Fungicides are used extensively to control diseases in greenhouses, nurseries, landscapes, and turf areas. The following is an article on considerations in applying fungicides.
1. Apply fungicides prior to the development of disease. Most fungicides do not have a “kick back” action. That is, they do not effectively eradicate diseases after they have started. And by the time a single disease lesion is observed, many more lesions too small to observe are already working on your plants. Even those fungicides with systemic activity and some curative action are much better applied before the disease is present.
2. Use shorter spray intervals during weather conducive to plant disease. Each plant disease has its own “personality” and thus prefers different weather. However, most plant diseases require leaf wetness. Therefore, during periods of rain and heavy dews, more frequent fungicide applications are a good idea. The normal range of spray applications is every 7 to 14 days during the period the disease is active. Use disease forecasting tools where available to schedule applications.
3. Apply fungicides before a rain if possible. Water is necessary for most fungal spores to infect a leaf or stem and for the splash dispersal of many spores. Therefore apply fungicides before a rain if it appears that the fungicide will have a chance to dry before the rain. It is not necessary to apply fungicides again after every rain. Most modern fungicides have a good sticker and will persist through rains pretty well.
4. Avoid applying fungicides in the heat of the day. It is possible for any foliar applied chemical to cause some plant damage if applied under conditions of heat and direct sunshine. Also remember that if fungicides and insecticides are applied together, make the applications so that bees are unharmed.
5. Timing of fungicide applications and coverage is more important than nozzle type and spray pressure. Studies have found that nozzle type and spray pressure don’t make as much difference as we once thought.
6. Some diseases cannot be managed by foliar sprays. Problems caused by soil borne fungi or nematodes cannot be controlled with foliar fungicides. No amount of fungicide will improve a problem caused by soil fertility.
7. Do not apply foliar fungicides to the soil. Although fungicides may kill or inhibit the growth of fungi which cause plant diseases, the application of those same fungicides to the soil will be wasteful and off label. Foliar fungicides are designed to protect the surfaces of plants. Only use fungicides labeled for soil treament
8. Make certain the fungicide matches the crop and disease. That is, READ THE LABEL. The label is the law. Plus, considerable time and money was spent to test each fungicide with a particular crop and disease. Off label applications also waste your time and money.
9. Double – check the label for the current rate. Rates may vary widely based on label changes and different formulations. While you are checking the rate, also check to make sure your application method is labeled. For example, some fungicides are labeled for greenhouse use, others only for use outside
10. Play it safe. Always adhere to the Re-Entry Intervals and Worker Protection Standards listed in the label. No one wants an accident or lawsuit. Besides, the label is the law.
11. Rotate fungicide chemistries to avoid the development of fungicide resistant strains of the diseases.
Adapted from an article by Dr. Dan Egel, Purdue University
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