Grasshoppers heating up
By Erin Volheim
In 1874, there was a giant grasshopper plague that swept in a Z-shape across Eastern Oregon, the Dakota Territory, Kansas and Missouri. A news correspondent in the July 28, 1874, issue of The New York Times describes the scene:
“The present Summer has been remarkable for the immense swarms of destructive insects which it has given life to all over the West, from Illinois to distant Oregon, and from Texas to Dakota…These pests are leaving nothing green or edible above the surface of the ground…In my rambles through the country I have heard much complaint of expected hard times, and probable want of food in certain districts where the grasshoppers have been a visitor.”
This past summer, the grasshoppers in our part of Southern Oregon were unusually abundant in our lower pasture and garden. Though not at plague proportions, one human step sent a dozen fleeing over the tomatoes and pumpkins. My three plus years on the land give me only a limited perspective on the ebb and flow of the local grasshopper populations, so to be sure of my hunch I asked around. Farmer friends who have been working the soil for around 10 years now, concurred my perception. They have also seen some extensive damage to certain field crops.
Grasshoppers are native to this country. There are hundreds of species of grasshoppers on western rangeland. About a dozen of these cause economic damage, with five to seven species considered the most destructive. Localized outbreaks, covering thousands of acres, occur almost every year. But when climatic conditions are right, a few of these species reproduce in astounding numbers. Trillions of their offspring can spread across millions of acres in the West. Over 450,000 acres in 11 Oregon counties were estimated to be at risk of economic infestations of grasshoppers in 2005.
\Back in the 1870s, there weren’t many known options to protect crops from damage. The first “mechanical method” documented in 1877 was an early incarnation of the “hopper dozer,” a metal scoop coated with tar that was dragged across the fields to trap grasshoppers. Nowadays, when an infestation hits a conventional farmer or rancher, they shell out money for planes loaded with pesticides to fly over and spray or drop poison bait. Early last summer in Baker County, Eastern Oregon, a grasshopper invasion moved 60 farmers and ranchers to jointly fund a $46,000 aerial pesticide application covering more than 3,500 acres. It was deemed the worst infestation of that county in 22 years. The USDA defines a grasshopper infestation by eight insects per square yard. In Baker County, they found 100 to 120 grasshoppers per square yard.
Observation is a very important element of farming. All farmers need to be aware of trends, “the general direction in which something tends to move.” Insect infestations tend to peak around four years, when food runs out, disease strikes or predators notice the new tendency. One bird population in England has managed to adapt to global warming trends. Parus major, a bird commonly known as the “great tit” has adapted its breeding season over the last five decades so that their chicks hatch when their main food source, the winter moth caterpillar, is the most abundant. With continued observation, it’s possible that farmers can adjust their practices in response to these fluctuations.
Phenology is the scientific study of periodic biological phenomena, such as breeding in relation to climatic conditions. Climate change has led to an adaptation in some species, like the example above. Yet the relationship between different species within a food chain may be disrupted if an increase in temperature affects one species differently than another, as is the case with insects.
Insects are highly adaptable organisms, with the highest diversity in the Animal Kingdom. Around 925,000 species have been described, though the real number may be at least three times higher. Their adaptability enables them to cope with many environmental changes, including climate shifts due to global warming. A recent study from the University of Washington suggests that global warming leads to far more insects. Warmer climates seem to increase their reproductive rate and population growth, with widespread effects on agriculture.
Grasshopper outbreaks are determined by a complex interaction of several factors, of which weather is the most important. Warm and dry spring conditions encourage nymphal growth. An early spring followed by cloudy, damp weather encourages diseases that sicken and kill grasshoppers. A long, hot summer ensures a plentiful food supply and encourages early maturity and a long egg-laying period. On the other hand, a cool summer and early fall slows down grasshopper maturity and reduces time for laying eggs.
More than 55 million years ago, the Earth experienced a rapid jump in global carbon dioxide levels that raised temperatures across the planet. Researchers studying plants from that time period have found that the rising temperatures may have boosted the foraging of insects. Because food webs involving plant-eating insects affect as much as three quarters of organisms on Earth, researchers believe that the current increase in temperature could have a profound impact on present ecosystems, and potentially to crops, if the pattern holds true in modern times.
The 2001 Intergovernmental Panel on Climate Change Third Assessment Report concluded that the poorest countries would be hardest hit, with reductions in crop yields in most tropical and sub-tropical regions due to decreased water availability, and new or changed insect pest incidence. Many agronomists believe that agricultural production will be mostly affected by the severity and pace of climate change, not so much by gradual trends in climate.
There are three stages in a grasshopper’s life cycle, the egg, nymph (the young grasshopper), and the adult. Most grasshopper species over-winter as eggs, which are laid in clusters in late summer and early fall and hatch in spring, when soil temperatures warm up. It takes approximately 40 to 60 days for the nymph to develop into an adult. During this time, it sheds its exoskeleton several times as it moves from one nymphal stage—called an instar—to another. The best time to control the insect pest is during early nymphal development, when it is most vulnerable to disease, parasites, predators, insecticides and unfavorable weather.
The biological growth regulator Dimilin 2L is used to kill young larvae and nymph grasshoppers. If they reach the adult winged stage then broad-spectrum pesticides like Mustang Max are considered the only option. Mustang Max replaces Mustang insecticide in the northern U.S. and Fury in the South. It’s a pyrethroid, who’s active ingredient is Zeta-cypermethrin. Broad spectrum pesticides kill beneficial insects ranging from lady bugs to honeybees.
Pesticide should only be applied when the potential for drift to adjacent sensitive areas (e.g. residential areas, bodies of water, known habitat for threatened or endangered species, non-target crops) is minimal (e.g. when wind is blowing away from the sensitive areas).
During periodic infestations of native marsh grasshoppers around Klamath Falls National Wildlife Refuge, the U.S. Fish and Wildlife Service (USFWS) is required to drop poison bait or do aerial spraying in a percentage of the refuge to aid surrounding farms and ranches.
Pesticides can negatively effect aquatic and non-vertebrates species in the refuge. There are minimal laws protecting those species, but due to hard-won efforts to protect nearby bald eagle nests, no poison was applied by the USFWS along the eastern edge of the refuge near a ranch that was infested in 2004. Instead, for $27,000, a rancher hired workers to spray his rangeland, first with Dimilin, and later with Malathion, a powerful insecticide. The breakdown products (oxons) of this pesticide is 10 - 100 times more toxic to amphibians than its parent compound.
The estimated annual domestic use of Malathion ranges from 10 to 15 million pounds. In these warming times, it is reasonable to expect that weed productivity will increase in parallel with that of crop and pasture plants; potentially raising the use of herbicides on conventional farmlands and landscapes. Instead of making the necessary changes to our agricultural systems, we keep throwing fuel on our global warming fire.
The long-term control of grasshoppers is possible through practices like tillage, fall clean-up, trap cropping, early seeding, and early harvest. These methods should be guided by fall egg counts and regular scouting to identify their hatching locations. Cultural measures, in conjunction with biological controls and practices that increase farm biodiversity, can provide good sustainable control even within the seasonal fluctuations of global warming. Certainly, the alternative is a better option and should be explored, instead of repeating the same human assaults on our environment that led us to “global weirding” in the first place. Let’s follow the philosophy of this old English proverb, “A farmer must live as if he’s going to die tomorrow, but he should farm as if he’s going to live forever.”
Erin Volheim is a writer residing in the Little Applegate of Southern Oregon.