![]() This means diseases are more likely to become established inside the plant canopy than on the outside. Plants shade the soil, slowing the drying time and raising the humidity levels around the plants. The inside leaves are sheltered from direct sun and drying winds, so water will stay longer on them. If watering in the morning, stop early enough that the watered areas dry at the same time as or before unwatered areas.Ī plant has leaves on the outside and on the inside of its canopy. If watering in the evening, make sure you stop watering early enough that the watered areas dry before dark. Dew is usually present from about midnight to 8:00 in the morning. Observe how long the dew stays on the plant canopies and turf then water when the dew would normally be on the plants. This lessens the length of time the leaves stay wet and reduces disease. You cannot control how heavy or long a dew is, but you can water while the dew is still on the plants. Free water on plant leaves is a major contributor to plant disease. Extending the period of leaf wetness will let more pathogen “seeds” germinate.įigure 2. Do not extend the period of leaf wetness by watering as the dew is beginning to dry in the morning or before it forms in the evening (Figure 2). Remember that dew is water, too, so your watering schedule has to account for it. Reduce the amount of time leaves are wet. Reduce the number of periods by watering only when needed, and then water deeply. You can control many plant diseases by controlling the number of the free moisture periods and how long those periods last. The amount of disease development depends on the number and length of wet periods per unit of time. Moisture is the critical factor determining active disease and little or no disease. Drying the leaf kills the fragile spores. Water on top of the leaf lets the spores and bacterial cells penetrate the plant and cause infection. The surface of the leaf often has a cuticle, beneath which are living cells (represented by square blocks). ![]() Diagram of the cross-section of a leaf with fungal spores (top of leaf, left) and bacterial cells (top of leaf, right). The “seeds” may move longer distances by windblown water droplets. The splash carries the “seeds” from the soil to lower plant leaves, from the lower plant leaves to the upper plant leaves, and from one plant to another. Splashing water droplets move pathogen “seeds” short distances. ![]() Some require slightly less time and others more. Many fungi require a film of free moisture for at least 9 hours to germinate and penetrate the plant leaf. Like plant seeds, they require moisture to begin germination, and once they germinate, they die if they dry. Fungi and bacteria must have water to spread and infect plants.įungal spores are small and delicate (Figure 1). Once released, they may be carried on the wind, in raindrops, or in irrigation water. The fungal spores and bacterial cells are often not released until they have been wet for a certain period. They spread by seed-like structures called spores or by cells. Fungi and bacteria that can cause disease are called pathogens. ![]() Most plant diseases in the state are caused by fungi, but bacterial diseases also occur. By understanding a few basic principles of how free water (water droplets and films of water on the surface of plant tissues) relates to plant disease and by watering appropriately, you can limit disease in your garden. Unlike other important factors, such as temperature, you can sometimes control water and moisture. Water, especially water droplets on leaves and stems, plays a major part in plant diseases.
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