Buckwheat has taken off as a crop in central Washington’s Columbia Basin in the last 10 years. Now, over 10,000 acres grow, some for export to Japan.
Baby leaf spinach is another new crop in the area, a testament to the fact that the Columbia Basin is gaining repute as a good area to raise a range of crops. Farmers are drawn to the amount of land and irrigation available, expertise among growers and presence of numerous seed companies that bring contracts to growers. Yet with opportunity comes risk – in this case, new diseases that prey on the area’s newly established crops.
Researchers at Washington State University have identified new pathogens in Washington’s buckwheat crops that were never reported in the United States before 2015.
Pathogens are living populations of organisms. These populations are constantly shifting. Plant pathologists monitor shifts in populations over time to be aware of what’s happening with pathogens in relation to environmental changes and in response to farming practices. This is especially important in the context of climate change, because insects, pests and pathogens worldwide are adapting to the changing climate. Researchers at the U.S. Department of Agriculture (USDA) and Cornell University, Rutgers University and Washington State University are monitoring changes in environmental conditions (some caused by climate change) and changes in pest populations throughout the country. As reported in the 3rd National Climate Assessment, “Insects are directly affected by temperature and synchronize their development and reproduction with warm periods and are dormant during cold periods. Higher winter temperatures increase insect populations due to overwinter survival and, coupled with higher summer temperatures, increase reproductive rates and allow for multiple generations each year.”
In the Northeast, the growing season is lengthening and Cornell’s Mike Hoffmann said this increases the chance of more generations of pests during that warmer period, which could result in greater damage. “The life span varies by pest,” he said. “But adding 15-20 days to the growing season gives some pests that much more time to develop and damage the crop.”
From 1990 to 2012, plant hardiness zones shifted a full zone north. “We can now grow canola in New York, which we could not (do) in the 1990s, for example. That also means that some insect pests that used to not survive over winter in certain areas are now able to survive because of the warmer winters,” Hoffmann said.
Marjorie Kaplan, associate director of the Rutgers Climate Institute, shared reports of southern pests like tomato pinworm and a northward expansion of beet armyworm in New Jersey fields. “Similarly, we have had reports that peaches have been developing ahead of schedule and in recent years, peach rusty spot and peach blossom blight have been showing up in higher levels, occurring early in the growing season,” she said.
Two pests that affect sweet corn are thriving in the changing climate. The corn flea beetle used to be wiped out during most winters in the Northeast by cold temperatures. Now that it’s much warmer, it survives and is a pest almost every year. The corn earworm used to arrive late in the summer on storm fronts. Now, Northeast growers and researchers find corn earworm early in the season, because it’s able to overwinter in the area’s warmer winter conditions.
According to a paper in the scientific journal Biological Control in January 2017, brown marmorated stink bug, a pest of many important crop plants native to Asia, has invaded the United States, including the North Central states. Researchers investigated the efficacy of classic biological control agents because the stinkbug’s natural native enemies are not present in areas where the stinkbug is invasive.
Another recent USDA project investigated the extremely invasive pathogen Candidatus Liberibacter asiaticus and a presumed virus that causes citrus chlorotic dwarf in Turkey. According to USDA literature, the pathogen is transmitted by a whitefly already widespread in the United States and thus has very high potential for invasiveness. The research was designed to improve scientific knowledge of invasive pathogens of citrus and provide new tests useful for their detection and management.
Although neither of the aforementioned projects specifically targets climate change, Washington State University’s Lindsey du Toit pointed out that projects like these are highly intertwined with climate change. “Plant pathogens for the most part are very strongly influenced by environmental conditions. Their ability to reproduce, to sporulate, to thrive, to spread are very strongly influenced and on a very narrow scale. A few degrees (of) temperature shift can make a huge difference in conditions becoming more favorable or less favorable for particular types of pathogens. That’s true for insects as well. Some of the pathogens I work with are vectored by insects and the influence of environmental conditions, particularly temperature, heat, relative humidity – all that influences things like duration of leaf wetness, amount of dew, amount of rainfall, amount of frost or lack of frost, how long the season goes into the fall or how early it starts in spring.”
du Toit works with vegetable seed crops grown in the Pacific Northwest, including spinach, the cabbage family, table beet, Swiss chard, onion, carrot and coriander. “With changing climate you see a shift in which pathogens tend to be more problematic or less problematic,” she said.
The years 2013, 2014 and 2015 were some of the hottest summers on record in eastern Washington, which made conditions more conducive for opportunistic onion bulb-infecting bacteria and fungi. In addition, warm spring temperatures starting earlier in the year allowed some pathogens to get active earlier. The onion seed crops du Toit grows are biennial, so they must go through a winter to change from an onion bulb crop to a flowering crop of seed. If spring is particularly warm, as it was in 2016, diseases like downy mildew become active earlier in the season. That creates a longer window of susceptibility. “We had the worst problem with downy mildew last year that I’ve seen in 16 years of working with onions in the Columbia Basin,” du Toit reported.
Managing pests and pathogens has always required awareness of the fact that these are living organisms influenced by the environment in which they live. They’re also living organisms that adjust and evolve, within their biological limits, to environmental pressures put on them. du Toit said, “Climate change is just one set of pressures. As scientists, we try to figure out what are the limits of those boundaries – developing an awareness of the whole system we’re working in. Climate is one big factor behind that.”