A talent for diagnosis is necessary — but not sufficient — to produce a great crop. Scouting regularly and thoroughly for symptoms and interpreting them correctly does give you the luxury of early detection, but it also is critical to practice good overall greenhouse management. Following are some best management practices (BMPs) that will help you reduce the chance that there will be symptoms you’ll need to interpret. The goal of your BMPs is to solve problems in advance, safeguarding the environment by using pesticides only when necessary.
1. Let the greenhouse structure work for you, not against you. Maintain the right light level for the crop. Arrange for optimal ventilation to reduce problems with diseases like downy mildew and Botrytis. Eliminate bench and floor unevenness to eliminate puddling that exposes crops to Pythium root rot. Choose benches with impermeable surfaces like metal or plastic, so they can be easily cleaned. Consider installing thrips-exclusion screening and positive pressure for stock plant areas.
2. Bring only clean plants into your clean greenhouse. Cuttings taken from stock plants may bring insects, mites, and pathogens with them. Purchase cuttings from reliable propagators with certified clean stock programs. Growing your own crops from seed is less risky, but some pathogens can be disseminated on seeds — including Xanthomonas, Pseudomonas, Alternaria, Rhizoctonia, Phytophthora, Cucumber Mosaic Virus, and Tobacco Ringspot Virus. Make an effort to introduce clean plants, but be prepared for the occasional breakdown in quality control from your supplier. If possible, quarantine new plants by placing them in an isolated greenhouse until you can confirm they are healthy or you can restore their health.
3. Grow only crop plants in your greenhouse. This means eliminating pet plants as well as weeds. Weeds under benches are often reservoirs for Impatiens Necrotic Spot Virus.
4. Eliminate potential sources of trouble in and around the greenhouse. Weedy areas just outside the vents are an invitation to insects that can fly in, bringing diseases with them. Tomato Spotted Wilt Virus can easily be transferred into the greenhouse from weeds outside.
5. Inspect plants on arrival. By examining incoming plants closely, it’s possible to find hitchhiking insects or diseases before they are set loose among the crops. Check for thrips, aphids, mites, powdery mildew, and rust so these problems don’t surprise you later on.
6. Monitor your fertility program with periodic soil tests and foliar analyses. Test the accuracy of the fertilizer proportions every three months, or as unusual water dye color or crop symptoms indicate.
7. Address water quality problems (excessively high or low bicarbonate levels, for example). Establish a program that minimizes the effect of the troublesome factor.
8. Keep good records. When observations are made, record them for future reference. Also record fertilizer and pest control applications with the date and time, amounts used, volume of solution delivered and equipment used. This information will be invaluable for troubleshooting, improving efficiency and reducing application cost.
9. Practice careful sanitation. Never place plants, pots, flats or hose ends on contaminated surfaces. If you reuse your pots, disinfect them by removing loose mix, soaking in disinfectant for 10 minutes, then rinsing. Have soap and water easily available and make sure workers use them. With major crops, change disposable gloves when moving between cultivars or when moving between groups of plants from different suppliers. Be quick to remove plants that have disease symptoms or heavy insect infestation. Place these directly into garbage bags, handling carefully to prevent spores from dislodging. After removal, clean hands, change clothing, and clean shoes to prevent spreading spores and insects to other plants and other sections of the greenhouse.
10. Deliver pesticides efficiently and effectively. Your equipment should deliver small droplets, distribute particles uniformly, penetrate the canopy well, and give good coverage of lower leaf surfaces. Materials with translaminar or systemic action help to compensate for incomplete coverage. Pay attention to storage life. Monitor efficacy using sticky cards and direct plant examination so you can tell if resistance becomes a problem with a previously effective material. Know which life stages the material is effective against, so that you can choose the appropriate material and evaluate its performance appropriately.
11. Avoid resistance. Minimize insecticide use, avoid persistent applications, avoid tank mixes, use long-term insecticide rotations, use insecticides with non-specific modes of action, and integrate chemical and biological controls. To slow the development of fungicide resistance, try to rotate among two or three effective materials–in particular, use protectant materials in alternation with systemic fungicides to limit resistance to the systemic products.
12. Choose the appropriate fungicide, insecticide, or miticide for the problem detected, and pay close attention to rates and cautions given on the label. Use the least toxic product that will do the job. Stay abreast of university test results that compare product performance — particularly for new materials.
13. Adjust the fertilizer program based on test results. Just because a trade magazine article says a grower or scientist found a beneficial crop response to a nutrient, doesn’t mean it will work for you. Crops respond when they are deficient, and that’s determined by test results.