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pigweed-butterfly-ga-field-2016 Brad Haire  Feb 06, 2017
Herbicide-resistant weeds didn’t fall from the sky or rise from fields in a mutant mutiny, but they are here nonetheless. With new herbicide technologies going mainstream this season, growers must continue dogged resistant-weed management programs to preserve viable chemistries for as long as possible.

Herbicide-resistant weeds didn’t fall from the sky or rise from fields in a mutant mutiny, but they are here nonetheless. With new herbicide technologies going mainstream this season, growers must continue dogged resistant-weed management programs to preserve viable chemistries for as long as possible.

“In general, herbicide-resistant weeds become a problem over time when they are selected to survive by the overuse of a single herbicide or single mode of action. In all weed populations, there are very low levels or frequencies of herbicide-resistant plants in comparison to susceptible plants,” said Eric Prostko, University of Georgia Extension weed specialist during an American Society of Agronomy webinar “Growing for Tomorrow: How Weed Resistance Management Can Lead to Sustainability”Feb. 1 sponsored by BASF.

The U.S. leads the world with 156 unique cases of herbicide-resistant weeds. “If you grew up in the U.S. like me, you are likely always proud to see American athletes win Olympic gold medals. The more the better, right? Unfortunately, the U.S. is also the gold medal winner for herbicide resistant weeds,” Prostko said.

Australia currently comes in second place with 84 unique cases of herbicide-resistant weeds, and Canada takes third with 64 cases.

Worldwide there are 478 unique cases of herbicide-resistance weeds. The most frequent modes of action that weeds have developed resistance to are the ALS inhibitors (SUs and IMIs), PS II inhibitors (triazine and ureas)  and the ACCase inhibitors (dim and fop grass herbicides), he said.

The over-use of glyphosate on glyphosate-tolerant crops has led to the rapid development of glyphosate-resistant weeds over the last two decades, he said. Today, there are 36 weed species worldwide with resistance to glyphosate with 16 of those species in the U.S.

PPO-resistance is now a growing concern, too. “The evolution of PPO resistance is scary because many growers have been relying on herbicides with this mode of action to help manage herbicide-resistant pigweed. Currently, three weed species have evolved PPO-resistance in the U.S., including tall waterhemp, Palmer amaranth and giant ragweed. PPO-resistant Palmer amaranth is under investigation in Alabama, Mississippi, North Carolina and South Carolina,” he said.

But resistant weed problems do not necessarily result in yield loss. In Georgia where farmers have dealt with glyphosate-resistant pigweed for more than a decade, cotton and peanut yields have continued to increase. But it has come at great cost.

The cost to fight resistant weeds with herbicides in Georgia cotton, for example, has increased since 2004 from $28 per acre to $68 per acre plus a 10 percent to 20 percent increase in cost of mechanical cultivation and an increase in the need for hand weeding going from just under $3 per acre to almost $24 per acre today.

So what can growers do or do better, especially in handling herbicide-resistant Palmer amaranth?

1 – Start weed-free at planting using a combination of tillage, cover crops and herbicides. Although the benefits of reduced tillage systems are many, they have also helped contribute to some of our resistant weed problems. “The deeper and longer Palmer amaranth seeds are buried, the less seed germination will occur. Burying pigweed seed with a moldboard plow every three years or so can be beneficial, particularly in problematic fields. In some cases, deep tillage may not be a practical option,” he said.

2 – For growers who cannot or will not use deep tillage, well-managed cereal cover crops can be used to help reduced the emergence of some weeds. Since Palmer amaranth seed requires light for germination, a heavy rye biomass, for example, can prevent light from reaching the soil surface which ultimately influences germination and emergence. Getting an adequate crop stand in extreme cover crops can often be challenging and requires diligence and practice.

3 – Another tactic that exploit’s the influence of light on weed seed germination and emergence is narrow-row planting. Studies in many crops show narrower rows typically result in better overall weed control.

4 – Use herbicides with multiple effective modes of action. Most, if not all, herbicide labels today have their modes of action listed in plain view. “You no longer have to be a weed scientist to identify different modes of action,” he said.

5 – A strict crop rotation “can be extremely beneficial for the management of herbicide-resistant weeds because multiple herbicide modes of action can be used over time. In the case of a typical cotton-and-peanut rotation in the Southeast, eight different herbicide modes of action can be used over a two year period,” he said.

6 – Don’t cut rates to save money or for any other reason. “The use of reduced herbicide rates has been proven to be one of the factors that can increase the rate of herbicide resistance development. … The bottom line: only full-labeled rates should be used for weed control.”

7 – Reduce the seed bank in field. Many growers know it but it’s worth saying again: pigweed is a ‘seedy’ plant, producing 500,000 to 1 million seeds per plant.

Cotton and soybean seed traits tolerant to new formulations of dicamba and 2,4-D, which are on track to be widely available and legal to spray over the top of crops this season, are expected to be planted in some regions. Both herbicides are in the same auxin herbicide family. “First and foremost, these new auxin technologies are not a miracle cure for all your current weed problems. You will still need to start clean, use residuals and make timely postemergence applications,” he said.

“Although much is being said about the new auxin technologies these days, I am not hearing very much about the fact that auxin resistance in weeds has already occurred,” Prostko said. “These herbicides are not new. Currently, eight weed species in the U.S have already developed auxin-resistance. Auxin technology stewardship will be even more important as we head into the future.”

Chad Asmus, technical marketing manager for BASF, spoke during the webinar and echoed Prostko’s concerns and recommendations for growers to reduce the risk of herbicide resistance developing in their fields, highlighting the company’s newly formulated dicamba herbicide Engenia, which can be sprayed over the top of dicamba-tolerant cotton and soybean.

The new herbicide has a BASF patented molecule called BAPMA, which, Asmus said, is the lowest volatility salt of dicamba with the highest loading and lowest use rate at 12.8 fluid ounces per acre; and it’s rain fast in 4 hours.

The Engenia label comes with many requirements, including buffer areas. Asmus stressed that growers must follow the label requirements thoroughly. Here are a few of the general federal requirements for Engenia:

  • Use the TTI11004 spray nozzle.
  • Boom Height: ≤ 24” above the target.
  • Application Volume: ≥ 10 GPA.
  • Ground Speed: ≤ 15 MPH.
  • Wind Speed and Direction: 0 to 15 MPH
    • For wind speeds ≤ 3 MPH confirm there is no field level temperature inversion.
    • Do not spray with wind speeds >10 MPH blowing toward neighboring sensitive non-specialty crops.
    • Do not spray with any wind blowing towards neighboring specialty crops.

Asmus said growers need to also pay special heed to any state-specific label requirements that might apply to Engenia this year. An updated list of EPA-approved tank-mix products for Engenia can be found at http://www.EngeniaTankMix.com.

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Spray That Stays

spray that stays.png

When farmers spray their fields with pesticides or orange growers spray water on their crops to prevent frost damage, only about 2 percent of the spray sticks to the plants. The rest of the droplets either bounce right back off the leaves or get blown away by the wind. All that waste costs money and, in the case of pesticide application, contributes to pollution of waterways and exposes farmers unnecessarily to hazardous chemicals. But a team of MIT researchers has found a way to fix that.

A clever combination of inexpensive additives allowed the researchers, led by associate professor of mechanical engineering Kripa Varanasi and grad student Maher Damak, to drastically cut down on the amount of liquid that bounces off, potentially making it possible to use just one-tenth as much pesticide or other spray as would otherwise be needed.

Previous attempts to reduce this droplet bounce rate have relied on additives such as surfactants, soaplike chemicals that reduce the surface tension of the droplets and cause them to spread more. But tests have shown that this yields only a small improvement; the speedy droplets bounce off while the surface tension is still changing, and the surfactants cause the spray to form smaller droplets that are more easily blown away.

The new approach uses two different kinds of polymer additives, each added to a separate portion of the spray.  One gives its part  of the solution a negative electric charge; the other causes a positive charge. When two of the oppositely charged droplets meet on a leaf, they form a hydrophilic (water-attracting) “defect” that sticks to the surface and makes other droplets more likely to adhere.

The project was developed in collaboration with the MIT Tata Center for Technology and Design, which aims to develop technologies that can benefit communities in India and throughout the developing world. Spraying of pesticides there is typically done manually with tanks carried on farmers’ backs, and since the cost of pesticides can be a significant par of a farmer’s budget, reducing the amount that’s wasted could improve the overall economics of small-scale farming. It could also reduce soil and water pollution and spare farmers excessive exposure to the spray chemicals. And for those spraying water, limiting the waste of often-limited freshwater resources can be significant.

“We can use normal sprayers, with two tanks at a time, and add one material to one tank and the oppositely charged material to the other,” Damak says. The farmer “would do everything as usual, just adding our solutions.”

David L. Chandler

www.technologyreview.com                                                                                                                                                                           November/December 2016  MIT News                                                                                                                              9

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  • Fall armyworms in soybeans can be most economically controlled with a pyrethroid insecticide. Armyworms are a pest that can be controlled at two to three dollars per acre.
University of Tennessee Extension

Fall armyworms have been a problem for most Alabama farmers in pastures and hayfields during the summer months. Alabama Extension entomologists have spotted fall armyworms in soybean fields in north Alabama.

Dr. Ron Smith said armyworm numbers statewide are higher than they have been in a very long time.

“The biggest issue for farmers is detecting the armyworms in time to treat pastures and hayfields, especially in central Alabama,” Smith said. “In north Alabama, the armyworms are in soybean fields. While some of the worms may have moved from a pasture to the soybeans, there are armyworm eggs being laid in soybean fields.”

Movement and scouting

Smith said earlier in the season, the armyworms move from a ravaged pasture to a field of tender soybeans. But now, worms are going directly to the soybean plants to deposit their eggs. There are two strains of armyworms, one prefers grasses and soybeans the other prefers cotton. In this case, the armyworms in north Alabama are the grass-eating strain.

About three weeks ago fall armyworms were the primary caterpillar species leading farmers to spray in some north Alabama soybean fields.

Now in the Tennessee Valley and other parts of the state, the fall armyworm is a member of a complex of foliage feeding caterpillars infesting soybeans that include green cloverworms, soybean loopers, pod worms (cotton bollworm), a few yellow striped armyworms and velvetbean caterpillars. Pod worms are generally feared for their bloom and pod feeding, but early in August they were observed feeding on foliage as well as blooms in double-cropped soybeans.

Alabama Cooperative Extension System conservation crop specialist Dr. Dennis Delaney said soybeans would offer tender vegetation, which is what armyworms feed on in pastures.

“Just like in pastures, armyworms can eat most of the soybean plant,” Delaney said. “The armyworms tend to eat the leaves and leave the tougher part of the plant. They also often move from grass weeds in soybean fields to soybean plants when the grass is eaten up, or killed by herbicides.”

Delaney said their movement from plant to plant is quick, and an infested field can be seriously damaged in a short amount of time. After bloom, the threshold for lower leaf loss is 20 percent or less.

Caterpillar thresholds

Dr. Kathy Flanders, an Alabama Extension entomologist, said she recommends treatments in pastures when there are more than two caterpillars per square foot. One way to determine the number of caterpillars in a field is to physically look for them, but sometimes finding them is difficult.

In the field, Smith said the soybean threshold is normally six to eight caterpillars per row foot. The sweep net threshold for fall armyworms is 1.5 medium to large size caterpillars per sweep, and a foliage loss potential of more than 20 percent in soybeans in the reproductive stage.

Life Cycle and treatment

It takes about 30 days for a female armyworm to develop into a mature, egg-laying worm. The length of this cycle coincides with reports of armyworms in the state. Some of the first armyworm reports were in late June. Producers are now seeing a recurrence of armyworm issues they thought were taken care of earlier in the summer.

“Fall armyworms in soybeans can be most economically controlled with a pyrethroid insecticide at a mid-label rate,” Smith said. “Armyworms are a pest that can thankfully be controlled at a rate of two to three dollars per acre.”

Alabama Cooperative Extension System entomologists have been watching soybean looper numbers rise for several weeks. The major outbreak entomologists warned against earlier in the summer is happening in soybean fields in south and central Alabama.

Loopers increasing

Soybean loopers are also increasing in number in many north Alabama soybean fields. These are the key species triggering treatments during the third week of August in some fields in the Tennessee Valley for the complex of foliage feeding and pod feeding worms infesting double-cropped soybeans. The most recent year in which the soybean looper was a serious pest of north Alabama soybeans was 2012 when treatments were initiated the first week of September.

Soybean looper

Extension researchers have pest traps scattered at locations throughout the state. High soybean looper trap counts in July gave entomologists reason to believe the looper numbers would be higher than-average in early August.

Reed and Smith are encouraging farmers to diligently scout soybean fields.

“The occurrence of soybean loopers is widespread in soybean fields in south and central Alabama at this time,” Smith said. “With widespread pest pressure, if a grower does not have a commercial scout, it is important to actively look for soybean loopers themselves.”

Adding insecticides to fungicide

Farmers in the Gulf Coast area of Alabama began adding insecticides to their fungicide sprays for some fields during the first half of August to slow the increase in soybean looper numbers.

Soybean looper larvae feed primarily on foliage. They will normally start feeding in the lower half of the plant canopy and move upward over time. Reed said scouts should try get their sweep nets into the lower half of the canopy if possible to get a more accurate estimate of soybean looper numbers. Soybean loopers are more difficult to dislodge from soybeans than other foliage feeding caterpillars.

“Early on, farmers will see leaves with a window pane effect,” Reed said. “The very small soybean looper larvae eat only the green portion of the leaf leaving behind the transparent cuticle layer. As larvae mature, they become more aggressive feeders and once soybean loopers begin feeding on the upper canopy, they can soon consume more than 50 percent of the foliage when numbers are high.”

Smith said soybean loopers are the most expensive pest to control. While there is more than one option, there are a limited number of control options available for soybean loopers—ranging from less than $10 per acre to nearly $20 per acre. Intrepid, Intrepid Edge, Belt, Besiege, Prevathon and Steward are the only four products available to farmers for soybean looper control.

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Kudzu bugs move toward Arkansas soybeans

Patience is key to proper control

Chuck Capps, DeShea County, Ark., Cooperative Extension Service agricultural agent, examines a vial containing kudzu bug specimens during field training in Phillips County, Ark. Agents and specialists with the University of Arkansas System Division of Agriculture collected kudzu bugs from both a commercial soybean field and a large kudzu patch in Phillips County on July 6, 2016. The pests, which overwinter in kudzu, were discovered in soybeans for the first time this year, after having been first detected in the state in 2012.

(Photo: University of Arkansas System Division of Agriculture/Ryan Mcgeeney

After almost five years of waiting, the inevitable has finally arrived: Kudzu bugs have made their way across the Delta, into Arkansas, and are poised to begin affecting soybeans in the fall.

The pest, which overwinters in kudzu, was first detected in Arkansas in 2013, mostly in small numbers. Robert Goodson, Phillips County agricultural agent for the University of Arkansas System Division of Agriculture, said that only within recent weeks had the pest been discovered in large numbers in a commercial soybean field near Helena, Ark.

“It’s an unusually high amount,” Goodson said. “We’ve never had these numbers in the state of Arkansas before. We found them here in Phillips County last October for the first time.”

Nick Seiter, Extension entomologist for the Division of Agriculture, said research in North Carolina had shown that, left unchecked, heavy concentrations of kudzu bugs can sap the vigor of soybeans in the field, and lead to large-scale yield losses.

However, growers were unlikely to see such concentrations in real-world scenarios, and growers who actively scout their fields will be in the position to effectively control the pests before they inflict serious damage.

The key, however, is recognizing the pest’s true threat: the nymphs, rather than the adults, Seiter, Goodson and others said.

Addressing a group of about 20 Cooperative Extension Service agricultural agents from throughout the Delta region, Seiter emphasized the importance of growers focusing not on the adults, which are mobile, but on the nymphs, which will stay on a given plant and do far more damage.

“If you find a lot of those, if it’s your first time, you’re going to panic a little bit,” Seiter said. “What’s happened in the Southeast, in just about every state it’s come over, is, people have tried to spray those adults. And they end up in that situation where you’re putting out multiple sprays, trying to control these adults that are coming right back into the field.”

The treatment threshold for kudzu bugs is 25 nymphs per 25 sweeps, Seiter said. Because the insects have a maturation window of about six to eight weeks from nymph to adult, growers will have plenty of time to control them.

Controlling kudzu bugs in soybeans will bring trade-offs, Extension experts warned.

Gus Lorenz, Extension entomologist with the Division of Agriculture, said spraying pyrethroid insecticides will likely impact beneficial insects, including nabids and parasitoids, which would in turn lead to greater management challenges regarding pests such as bollworms and loopers.

“It’s the whole complex of predators and parasites we have in the field that maintain those populations below treatment level,” Lorenz said. “When you spray a pyrethroid and wipe them out, it kind of opens the door for those other pests.”

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sn-honeybees

Corey Barnes/Flickr/Creative Commons

A new pesticide could be the bee’s knees. Honey bees (Apis mellifera, pictured) pollinate 90% of all U.S. flowering crops, but in recent years their numbers have drastically dwindled. Accumulating evidence implicates several commonly used insecticides in honey bee deaths, sparking a growing demand for bee-safe alternatives. Online today in the Proceedings of the Royal Society B, a team of researchers reports the creation of a bee-friendly pesticide produced by fusing Australian funnel-web spider (Hadronyche versuta) venom with snowdrop flower (Galanthus nivalis) proteins. The team says its toxin selectively attacks the central nervous systems of common agricultural pests, such as beetles and aphids, while leaving honey bees unharmed. After exposing bees to their new pesticide for 7 days, the researchers found no detrimental effects on learning or survival. Even when the team directly injected the pesticide into the honey bees, only 17% died within 48 hours. The team next plans to test the toxin’s effect on other beneficial pollinators, such as bumblebees and parasitic wasps.

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Western

Farm

Press

Gill’s mealybug in pistachio– does the spray pay?

The adult female Gill’s mealybug, Ferrisia gilli, has a pink body and is covered in white wax. Photo by David Haviland.

 

To spray or not – that’s a question that often plagues pistachio growers faced with pests including Gill’s mealybug, which may or may not wreak economic havoc on their crop.

And that’s where David Haviland, University of California integrated pest management advisor for Kern County, comes in.

Haviland has published a paper with the Journal of Economic Entomology which presents a formula for determining the economic injury level that might or might not be tolerated by a grower.

The paper is based on several factors, including the treatment cost, the expected price per pound for the crop, and the anticipated yield.

It’s a matter of “does the spray pay?” Haviland said.

It could be that if an infestation is just beginning and a grower is trying to prevent spread, it might be best to be more aggressive, he adds.

The economic injury level formula adds the cost per acre for control with the anticipated yield in pounds per acre and the anticipated price, and then divides it by 0.094.

The result will be the economic injury level per cluster in May. As the cost goes up and the price and yield drops, there may be a greater tolerance for the number of mealybugs per cluster.

Haviland says a higher payment per pound of around $4 means the threshold for treating the pest “is really low.”

The ideal treatment timing is around June 1, or 10 days or so earlier when temperatures are higher.

Haviland said adult females emerge in late April or May, “and that’s when you monitor the number of mealybugs per cluster.” They can be found when the old wood connects with new growth – basically where the bud was.

Among the pesticides effective on the pest are Centaur (Buprofezin), Movento (Spirotetramat), Assail (Acetamiprid), and Admire (Imidacloprid).

Haviland said Admire is not as effective as the others but it is inexpensive and has no application costs when used in drip systems. Admire, he says, might not be the best choice in a bad infestation, but if the level is creeping back it can be used for suppression.

Haviland said Centaur, Assail, and Movento are all “extremely good.” Another good product he shared is Closer, which has been re-named Sequoia, a Dow AgroSciences product where the registration was pulled. Dow is seeking product re-registration.

Movento is costly, Haviland said, but researchers have learned it can be used at lower rates, six ounces rather than nine ounces, shaving one-third off the cost.

The pest was introduced into Tulare County in the mid-to-late 1990s. It spread slowly initially, reaching 2,000 acres in 2004 in at least five counties and was also found in almonds and wine grapes.

By 2005, 3,000 acres were infested. There were 6,000 aces infested by 2007. And pesticide reports indicate treatment on 80,000 acres in California by 2013.

Gill’s mealybugs are roughly ½ to 1/5 inch in length and pinkish grey in color. The pest is often covered with white wax secreted from a pore.“They muck up the clusters,” Haviland said.

He explained that they “intercept carbohydrates intended for kernel development.”

Smaller kernels mean less weight and less splitting.

“The small kernel is never big enough to push them open,” Haviland said, “and the biggest problem is closed shell nuts.”

The pest can cause shell staining and an increase in adhering hulls with later harvests. But it has no association with aflatoxin.

Pistachio growers should be cautious not to confuse Gill’s mealybug with grape mealybug.

Grape mealybug is sometimes found on pistachios, but does not cause economic damage but requires treatment. Grape mealybug has four slender white tails. The female Gill’s mealybug has two broad white tails.

When poked, adult females of grape mealybug extrude a bright red liquid through structures called ostioles towards both the rear and front of the top of the body. Gill’s mealybug does not extrude such a liquid.

Mealybug feeding produces large amounts of honeydew that results in black sooty mold that can reduce photosynthesis.

The most common predators of mealybugs in pistachios are brown lacewing and lady beetle whose larva resembles a mealybug.

One way to peg problem areas is to check trees before dormancy in the fall and look for sooty mold and leaves and for mealybugs within clusters. Note those locations for further evaluation the following spring.

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Copied from: PestNet

The “big rust’s” impact on coffee disease management Coffee rust has made significant headlines in recent years for its devastating effect on coffee crops. According to the United States Agency for International Development (USAID), losses in Latin America and the Caribbean alone have totaled well over $1 billion, causing hardship to coffee plantations, their labourers, coffee retailers, and the consumers who pay more for their morning coffee.

But this fungal disease, also known as “the big rust,” has a much longer and more encompassing history that goes all the way back to its discovery in 1869. This history is reviewed in detail through a new Phytopathology article entitled, “The Big Rust and the Red Queen: Long-Term Perspectives on Coffee Rust Research,” written by Stuart McCook, historian at the University of Guelph in Ontario, Canada, and John Vandermeer, professor of ecology and evolutionary biology at the University of Michigan, USA.

In this essay, the authors discuss the big rust in a broader historical context, chronicling coffee rust epidemics, the social and ecological conditions that produced them, and the evolving scientific responses to this threat. The article highlights the many innovations used to combat coffee disease outbreaks, such as the efforts to develop disease-resistant plants, chemical and agroecological control, and even a network of international coffee research institutes. It also incorporates the broader social and economic histories of coffee production into particular stories of rust epidemics and rust research. The article also points out examples of the current research and disease mitigation challenges in developing nations versus affluent parts of the world.

By taking this broad perspective, the authors suggest we are entering a new phase in the global history of the coffee rust.

“Up until the mid-1980s, the story of the coffee rust was largely the story of invasions, as the disease spread into regions where it was not previously present,” McCook said. “By the mid-1980s, however, the disease had reached almost every coffee-producing region in the world.”

“For a brief while, in the 1980s and 1990s, it looked as if coffee farmers-with the help of scientists-had adapted to the disease, making it ‘just another disease’ on the farm. But we suggest that this fragile equilibrium has begun to break down, both because of broader ecological changes that we are only beginning to understand, and also because of increasing volatility in the global coffee economy,” he said.

Read this paper in the September 2015 issue of Phytopathology.

(Phytopathology News, November 2015)

http://www.isppweb.org/nldec15.asp#2

 

 

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