Gardening is a very satisfying hobby for homeowners, however controlling plant diseases every year can be very frustrating to many home gardeners, especially when weather condition favors the development of plant pathogens. Here are methods that we can implement to prevent potential diseases and reduce possible factors that affect plant performance and yield:
What to and what not to plant?
Crop rotation
If certain fungal diseases were confirmed in the previous growing season, gardeners may need to rotate away the same plant as well as the plants belong to the same family. The reason of doing it lies in the longevity of certain pathogens which can survive in soil and keep viable for multiple years. Once pathogen is established in soil, planting the same plant in the same spot will cause severe damages to production and assist in building up pathogen population. For example, bacterial canker disease of tomato caused by a bacterium called Clavibacter michiganensis subsp. michiganensis can reside on plant residues in soil for as long as 3 years, and will persist on stakes and equipment for up to 7 months (Figure 1). To control it, it is recommended to rotate away from tomatoes and other Solanaceous crops such as potatoes, peppers or eggplants for at least 3 years.
Figure 1 Tomato leaf necrosis caused by bacterial canker disease. Photo: Morgan Goodnight
Pathogen-free seed and transplants
Soil borne disease is difficult to control and controlling diseases that are both soil borne and seed borne is extremely difficult. Therefore, gardener should avoid saving seeds of the plants that had disease history from the previous years. Gardeners should use certified seeds that have been treated by fungicide by seed companies or seeds that are produced from an area in the United States where the seed borne diseases are not reported. Transplants need to be purchased from reliable nurseries and examined thoroughly before planting.
Resistant varieties
Among all the disease management strategies, the use of resistant varieties is considered the most effective and efficient. Yes, why not solve all the problems in the beginning? When purchasing resistant varieties through the garden shop, gardeners should read labels to see what disease resistance is listed and corresponding level of resistance. Please note that resistance is always better than tolerance.
Where to plant?
Location! Location! Location! I hope I don't sound like a realtor but the spot selection for home garden is vital because it will help avoiding unnecessary environmental stress for plants. A site with good drainage and full sunlight is always recommended because root rot diseases are normally resulted from highly saturated soil and foliar diseases are attracted to shade areas (Figure 2). If using an old spot, gardeners should remove all the plant materials from previous growing season because plant debris and dead roots can serve as a reservoir for multiple pathogens.
Figure 2 Vegetable Raised Garden Beds. Photo: Columbia Center for Urban Agriculture
When to plant?
The weather is definitely getting warmer. I get it, but don't be fooled by April. Newly planted seedlings may suffer frost damage or cold injury under fluctuating weather conditions. Low soil temperature may cause root injuries that attract soil borne diseases. Patience is key. Home gardeners should refer to both the recommended planting dates for each different plant as well as follow up with the weather report. The MU Extension Garden Hour currently offers a weekly webinar including detailed weather information that you will need.
How to plant?
Home gardeners tend to plant more than what they need and they love to share their produces with neighbors. However, if the plants are crowded as they grow bigger, it may reduce air circulation which is important to reduce the chances of bacterial and fungal infections. Therefore, proper spacing and trellising will limit soil-plant contact as well as increase the air flow. In addition, proper mulching is important in weed control and keeping soil moisture.
Water and fertilization
All plants need water and everyone knows it, but you may not know that if a plant is being overwatered, it may show symptoms exactly like drought stress. That's due to the fact that roots need oxygen too. Excessive watering can cause stress and attract diseases such as seed decay, damping-off and root and crown rot diseases. Regarding the foliar diseases, avoiding splashing water can help preventing the plants from the spores or bacterial cells of plant pathogens. If foliage watering is inevitable, watering in the morning allows foliage dry through the day. In addition to water, plants need food too. Adequate fertilization helps build up the plant health and resistance against plant diseases. About three months prior to the planting, gardeners can send soil sample to MU soil testing lab for detailed recommendations to improve the soil fertility and nutritional level.
Oh, there are weeds!
Weeds are not only the competitors of your plants. They are the inoculum source of multiple plant pests such as virus, insects and bacteria. In addition to placing mulch, good scouting and manual removal of the weeds is necessary. With good weed control, gardeners can increase air circulation and effectively reduce excessive moisture.
What about insect management?
Measurements in controlling insect shares similarities with plant disease control. A good scouting program of insects such as spider mites, white flies, scales and mealy bugs is helpful for managing them in very early stage. Tilling can expose soil insects to beneficials as well as environmental effects in the beginning of the growing season.
Take home message
Humans easily get sick when being under mental or physical stresses. Likewise, a healthy plant is more resistant to plant pests comparing the plants under environmental stresses. Therefore, proper cultural practices as well as use of disease-free seeds and resistant varieties in the beginning of the season is very important for keeping plants healthy.