South Africa: Biocontrol of invasive water lettuce plant

[ad_1]

Published: April 9, 2024 11:01am EDT

Author

  1. Julie CoetzeeDeputy Director of the Centre for Biological Control at Rhodes University and Biological Control and Freshwater Alien Invasive Species Management, South African Institute for Aquatic Biodiversity

Disclosure statement

Julie Coetzee receives funding from the National Research Foundation. She is affiliated with the South African Institute for Aquatic Biodiversity (SAIAB).

Partners

View all partners

CC BY NDWe believe in the free flow of information
Republish our articles for free, online or in print, under a Creative Commons license.

Republish this article

A small insect with a light brown body and protruding mouth parts is pictured up close on a green leaf
The water lettuce weevil, Neohydronomus affinis, is a powerful biocontrol agent. David Taylor, Centre for Biological Control, Author provided (no reuse)

 Email

 X (Twitter)

 Facebook115

 LinkedIn

 Print

Water lettuce (Pistia stratiotes L.), also known as Nile cabbage, is a free-floating aquatic plant from the family Araceae, the same family as the arum lily.

It’s found on every continent except Antarctica and grows well in tropical to sub-tropical climates. Research suggests it may have originated in South America because it has natural enemies there which have co-evolved with the plant. However, fossil records and ancient Egyptian hieroglyphics depicting water lettuce indicate that it may have been present in other regions for millions of years. It was likely spread around the world by early colonists as an ornamental plant for ponds and aquatic gardens.

Today, water lettuce is considered an invasive species in many parts of the world, including African countries, where it has caused significant negative impacts on aquatic ecosystems and human activities.

Recently, water lettuce has invaded one of South Africa’s most important rivers, the Vaal River, on the border of the Gauteng and Free State provinces. This has raised huge concerns for local communities, businesses and stakeholders, as well as Rand Water. Rand Water is the largest bulk water utility in Africa and is one of the largest in the world, providing bulk potable water to more than 11 million people.

An expanse of water is covered almost entirely with what looks like a mat of vividly green grass
Water lettuce blankets the surface of the Vaal River. Julie Coetzee, Author provided (no reuse)

I am the deputy director of the Centre for Biological Control at Rhodes University, where I manage the biological control programme on aquatic weeds in South Africa. My team and I are currently working with Rand Water on an integrated management plan for water lettuce control in the Vaal River. This comes after good results in controlling water lettuce in other parts of South Africa and in neighbouring countries such as Zimbabwe and Mozambique since 1985 – thanks to a small species of weevil.

The damage

Water lettuce forms dense mats on the water surface. This can reduce light penetration and oxygen levels in the water, negatively affecting all aspects of aquatic life from microscopic plankton to large fish. The mats can also impede water flow, leading to stagnation and increased mosquito breeding sites. Water lettuce can clog agricultural irrigation canals too. Its rapid growth can also interfere with fishing and boat navigation.

Management of water lettuce can include manual removal and the use of herbicides to prevent spread. Herbicides were routinely used to combat water lettuce in South Africa in the early 1980s, and are still relied on heavily in the US, particularly in Florida.


Read more: Invasive alien species are a serious threat to the planet: 4 key messages for Africa


However, these methods are labour-intensive and often insufficient to control the plant’s rapid growth. They can also damage other vegetation.

That’s where biological control comes in. This involves the introduction of natural enemies like insects or pathogens, which can help manage the plant’s population more sustainably and effectively. By importing and releasing a suitable biological control agent, such as the water lettuce weevil Neohydronomus affinis, the negative effects of water lettuce on the environment and local communities can be mitigated.

The weevil

This Brazilian weevil species was first introduced to Africa in 1985 via Australia, following successful control of water lettuce infestations there. The then Department of Agriculture gave permission to release it in South Africa and 500 weevils were released into a heavily invaded pan in the northern Kruger National Park.

Since then, it has been used to control water lettuce infestations in Botswana, Benin, Ghana, Senegal, Zimbabwe, Zambia, Republic of Congo, Côte d’Ivoire, Kenya, Nigeria, Togo, Mozambique and Morocco. Invasions at sites in these countries, no matter how extensive, were generally brought under control within a year.


Read more: New bugs, found in Kenya, can help to control major maize pests


The impact of N. affinis on water lettuce populations is significant: the combined feeding activities of adult and larval weevils cause substantial damage to the plants, reducing their growth and reproductive potential. Adult weevils chew small holes in the leaves, while larvae tunnel through the leaves, causing them to waterlog and sink.

The ability of N. affinis to produce multiple generations per year enables it to quickly build up populations and maintain pressure on water lettuce populations over time, making it an effective biological control agent for managing water lettuce in affected areas.

As a host-specific insect, N. affinis poses little risk to non-target species or the environment. Biological control of water lettuce in Africa is considered one of the most successful programmes in the fight against invasive species.

So, how are these powerful weevils being used in the Vaal River?

The Vaal River

Water lettuce was first identified on a tributary to the Vaal River in 2021, but local conditions (floods and cold winters) appeared to have limited the spread of this plant. However, at the end of 2023, a large infestation was noticed on the Vaal River and was reported to relevant authorities.

Since then, the infestation has covered up to 40km of the river in the Vaal Barrage area, around the town of Vanderbijlpark, and threatens to spread downstream of the 1,200km long Vaal River.

Rand Water is following an integrated strategy to control and reduce the invasion. Biological control, using the water lettuce weevil, is key to the long term management of the water lettuce invasion. The Centre for Biological Control at Rhodes University is working closely with Rand Water to ensure a constant and abundant supply of the weevils – to do so, the centre has established weevil rearing stations.

A group of ten people posing, smiling, alongside large pallets containing big leaves
The team that rears weevils in Makhanda at the Centre for Biological Control. Julie Coetzee, Author provided (no reuse)

Thousands of weevils have already been released into the Vaal River since November 2023 from our mass rearing facility in Makhanda. Weevils are also being reared by businesses and residents who live near the river, as well as Rand Water. The weevils will be released frequently and en masse, at crucial times, particularly after winter when the plants will germinate from seeds. This is termed inundative biological control.

Water lettuce is one of the easier invasive aquatic plants to control, biologically – soon the infestation will be under control. What lurks alongside this invasion on the Vaal River, however, is the water hyacinth, which remains South Africa’s most problematic aquatic invasive plant. It is a super competitor, thriving in the country’s nutrient rich waters. Efforts are underway by the Centre for Biological Control to highlight this threat. The quality of water upstream from the Vaal needs to be urgently remediated, as this is the ultimate cause of both the water lettuce and water hyacinth invasions.



[ad_2]

XX International Plant Protection Congress, Athens, Greece, 10-15 June 2023

[ad_1]

XX International Plant Protection Congress,
Athens, Greece, 10-15 June 2023
XX IPPC ATHENS 2023

The Hellenic Society of Phytiatry (HSP) is very pleased and honored to announce that the International Association for the Plant Protection Societies (IAPPS) has accepted the Greek bid proposal for the organization of the XX International Plant Protection Congress in Athens, Greece. The congress is under the aegis of the Agricultural University of Athens and is going to take place at the MEGARON Convention Center in Athens 10-15 June, 2023.

Please note that most of the members of the local organizing and scientific committee are world-known scientists with experience in research, teaching and application in plant protection with profound scientific achievements either in Greece or  abroad.

As for the venue of the Congress, natural and cultural beauty of Greece and its cosmopolitan capital, the world famous city of Athens, the history, the tradition and the hospitality, are significant reasons justifying broad international participation. Apparently Athens, has a great organizational advantage since it is easily accessible from Europe, Africa and several countries of Asia, while several American countries have direct flights to Athens.

Greece, as a Mediterranean and South European country, covers a vast diversity of agricultural temperate, subtropical and even tropical cultivations with highly specialized scientists on plant protection sciences working in Universities, Research Centers and in the Private Sector.  Thus, Greece is one of the few countries where scientists can meet a very broad diversity of cultivations and plant protection problems.

It is certain that participants of the XX IPPC ATHENS 2023 beyond science will enjoy long-standing history, the ancient and modern city of Athens, the birth place of democracy, the fantastic environment and finally Greek tradition, special Mediterranean food and legendary hospitality.   The organizers are looking forward to the successful organization and realization of the congress at all stages till the final day of the congress.

On behalf of the Local organizing committee

Professor Eleftherios (Eris) Tjamos,
President of the Hellenic Society of Phytiatry
Agricultural University of Athens, Athens, Greece,
Department of Plant Pathology,
75 Iera Odos str., 18855 ATHENS, GREECE
e-mail: 
tjamatika@gmail.com  and or  e-mail: ect@aua.gr
mobile phone 0030 6932 365566

 

Eris Tjamos

 

[ad_2]

Argentina: Maize stunt disease cutting yields

[ad_1]

Sunday, 21 April 2024 08:16:00

Grahame Jackson posted a new submission ‘STUNT DISEASE, MAIZE – ARGENTINA’

Submission

STUNT DISEASE, MAIZE – ARGENTINA

ProMED
http://www.promedmail.org

Source: Reuters [summ. Mod.DHA, edited]
https://www.reuters.com/markets/commodities/argentina-corn-harvest-faces-more-deep-cuts-stunt-disease-spread-2024-04-17/
Argentina’s maize harvest faces deep cuts due to a stunt disease spread by leafhoppers. The crop has been hit by an unprecedented outbreak of the insects that carry the harmful spiroplasma. Leafhopper populations tend to increase in hot and dry conditions. They have badly dented the 2023/24 maize crop, which is very badly affected.

In the worst-hit northern provinces the losses caused by the disease range between 40% and 50%, when normally the figure reached only 5% at worst. Severe cases of leafhoppers were also being seen in regions where they usually do not appear. The unusually damaging outbreak this year has reached areas where it never reached before.

In response, the government announced it was accelerating approval procedures for 2 insecticides recommended to combat the spiroplasma disease, although that comes largely too late for the current harvest. Another factor that will determine how the outbreak progresses is the arrival of low temperatures, as the insect cannot resist temperatures below 4 degrees Celsius. However, scientists at the University of Buenos Aires said that a rapid decrease in temperatures was not expected in northern Argentina, the location of the worst outbreaks.

[Byline: Maximilian Heath]

Communicated by:
ProMED

[_Spiroplasma kunkelii_ causes maize stunt disease on _Zea_ species in the Americas. The maize leafhopper _Dalbulus maidis_ is the main vector. Some crop hybrids resistant to the vector have been identified which potentially may be helpful in disease control (see links below).

Spiroplasmas are plant cell parasitic bacteria without a cell wall and, like phytoplasmas, belong to the mollicutes. The name is derived from their helical morphology. Spiroplasmas can be cultured on artificial media, unlike phytoplasmas, which cannot be cultured in vitro. Mixed infections with phytoplasmas have been reported to occur.

The pathogens are transmitted by leafhopper species. Disease management for spiroplasmas mainly relies on exclusion by use of certified clean planting material, but may also include phytosanitation to remove inoculum and prevent spread within plantings. Vector control has not shown to be effective due to the very rapid transmission.

The related _S. citri_ causes citrus stubborn disease (CSD, also called little leaf); yield losses may be severe (ProMED post 20200710.7559217). The pathogen is also known to affect other crops causing, for example, carrot purple leaf (ProMED post 20110916.2824) and horseradish brittle root diseases.

Pictures
Maize stunt symptoms:
https://bugwoodcloud.org/images/768×512/1235015.jpg,
https://live.staticflickr.com/4095/4927676830_083918e066_b.jpg,
https://bugwoodcloud.org/images/768×512/1524072.jpg
https://agribrasilis.com/wp-content/uploads/2023/02/Hibrido-suscetivel-777×437.jpg (ears) and
https://www.researchgate.net/profile/Pablo-Carpane/publication/280309801/figure/fig1/AS:934279647354880@1599761034390/Figura-1-Corn-stunt-spiroplasma-en-maiz.png
Citrus stubborn disease symptoms:
https://www.dpi.nsw.gov.au/__data/assets/image/0004/597370/reduced-size-fruit.jpg,
https://www.plantmanagementnetwork.org/pub/php/symposium/melhus/8/stubborn/image/stubborn4sm.jpg and
https://content.peat-cloud.com/w600/citrus-stubborn-disease-citrus-1.jpg
_S. citri_ microscopy:
https://iant.toulouse.inra.fr//bacteria/annotation/web/img/spiroplasma.jpg

Links
Information on maize stunt disease:
https://doi.org/10.3390/plants9060747,
https://doi.org/10.1371/journal.pone.0234454,
https://doi.org/10.1371/journal.pone.0259481,
https://agribrasilis.com/2023/02/27/corn-stunt2/,
https://www.gardeningknowhow.com/edible/vegetables/corn/treating-stunt-disease-in-corn.htm,
https://link.springer.com/article/10.1007/s40858-023-00598-1 and via
https://www.ars.usda.gov/northeast-area/beltsville-md-barc/beltsville-agricultural-research-center/molecular-plant-pathology-laboratory/docs/spiroplasma-kunkelli-genome-sequencing-project/corn-stunt-disease/
Citrus stubborn disease:
https://doi.org/10.1079/cabicompendium.50977,
https://www.planthealthaustralia.com.au/wp-content/uploads/2015/01/Citrus-stubborn-disease-FS.pdf,
https://plantix.net/en/library/plant-diseases/300017/citrus-stubborn-disease and
http://www.plantmanagementnetwork.org/pub/php/symposium/melhus/8/stubborn/
Spiroplasma taxonomy via:
https://www.uniprot.org/taxonomy/2132
Information on leafhopper vectors via:
https://bugguide.net/node/view/63
– Mod.DHA


[ad_2]

New tools for science on the farm – Pakissan.com

[ad_1]

The value of “connected agriculture” in making life easier for farmers, and helping them reduce the environmental impact of their practices, is no longer unproven. Another of its advantages is beginning to emerge: by producing large amounts of data of near- research quality, it helps align agronomic and zootechnical research closer to farmers’ requirements, and could better inform agricultural public policies.Digital agriculture is a concept which is beginning to reach grass-roots level, as the high visibility of the subject at the Paris Agriculture Fair demonstrated. In the gloomy atmosphere generated by the feeling of “agri-bashing” experienced by many farmers, it was one of the few subjects that gave a positive and attractive picture of recent developments in agriculture.

Digital farming tools were first designed to make life easier for farmers (GPS guidance, herd monitoring sensors), and to help them optimise their farming practices on an environmental level (connected weather stations, crop models used to optimise input usage). They have also strengthened ties with the consumer, who, thanks to the development of traceability and social networks, can now put a face and a name to the food he buys.

More behind the scenes, connected agriculture is also beginning to have a new beneficial effect, which could in future play an even more positive role for the agricultural world: bringing farmers closer to the research world… and as a result to the policy makers who make use of it.

When science has to be done at the farm level

This development is already a reality in some areas of R & D in digital agriculture. To take the example of herd monitoring sensors: they were first developed to detect unusual and clearly identified events, such as detecting temperatures or calving. These initial applications were developed in a conventional research setting, top down from the lab to the field: algorithms for event detection were developed in tests in experimental farms at research or technical institutes, then tested on a small range of farms before being launched commercially.

As these initial applications have reached maturity, research is now focused on analyses of the daily behaviour and welfare of animals: for example, measuring time spent standing or lying, feeding and rumination times. In these areas it is important to detect more subtle changes in the “daily life” of animals, compared to their ordinary activity.

That makes it very difficult to develop this type of algorithm on experimental farms, where the usual activities of livestock (milking, being put out to pasture, etc.) are frequently disturbed by experiments that modify their usual behaviour, and generate movements or immobility that would not happen in a commercial farm. This type of work should therefore be carried out directly in the field, with experiments in controlled conditions being used only as spot checks in a minority of situations. This is an example of an inversion of the classic relationship between scientific experimentation and field data.

From the lab to the vineyard… and back!

Another example of linking research to farmers’ concerns is the use of mechanistic crop models in decision support tools. These models, derived from agronomic research, are increasingly being used for yield forecasting and management of the required inputs (irrigation, fertilisation). Similar epidemiological models are also used to predict the occurrence of diseases or pests threatening crops, in order to position pesticide treatments most accurately.

By design, the result of extensive research in ecophysiology, these models are sufficiently robust and predictive to lend themselves to plausible simulations on the potential effect of changing practices for agro-ecological reasons, or to adapt to climate change. They also have the advantage of objectively quantifying the environmental conditions to which crops are exposed.

Evapotranspiration is a classic example of a simple indicator for measuring crop water demand, which can then be used as a benchmark to check whether irrigation by the farmer has avoided water waste. However, it remains a relatively basic indicator, which is relevant only in the simplest cases: those where we are only seeking to maintain the yield potential by avoiding water deficit for the crop. For some produce, irrigation issues are more complex, because a small, well-controlled water deficit improves the quality of production: the best known case being vines, where the ideal method, defined by the specifications of the wine appellation, aims to create a moderate water deficit during the maturation of the grape, with varying degrees of severity depending on the type of wine you want to produce.

In this case, irrigation management requires much more complex models than a simple evapotranspiration calculation, and they will use not only climate data, but also soil characteristics and the volume of vegetation in the vineyard. At first glance this is once again a top-down approach to the maximisation of research value, from the laboratory to the field. But the use of these models on farms then permits valuable feedback, which will bring the theoretical work closer to the practice of farmers or their consultants.

The Vintel software, developed by iTK in partnership with (among others) INRA and CIRAD, offers a good example of these two-way exchanges between lab and field. Designed to optimise precision irrigation on vines, it is based on a model derived from research work, based on a classic indicator in research of conventional water stress, the basic leaf water potential.

This indicator is the most reliable for measuring the moisture condition of a vine plant, but its measurement is fiddly, which limits its use in vineyards: it has to be measured at dawn with a specific instrument, the pressure chamber. Some wine consultants, particularly in California, use pressure chambers to advise winegrowers. However, they use these measures at noon for convenience, but also to better understand the water deficit of the plot at the time of the day when it is at its height.

This way of measuring is much less common in research, and so originally it was impossible to develop a mechanistic model to simulate it. Vintel was initially released with a model which only estimated the basic leaf water potential. A few years of use of this first version, by consultants expert in the use of the midday potential measurement, then allowed the development of a second model for midday leaf water potential, combining meteorological data and indicators from the base potential, without going through the laboratory process again.

This example clearly demonstrates the new complementarity between research and digital tools for farmers: it is obviously the data from the field that made it possible to develop a model of midday leaf water potential, in line with the habits of winegrower technicians. But that alone would not have been enough to develop a reliable statistical model: only combining them with indicators from a mechanistic model derived from research could lead to the development of a model robust enough to be entrusted to winegrowers and consultants.

“Medium Data” vs Big Data

A few years ago, the explosion of Big Data technologies, and their introduction into the agricultural world, gave rise to a rather binary view split between two scientific approaches:

  • On the one hand, the classic approach of agronomic or zootechnical research, relying on high-quality but relatively sparse experiments, to develop predictive models that can be used in decision support, based on the human expertise of researchers,
  • On the other hand, the new data-centred Big Data approaches applying machine learning techniques (machine learning, deep learning) to massive volumes of data from new sensors deployed in agriculture (combine yield sensors, data collected by milking robots),

The enthusiasm for Big Data was based on the assumption that deep learning would allow the development of reliable predictive models, despite the “noise” generated by the information from the masses of data collected, which exceed what human expertise is capable of analysing. In fact, this hope quickly came up against the major pitfall of machine learning techniques: their lack of user-friendliness…both for end users (farmers or breeders), and service designers! Machine learning certainly now makes it possible to define seemingly satisfactory decision rules or models from any sufficiently large dataset.

But without knowing the “reasoning” underlying these models, even their designers are unable to predict to what extent these rules or models can be used in new contexts: a rather distressing uncertainty when developing new agricultural services beyond the region where they were initially proven, or in new climate situations.

In addition to its sensitivity to unpredictable climate risks, agriculture has another unfortunate feature for machine learning: the real data that can be accumulated on the ground is far from covering all possible combinations of cultivation techniques. The technical strategies used by farmers are influenced by their habits, experience and the expertise of their consultants, and are therefore absolutely implicitly limited by human rationales.  The situation is in this regard completely different from areas such as machine learning applied to games such as chess or go: in the latter case, the algorithm is able, based on the rules of the game, to test all possible and imaginable combinations, even those that a human expert would not think of. In agriculture, artificial intelligence is hampered by the fact that the available data is the result of human reasoning, which prevents it from finding original “solutions” to invent new practices.

The result of these constraints is that purely data-driven approaches are struggling to make a decisive breakthrough in agricultural decision support. The future is undoubtedly, as we have seen from Vintel’s example, the combination of data-driven approaches and mechanistic models to integrate human expertise into Artificial Intelligence. This new vision, hybrid AI, has been chosen as one of the major themes of ANITI, the new Institute of Artificial Intelligence currently being created in Toulouse… and agriculture has been identified as one of its priority areas of application.

This close interconnection between scientific expertise and farm data has an obvious corollary: the need to bridge the gap between Big Data and research data. This is the mission of what can be called “Medium Data”: well-founded data from farms, or at least from plots run under conditions similar to those of farms. Until now, this role of producing intermediate data has been entirely devolved to experiments at agricultural development agencies: technical institutes, chambers of agriculture, cooperatives[4]. Digital agriculture will allow for the emergence of a new category of “medium data”: data of near-research quality, but spread across hundreds or thousands of farms.

Between the scientific data of research, high quality but sparse, and the “Big Data” of sensors embedded on agricultural equipment, connected agriculture allows the emergence of a “Medium Data”: data of near-research quality, acquired on farms, and not small, unrepresentative experimental plots. It is this continuum of data that will fuel hybrid artificial intelligence (a combination of machine learning and mechanistic human expertise), one of the most promising avenues in today’s AI.

 

Information to ground agricultural public policy

We have seen, with the example of irrigation, that agricultural decision support tools lend themselves well to the creation of objective indicators of crop needs: the same approach is easily transferable to fertilisation, as well as crop protection. Epidemiological models, already used to advise optimal treatment dates for diseases and pests, could also be used at plot level to quantify the still vague and subjective idea of “threat of disease”  Such indicators would be valuable in improving the monitoring of Ecophyto, the plan to reduce the use of pesticides launched in 2010 following the “Grenelle de l’Environnement” debate.

It’s not overstating the case to say that, almost 10 years after its inception, the plan is far from the 50% reduction target (“if possible”) assigned to it: pesticide consumption shows no significant changes on the national average. Even more disturbing, even the plan’s flagship farms, the Dephy network, are a long way from achieving the expected goal. In view of what can hardly be described other than as a failure, the Académie d’Agriculture de France has recently made recommendations to improve the management of the Ecophyto Plan, including the creation of this kind of indicator of health pressure on crops. Digital agriculture could also play a major role in another of the Academy’s proposals: annual surveys of agricultural practices, the only references that can be used to calculate farmers’ pesticide consumption in any detail.

Indeed, the current indicator for the Ecophyto Plan, NODU, is not suited to an agronomic interpretation, which would allow calculation of the potential reduction in pesticide use at farm level. Another indicator, the TFI, would allow for this calculation, although it is currently calculated only every three years, due to the cost of the surveys currently required to collect the data. This still remains the situation, but plot management software enables the automatic calculation of this indicator for farmers who have the equipment. A representative network of farms equipped with this software would therefore allow the annual TFIs to be calculated at a lower cost and cross-linked with the health pressure indicators mentioned above. It should thus be possible to follow up the Ecophyto plan with greater accuracy… and probably to redefine a more realistic set of goals for it, differentiated by crop and region!

Participatory science, which draws on the knowledge of its future users and civil society stakeholders, is one of the key trends in current research. INRA has also been heavily involved in this area. However, much participatory science work remains very asymmetrical: researchers are often the only players putting forward the theories based on the informal and unorganised knowledge of the stakeholders involved in the project. Connected agriculture offers a unique opportunity for farmers to take ownership of research topics that affect them, producing data for themselves which is as understandable for them as for the researchers who will make use of it. Beyond its impact on the daily work of farmers, it therefore has great potential to bring research closer to their needs and enable politicians to better understand their practices. This is how agriculture will be able to meet society’s many expectations of it.

www.europeanscientist.com

[ad_2]