- Garlic mustard, an invasive plant affecting forested areas in the Midwestern and Eastern United States, secretes a chemical called sinigrin into soil to deter the growth of other plants and decrease competition.
- Researchers have found that sinigrin concentrations decrease as garlic mustard populations age, demonstrating evolutionary change due to ecological processes.
- Ecological-evolutionary feedbacks are assumed to occur, but are rarely observed. This is the first study to show a negative feedback loop for an invasive species.
- Researchers predict that garlic mustard will decline and reach a balance with native species that re-colonize invaded areas.
URBANA, Ill. – Invasive plants are often characterized as highly aggressive, possessing the power to alter and even irreversibly change the ecosystems they invade. But a recent University of Illinois study shows that one such invader, garlic mustard (Alliaria petiolata), actually becomes less aggressive over time.
“One of the things we’ve seen over the last 20 to 30 years is that garlic mustard becomes less of an issue, and actually balances out over time,” says University of Illinois and USDA Agricultural Research Service ecologist Adam Davis.
When garlic mustard arrives in a new location, it releases a chemical known as sinigrin into the soil. Sinigrin is toxic to other plants and to the mycorrhizal fungi community, which other plants depend on to facilitate uptake of certain nutrients and water. Without their fungal partners, and through direct competition with growing garlic mustard populations for physical space, native plants quickly die out.
But when a garlic mustard population has been around for awhile, it produces less sinigrin.
“There’s a fitness cost to producing sinigrin. So, when the native competitors drop out, it makes sense for garlic mustard to slow its production of this chemical,” Davis explains.
In demonstrating the relationship between competition, an ecological phenomenon, and sinigrin production, an evolutionary phenomenon, the research team provided the first empirical example of a negative evolutionary feedback on an invasive species. That is, as garlic mustard populations become larger and more dense as a result of their superior competitive advantage, natural selection begins to act against the very mechanism that allowed for their initial success.
“Even though you might expect ecological processes to influence genetic and evolutionary ones, it has been shown very few times. It’s an unusual thing to quantify, and, as far as we know, negative feedbacks haven’t been demonstrated for other invaders,” Davis says.
If garlic mustard becomes less aggressive over time, should landowners just leave it alone? Davis doesn’t recommend a completely hands-off approach, but thinks landowners and managers should take a more holistic view of the ecosystems that garlic mustard invades.
“It may be satisfying to pull garlic mustard, but the damage you’re doing to the herb layer by trampling it or by hosing it down with a chemical is probably worse than the garlic mustard itself. The main thing that creates space for garlic mustard is repeated disturbance. Landowners should try to minimize those disturbances and promote a healthy forest without micromanaging it,” Davis suggests.
It might take decades to see garlic mustard fade out after its initial invasion, but Davis thinks there’s reason to believe it will happen. “Ultimately,” he says, “our results tell us we should have some faith in the ability of the ecosystem to achieve a new balance.”
The article, “Evolutionary feedbacks on the ecology of the invasive plant Alliaria petiolata,” is published in Functional Ecology.
URBANA, Ill. – Remember when you were a kid and the best part of the summer was collecting fireflies in a jar or discovering elaborate spider webs? University of Illinois Extension horticulture educator Kelly Allsup encourages us to reawaken that childlike wonder this summer by exploring natural areas to find the enigmatic inhabitants that come out at night.
Entomologists use “black lights” to find nocturnal insects, which detect light in the ultraviolet spectrum. Shining a black light in front of a white sheet encourages insects to land and be observed. Non-flying insects like walking sticks can be found by placing a white sheet under trees and beating the branches to see what falls off. Although not technically insects, spiders can be found perched in webs or in the distance using a flashlight to reflect their glowing eyes.
“One of the insects you may find flying is the green lacewing,” Allsup says. “Adults are small, pale, and green with delicately veined wings. Eggs are distinctively stalked to avoid predator insects or cannibalism. Larvae, also known as aphid lions, look like miniature alligators. They use their hooked jaws to drain fluids out of prey, including caterpillars, beetles, and aphids. Larvae can eat hundreds of prey, even though they are only in that stage of their life cycle for seven to ten days.”
Another fascinating nighttime insect is the luna moth. Luna moth adults are a bright lime green with a 4-inch wing span and eyespots on their wings, which are meant to startle predators. They hatch from pupae on host plants of walnut, hickory, or persimmon. They emerge in late May to June, with a second generation appearing in late July to August.
“The adults live for only seven to ten days, and their only goal is to reproduce. Females rest on trees and give off pheromones so males can locate them. Mating pairs couple for long periods of time. They lay their eggs on the leaves of host plants. Lime green caterpillars with magenta spots emerge and feed on leaves,” Allsup notes.
Big dipper fireflies are a type of beetle. Their unique yellow flash attracts mates. Some firefly species prey on other species, with the females mimicking their flashing patterns to attract and eat males. Larvae glow, as well. They live in soil eating snails and other insects.
Katydids are more often heard at night than seen. They are 2 inches long, leaf
green, and have oval wings. They live in the tops of trees and on the deciduous shrubs on which they feed. They breed in late summer to early fall, when the males make loud mating calls at night.
Allsup says another interesting insect to look for at night is the northern walking stick.
“Mimicking sticks to evade predators, wingless northern walking sticks eat leaves in a slow and deliberate fashion,” she says. “Eggs mimic seeds, overwinter in leaf litter, and hatch in the spring. Nymphs hide in leaf litter and wait until night to come out and feed on plants. If attacked, they can release a bad smelling liquid, so try not to startle them!”
The yellow garden spider might not be everyone’s favorite nighttime creature. These spiders are large, with females reaching a “legspan” of up to 2.5 inches and with webs up to 2 feet in diameter. Yellow garden spiders make a new web daily with a large zig-zag marking in the center. Young spiders build small webs close to the ground amid vegetation, with webs becoming larger later in the season. Yellow garden spiders prefer sunny areas with little or no wind and plenty of prey species.
Another spider to watch for at night, says Allsup, is the ghost spider.
“The ghost spider has fangs that open laterally. These orb-weaving spiders are sensitive to motion. It is easy to see them at night as their eyes will reflect flashlights. Ghost spiders actively hunt for small insects and other spiders at night. During the day, they retreat behind loose bark, folded leaves, or crevices in the garden,” Allsup notes.
Barn spiders often construct orb webs on manmade structures near lights. They are oval and usually beige. At night they will be seen in the center of the web, but hide during the day. Barn spiders remove, eat, and reconstruct their webs every day.
Wolf spiders are active nighttime hunters that patrol the ground for insects and other small spiders. Once they detect their victim, they chase, capture, and inject it with paralyzing venom. Soon the victim’s dissolved tissues are sucked out. Spookily, their eyes have a layer of light-reflecting crystals that cause them to shine brightly in a beam of light.
“Their activity can sound threatening, but they really just want to be left alone,” Allsup states. “Also, there is no need to worry about infestations, because the female spider will carry her egg sacs on her belly until they hatch and then carry the little spiderlings on her back until they are ready to fend on their own.”
So, grab your flashlight and head outside tonight.
Corn stocks, acreage, and yield
URBANA, Ill. – Corn futures prices have increased about 75 cents per bushel since the surprisingly large 2016 corn planting intentions were reported on March 31. According to a University of Illinois agricultural economist, the increase reflects declining South American production prospects and the associated strength in export demand for U.S. corn; expectations that planted acreage fell short of intentions; and recent yield concerns associated with an extended period of hot weather.
“Prices will continue to reflect weather conditions and summer weather forecasts, but will also be influenced by the USDA’s Grain Stocks and Acreage reports to be released on June 30,” says Darrel Good. “The estimate of corn stocks as of June 1 will reflect the recent increase in the pace of exports and will reveal the pace of feed and residual use during the third quarter of the marketing year. The expected size of June 1 stocks can be calculated based on consumption data that are currently available and on the assumption that feed and residual use is on pace with the USDA projection of 5.25 billion bushels for the year.”
Based on the USDA’s Grain Crushings and Co-Products Production reports for March and April and on the U.S. Energy Information Administration (EIA) weekly estimates of ethanol production during May, corn used for ethanol production during the third quarter of the marketing year is estimated at 1.24 billion bushels. Corn used for other domestic industrial and food products is estimated at 360 million bushels.
Cumulative export inspections during the first three quarters of the marketing year (September 2015 to May 2016), totaled 1.149 billion bushels. Through April, however, cumulative Census export estimates exceeded cumulative inspections by 49 million bushels. If that margin persisted through May, exports during the first three quarters of the year totaled 1.198 billion bushels and exports during the third quarter totaled 555 million bushels.
For the marketing year, the USDA projects feed and residual use of corn at 5.25 billion bushels. Based on the Dec. 1, 2015, and March 1, 2016, corn stocks estimates, feed and residual use during the first half of the year totaled 3.634 billion bushels.
“Use during the last half of the year needs to total 1.616 billion bushels for total use to reach the USDA projection,” Good says. “The historical distribution of feed and residual use between the third and fourth quarters has varied considerably. Use near 1.05 billion bushels during the third quarter this year would be near the mid-point of expectations based on the historical range. With March 1 stocks of 7.808 billion bushels and imports during the quarter of 20 million bushels, the estimates of consumption during the quarter point to June 1 stocks being 4.623 billion bushels,170 million larger than stocks of a year ago. Stocks would likely have to differ from that estimate by more than 50 million bushels to produce a price response.”
According to Good, the June estimate of planted acreage of corn is expected to be less than intentions of 93.6 million acres reported in March. Some acreage may have been switched to soybeans due to the increase in soybean prices relative to corn prices and due to some delayed corn planting in the eastern Corn Belt. However, with the decline in prevent-plant acres this year and some increase in crop prices during the planting season, total acreage of spring-planted crops may have exceeded the surprisingly small March intentions.
“That potential increase creates some uncertainty about the magnitude of corn acreage,” Good says. “A June estimate near March intentions would be somewhat bearish, depending on late month weather and weather forecasts. The June acreage estimate will not likely be adjusted until FSA certified acreage data becomes available in October, but there is a strong history of the final acreage estimate released in January to be less than the June estimate. During the past 20 years when planting decisions were not directly impacted by farm programs, the final estimate of acreage exceeded June intentions only four times.”
Good says that without substantial surprises in the upcoming USDA reports, corn prices will be mostly influenced by weather and yield expectations, which is usually the case this time of year. The market has begun to price the elevated risk of a 2016 average yield that is below trend that have been discussed for a few months. Increasingly, analysts are drawing parallels between the late 1982-83 weather pattern that resulted in very low corn yields and the 2015-16 weather pattern to date.
“Producers have waited for and now welcome the higher corn prices,” Good says. “The higher prices coupled with uncertainty about summer weather means that producers now have more price risk along with some production risk. December futures prices are now 60 cents above the crop revenue insurance price established in February so there is revenue risk for unpriced new-crop corn. Still, prices would continue to increase with unfavorable weather conditions. What to do? Managing the current new-crop price risk can be accomplished with a combination of the timing of incremental sales and the use of options or options-based cash contracts. The choice of strategy will be influenced by local crop conditions and production expectations. While developing a marketing strategy is challenging, it is important to have a strategy because weather markets provide a window of pricing opportunity that typically persists for a relatively short period. The strategy probably should include plans for pricing some of the 2017 crop,” he says.
Pruning perennials for better shape
URBANA, Ill. – The time between Mother's Day and Father's Day is ideal for pruning many garden perennials, providing more branching and even more flowering in the fall. Overall, proper pruning can result in shapelier and more floriferous perennials with blooms that may be smaller in size, but more numerous.
“Gardeners can think of late spring/early summer pruning as pre-emptive because it takes place before a perennial achieves its full potential growth and before bloom,” notes University of Illinois Extension horticulture educator Candice Miller. “This type of pruning is not technically necessary to the survival of our perennials, but instead becomes more of an art, allowing the gardener to be creative in the garden.”
Mid- and late summer perennials that could benefit from early pre-flowering pruning include chrysanthemums, “Autumn Joy” sedum, monarda, or New England aster. It's common in many years for these perennials to flop open in the center later in the season, making them rather unsightly. A pre-emptive pruning earlier in the season could prevent this.
“I often do this on the ‘Autumn Joy’ sedum and asters in my garden, and it works wonders,” Miller says. “Knowing when to prune is the most critical part.”
Mid- to late summer bloomers could be pruned until early summer.
“Just keep in mind that you are manipulating the plant and can expect a slightly later bloom time in most cases,” notes Miller.
The amount to cut off depends on the vigor of the perennial. On a more vigorous perennial, it might mean cutting back one-half to two-thirds of the foliage. On a less vigorous plant, no more than one-third of the foliage should be pruned off at a time. Cuts should be made back to a lateral flower, bud, or leaf so that the new growth will hide those cuts quickly.
The intended goal in pre-emptive pruning is to cut back those perennials before flowering for height control, and to stagger or delay bloom time. Pruning is a great way to control when a plant will bloom.
“There may be plants in your garden that you do not want to flower at the same time because of a bad color combination,” Miller suggests. “Staggering the bloom time is a great way to avoid clashing colors.”
Some spring flowering perennials could benefit from a pruning after flowering, as well. The following is a short list by Minnesota Extension of spring-blooming perennials that could benefit from this type of post-bloom pruning: columbine (Aquilegia hybrids), rock cress (Arabis caucasica), siberian bugloss (Brunnera macrophylla), ground clematis (Clematis recta), maiden pink (Dianthus deltoides), evergreen candytuft (Iberis sempervirens), bearded iris (Iris hybrids), spotted deadnettle (Lamium maculatum), catmint (Nepeta mussinii), wild sweet William (Phlox divaricata), moss phlox (Phlox subulata), and wooly thyme (Thymus praecox).
“If you've never done this practice before in your garden, do some experimenting this season and see what results,” Miller encourages. “Try pruning a portion of the plant and see what happens. Perennials are resilient, and through trial and error, you might discover that you can create a much more appealing plant with a little manipulation.”
Drip irrigation in the home garden
URBANA, Ill. – With demand for water resources and concern for water conservation increasing across the U.S., drip irrigation is becoming a common method to reduce the water bill and safeguard water resources.
“Drip irrigation is a technique that allows water to slowly drip onto the soil surface or directly to the root zone using a system of piping, valves, tubing, and emitters,” explains University of Illinois Extension educator Chris Enroth.
According to Enroth, there are a number of reasons gardeners should incorporate drip irrigation into their landscapes and gardens.
Depending on the soil type and daily climate conditions, traditional watering methods can result in water running off before it penetrates the soil. Drip irrigation, on the other hand, is highly efficient. The majority – 90 to 95 percent – of the water applied in this way infiltrates the soil.
“Another benefit of drip systems is that they are highly efficient,” Enroth notes. “They usually use 30 to 50 percent less water than sprinkler irrigation.”
Other pros of drip systems include minimizing leaf wetness, which can reduce disease occurrence; the ability to direct moisture only to desirable plants, keeping weeds out of the path of irrigation; and the ability to set timers to deliver the exact amount of water desired.
“In the past, drip irrigation was a bit intimidating for homeowners,” Enroth says. “Early systems had their share of problems, ranging from clogged emitters to uneven distribution of water.”
The development of new materials has improved and simplified today’s drip irrigation systems.
“There are almost endless combinations of drip irrigation systems that can be set up for use in landscaping beds or in the vegetable garden. Many local garden centers and online retailers sell customizable drip irrigation kits that can easily be hooked up to an outdoor water spigot,” Enroth notes.
A drip system can be as simple or complex as the gardener desires. Enroth recommends drip tape for use in row crops and vegetable gardens. Single mounted drip devices called emitters are typically used to irrigate trees, shrubs, containers, and hanging baskets. Emitters are plugged in to polyethylene pipe and run to wherever water is required. Finally, drip tube is typically used in landscape beds.
Drip irrigation systems require a backflow prevention device to prevent contamination of the water source. They also operate on very low water pressure, so every system also requires a pressure reducer.
Enroth cautions, “The typical water pressure found at the spigot is 30 PSI. If a drip irrigation system is run from a water source without a pressure reducer, emitters can be damaged and a drip system’s lifespan will be shortened.”
Contact your local Extension office for resources on setting up your drip irrigation system. You can find your local office at http://web.extension.illinois.edu.
University of Illinois Plant Clinic: Celebrating 40 years of service to Illinois
URBANA, Ill. – Since 1976, the University of Illinois Plant Clinic has served as a clearinghouse for plant problems. The Plant Clinic was originally developed to help County Cooperative Extension staff and campus-based specialists with requests for diagnoses on a wide variety of plants.
“By acting as a centralized diagnostic laboratory, the Plant Clinic also serves as a source of information about plant problems in Illinois,” says University of Illinois Extension educator Diane Plewa.
For most of its existence, the Plant Clinic was open from May through October. Since 2010, the Plant Clinic has been open year-round. During the off-season, staff compile reports, write fact sheets, and present at conferences and meetings around the state. The Plant Clinic has taken a lead role in the Illinois First Detector Invasive Species Workshops, which started in 2013. The workshops are held every year in various locations across Illinois and educate green professionals, city and municipal employees, and concerned public about invasive plants, insects, and diseases that threaten Illinois horticulture and agriculture.
For the past several years, the Plant Clinic has processed over 4,000 plant and soil samples annually. The vast majority of the plant samples are analyzed for disease and insect problems, though plant and insect identification is also performed. Soil samples are analyzed for nematode populations, including soybean cyst nematode and vermiform pathogenic nematodes.
“Last year, a new service testing for herbicide resistance in waterhemp was offered,” Plewa notes. “Protocols for molecular testing for glyphosate and PPO-inhibitor resistance were adapted from ones developed in U of I researcher Patrick Tranel’s laboratory. Over the course of the year, 338 fields (representing 1350 plants) were analyzed. Plants were submitted from Illinois and four other Midwestern states.”
The Plant Clinic has worked with the Soybean Board and the Sentinel Plant Network to stay aware of new threats in Illinois. Last year, several new pests were identified, including jumping worms (an invasive earthworm) in northern Illinois, and tar spot of corn in north/central Illinois. This disease was found in Illinois and Indiana in 2015 and was a first find in the country.
The Plant Clinic also works with the Illinois Department of Agriculture and Illinois Crop Improvement Association to certify crops for export, and has a partnership with the Illinois Department of Natural Resources to monitor the health of natural areas in Illinois.
“The Plant Clinic employs undergraduate and graduate students, providing them with hands-on experience working in a plant diagnostic laboratory and expanding their outreach skills,” Plewa says.
Staff write articles for various online newsletters, including the Home, Yard, and Garden Pest Newsletter (http://hyg.ipm.illinois.edu/) and The Bulletin (http://bulletin.ipm.illinois.edu/). The Plant Clinic participated in the ACES Family Academies in 2015, where youth ages 6-13 got a chance to use microscopes, inoculate plants, and wash soil to collect nematode eggs. Departmental service includes opening the laboratory for tours and hands-on activities for students, and outreach at events such as Agronomy Day held every August.
For more information about the Plant Clinic, including contact information and instructions on submitting samples, please see our website at: http://web.extension.illinois.edu/plantclinic/. The clinic is celebrating 40 years of service to the state of Illinois all season long on its Facebook page (https://www.facebook.com/UofIPlantClinic/) and is looking forward to another 40 years of helping people with their plant problems.