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There is increasing interest in producing plants sustainably. When it comes to insects, sustainable insect management can only be achieved by combining different management tactics.
When a new problem is found, it needs to be properly identified. Poor identification can lead to failure in control. New insect pests have been introduced in recent years and you need to be vigilant so you can adjust management practices accordingly. If you cannot identify a particular insect, then you need to send samples to facilities that specialize in providing identification and control recommendations. An example is The C. Wayne Ellett Plant and Pest Diagnostic Clinic at Ohio State University (ppdc.osu.edu/). Make sure to contact these diagnostic facilities beforehand so you follow all the proper procedures for collecting and shipping samples.
Various sampling methods can be used including sticky cards and visual inspection. Sticky cards need to be placed about 1 inch above the crop canopy. However, sticky cards will only let you see if the insect populations are growing or not and they will not catch all types of insects/arthropods (i.e. they will not catch spider mites). Usually, yellow sticky cards are used because they catch various types of insects. Visual inspection of plants is one of the best sampling methods, but it is time consuming and employees need to be properly trained. In a recent Ohio survey, I found that approximately 94 percent of growers have someone on staff in charge of identifying pests and diseases. In addition, about 68 percent of growing operations sample once a week. Not surprisingly, those companies that actively sample at least once a week are capable of preventing major insect problems.
Inside the greenhouse eliminate any pest harboring places such as those having weeds and algae. Inspect hard-to-reach areas, such as below benches and remove any weeds or leftover plant material. Make sure trash cans have lids and that any discarded plants and/or plant debris deposited in them is disposed off regularly. Plants that are held for customers, employees or family need to be sampled periodically and treatments should be applied to remove or kill insects found on them. Unsold plant material needs to be treated as a regular crop and needs to be maintained free of pests. If this plant material is not sold it needs to be removed from the facility. Start with clean plants. Incoming plants must be inspected before they are placed inside production areas. Incoming plants can be placed in a separate area for inspection and/or treatment. If plants are used for propagation, employees need to clean their hands and tools periodically to prevent contaminating other areas. It is important to train people properly, so they understand the importance of these practices. Ideally, once a crop is finished and removed, the area should be cleaned before a new crop is introduced. For some insects, leaving an area free of plant material for at least a week or two (best) helps break the insect life cycle. If this is not possible because of logistics, then the area must be cleaned as thoroughly as possible. Keep in mind that insects such as thrips go into the ground to pupate and then will emerge as adults.
Arthropods, including whiteflies and spider mites, respond positively to increased nitrogen levels, which increase their fecundity. This affects control management as their populations grow faster. A way to make sure plants are being fertilized properly is to measure electrical conductivity periodically. Management of irrigation is also very important. Insects such as fungus gnats and shoreflies thrive in areas that are very moist. Fungus gnat larvae do very well when the growing medium moisture level is between 50-90 percent. One way of reducing problems with fungus gnats is to make sure the medium dries to approximately 35-40 percent soil moisture before the next irrigation. This is difficult to achieve with manual irrigation. A better way to manage moisture levels is to use irrigation techniques such as drip, boom or ebb-and-flow systems that can be automated. Using a soil moisture probe is also helpful. Growers using manual irrigation must teach employees how to water the plants to prevent overwatering and algae formation. Be mindful that some insects prefer particular plant types or varieties. Historic sampling data can be evaluated to see patterns and or tendencies that show particular varieties being preferred or affected more. For example, research in my lab has shown that the silver leaf whitefly shows preference for poinsettia varieties that have light green foliage color.
Before spraying or applying any control product it is very important to double inspect application equipment to make sure it is operating properly. Often applications fail, not because the product is ineffective, but because the application equipment is not operating properly. Before applying any controls be aware of the water pH and alkalinity, water volume, nozzle type and application pressure. This means the equipment and all related factors (water delivery, penetration, etc.) have been tested and calibrated at least once before the start of the production season. Water sensitive paper can be used to measure application deposition. In another 2008 Ohio survey, I found that about 70 percent of greenhouse growers had calibrated their spraying equipment during the past year. But 30 percent had not calibrated their equipment in about two years. This increases the chances of control failure when using chemicals. When applying chemical controls, rotate pesticides that have different modes of action to avoid or reduce the chance for insect resistance.
Biological controls usually need to be applied earlier when insect pest populations are small so that the biologicals become established and work properly. Also, insect pest identification is very important to ensure that the right type of biological control is used. When using biological controls be careful to avoid releasing them when pesticides have been applied. Also, some of these organisms are susceptible to solar radiation, and should be released when temperatures are not too hot. Biological controls are often shipped on cards or in satchels so that they can be placed below the plant canopy level and protected from the sun. It is important to learn how to recognize these biological controls and how to evaluate their quality so you can assess if they are successfully killing the target pests. Train employees to identify evidence of biological control agent activity. Become familiar with the biology of these organisms so that the best conditions can be provided when using them.
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