Across the world, the tomato leafminer is wreaking havoc on agricultural producers. The relentless march of these pests inspired a team of Virginia Tech researchers to apply new methods of modeling and simulation previously used in infectious disease research to halt their spread. A new USAID grant will help them do just that.
The tomato leafminer, Tuta absoluta, is an innocuous-looking moth, easily hidden by the burgeoning foliage of young tomato plants. But once the eggs of the moth hatch, the larvae tunnel through the plants’ leaves, quickly giving a once green, productive field a scorched appearance. In Europe, West and Central Africa, and the Middle East, these pests have caused 50 percent to 100 percent crop loss since their accidental introduction to Europe in 2006.
“Entomologists normally use CLIMEX, a software modeling program that estimates the geographical distribution of an insect, and insect life tables, an analysis of an insect’s life cycle, to theorize how an insect will spread,” said Muni Muniappan, entomologist and director of the agricultural development program that is managing the grant. “But the Biocomplexity Institute is introducing human movement into the equation. This is a new angle.”
Managing these insects is not as simple as spraying insecticides. Virginia Tech’s Integrated Pest Management Innovation Lab works to provide solutions to farmers of developing nations using integrated pest management techniques that take into account the long-term health of people and ecosystems, as well as sustainable agricultural productivity.
However, halting the incredibly fast spread of these pests can be very difficult. Thus, researchers are turning to computational modeling in an effort to better understand when and where the insects will appear next. Using agent-based models in a novel approach, the research team will incorporate multiple data sources and find the most significant factors in the spread of these insects.
In the tomato leafminer study, the research team will view pest dynamics as an integrated biological, informational, social, and technical system consisting of several interacting models. This interaction-based approach is aimed at capturing the complexity of pest dynamics.
A key feature of this approach is understanding how humans hasten the speed at which pests spread. This includes not only human mobility but also supply chain infrastructures used to move goods across continents. These systems can have unintended side effects, one of which is the spread of invasive pests. This study will lead to a much better understanding of how human systems contribute to the spread of pest infestation.
“Our model will be an extremely useful tool for risk analysts, domain experts, and policy makers to develop strategies to combat these pests. Further, the methodology will not be limited to studying the tomato leafminer, but can be applied to any agricultural invasive species,” said Abjijin Adiga, research faculty member at the Biocomplexity Institute.
A juvenile root-knot nematode, Meloidogyne incognita, penetrates a tomato root. Once inside, the juvenile, which also attacks cotton roots, causes a gall to form and robs the plant of nutrients. Photo by William Wergin and Richard Sayre. Colorized by Stephen Ausmus.
19th Biennial Group Meeting of the “All India Coordinated Research Project (AICRP) on Nematodes in Cropping Systems”
At the 19th Biennial Group Meeting of the “All India Coordinated Research Project (AICRP) on Nematodes in Cropping Systems” recently held at University of Agricultural and Horticultural Sciences, Shivamogga (Karnataka) India; experts from the country conveyed that an aggressive (with high reproduction rate, more damage to host plants and wide host range) root knot nematode, Meloidogyne enterolobii, got introduced and established through guava root stocks from Chhattisgarh, is causing huge losses in Dindigul, Coimbatore, Villupuram, Dharampuri and Krishnagiri districts of Tamil Nadu. The group emphasized that there is an urgent need to strengthen and enforce domestic quarantine mechanism to suspend spread of plant parasitic nematodes with vegetative propagules, especially through seed potatoes and rooted plants – along with soil, from nurseries/ sick plots/ hot-spot areas to disease free niches. In their opinion, presently nurseries in the country are having a field day and incorrigible for spreading pests without meeting any cleanliness standards or phytosanitary regulations. To break the pathway, it was suggested to enforce registration and licensing of plants and horticultural nurseries.
The recommendation from the Biennial Workshop is immensely important for reducing crop losses of horticultural crops in the country. Horticulture plant nurseries are extremely complex agricultural systems, recorded as pathways for several pests and diseases. Dr. Rajan said that the situation has become further cumbersome with ‘on line’ availability and sale of live ornamental and horticultural plants in the country. As disease management in nurseries/ green houses require specialisation; nematologists from the group ventured a draft road map – with details of detection, exclusion, risk analysis, critical control points for nursery stocks, infrastructure required for prophylactic measures, and costs involved for a prophylactic holistic system approach for registration/ certification for Nurseries and Green Houses.
In the address, Dr. D. J. Patel (Former Dean, Anand Agriculture University) and Dr. P. P. Reddy (Former Director, Indian Institute of Horticulture Research), well known experts in the subject expressed deep concerns about new nematode diseases in pomegranate, guava, coconut, banana, spices and vegetables all over the country through propagules. There is urgent need for policy support from Indian Council of Agricultural Research (ICAR), Department of Agriculture and Cooperation as well as Horticulture Mission for framing mandatory regulatory provisions for registration, licensing and certification of protected cultivation houses, nurseries and green houses especially for pest / quarantine requirements.
Dr. R. K. Walia, Project Coordinator (Nematodes), presented a brief history, background and the salient achievements of the AICRP on nematodes and overall scenario Plant Nematology research in India. He expressed serious concerns about the losses in crops due to nematode diseases and urged upon the nematologists to devise integrated approaches to manage root knot nematode (Meloidogyne spp.) problem in recently established poly-houses (for promoting cultivation of vegetables and ornamental) all over the country.
New publications “Pictorial guide on important nematode diseases of Karnataka”, “Comprehensive monograph of rice root-knot nematode (Meloidogyne graminicola)”, “Status of plant nematode diseases in Karnataka – a review”, and “Compendium of new plant parasitic nematode diseases of Karnataka”, along with a number of bulletins on serious issues were also launched on the occasion.
[KAMPALA] A banana strain resistant to a common fungal disease could help smallholder farmers in East Africa better control the crippling disease, which has been spreading across the region over the last three decades.
The results of confined field trials of a genetically modified (GM) banana with improved resistance to a black sigatoga disease, the devastating leaf spot fungus, are promising, researchers have told SciDev.Net.
The disease is caused by the fungus Mycosphaerella fijiensis and it can halve fruit production in affected plantations. It is easily spread by airborne spores, rain, planting material, irrigation water and packing material used in transporting goods between banana-growing countries.
The dark leaf spots caused by the fungus eventually enlarge and merge together, causing much of the leaf area to dry.
The team led by Andrew Kiggundu — head of banana biotechnology research at the Uganda’s National Agricultural Research Laboratories Institute (NARL) in Kawanda — analysed 19 lines of GM bananas and found promising results in five of them. Andrews told SciDev.Net further research is needed to calculate the exact yield gains from using the resistant banana strain.
The researchers inserted genes for chitinase — an enzyme that breaks down chitin, the hard substance that makes up the cell walls of the invading fungi — preventing the fungus from invading the plant cells and causing the disease.
Kiggundu said laboratory tests using leaves from transgenic plants showed almost full immunity when cultured fungi were applied to the leaves.
Researchers collaborated closely with the Catholic University of Leuven in Belgium, where several banana lines were engineered to include the chitinase gene before being brought to NARL for testing.
However, Settumba Mukasa, resident banana expert in the department of crop science at Uganda’s Makerere University, said the field trials had more significance for building research capacity in Uganda than the development of a new disease-resistant banana.
“[The project] is a stepping stone for subsequent breeding programs and genetic engineering programmes. As a consequence of this project we can now do transformations of other varieties of bananas and other crop species,” said Mukasa.
While black sigatoka is among the top three diseases affecting bananas in Uganda it mainly affects Cavendish, which are not as widely cultivated as other types of bananas.
But for the few farmers in Uganda who do grow Cavendish bananas, the development may be useful since the disease is currently controlled by aerial pesticide spraying which is expensive for smallholders and affects their health.
“Farmers cannot afford that because they are small and they have few plants. Here, chemical control is not viable, so this approach may be the only available method to manage the disease,” Mukasa said.
The findings offer hope of limiting the impact of Xylella fastidiosa that experts described as one of the “most dangerous plant pathogens worldwide”.
If it is not controlled, it could decimate the EU olive oil industry.
The study, carried out by Italian researchers and funded by the European Food Safety Agency (EFSA), began in 2014 and consisted of two main types of experiment: artificial inoculation (via needle) and inoculation via infected vectors (insects) collected from the field.
The tests were carried out on a variety of species, including a range of olive, grape, stone-fruit (almond and cherry) and oak varieties.
“The first results are coming from the artificial inoculation because the field experiments began in the summer so it is only six months old, therefore only part of the results are available,” Giuseppe Stancanelli, head of the EFSA’s Plant and Animal Health Unit, told BBC News.
“The key results are that, 12-14 months after artificial inoculation on different olive varieties, the team found that young plants typically grown in the region displayed symptoms of the dieback.
“The research team also found evidence of the bacterium moving through the tree – towards it root system as well as towards the branches.”
But he added: “What has also been shown is that some varieties have shown some tolerance. They grow in infected orchards but do not show strong symptoms, as seen in more susceptible varieties.
“They are still infected by the inoculation but this infection is much slower so it takes longer for the infection to spread, and the concentration of the bacterium in the plant is much lower.
Dr Stancanelli added that these results were important in terms of providing information for tree breeders.
However, it was too early to say whether or not the olive yields from the varieties that have displayed tolerance to the infection are nonetheless reduced or adversely affected, he observed.
The EFSA Panel on Plant Health produced a report in January warning that the disease was known to affect other commercially important crops, including citrus, grapevines and stone-fruit.
However, the results from the latest experiments offered a glimmer of hope.
“Olives seemed to be the main host of this strain while citrus and grapes did not show infection, either in the field or by artificial inoculation,” Dr Stancanelli said.
He added that the infection did not spread through the citrus and grape plants that were artificially inoculated, and the bacterium was not found beyond the point it was introduced to the plant by injection.
But he added that more research was needed on stone-fruit species.
“The tests on the artificially inoculated varieties of stone-fruit need to be repeated because there is a mechanism in the plants that makes artificial inoculation difficult,” Dr Stancanelli explained.
“Another uncertainty we had was about (holm) oak. Quercus ilex is a typical Mediterranean oak that grows in the landscape and is natural vegetation.
“At the beginning of the outbreak in 2014, some symptoms were found on oaks and the tests were positive but this was never confirmed so this was probably a ‘false positive’.
“The artificial inoculation test appears to have shown that the holm oak is resistant (to the disease).”
The Xylella fastidiosa bacterium invades the vessels that a plant uses to transport water and nutrients, causing it to display symptoms such as scorching and wilting of its foliage, eventually followed by the death of the plant.
Since it was first detected in olive trees in Puglia, southern Italy, in October 2013, it has been recorded in a number of other locations, including southern France. To date, it has yet to be recorded in Spain, the world’s largest olive oil producer.
Experts warn that should the disease, which has numerous hosts and vectors, spread more widely then it has the potential to devastate the EU olive harvest.
Globally, the EU is the largest producer and consumer of olive oil. According to the European Commission, the 28-nation bloc produces 73% and consumes 66% of the the world’s olive oil.
Recent reports suggest that the X. fastidiosa outbreak has led to a 20% increase in olive oil prices during 2015.
In November 2015, the European Commission announced it was providing seven million euros (£5m) from the EU Horizon 2020 programme to fund research into the pathogen.
One of the areas of the Horizon 2020-funded research will be on plant selection to strengthen tolerance and resistance to the disease.
Dr Stancanelli explained that the experiments established in this study would continue as part of the EU-funded Ponte programme.
“The experimental field realized within the pilot project will serve as unique source of plant material for future project actions aiming at investigating the host-pathogen interactions,” he said.
“Investigations will be extended to an additional panel of 20 cultivars which will be planted in… April in the same plot.”
The disease plagued citrus farmers in North and South America for decades. It remained confined on these continents until the mid-1990s when it was recorded on pear trees in Taiwan.
According to the European and Mediterranean Plant Protection Organisation (EPPO), which co-ordinates plant protection efforts in the region, the pathogen had been detected prior to 2013 by member nations on imported coffee plants from South America. However, these plants were controlled and the bacterium did not make it into the wider environment.
Earlier this year, when a cold-tolerant subspecies of the bacterium was identified in the southern France outbreaks, UK government plant health officials published information for horticulture professionals, especially those importing plants. They were advised of their obligations – such as obtaining the necessary plant passports – and given details of the visible symptoms to look out for on potentially infected plants.
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.
Alarmed scientists first discovered the beetles last year along a front stretching more than 200 miles, from central Long Island to Cape Cod and Martha’s Vineyard, a region long thought to be far too frigid for these tiny beetles, barely different in size and color from a chocolate sprinkle.
“When I heard they caught a live beetle in Massachusetts,” Dr. Rutledge said, “that really freaked me out.”
Now that the beetles are in New England, they are probably there to stay, state and environmental officials said. And if there is a severe outbreak, the region could lose much of its pitch pine forests. Many of the forests are already unhealthy, a result of overcrowding, making them especially susceptible to the pine beetle’s attacks — boring through bark, laying eggs and spreading a crippling fungus — and many state forestry divisions do not have the resources to combat them.
Scientists are concerned that the beetles could destroy the remaining tracts of the pitch pine forest, an ecosystem that once carpeted the Eastern Seaboard but now exists mostly in pockets — the Cape Cod National Seashore, the Albany Pine Bush Preserve and smaller forests — and is home to more than a dozen endangered species, such as the tiger beetle and several types of butterflies.
“I don’t think people have a strong understanding of how at risk these forests are,” said Kevin J. Dodds, a scientist who runs the southern pine beetle response in the Northeast for the United States Forest Service.
An invasion in New England could mean a repeat of what happened in New Jersey and on Long Island, where state agencies were caught off guard, officials say.
“We’re still scratching our heads and asking why we didn’t find this sooner” on Long Island, said Robert Davies, New York’s state forester. By the time they had discovered the infestation, he said, it had ballooned to 10,000 acres. (They have since contained the infestation to about 8,000 acres.)
State environmental officials and federal foresters warned Connecticut that the plague could be headed their way toward the end of 2014, and soon after, they found infested trees in about 20 places across the state. So last spring in much of New England and New York, foresters and state officials set traps to determine if there were more beetles. And there they were, in traps in Bear Mountain State Park in New York; southern Connecticut; Rhode Island; central Massachusetts; and in Cape Cod, Plymouth and Martha’s Vineyard, Mass.
Some scientists see the beetles’ march north as another sign that climate change is disrupting the environment, and not just in ways that damage ecosystems. Heat-loving creatures like ticks and mosquitoes are expanding their ranges, too, carrying illnesses like Lyme disease to Canada and dengue fever to parts of the United States.
And the environmental costs are steep, too. For all the damage wrought by the southern pine beetle, the mountain pine beetle has exacted a far greater toll, ravaging pine forests across the western United States and Canada, destroying tens of millions of acres in places and altitudes once thought beyond their reach.
According to Matthew P. Ayres, a Dartmouth College biologist who studies the southern pine beetle, the warming of winter’s coldest night is the primary cause of their spread.
Most beetles die if temperatures fall to around minus 8 degrees Fahrenheit. And while this winter had an unusually cold snap, the low temperatures did not last long enough to wipe out the beetles, Dr. Rutledge said.
Mr. Davies said, “We were still hearing about beetles flying on Christmas Day, and that’s not a good thing.”
Dr. Dodds and others say that many longstanding practices unintentionally damaged the forests. They were largely left to themselves, resulting in overcrowded stands, where trees had to compete for sunlight and nutrients. In crowded forests, beetle attacks can spread more easily, and the beetles thrive in unhealthy forests like these because they can overwhelm a tree’s defenses by laying eggs that, when hatched, hijack the tree’s circulatory system, and also carry a fungus that clogs the tree’s waterways.
With this one-two punch, beetles can wipe out thousands of trees in a season, Dr. Rutledge said. Natural fires, for all the damage they cause, do thin forests and lead to regrowth, but states have worked quickly to extinguish them.
Trees have some defense mechanisms — they release resin, which hardens into little yellow clusters on the bark (commonly referred to as “popcorn”) to fill the holes made by beetles and kill them — but they do not always work.
The pine beetle is no longer considered a big threat in the South because the forests are healthy, a result of decades of thinning efforts, Dr. Ayres said, aided by the region’s large lumber market, where salvaged pines can be sold to mills.
By contrast, there is not always a market for the trees in much of the Northeast.
This spring, scientists and state officials will set more traps in New England and New York. Depending on what they find, they may conduct aerial surveys to see if any trees are in distress. When the trees are in trouble, their needles turn from green to yellow andred, an effect that can be seen best from above.
Dr. Ayres said that if precautions were not taken, a widespread invasion could leave only a few pitch pines in the region.
He also said he could foresee the beetles possibly reaching the Great Lakes states and Canadian provinces, which are heavily forested with red and jack pines and could be vulnerable. From there, they could infiltrate much of Canada, spreading west to meet the mountain pine beetles that have been moving east into Alberta and Saskatchewan, leaving a ring of dead forests around the continent.
“It’s an example of something that’s happening all over the world,” Dr. Ayres said. “It’s old pests in new places, and with that comes a whole new set of challenges.”
12:00 AM, March 01, 2016 / LAST MODIFIED: 03:44 AM, March 01, 2016
‘Wheat blast’ threatens yield
Farmers in 6 districts complain of infection
A farmer showing wheat sheaves infected with wheat blast disease. After being infected with the disease, the crop’s flowers turn yellow and white and the plants dry up without producing any grain. The photo was taken at Gangni in Meherpur yesterday. Photo: Star
Wheat blast disease has become a serious threat to grain quality and yield, incurring losses to the farmers in six southwestern districts.
Scientists and specialists after laboratory tests claimed that this is the first time in Bangladesh in which the seasonal crop got infected with this disease.
Officials at the Department of Agricultural Extension (DAE) and Wheat Research Centre (WRC) of the Bangladesh Agricultural Research Institute said they have examined samples from the fields and confirmed that the disease is a blast infection.
They identified the fungus that might have grown due to unexpected temperature fluctuation and several days of continuous rain in the first week of February.
Experts also have tested the seeds used to be sure of the infection, the officials said.
The affected districts include Kushtia, Meherpur, Chuadanga, Jhenidah, Jessore, and Magura.
DAE officials, who visited the affected fields, said Meherpur was the badly hit. Around 2,000 hectares of wheat fields had been damaged by the fungus.
According to farmers, they have marked yellow and black spots on the leaves and sheaves of wheat. After a few days, the spots got larger and spread over the entire plant.
At one stage, both the sheaves and flowers turned yellow and white, and finally the plant dried up without producing any grain.
Mustafizur Rahman, deputy director of Meherpur DAE, said farmers started informing them about the matter from mid-February.
“We told the higher authorities about the problem after visiting the fields,” he said.
A team, led by Paritosh Kumar Malaker, chief scientific officer of Wheat Research Centre in Dinajpur, visited the affected fields in Meherpur, Chuadanga, and Jhenidah on Wednesday.
“We have made pathogen tests using the diagnostic technique, called ‘field pathogenomics’, and confirmed the symptoms of the disease,” he said.
He said, “As it [disease] is the first infection in Bangladesh, we need to be more careful.”
Farmers and DAE officials said the areas experienced rain in the first week of February. After five to seven days, farmers observed spots on wheat leaves and sheaves.
This correspondent visited Garadoba, Saharbati, Dhankhola, Bamundi of Gangni upazila, and Khoksa, Chandbeel, Madandanga in Meherpur Sadar upazila and found a large number of affected fields.
Farmers Ripon and Mawla Boksh of Madandanga told this correspondent that they jointly cultivated wheat on five bigahs of land. About half of the crop was damaged. They have to incur a huge loss, they said.
Sources at the DAE divisional office in Jessore said farmers in the six southwestern districts cultivated wheat on around 58,135 hectares. Some 16,710 hectares are in Kushtia, 10,320 hectares in Jhenidah, 7,020 hectares in Magura, 5,810 hectares in Chuadanga, 4,400 hectares in Jessore and 13,875 hectares in Meherpur.
Mustafizur Rahman, deputy director of Meherpur DAE, said they were holding meetings with the farmers and distributing leaflets to create awareness among the farmers.
The DAE office also advised the farmers to spray Nativo and Folico on the affected fields.
He primarily estimated that 5 percent of the total production might be affected.
However, Chief Scientific Officer of WRC Paritosh Kumar said wheat production would decrease by around 10-40 percent.