Direct control measures

Learning Outcomes:

• Explain the main focus of direct control measures.
• Classify direct control measures.
• Describe which methods each direct control measure involves.

Pest and disease management consists of a range of activities that support each other. Most management practices are long-term activities that aim at preventing pests and diseases from affecting a crop. Management focuses on keeping existing pest populations and diseases low. Control on the other and is a short-term activity and focuses on killing pest and disease. The general approach in organic agriculture to deal with the causes of a problem rather than treating the symptoms also applies for pest and diseases. Therefore, management is of a much higher priority than control. Direct pest control measures control the population of pests present in the fields or in the places where the pest population is maintained and which are the source of infection. In addition to mechanical and physical control measures, direct measures include the use of inorganic plant protection products or products of synthetic or biological origin. If agents of biological origin are applied, it is referred to as biological pest control.

Mechanical control

Mechanical control measures include a number of procedures by which we collect and destroy pests or, with the help of various mechanical barriers, prevent them from reaching crops. Some mechanical pest control measures are carried out when the pests attack the host plant and are aimed at preserving yields, and some measures are carried out when the vegetation is dormant or when the pest does not cause direct damage to plants and is aimed at reducing the population in the future.

Mechanical measures prevent the spread of pests mechanically, and this is achieved by deep plowing of plant residues, cultivation, dusting of stubble, hoeing, handpicking, pruning branches with overwintering forms of pests or pathogens, gathering on small areas or plowing rotten fruit, removing infected leaves, destroyed plants or possible hosts, by digging canals for collecting pests, placing sticky traps on trunks, cleaning seeds and weeds, setting traps for voles and nets to protect against birds and insects, even spraying plants with a water hose to knock off aphids and mites is considered a mechanical practice.

• Destruction of plant debris

Plant debris or residues in which some pests can overwinter must be destroyed by chopping into small pieces and by deep plowing (20-30 cm). Another solution is burning; however, this method is not recommended as burning crop residues eliminates the possibility of humus improvement, and can potentially lead to significant nutrient loss. Likewise, it may affect other organisms living on or in the soil. In greenhouse production, the destruction of plant residues is necessary and may include burning of plant residues.

• Manual or machine collection and direct destruction

Hand destruction or removal of insects and egg masses ensures quick and positive control. This method is especially effective with foliage-feeding insects. Handpicking is also generally useful for the management of caterpillars, leaf rollers, tobacco caterpillar, cabbage butterfly, mustard sawfly, Epilachna beetle, white grubs etc. Excluding labor, handpicking is the least expensive of all organic or natural control practices. However, handpicking also has disadvantages in that it must be performed long before insect damage is noticeable and at the key stage of development of the insect. Farmers must actively monitor their crops, watching for the first sign of damage before insect populations get too high. Collecting pests using machinery greatly facilitates this method but it is more expensive.

• Mechanical trapping

Several types of mechanical devices are used for collecting insect pests. Corrugated cardboard banding, applied to the trunks of host trees, works as a trap for many insect larvae as they crawl on the tree in search of a place to pupate and overwinter. Banding is a useful tool that can aid in assessing the level of pests’ presence in particular trees as well as in control. Simple vessels or traps filled with water or a mixture of water and vinegar can be used in places accessible to insects. Various traps can be used for cockroaches, wasps, rodents. Adding a bait can help in attracting the pests.

• Mechanical barriers

Mechanical barriers include various types of barriers such as mechanical barriers for snails, game fences, canals for insects that come to the fields by walking, nets that are placed on windows and entrance openings of greenhouses or warehouses, nets or other materials that cover crops or are used to wrap plants. With the necessary preventive measures, weed density can be reduced, but it will hardly be enough during the critical periods of the crop at the beginning of cultivation. Therefore, mechanical methods remain an important part of weed management.

• Manual and flame weeding

Manual weeding is probably the most important one. As it’s very labor intensive, reducing weed density as much as possible in the field will bring less work later on and should therefore be aimed at. There are different tools to dig, cut and uprooting the weeds; hand, ox-drawn and tractor-drawn tools. Using the right tool can increase work efficiency significantly. Weeding should be done before the weeds flower and produce seeds.

Flame weeding is another option: Plants are heated briefly to 100°C and higher. This provokes coagulation of the proteins in the leaves and a bursting of their cell walls. Consequently, the weed dries out and dies. Although it is an effective method, it is quite expensive, as it consumes a large amount of fuel gas and needs machinery. It is not effective against root weeds.

Physical control

Physical plant protection measures include the application of low and high temperature, irradiation, high frequency sounds, light, carbon dioxide, ozone etc., and visual and olfactory baits that cause a reaction of pests to certain stimuli. These measures are used more in insect control than in disease control. The most commonly used are:

• high temperature for thermal soil disinfection. Destruction of harmful microorganisms, pests and weed seeds is achieved by heating the soil to 95 ° C to a depth of 30 cm for 5 minutes;
• solarization or use of solar energy, is a very effective measure for soil disinfection, and is carried out by covering the soil during the summer with a thin, transparent, polyethylene foil for 1-2 months;
• differently colored adhesive boards (sticky traps) attract pests that stick to the adhesive surface. In this way, the attack can be reduced and the number of pest populations can be determined, as well as the beginning of control. Yellow sticky traps that attract aphids and moths, and blue sticky traps that attract thrips are most commonly used in the protected area. In fruit growing, yellow traps are used to attract cherry and olive flies, while white traps attract wasps and red bark beetles;
• light traps can be used to determine the presence and thus reduce the insect population on agricultural land and in warehouses. They are used to catch moths such as armyworms, cutworms, stem borers and other night flying insects. However, light traps have the disadvantage of attracting a wide range of insect species. Most of the attracted insects are not pests. In addition, many insects that are attracted to the area around the light traps (sometimes from considerable distances) do not actually fly into the trap. Instead, they remain nearby, actually increasing the total number of insects in the immediate area;
• reducing the humidity and temperature of stored agricultural products in silos;
• controlled atmosphere in refrigerators for fruit storage. Carbon dioxide is toxic to insect, but its action is low. Eggs and adults of pulse beetle die when exposed to 100% CO2 at 32°C and relative humidly of 70%. Carbon dioxide under high pressure is found to be effective against stored grain pests. Carbon dioxide and nitrogen treatment have been found effective for grain beetle. A nitrogen atmosphere effectively controls all stages of fruit fly;
• irradiation (microwaves and gamma radiation) are being used against stored grain pests effectively. Infrared radiation can be used dually to the insects or to the stored grain infested with insects. Ionising radiation (X-rays) are sterilizing at lower dosages but lethal at higher dosages;
• sound - low frequency sound waves cause adverse effect on development of insects. Sound produced by male and response of female of a species to the sound can be utilized for their control.

Biotechnical control

Pheromone pest control is often classified into biotechnical control methods along with the application of biotechnical insecticides and some other methods. Pheromones are messenger substances used by insects and other animals to communicate with each other. Insects send these biochemical signals to help attract mates, warn others of predators, or find food. Using specific pheromones, traps can be used to monitor target pests in agriculture areas or to early detect quarantine pests. By constantly monitoring for insects, it may be possible to detect an infestation before it occurs and to determine the need for control. Early detection of pest insects using pheromone traps can also lessen damage to agriculture and other plants as they can be used for massive control of some pests.

Biological control

Biological control is the use of natural enemies and natural products to manage populations of pests and diseases. These are measures that contribute to the conservation of natural enemies, and include the targeted release of natural enemies on agricultural land. There are three types of biological protection: classical (inoculation), augmentative (seasonal) and conservation. The classical method is used to control foreign pests that invaded new countries. Augmentative protection refers to all forms of biological protection in which natural enemies are commercially produced and conservation protection refers to the applying all technics and tactics that preserve indigenous predators and parasitoids.

Biological plant protection products are usually called biopesticides. Biopesticides can be mass-produced and used as products for classical pest control. Biopesticides are most often divided into macrobiological agents (predators, parasitoids, nematodes) and microbiological agents (bacteria, fungi, viruses, etc.), natural pesticides and derivatives of some organisms.

Macrobiological agents

They include predatory and parasitic macroorganisms. Predators comprise insects (true bugs, coccinellids, chrysopids), predatory mites, spiders, insect pathogenic nematodes, birds and mammals. Of the parasitoids, for example, wasps, caterpillar flies and nematodes are used.

If populations of natural enemies present in the field are too small to sufficiently control pests, they can be reared in a laboratory or rearing unit. The reared natural enemies are released in the crop to boost field populations and keep pest populations down. There are two approaches to biological control through the release of natural enemies:

1. Preventive release of the natural enemies at the beginning of each season. This is used when the natural enemies could not persist from one cropping season to another due to unfavorable climate or the absence of the pest. Populations of the natural enemy then establish and grow during the season.
2. Releasing natural enemies when pest populations start to cause damage to crops. Pathogens are usually used in that way, because they cannot persist and spread in the crop environment without the presence of a host (“pest”). They are also often inexpensive to produce.

Microbiological agents

They include microorganisms that cause diseases of harmful organisms, and these can be bacteria, fungi, viruses, mycoplasmas and microsporidia, which come on the market as formulated as preparations similar to chemical preparations for plant protection.

The soil-borne fungus Fusarium oxysporum is very effective in reducing the witch weed (Striga hermonthica and S. asiatica) in different cereal crops, leading to yield increases in scientific trials. Other Fusarium species are very effective, too (Fusarium nygamai, F. oxysporum and F. solani). Rhizobacteria capable of suppressing germination of witch weed (Striga spp.) seeds or actually destroying the seeds are particularly promising biological control agents since they can be easily and cheaply formulated into seed inoculants. Pseudomonas fluorescens putida isolates significantly inhibited germination of Striga hermonthica seeds. However, currently no biocontrol product is available.

Natural pesticides

Some plants contain components that are toxic to insects. When extracted from the plants and applied on infested crops, these components are called botanical pesticides or botanicals. The use of plant extracts to control pests is not new. Rotenone (Derris sp.), nicotine (tobacco), and pyrethrins (Chrysanthemum sp.) have been used widely both in small-scale subsistence farming as well as in commercial agriculture.

Most botanical pesticides are contact, respiratory, or stomach poisons. Therefore, they are not very selective, but target a broad range of insects. This means that even beneficial organisms can be affected. Yet the toxicity of botanical pesticides is usually not very high and their negative effects on beneficial organisms can be significantly reduced by selective application. Furthermore, botanical pesticides are generally highly bio-degradable, so that they become inactive within hours or a few days. This reduces again the negative impact on beneficial organisms and they are relatively environmentally safe compared to chemical pesticides.

The preparation and use of botanicals requires some know-how, but not much material and infrastructures. It’s a common practice under many traditional agricultural systems. Some commonly used botanicals are:

Neem:

Neem derived from the neem tree (Azadirachta indica) of arid tropical regions, contains several insecticidal compounds. The main active ingredient is azadirachtin, which both deters and kills many species of caterpillars, thrips and whitefly. Both seeds and leaves can be used to prepare the neem solution. Neem seeds contain a higher amount of neem oil, but leaves are available all year. A neem solution loses its effectiveness within about 8 hours after preparation, and when exposed to direct sunlight. It is most effective to apply neem in the evening, directly after preparation, under humid conditions or when the plants and insects are damp.

Pyrethrum:

Pyrethrum (Tanacetum cinerariifolium) is a daisy-like Chrysanthemum. Pyrethrins are insecticidal compounds extracted from the dried pyrethrum flower. The flower heads are processed into a powder to make a dust. This dust can be used directly or infused into water to make a spray. Pyrethrins cause immediate paralysis to most insects. Low doses do not kill but have a “knock down” effect. Stronger doses kill. Pyrethrins break down very quickly in sunlight so they should be stored in darkness. Both highly alkaline and highly acid conditions speed up degradation so pyrethrins should not be mixed with lime or soap solutions. Liquid formulations are stable in storage but powders may lose up to 20% of their effectiveness in one year.

There are many other extracts of plants known to have insecticidal effects like tobacco (Nicotiana tabacum), yellow root (Xanthorhiza simplicissima), fish bean (Tephrosia vogelii), violet tree (Securidaca longepedunculata), and nasturtium (Nasturtium tropaeolum) which are traditionally used to control pests in Africa. However, one shall be very careful since some of those plants have very negative effect on humans or other non-target organisms and are actually banned to be used for crop protection. Anise, chillies, chives, garlic, coriander, nasturtium, spearmint and marigold are plants known to have a repellent effect on different pest insects (aphids, moths, root flies, etc.) and can be grown as intercrop or at the border of crop fields.

Pesticides of natural origin for disease control include:

Sulphur is mostly used against plant diseases like powdery mildew, downy mildew and other diseases. The key to its efficacy is that it prevents spore germination. For this reason, it must be applied prior to disease development for effective results. Sulphur can be applied as a dust or in liquid form. It is not compatible with other pesticides. Lime-sulphur is formed when lime is added to sulphur to help it penetrate plant tissue. It is more effective than elemental sulphur at lower concentrations. However, the odor of rotten eggs usually discourages its use over extensive fields

Bordeaux mixture (Copper sulphate and lime) has been successfully used for over 150 years, on fruits, vegetables and ornamentals. Unlike sulphur, Bordeaux mixture is both fungicidal and bactericidal. As such, it can be effectively used against diseases such as leaf spots caused by bacteria or fungi, powdery mildew, downy mildew and various anthracnose pathogens. The ability of Bordeaux mixture to persist through rains and to adhere to plants is one reason it has been so effective. Bordeaux mixture contains copper sulphate, which is acidic, and neutralized by lime (calcium hydroxide), which is alkaline.

Acidic clays have a fungicidal effect due to aluminum oxide or aluminum sulphate as active agents. They are used as an alternative to copper products but, are often less efficient.

Milk has also been used against blights, mildew, mosaic viruses and other fungal and viral diseases. Spraying every 10 days with a mixture of 1 L of milk to 10 to 15 L of water is effective.

Baking soda has been used to control mildew and rust diseases on plants. Spray with a mixture of 100 g of baking or washing soda with 50 g of soft soap. Dilute with 2 L of water. Spray only once and leave as long gaps as possible (several months). Do not use during hot weather and test the mixture on a few leaves because of possible phytotoxic effects.

Plant protection products and active substances allowed in organic agriculture

European Union organic farming rules cover agricultural products, including aquaculture and yeast (EU regulation 834/2007). They encompass every stage of the production process, from seeds to the final processed food. This means that there are specific provisions covering a large variety of products, such as:

• seeds and propagating material such as cuttings, rhizome etc. from which plants or crops are grown.
• living products or products which do not need further processing.
• feed.
• products with multiple ingredients or processed agricultural products for use as food.

EU regulations on organic production exclude products from fishing and hunting of wild animals but include harvest of wild plants when certain natural habitat conditions are respected. There are specific rules for wine and aquaculture.

One of the objectives in organic production is to reduce the use of external inputs. Any substance used in organic agriculture to fight pests or plant diseases must be pre-approved by the European Commission.

Additionally, specific principles guide the approval of external inputs such as fertilizers, pesticides, and food additives so that only substances and compounds listed as approved in specific legislation can be used in organic productions.

Processed food shall be produced mainly from agricultural ingredients only (added water and cooking salt are not taken into account). They may also contain:

• preparations of micro-organisms and enzymes, mineral trace elements, additives, processing aids and flavorings, vitamins, as well as amino acids and other micronutrients added to foodstuffs for specific nutritional purposes can be used but only when authorized under organic rules.
• substances and techniques which reconstitute properties that are lost in processing or storage that correct any negligence in the processing or that otherwise may be misleading on the true nature or the products shall not be used.
• non-organic agricultural ingredients can only be used if they are authorized within the annexes to the legislation or have been provisionally authorized by an EU country.

And above all, any substance listed for use in organic agriculture must be compliant with horizontal EU rules and then be thoroughly assessed and approved by the European Commission for use in organics.