Home Greenhouse Disease And Pest Control Tips
Growing plants at home, especially in greenhouses, is much more enjoyable and manageable today than it was 50 years ago. Advances in technology, horticultural science, and pest control have transformed how home gardeners maintain healthy greenhouse environments.
One major improvement is how much easier it has become to manage insect pests. Thanks to the development of both synthetic and organic insecticides, along with the widespread adoption of Integrated Pest Management (IPM) strategies, greenhouses today can be kept largely pest-free with less effort and risk.
Old Pest Control Methods
Back in the 1950s, aerosol “bombs” were commonly used to distribute insecticides in fine mists. These devices worked by dissolving insecticides in volatile carriers such as methyl chloride or Freon-12 and then pressurizing them in metal canisters. When released, the mixture created a fine spray that suspended the insecticide in the air, allowing it to settle on plant leaves and pests. While efficient for their time, these aerosol methods required tightly sealed greenhouses and posed health and environmental risks that modern approaches have since helped to mitigate.
Disease And Pest Control Tips
Today, many home gardeners prefer liquid emulsifiable concentrates over wettable powders. Emulsifiable solutions tend to leave less visible residue and are often more effective. However, some greenhouse plants may be sensitive to certain solvents used in these products, so it’s important to test on a small number of plants before widespread application.
For better spray coverage, especially on waxy or hairy leaves, adding a small amount of surfactant can help. In home settings, a drop or two of mild liquid dish soap per gallon of water is often sufficient to break surface tension and improve pesticide or fungicide coverage. Always mix the surfactant with water before adding any chemicals.
Systemic insecticides, applied to the soil, can be useful for controlling pests on houseplants like African violets, cyclamen, delphinium, and other ornamentals. These products move through the plant's vascular system and are effective against many sap-sucking insects and mites. Be sure to water thoroughly after application to help distribute the product evenly through the soil. You can also apply them using a hose-end sprayer or a fertilizer injector for precision. Just keep in mind that soils treated with systemic insecticides are not safe for growing edible crops.
Watering Wisely: Disease Prevention Through Irrigation
Proper watering practices are crucial in preventing greenhouse diseases. Overwatering, especially in heavy soils, can lead to root and stem rot caused by pathogens such as Pythium, Phytophthora, and Sclerotinia. Plants like African violets, primroses, and begonias are particularly susceptible to damage from overly wet conditions.
To minimize the risk of foliar diseases, water the soil directly and avoid wetting the leaves. Most fungal and bacterial spores require several hours in standing water to germinate and infect plant tissue. By keeping leaves dry and maintaining good air circulation, you can drastically reduce the chance of infection.
However, powdery mildew behaves differently. It actually thrives in dry air and infects leaves more readily in drafty areas like near doors or broken windows where evaporation is high. This fungus commonly affects roses, African violets, begonias, verbenas, calendulas, phlox, and snapdragons. Unlike other fungi, powdery mildew spores don't need standing water to cause infection in fact, moisture can inhibit them.
Another common issue in humid conditions is Botrytis, also known as gray mold. This fungus flourishes in cool, damp environments and attacks a wide variety of plants. On begonias, it causes stem rot; on cyclamen, it damages leaves; and on geraniums, lilies, bougainvillea, and snapdragons, it affects both foliage and blooms.
Old-Fashioned Wisdom That Still Works
One of the best ways to reduce the spread of Botrytis is simply to keep your greenhouse clean. Remove and dispose of infected leaves and flowers as soon as you see them. Never toss plant debris under benches or into greenhouse corners bag and discard it or burn it if permitted in your area.
Reducing humidity through proper ventilation, using fans to increase air movement, and watering carefully to avoid splashing are all effective strategies. If the problem persists, occasional treatment with fungicides such as zineb or captan can help suppress outbreaks.
Soilborne diseases, however, remain some of the hardest to control. That’s why preventative practices like good drainage, crop rotation, and sterilizing tools and pots are essential for long-term greenhouse success.
