Archive for the ‘Emerging/invasive pests’ Category

Fresh Plaza

For the first time in the United States, a pesticide-resistant whitefly, which carries crop-devastating viruses, has been found outdoors, raising concerns among fruit and vegetable growers.
The Q-biotype whitefly turned up in April in south Florida’s Palm Beach County, where landscapers were spraying the flowers and shrubs regularly with insecticides. Its discovery outdoors comes more than a decade after it was first found in a US retail nursery in Arizona.
Since 2005, the whitefly has also been found in about two dozen US states, but only in greenhouses.
It is already considered a major invasive pest worldwide.
Now that the Q-biotype whitefly is outdoors in the United States, researchers say it poses a serious threat to crops such as tomatoes, beans, squash, cotton and melons.
Having whiteflies outdoors makes the problem “much more difficult to control,” and they may never be fully eradicated, said Dr Lance Osborne, a professor of entomology at the University of Florida.
“The resistance to pesticides — that is what really sets them apart,” he told a few dozen growers who attended a recent session to learn about the whitefly in Homestead, an agricultural area south of Miami.
“The best single treatment we have kills 90-91 per cent of them. That is as good as we can do without multiple applications.”
The insects can also spread more than 100 viral diseases that weaken the plants and can make fruits and vegetables inedible.
Since its discovery outdoors in Florida in April, they have been found in more than 40 locations across the state, including residences, wholesale nurseries and retail plant outlets, crawling on the leaves of hibiscus, eggplant, lantana, ficus hedges and porter weeds.
‘A serious risk’
Whiteflies can live on 600 different kinds of plants, 300 of which are grown in Florida, according to the state agriculture department.
“The reason we are worried about the Q is because it has such a huge host range and is resistant to pesticides,” explained Dr Osborne.
“They attack so many crops — there is always something in the ground these things will attack.”
While the Q-biotype whitefly has not done any major damage yet in Florida, its emergence has kept agriculture officials busy organising inspections, working on plans to control the bugs and imposing quarantines around positive finds as necessary, a spokesman said.
“With our climate, robust international trade and more than 100 million visitors a year, Florida is a hotbed for agricultural pests and diseases,” Florida agriculture commissioner Adam Putnam said in an email to AFP.
“The Q-biotype whitefly poses a serious risk to Florida’s US$120 billion (S$160 billion) agriculture industry and the more than two million jobs it supports.”


Publication date: 8/18/2016


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From PestNet

Insect and Control Newsletter 87 July 2016 (FAO, IAEA) page 13

Supporting a Feasibility Study on Using the
Sterile Insect Technique against the Cocoa
Pod Borer (PAP5001)

Cocoa is an important agricultural commodity in Papua
New Guinea (PNG) and 80% of the export is produced by
smallholders, who are dependent on it for their livelihoods.
The cocoa pod borer (CPB) Conopomorpha cramerella,
was first detected in PNG in 2006, and available data seem
to indicate multiple entry points. The CPB is now considered
one of the most serious threats to the global cocoa industry.

In East New Britain cocoa production plummeted
by 82% between 2008 and 2012, i.e. from 25,000 tons to
4,000 tons. National cocoa production dropped from
50,000 tons in 2008 to 34,000 tons in 2014. There is plenty
of room to expand cocoa production on PNG, and it is estimated
that only 2% of the land that is suitable for cocoa
production is actually planted with cocoa trees. The Government
of PNG has set a very ambitious goal of reaching a
production/export volume of 300,000 tons per year by
2030. All stakeholders seem to agree that this will not be
possible without adequate management of the CPB.
Cocoa fruits in a well-managed orchard.

The TC project PAP5001 “Supporting a Feasibility Study
on Using the Sterile Insect Technique against the Cocoa
Pod Borer” will be providing support to a feasibility study
to assess whether the SIT can be developed against the
CPB. This will entail developing rearing techniques, with
special emphasis on an artificial larval diet. Some expertise
is already available in the region (e.g. Indonesia, Malaysia)
and it is proposed that a workshop be organized to bring all
this expertise together and to jointly develop a strategy to
the rearing of the CPB.

Grahame Jackson
24 Alt street
Queens Park
NSW 2022

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Reprinted from PestNet

This article is obviously a promotion by the company Biobet, but it might be of interest to members nevertheless. We are putting it out as leafminers can be a serious pest, and there maybe members interested in these Diglyphus wasps

Obviously, this comes with no endorsement by Pestnet which has no involvement in the company or the report.

There are other companies that sell these wasps


Complete leafminer control strategy available for tomatoes

Biocontrol options to control leafminer include two well-known natural enemies Diglyphus isaea and Dacnusa sibirica. “Biobest ’s UK team has developed valuable experience in tomato on how to use these two parasitic wasps in a robust combination strategy. As leafminer pressure increases in tomato crops in the Netherlands, France and other Western European countries, more growers are adopting this highly effective control strategy, taking advantage of Biobest’s advice and broad product offering” says Biobest’s Product Manager for Macrobials, Yann Jacques.

Several species of Lyriomyza genus occur in commercial crops: most importantly the tomato leafminer (Lyriomyza bryoniae), the serpentine leafminer (L. trifolii) and the pea leafminer (L. huidobrensis). Leafminer has become a serious pest in European tomatoes. The main issue is the damage done by larvae tunneling through the leaf. These mines reduce the plants’ photosynthetic capabilities, slow down the production of flowers and ultimately affect fruit yield. Leafminer is particularly damaging for sweet tomato varieties where it develops faster.

Phil Walker, General Manager of Biobest UK: ”In UK tomato crops we have developed quite some expertise using a combination of two complementary parasitic wasps – Diglyphus isaea and Dacnusa sibirica. We were able to develop robust strategies, capitalizing on the complementarity between the biological characteristics of these two parasitic wasps.”

Yann Jacques explains: “Effective early in the season, Dacnusa comes in first to manage and slow down the pest build up. To identify when to start introductions we recommend yellow Bug-Scan sticky traps to detect adults, plus regular inspection of the crop to look for the tell-tale stings.”

Dacnusa has a very high search capacity and, hence, can already establish at very low pest densities. Dacnusa is an endoparasite. It lays eggs directly in leafminer larvae tunneling through the leaf. Dacnusa females looking to oviposit distinguish non-parasitised from parasitised leafminer larvae. Dacnusa is very well adapted to early season conditions, less to conditions prevailing later in the season or in the south. That is where Diglyphus has complementary strengths.

Diglyphus, explains Yann, is an ecto-parasite. “The female punctures a leafminer larva to paralyse it, before depositing an egg next to it. Diglyphus not only parasitizes leafminer larvae, it also host feeds on young larvae. Capable of fast population build up, this wasp can rapidly gain control of a rising leafminer population.”

For more information, please visit www.biobestgroup.com.

Publication date: 8/1/2016

Grahame Jackson
24 Alt street
Queens Park
NSW 2022

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Concern about the lack of controls

The banana crops of Colombia and other Latin American producers faces the risk of being affected by the arrival of a harmful fungus due to the increase in illegal migration from Asia and Africa, as well as the low health controls in Venezuela, said an official from the agricultural sector.
The Fusarium Tropical Race 4 fungus, which causes the Panama disease and can remain in the soil for up to 30 years, attacks the roots of the Cavendish banana variety and plantain.
The eventual arrival of the Fusarium to the region would negatively affect the economies of the banana producing countries and jeopardize food security, said the assistant manager of plant protection at the Colombian Agricultural Institute, Carlos Soto.
“It would be devastating if the fungus arrived, it would destroy everything. We can only take preventive actions, there is no cure for this fungus,” Soto said in a telephone interview with Reuters.
Colombia, the world’s fourth largest banana exporter after Ecuador, Costa Rica, and Guatemala, is working with Peru, Ecuador and Bolivia on a regional campaign to identify the presence of the disease and to increase health checks at borders.
The plan will also be presented to Central America in the coming weeks.
The fungus, which can be transported from one continent to another by migrants  shoes, clothing or agricultural products, has been detected in Indonesia, China, Philippines, Malaysia, Pakistan, Australia, and Mozambique.
Colombia leads the regional campaign because it has become an important transit country for migrants from Asia and Africa that walk across the border with Panama, one of the main areas of cultivation, as they seek to reach the United States illegally through Central America.
Even though the fungus has not been detected in Latin America yet, Soto expressed concern about Venezuela’s lack of controls.
“I’m very concerned about Venezuela because it has no health management and that means they can have the disease and not know they have it, since there is a lot of migration and illegal trade coming from that border, it can be a real danger for us,” he said.
Colombia has 47,000 hectares of banana that generates 30,000 direct jobs. Additionally, the country has over 400,000 hectares of bananas for domestic consumption.
In 2015, Colombia exported 92 million boxes of bananas worth 800 million dollars to the European Union and to the United States.
In the middle of the last century, several banana plantations in Latin America and the Caribbean were infected with a strain of the fungus and had to be replaced by more resistant crops.
Source: gestion.pe


Publication date: 7/28/2016

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July 26, 2016 4.52pm EDT

The mesquite tree was introduced into South Africa to aid farmers and local communities. It is now invasive in most parts of the country. Shutterstock

One such tree genus, Prosopis, or mesquite, originally from the Americas, has been introduced to more than 100 countries. It was introduced into the arid parts of South Africa to aid farmers and local communities with fodder production, provide shade for livestock and produce firewood.

It has now invaded large parts of the country and has become the second most widespread invasive tree after Australian acacias. It has had a negative impact on biodiversity, livestock production, land value, human health, infrastructure and water supply. These are all crucial factors for the economy and for local people’s livelihoods.

The negative effects of these invasions have led to the initiation of programmes to manage them across the world. In South Africa the Working for Water programme drives management on state and private land along with input from private landowners. Without active management these invasive plants would become more widespread and their impact on people and the environment would be more pronounced.

Reducing the impact

Management initiatives, such as Working for Water, aim to reduce the impact and spread of invasive plants. In South Africa the initiative also aims to create jobs and drive rural development.

We recently conducted a study to assess the barriers that impede the effective management of widespread Prosopis invasion. More than 100 barriers were identified in the study, which tried to identify the problems that hinder current management operations. The results could be used to come up with solutions about how to overcome these problems.

Prosopis invasions in South Africa: a blessing or curse?

The key barriers identified were:

  • Using versus removing the tree and control options. Some parties wanted to continue using Prosopis for fodder and fuelwood and did not want them removed. Others pointed to the serious negative impact they have. There was also controversy about labour-intensive management, which is time consuming and makes progress slow. Mechanical and biological control approaches are obviously faster but employ fewer people.
  • The ecology of the species. It is hard to control because it grows very fast and spreads rapidly. It is also capable of regrowing from cut stumps if herbicide is not applied correctly.
  • Poor planning and prioritisation. Often no systematic control strategy is followed.
  • Coordination and cooperation, which is linked to poor planning, inefficient management, corruption and lack of collaboration between different government departments and farmers.

There were differences in how the importance of some barriers were perceived. Most farmers – 80% – placed high importance on a lack of planning and poor management as important barriers. Few managers – 20% – regarded these as important. This reflects different views about the context in which management projects operate.

Adaptation responses

Many of the barriers can be overcome and ways to do this were identified in some instances. But not all were conducive to simple solutions.

Key adaption responses include the adoption of more effective clearing methods. These include:

  1. Mechanised options and biological control. These are more time and cost effective but can still allow for job creation.
  2. Raising awareness and building partnerships to ensure that different actors work together to control the problem.
  3. Ensuring landowner follow-up control. This will ensure state investment is not wasted and long-term control is guaranteed. It is also legally binding but not enforced.
  4. Improved monitoring to get an understanding if control is working and of its benefits. This can also help to reduce inefficient management.
  5. Incorporating systematic strategic planning at various levels to ensure the limited funds available are spent wisely and in a way that has the most benefit.

All of this will improve the effectiveness of control programmes with the funding available.

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Fresh Plaza

Malawi: Gov’t introduces improved banana variety

Banana bunchy top disease wiped out bananas in several districts of Malawi. In an effort to restart banana production, the Malawi government is introducing a new improved banana variety.
”The World Bank through the Agricultural Sector Wide Approach (ASWAP) program has assisted government to reintroduce an improved banana crop in the affected districts starting with a pilot project in Thyolo and Mulanje,” explains crop protection officer for Blantyre Agricultural Development Division (ADD), Joyce Nthenda.
However, Nthenda was quick to mention that the new variety is not resistant to the banana top bunchy disease but it is rather early maturing and high yielding as compared to the local varieties.
“We have been encouraging farmers in the areas to get rid of the existing bananas as the only way of ensuring a total swap of the banana bunchy top disease prior to the introduction of the new crop as it is not resistant and may easily get the disease too,” added Nthenda.
“So only those farmers who have completely removed their old banana crops in the selected areas will be getting the new crops,”emphasized Nthenda.
The to be introduced banana crop is a hybrid crop produced through tissue culturing which is a scientific process not yet available in the country hence the banana seedlings have been imported from as far as South Africa.
Source: allafrica.com


Publication date: 7/29/2016

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Driven mad by herbicide-resistant weeds? Here’s how they start, what they are, and how to manage them.

 How Resistance Spreads

Surprised at how a field full of herbicide-resistant weeds results? It had its origins years earlier. Birds do it, bees do it, even educated fleas do it, as the old Cole Porter song goes.

So why can’t waterhemp (or weeds) do it?

That last line probably isn’t funny if you’re battling herbicide-resistant weeds. Still, it says much about the way herbicide-resistant waterhemp infests your fields in the first place.

That field full of weeds – waterhemp, Palmer amaranth, marestail, or something else – started some time before.

Field Flirters
It’s akin to when a point guard catches a cute courtside TV reporter’s eye. Waterhemp is dioecious, with male and female plants. Sparks quickly fly.

“Since waterhemp is dioecious, pollen is already moving around,” says Pat Tranel, University of Illinois (U of I) weed scientist. “Pollen can be viable up to 120 hours, and it can move ½ mile from the pollen source.”

Initially, resistance is rare
Every herbicide selects for its own failure, even a brand-spanking-new one. In every weed species, rare genetic biotypes exist that resist a herbicide. This varies among herbicide sites of action, says Ian Heap, director of the International Survey of Herbicide-Resistant Weeds.

Rare herbicide-resistant biotypes exploit management uniformity, much as a star center who shreds double-teaming defenders.  Every herbicide application heightens the odds that resisters survive.

How quickly?
Really quick in the case of some weeds like Palmer amaranth. It’s double trouble if the weeds are herbicide-resistant biotypes. By producing up to 1.8 million seeds per plant, glyphosate Palmer amaranth infested 20% of the field areas in less than two years in a 2008 University of Arkansas analysis.

You may be doing a laundry list of best-management practices to forestall resistance. Rotating herbicides’ sites of action. Lacing your row-crop rotation with small grains. Regularly scouting fields and rounding oddball weeds.

Unfortunately, all can be for naught due to an often overlooked resistant-weed spreader: waterfowl.

Kevin Bradley, University of Missouri Extension weed specialist, reports an MU trial found that weed seeds can remain intact after passing through a mallard duck’s digestive system.

Think you’re cruising in a corn planter that goes 10 mph? It has nothing on mallard ducks, which can fly up to 48 mph for up to 38 hours. Potentially, they can move weeds like Palmer amaranth, waterhemp, common lambsquarters, giant foxtail, and smartweed nearly 1,740 miles in 1½ days.

Glyphosate seems synonymous with herbicide-resistant weeds. In most cases, though, weeds resist multiple sites of action. Here are herbicide action sites that waterhemp resists and initial U.S. confirmation year.

  • ALS Inhibitors – 1993
  • Triazines – 1994
  • PPO inhibitors – 2001
  • Glycines (Glyphosate) – 2005
  • Synthetic auxins (2,4-D) – 2009
  • HPPD inhibitors – 2009

“Waterhemp won’t stop at six herbicide sites of action,” says U of I’s Tranel. “It will develop resistance to anything being developed, whether it’s the seventh, eighth, or ninth.”

It’s important to note that no waterhemp biotype exists in all six herbicide sites of action. Still, multiple site resistance abounds. In 2009, for example, weed scientists confirmed an Illinois  waterhemp biotype that resisted four sites of action.

Nightmare crosses between pigweeds occur, but so far at a low rate.

Glyphosate-tolerant waterhemp and Palmer amaranth are bad now, but imagine how fearsome they could be if this weed equivalent of pro basketball’s Stephen Curry and LeBron James teamed up together! Could they cross-pollinate to create some sort of freak frankenweed?

Now that would be bad – and it is currently happening with pigweed species like waterhemp, Palmer amaranth, and spiny amaranth.

“There is some hybridization occurring,” says Kevin Bradley, University of Missouri Extension weed specialist. “There are some weeds I walk by and say, ‘Wait a minute. That doesn’t look quite right.’ The leaves will look like waterhemp, but the head looks like Palmer.”

2012. That’s the year Bill Molin, USDA-ARS plant physiologist in Stoneville, Mississippi, began tracking spiny amaranth and Palmer amaranth hybrid. Resistant to both glyphosate and ALS herbicides, the hybrid is the result of a cross between Palmer amaranth growing in a cotton field and spiny amaranth in a neighboring pasture.

Palmer and waterhemp are doing it, too
Researchers at the University of Illinois and Colorado State University have also discovered amaranthus hybrids of Palmer amaranth and waterhemp.

“The hybrids often look similar to the normal variation of the species,” says Pat Tranel, University of Illinois weed scientist. In many cases, hybridization between species can only be confirmed by genetic analysis, says University of Missouri’s Bradley.

The Good News
Imagine if that imaginary basketball player brimmed with hybrid vigor by crossing Curry with James. Fortunately for you, this hybrid vigor so far doesn’t extend to amaranthus species. Palmer amaranth and waterhemp shoot bricks when it comes to hybridizing. In 2011, field studies by Colorado State University weed scientists showed that glyphosate-resistant Palmer amaranth transferred glyphosate resistance to:

  • Spiny amaranth 0.4% of the time.
  • Waterhemp 0.2% of the time.
  • Smooth pigweed 0.01% of the time.

Remain watchful, though.

“I think the danger in Missouri is with pastures between crop fields,” says University of Missouri’s Bradley. “There, Palmer amaranth that transfers resistance to spiny pigweed in the middle of a pasture is something of which we are aware.”

It’s akin to the anxiety a coach feels when his star forward, at midshot, flashes an on-court smile at a cheerleader. “Wherever these two plants are close together, there is a chance to hybridize,” Molin says.

How to control?
Double- and triple-team it just as you would a 40-point-a-night forward. “Broaden the spectrum of herbicides used,” says Molin. It’s important that this spectrum include herbicides with multiple effective modes of action, he says.

Look beyond the field, too. Control weeds in fencerows, ditches, and other places these weeds can grow, he says.

Even more good news
Low hybridization of pigweed species also means low rates of hybridized seed being shed.

Still, bear in mind that the average waterhemp plant sheds 250,000 seeds. If waterhemp hybridizes just 0.2% of the time, the plant still sheds 500 seeds that can germinate and emerge the next year.

Precision weed control

No new tools are on the horizon, but there’s still technology to help you manage weed issues.

Herbicide-resistant weeds aren’t man-made, but that’s not to say man isn’t to blame. “Farmers have been selecting for herbicide-resistant weeds,” says Lisa Behnken, Extension educator for the University of Minnesota. “They do that by being very predictable.”

Herbicide-resistant weeds occur naturally in the weed population. Farmers became more predictable, and the repeated use of the same chemical tools caused resistant weeds to become a larger part of the population. “Waterhemp became resistant to ALS herbicides before glyphosate technology was even around,” says Behnken.

Missing free throws frustrate the crowd on game day. The same goes for weed specialists when applicators continue to use flat-fan spray nozzles. “They haven’t adopted the air-induction nozzles,” says Fritz Breitenbach, Extension specialist for the University of Minnesota.  “We’ve done enough work to show that they’re superior.” It’s a simple correction that could change the outcome of the game.

In a University of Minnesota study, Behnken found that only 9% of farmers were mapping weeds. “We’d like to see that change,” says Behnken. As you are going across the fields during harvest, map the weeds. That allows you to spend money wisely on your herbicide program, and you can focus on the spots where you have more difficult problems.

You only have one first chance to prevent a weed before it gets established, says Russ Higgins, University of Illinois Extension educator. Once it’s established, it becomes widespread across the field, and then it becomes costly and difficult to control.

Make Multiyear Plans
Last-minute-play calls are no longer acceptable management plans. Weed control needs to be a system approach, which includes multiple practices, says Behnken. “The majority of farmers are lucky if they make a one-year plan.”

Instead, she recommends farmers create multiyear plans with backup plans. In those plans, Behnken recommends tactics that have both chemical and nonchemical tools. Also, don’t include the same herbicide or mode of action every year.

Few new weed-control tools exist, says Breitenbach. “They have to rediscover old tools,” he says. Breitenbach recommends that you go back to incorporating cultural practices for more comprehensive weed control, such as:

  • Reevaluating planting dates
  • Considering cultivation
  • Diversifying rotations


Ever run into the former high school wallflower at a class reunion who now mimics a flashy NBA star? In the weed world, that’s waterhemp.

Why Waterhemp?
Waterhemp used to just line banks near streams and rivers. If this small-seed broadleaf did meander into your crop fields, tillage would bury it. No more. These days, less tillage ensures this shallow soil dweller has ample germination and emergence.

Season-Long Emergence
This emergence – which has started as early as late March in Illinois – can continue all through July, says Pat Tranel, University of Illinois weed scientist.

Late Flusher
Late-season flushes separate waterhemp from other weeds. A 1996 Iowa State University study showed that most wooly cupgrass emerged May 10-20. Peak waterhemp emergence didn’t start until June 24.


  1. Use full rates of preemergence residual herbicides as close to planting as possible.
  2. Follow with overlapping contact and residual postemergence herbicides.
  3. Apply multiple effective sites of action to help manage multiple-resistant weeds.

1 Million
The seeds one waterhemp plant can make with no competition, such as in a prevented-planting case.

It pays to control weeds early. That’s because 1% is the soybean yield loss that results when control occurs on 6-inch waterhemp with infestations of fewer than 10 plants per square foot.

Waterhemp is the league scoring champ when it comes to corn and soybeans. It infests row crops all the way from Louisiana to North Dakota. It’s particularly thick in Iowa and Missouri, infesting 90% or more of soybean acres.

Palmer Amaranth

That’s some wingspan. The seed head can reach up to 3 feet long!

Palmer amaranth is an aggressive, invasive weed native to the desert regions of the southwest U.S. Facing a drought? That won’t slow Palmer. Given it originates from the desert, it’s drought-resistant.

Palmer is akin to a towering center who grows every game. It grows nearly 2 inches per day. It’s also as prolific a scorer as a 3-point shooting guard.

The cheapest way to manage a weed is to prevent it from getting established in a field, says Iowa State University’s Bob Hartzler. He encourages farmers to hand-weed, especially the female plants, before it is established.

Why is Palmer a challenge? It’s already knocked out two main defenses. Most populations resist glyphosate and ALS-inhibitor herbicides. If you let Palmer amaranth play out all season, yield loss could be up to 91% in corn and 79% in soybeans.

Double Team
It’s easy to confuse Palmer and waterhemp seedlings, says Hartzler. Waterhemp has a shorter petiole and longer, narrower leaves than Palmer. The best trait to differentiate seedlings is the presence of petioles longer than the leaf blade on Palmer. Once they have flowered, the sharp bracts on female Palmer are a dead giveaway.

Diversity of weed management must expand beyond herbicides, says Mike Owen, Iowa State University Extension weed scientist. Repeated use of the same chemical tools selects for resistance. Instead, try a combination of cultural practices and chemical tools for control.

Harvest infested fields last. Otherwise, your combine will spread Palmer seeds. Flag areas where you spot Palmer amaranth, says Russ Higgins, University of Illinois Extension educator. When it’s in the introduction stage, there’s still an opportunity to eradicate it before it becomes a widespread threat, he says.

Palmer infests row crops from Louisiana to Ohio to North Dakota. In a 2015 survey, it was on 60,000 acres in Kentucky, according to University of Kentucky’s J.D. Green. Nearly one third of Illinois counties have documented cases of Palmer.


Lack of crop diversity and no-till spur this winter annual’s spread.

Marestail is number one, but not in a good way. It was the first glyphosate-resistant weed confirmed in the U.S. when it surfaced in Delaware in 2000. Since then, it’s moved at full speed into other areas like the Midwest.

Fall forward
Marestail rosettes often appear in the fall in the northern U.S. A fall application of 2,4-D or dicamba plus chlorimurin or metribuzin products offers the best residual control, says the University of Missouri’s Kevin Bradley.

Preemergence herbicides are a must! Larger weeds are tough to kill. Limited postemerge corn options exist, and there are even fewer in soybeans, say University of Nebraska weed scientists.

Springing back
Spring and summer flushes of marestail south of I-70 in the Corn Belt are becoming more common. This likely is signaling a change in plant biology, due to herbicide selection and changes in crop rotation.

Why not rye?
A cereal rye cover crop planted after corn, soybean, or wheat harvest can nix fall marestail emergence and aid control. “A glyphosate and Fierce preemerge provides nearly 98% control of marestail at planting,” Bradley says. “Take out the cereal rye, and the same treatment provides just 40% control.”

Glyphosate-resistant marestail migrated to the mid-South after its 2000 Delaware discovery. It now infests 90% of Kentucky soybean acres. It’s since moved to the Midwest and now plagues an estimated 30% of Iowa’s soybean acres.

Giant Ragweed

This old fencerow and ditch dweller now infests crops

Its 17-foot maximum height would make it any team’s starting center. Typically, though, it’s 1 to 5 feet taller than the field’s crop. Giant ragweed biotypes exist that have resisted ALS inhibitors (Pursuit) in seven states and EPSP synthase inhibitors (glyphosate) in 12 states. There are confirmed giant ragweed biotypes resisting both herbicide action sites in Ohio, Minnesota, and Missouri.

A single plant can produce an estimated 1 billion pollen grains during its lifetime. Its pollen triggers more than allergies; it creates cross-plant pollination potential. This creates genetic diversity that creates more herbicide-resistance potential.

Why is it a problem?
Giant ragweed used to dwell in undisturbed areas like fencerows and drainage ditches. Since the late 1980s, it’s moved into cropland. It’s now prevalent in cropland due to:

  • Crop rotation. It surfaces more when corn is rotated with soybeans vs. continuous soybeans.
  • Tillage. Buried giant ragweed seed escapes surface weed predators like insects and mice.
  • Stem-boring insects. They enable large giant ragweed plants to survive glyphosate applications.

The most effective herbicide programs combine preemergence and postemergence herbicide treatments with two or more herbicide sites of action. Scouting after the first post trip can pinpoint escapes.

Giant ragweed infests more acres in the eastern Corn Belt. In Kentucky, for example, giant ragweed infests 40% of soybean and corn acres, Still, infestations occur farther west, with infestations estimated at around 10% in Iowa, mainly in north-central regions of that state.


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