Design and Maintenance of Green House 3(2+1)

Lesson 28 Disease Control, Integrated Pest Management

28.2 INTEGRATED PEST MANAGEMENT

Integrated pest management (IPM) is a holistic approach to managing diseases, insects, and mites in the greenhouse, using the best tools, tactics, and strategies to control pests with the least disruption to the environment.  IPM can decrease pesticide exposure of workers and the environment, and can decrease pest control costs while still maintaining high-quality, pest-free plants.

Appropriate use and timing of pesticides and the use of non-pesticide methods is essential, particularly given increasing regulations on pesticide use, decreasing numbers of registered pesticides, and increasing resistance of pests to pesticides.  The most important aspect of IPM is prevention of epidemics, as many pest management decisions cannot be made in hindsight.  As a consequence, most of this fact sheet is devoted to the prevention of pest problems, such as maintenance of a healthy crop, exclusion of pest access to the facility, close monitoring of plant health, prompt remedial action when pests are detected and careful documentation of monitoring, pests found, treatments employed, and treatment efficacy.

“Integrated” is an essential word in IPM.  It means combining a variety of pest management techniques and strategies that can either reduce pest populations or lessen their economic impact while maintaining plant quality.  An IPM program is built on several basic components, many of which are already needed to grow a healthy crop.  While components may be modified to customize IPM programs for different operations, most components below should be included for a successful IPM program.

28.2.1 Sanitation

A basic component of IPM is sanitation.  Infestations are easier to prevent than to cure.  Start with a clean greenhouse. Walkways should be free of soil, organic matter, weeds, and algae.  Benches should be disinfected and pots, flats, and trays must be new or disinfected.  Water sources should be pathogen-free and hose ends kept off the floor.  Note any drainage problems and take corrective action.  Growing media should be clean, preferably pasteurized, and kept covered.

No plant material should be held in the media mixing area.  Do not accumulate contaminated pots or media near the growing area, and systematically remove unhealthy plants and plant parts from the greenhouse.  A weed-free zone should be maintained outside the greenhouse.

Insects and diseases are a major challenge to greenhouse production.  IPM is an important tool in the management of these pests.  The primary goal of IPM is to optimize pest control in an economically and ecologically sound way. IPM involves the integration of cultural, physical, biological, and chemical practices to grow crops with minimal use of pesticides. Monitoring, sampling, and record keeping are used to determine when control options are needed to keep pests below an economically damaging threshold.  Pest management, not eradication, is the goal of IPM. IPM is a simple, practical, and, most important, flexible way to manage insects, mites, diseases, weeds and vertebrates.

28.2.2 Techniques used to manage pests

• Monitoring or scouting program

-  Individual plant inspection

-  Yellow, blue, and hot pink sticky cards

-  Indicator plants

• Pest identification and life stages

• Record keeping to identify trends and direction for your pest management program

• Exclusion techniques to prevent pests from entering the production area

-  Insect screens to exclude aphids, whiteflies, and thrips from entering through doors and ventilating systems

- Cultural practices to prevent problems

   - Soil testing

   -  Sanitation

• Biological controls, living organisms used to reduce the incidence of pest organisms

• Insect growth regulators, insecticides that interfere with normal insect development or the molting process

• Chemical controls

-  Proper choice of pesticides

-  Proper timing of pesticide application

-  Proper application procedure

28.2.3 Several practices that increases the success of an IPM program:

• Cover all soil floor surfaces with concrete, black plastic or weed barrier.

• Use resistant varieties of plants.

• Keep people and “pet plants” out of crop areas as much as possible.

• Pasteurize growing medium.

• Keep doors closed.

28.3 GREENHOUSE DISEASE CONTROL

The greenhouse climate is ideal for the development of plant diseases.  An integration of cultural practices, environmental control, biological control, and natural control products will be needed to prevent widespread outbreak. Many fungicides are also toxic to beneficial organisms, and should be avoided if possible. Alternative disease control techniques include the use of disease resistant varieties, disease-free seeds and plants, well-drained soil, air circulation, weed eradication, humidity control, sanitation, disease-suppressive composts, compost watery extracts, and microbial antagonists.

Disease control may be classified into two approaches:

1) those aimed at the root environment, and

2) those aimed at the aerial environment

28.3.1 Cultural Practices

A healthy crop is less susceptible to most diseases.  As a general rule, pathogens do not thrive under good cultural conditions but take advantage of cultural errors and stressful conditions encountered by a crop.  Maintaining the proper environment for the crop being grown is the first step to eliminating problems.

28.3.1.1Fertilization

Soluble salt levels and the pH of growing media should be tested periodically.  Fertilization schedules for each crop should be implemented.  Nitrogen should be applied only as needed for optimal growth.  Periodic heavy applications will set up nitrogen surpluses that cause excessive growth, which enhance the population growth of aphids, pathogens, and other pests.  Excess nitrogen will also leach from pots and contaminate the environment.  Slow-release fertilizers are ideal to use when possible.

28.3.1.2 Irrigation

Watering is another cultural practice that can be manipulated to slow the increase of pest populations.  Plants should be watered only as needed, reduced on cloudy days, and avoided late in the day.  Wetting the foliage should be avoided because moist leaves provide ideal conditions for pathogens.  Plants should be watered thoroughly and then allowed a dry-down period.  The length of the dry-down period will vary with the species.  Proper spacing of plants to allow air circulation and drying will also decrease the incidence of moisture-loving pathogens.

28.3.1.3 Media

Always grow crops in pasteurized media. Disease-suppressive mixes are available. These mixes either naturally suppress soil borne pests or contain beneficial organisms (biological control agents).  Beneficial fungi are now available commercially and can be added to the media by the grower. Beneficial fungi compete with disease-causing fungi by competing for food, by parasitism, or by producing antibiotics, which kill the disease-causing fungi.  Using disease-suppressive mixes and biological control fungi can reduce the number of fungicide applications for root diseases on a crop.

28.3.1.4 Scouting and Monitoring

Monitoring is one of the most important principles of IPM. Pest management systems cannot be implemented if a grower does not know which pests exist and whether populations are significant.  Therefore, a scouting and monitoring plan must be devised for each greenhouse.  Correct pest identification is essential, and employees must be trained to monitor pests correctly.

Scouting and monitoring should be performed weekly or, preferably, twice weekly during the entire production season. Scouting procedures should be performed as routinely as any other greenhouse operation.  Maps should be made of the greenhouse and scouting should follow the same method in the same manner every time.  Scouting must be intensive; the more plants monitored the better.  Scouting should always start at a major doorway, which is usually an entry point of pests.  Special attention should be paid to plants around any openings in the greenhouse, especially those on outside rows of benches.

Scouts should walk every aisle and move from bench to bench in a snake-like manner.  At least 10 minutes should be spent inspecting 20 or more plants for every 1,000 square feet of production area.  Three or more randomly chosen plants on every bench should be inspected.  Inspection starts at the bottom of the plant by checking the soil for insect, mite, or disease pests and proceeds upwards, looking at older leaves, younger leaves, and new growth.  Pots should be tipped sideways for inspection of the underside of the leaves. Hanging pots and baskets should also be inspected.

A daily inspection of indicator plants and yellow sticky cards is recommended.  The first plant showing symptoms on a bench becomes an indicator plant.  This plant is marked with a stake or in some manner that allows the scout to check the same plant daily.  Pests on this plant are monitored for population increases.  A plant more susceptible to a certain pest(s) may be placed among the crop being produced to act as an indicator plant.  Flagging indicator plants also can improve the time efficiency of daily monitoring.

Yellow sticky traps should be placed throughout the greenhouse.  Many insects are attracted to the colour yellow (thrips are also attracted to the colour blue, and blue sticky traps are available), and insects caught on these traps will serve as an index of activity.  The traps should be placed in a grid-like fashion, at least one card per 1,000 square feet of production area.  Increasing the number of cards per square foot of production area may be beneficial.  Place the cards just above the plant canopy or up to 16 inches above the crop. The cards should be placed in the same position each time to allow a true picture of insect activity to emerge.  Traps should be changed and insect counts recorded at least weekly, or more often depending upon the level of pest population.

28.3.2 Treatment equipment

Pesticide application methods have a great influence, both on their efficiency and on the labour costs.  The application methods depend on the vehicle used to distribute the pesticide: (i) dust, when a solid is used (e.g. talc); (ii) spraying and fogging, when a liquid is used (usually in water); and (iii) fumigation when a gas is used.

The majority of horticultural treatments consist of spraying solutions or suspensions of the active materials. The most usual greenhouse sprayings are performed with a motor, provided with hoses and pistols to cover all areas of the greenhouse and direct the spray to the desired points. The service pressure must be sufficient to achieve a very small droplet size and to generate turbulence that helps the product cover the whole canopy (Aranda, 1994).

The ultra-low volume systems use a fan and  a fog mechanical generator in  association  with each  other, to obtain a very  small droplet size  and  great  canopy penetration, which allows for treating large  areas  from  a fixed  point. If located over a mobile trolley they can be operated in pre-fixed locations (as a semi-fixed system).

The thermo-foggers cause a very fine spray (of less than 100 mm diameter) by the explosion of a mix of fuel and air (Urban, 1997a).

Among the mobile automatic systems the most common is a treatment trolley that moves automatically along guiding pipes (also used for heating) between the crop rows.

28.3.3 Biological Control

Biological control is based on the use of natural enemies of the pests (parasitoids, predators and pathogens) to maintain their infestation   below an economic damage threshold. Although biological control has been known about for more than half a century, its use had not expanded until a few decades ago (Blom, 2002).

The biological control of diseases is not widely used in practice. Techniques that  may be highlighted include: (i) crossed protection techniques  (where the  organism that   arrives first to an infection point acts against the pathogen that arrives later; this is used for the control of tobacco mosaic virus (TMV) by inoculating the plant with an innocuous form of the virus); (ii) induced resistance (the  organism arriving first  induces a defence reaction in  the  host); (iii) passive occupation (previous occupation of the infection point by an innocuous organism); and  (iv) hyper-parasitism (Trichoderma). However, it should be pointed out that there are many other techniques (alelopathy, antibiosis) of possible use (Jarvis, 1997).

The use of biocontrol agents has been efficient against some diseases such as the use of Trichoderma against Pythium, Fusarium and Rhizoctonia (Elad, 1999).

The pest’s natural enemies, besides not competing for the resources, carry out a predatory activity, feeding on the pest species. Parasitoid insects carry out a particular parasitic activity (external or internal oviposition of one egg on the host, from which a larva emerges that eats the animal as it develops). Parasitoids are more specific (monophagous in many cases), whereas predators are usually polyphagous (García,  1994).

The use of entomopathogens in biological control in the   greenhouse, as an insulated enclosure, is of special interest. The  massive use of Bacillus thuringiensis for the control of Lepidoptera has expanded, whereas the use of other pathogens, such as Verticillium lecanii (limited by the  optimum temperatures range, Photo 28.3.1) or Archensonia (for white fly) and Beauveria  or   Paecilomyces  (for   white  fly, aphids or thrips) is not so widespread (Parrella,1999).

Photo 28.3.1 Adult thrip covered with Verticillium lecanii hyphae

(Source: Nicolas Castilla, 2013)

The use of Encarsia formosa, for the control of white fly (photo 28.3.2) (Trialeurodes), as well  as the use of Phytoseiulus persimilis for the  red  spider mite, are  widespread in  protected cultivation  all  over  the  world (Parrella, 1999).  In Spain, the  most  common control for  white fly  is  Eretmocerus mundus  (J.V.D.  Blom, 2007, personal communication).

Photo 28.3.2 White flies is one of the main pests of greenhouse vegetables.

(Source: Nicolas Castilla, 2013)

REFERENCE:

1. Nicolas Castilla, 2013. “Greenhouse Technology and Management.” Ediciones Mundi-Prensa, Madrid (Spain) and Mexico. PP.220-226.