by Courtney Llewellyn
Bindweed is bad news – but farmers already know that. The vining menace is considered a noxious weed because once it’s established, it’s nearly impossible to fully eradicate. It outcompetes native plants species and can reduce crop yields. It forms extensive root systems, often climbing or forming dense, tangled mats.
It can be controlled mechanically (but not well), culturally (through perennial plantings or tall, shade-producing crops), by using herbicides or via some organic controls currently being tested in the Pacific Northwest. Research on organic control was recently presented through an eOrganic webinar. The objectives of the research were to evaluate the integration of multiple weed control methods in organic perennial fruit systems (using blueberry as a model system) and to harness Tyta luctuosa (known as four-spotted moth or field bindweed moth) as a biological control agent.
Marcelo Moretti, a researcher in the College of Agricultural Sciences at Oregon State University, has been looking into bindweed since 2017. He explained that blueberry growers in the PNW traditionally use mulches, both natural and synthetic, in planting rows for weed control. Despite extensive use of plastic mulch, growers still see weed escapes. The weeds grow next to the mulch and at plant bases. Flame weeding is not an option for blueberries and hand-weeding is expensive. “The current options are not perfect,” Moretti said of weed control.
Fortunately, there are some new tools for weed management available: saturated steam, brush weeders and organic herbicides. Moretti specifically noted a saturated steam tool created by Weed Technics, based in Australia. A pump brings hot water from a water tank, and the user can set the boiler at different temperatures, but it needs to be at 250º F for effective weed control. Water usage is 160 gallons/hour, and heat comes from a diesel burner (using two gallons/hour). The gas pump uses a half gallon/hour. It’s fast acting, but as creating steam requires a lot of energy, application needs to be carefully targeted. For effective control, researchers needed 730 gallons of saturated steam per acre applied at 0.5 mph.
By moving quickly, a brush weeder cuts weeds at the surface and can even move the top layer of soil to cut some of the weeds below the surface of the soil. It can be used right at edge of plastic mulch. Moretti said for this to be effective, a 40 hp or greater tractor is recommended at 0.5 mph. Organic herbicides tested included Suppress, HomePlate (OMRI approved) and Axxe, and researchers used Suppress and Axxe at their highest recommended label rates.
In both spring and summer weed control tests, saturated steam and the brush weeder outperformed the herbicides. However, cost comparisons need to be taken into consideration for these treatments. For one-third of a field, the most expensive options were the herbicides, both costing at least $120. Hand-hoeing was next, at $64.50 (estimating six hours/acre). The steamer cost was estimated at $43 and the brush weeder was $32. Steam was as effective as hand-weeding.
Cost isn’t the only limitation though. “The amount of water consumption [used by the steamer] is almost irrigation,” Moretti said. Additionally, it only offers contact action (above ground control) and requires specialized equipment maintenance. Limitations with the brush weeder include dust raised and long-term impacts on the weed mat.
Is saturated steam, a newer, novel treatment, a viable alternative in blueberry? It’s safe to the crop, compatible with mulches and offers effective weed control, and it has lower costs than hand-weeding and less labor demand. On the other hand, it is high maintenance, parts availability may be limited and it demands high water usage. In Moretti’s opinion, saturated steam is not yet a viable alternative – it needs refinement. But it is on the horizon to help control bindweed.
Biocontrol with Field Bindweed Moth
“Management is not control. It’s reducing the weed to a manageable point for you,” said Jessica Green, Department of Horticulture, OSU, of field bindweed. Growers need to focus on prevention, competition and disturbance – and avoid contaminated compost, moving contaminated soil and equipment into clean fields, unintentionally feeding the weed and shallow cultivation in moist soil. “It takes constant vigilance,” she added.
There are nine biotypes of field bindweed (differentiated by their leaf shape and two flower colors). Knowing what you’re up against is a good idea to help you determine your best course of action.
Green noted that biocontrol is not a silver bullet but an integrative tactic. Biological controls work best in undisturbed areas and those with low agronomic inputs and with perennial crops. Currently approved to help with bindweed are Aceria malherbae (bindweed mite) and T. luctuosa (field bindweed moth). The mites are most effective in arid and semi-arid regions.
As for the moth… “We’re starting from scratch for research,” Green said. It feeds from the leaf edge inward and will clip the petiole. “They are very hungry caterpillars,” she noted. The large larvae ate 64% of 10 grams of bindweed in a week in their tests. Her team is currently working on shifting from a lab colony of the moths to field release.
“We have had success with this,” Green said, “but we need a large amount of larvae for field releases.”
Her team is also looking at behavioral modification, including host recognition and host acceptance. “We want to make insects come feed on it where we want bindweed gone,” Green explained. She’s evaluated the moths for three years so far and said that while they’re not an ultimate answer, they are a great way to add biocontrol to your system.
The field bindweed moth is a beneficial insect, a generalist pollinator currently established in western Oregon. It noshes on all bindweed biotypes. It seems to be better with humidity than the mites, and Green said it’s “pretty solid and easy to work with.”
Her work is ongoing, in partnership with USDA-NIFA along with Agricare and four growers in the PNW. If it turns out the field bindweed moth can be better utilized in the field, it may not be a silver bullet, but it could be more ammo against this noxious weed.