. It allows us to manage the microclimate in which we are raising our sugarbeets. High-yielding, high-quality sugarbeets are often the result of mindful and balanced irrigation.

This article appeared in the Spring 2020 edition of The Sugarbeet, the Amalgamated Sugar Company’s quarterly grower publication.