Plant diseases can often be very problematic. Frequently the only indication of a disease is a plant “symptom” such as yellowing leaves, necrotic (dead) tissue in the leaf or stems, stunting, curling, or some other plant response to the disease. Unfortunately, other problems can lead to the exact same symptoms so confirming how to correct the issue at hand can be difficult and often comes down to trial and error for the hobby gardener. So the best time to consider some defensive strategies is at the time of purchase and planting. Selecting plant types that are resistant to a common disease is a very good approach, especially in specific situations such as black spot on rose or apple scab on pome (apple and crabapple). In addition, selecting the proper plant type for the spot to be occupied is essential. At the very least, the plant should be selected for the anticipated sun exposure and soil drainage conditions. Fortunately, even in established landscapes, if some easily implemented strategies are employed, disease pressure can be prevented or at least minimized.
Fungal blights can be particularly devastating to susceptible plants. These diseases come in a variety of forms and severities. I am a strong advocate of non-synthetic (organic and/or natural) disease control products and strategies, therefore synthetic chemical options will not be discussed.
Here are a few things that can be done to help your plants win in this perpetual power struggle.
1. Watering Techniques: Water the plant, not the fungus. All biological organisms need water. The secret is to provide water for the plant at the exclusion of the fungus.
For shrubs and plants the ideal solution is to use soaker hoses on cheap disposable timers. To water the plant water the soil, to water the fungus water the leaves. Remember, these spores are on the leaf anyways, extended leaf wetness is just what they need to germinate and infect.
For Lawns, if overhead watering is used then it should be in mid morning or mid afternoon. If mid-morning wait until dew has been gone for at least several hours and if mid-afternoon the foliage should have a chance to dry for at least several hours before the onset of dew.
2. Fertilizing Techniques: Make sure the plant is properly fertilized. This doesn’t mean rush out and apply another dose of fertilizer. Too much fertilization is as frequent an issue as too little fertilization. Fertilization needs will vary according to the plant species. Just like people, if the plant is stressed or nutritionally deficient then the ability to fight off disease is severely compromised. Organic fertilizers are a superior choice to non-organic for a number of reasons including overall soil health, low salt levels, sustained release rates (nature’s slow release), reduced petroleum dependence in the manufacture, and promotion of recycling.
Important: Sewage sludge, processed or not, is NOT considered organic and has issues with disease exposure (human diseases, not the plants!!).
3. Pruning Techniques: Selectively prune the plant to thin the canopy. Once again, it is an issue of watering the fungus. Promoting rapid drying of the leaves after rain events, etc can have a dramatic effect on disease avoidance.
4. Air Flow Considerations: If there are structures that inhibit air flow and are not needed then they should be eliminated or minimized. Once again, maximizing the drying rate benefits the plant at the expense of the fungus.
5. Fungicides: Sometimes even the best of efforts can not overcome the conditions that Mother Nature throws at us. In that case there are organic materials that can help weather the onslaught. These include, but are not limited to sulfur, copper, biologicals, and soft chemistries such as potassium bicarbonate. For any of these materials it is important to read the label and apply as directed. Sulfur and copper have been used for hundreds of years and are broad spectrum in their activity. By broad spectrum I mean they can help control numerous diseases. This is a major benefit if you do not know what disease your plant has. Just keep in mind that these materials do NOT absorb into the plant (they are non-systemic). As such, to have any lasting benefit it is important to get uniform coverage of the entire plant. In addition, a heavy rain (or overhead irrigation) will remove them and they may have to be re-applied after these types of events.
In summary, keeping diseases in check is a multi-faceted strategy that encompasses many aspects of plant care. The secret is to tip the balance of power in the plant’s direction.
