Garden Guide: Disease prevention and control in the home garden

Mar. 20, 2013 @ 04:59 AM

Plant diseases have shaped the history of the United States — and for that matter the world. Saint Patrick’s Day last Sunday reminds us all of the many Americans with an Irish heritage. We all know of the Great Potato Famine that resulted in an exodus of Irish people to the United States. Did you know the cause of the famine was a plant disease called late blight, which still infects potatoes and tomatoes today?  

Another example is the Salem Witch Trials. The witch trials caused hysteria among the townspeople and resulted in the unnecessary deaths of local “witches.” One theory that may describe the hysteria is that the grain consumed by locals was infected with a fungus, Claviceps purpurea, which contains alkaloids used in the synthesis of LSD and can cause similar symptoms. This infected grain did cause the medieval disease Saint Anthony’s fire, which caused gangrene.  

Enough about how plant diseases have affected our history — how can we prevent and control plant diseases in our own yards?  

Crop rotation can be one of the most effective disease (and insect) control methods a gardener has available. The idea is simple — rotate the vegetables you plant amongst different areas in the garden to prevent the buildup of insects and diseases. When planning your garden for the season, plan for crop rotation. Split your garden area into four sections and each year rotate the types of vegetables you plant there. Be careful, many insects and diseases will infect vegetables that belong to the same family (such as pepper, tomato and eggplant). Here are some examples of related vegetables: tomato family, corn and grain, cucurbits (cucumber, melons and squash), brassicas (cabbage, broccoli and kale) and legumes (beans and peas).

Pick vegetable cultivars that are resistant to some of the diseases we experience in North Carolina. For those of you who do not hail from North Carolina, it will not take long to figure out that the hot, humid days that we hate, diseases love.

Tomatoes are perhaps the most quintessential garden vegetable; everyone grows them. Take time now to pick out tomato cultivars that are resistant to Verticillium and Fusarium wilts. These fungal diseases survive in the soil (which is why crop rotation is important) and are extremely common; however, resistant cultivars have been developed and should be utilized. Other resistant vegetable crops have been developed — contact our center for a list of recommended vegetable cultivars.

Once your garden has been planted, your job is not done. Take time every day to look at your garden. This will help you establish a feeling for what is normal plant appearance and can help you to identify problems as they arise. You might want a magnifying glass or a small hand lens to assist you with this. Our center can also assist you with identification of disease problems. Bring as large a sample as possible with both healthy and problem tissue present.

Identification of the disease is extremely important. Not all pesticides are created equal, and there is no product that cures everything. In fact, some problems cannot be “cured” this year, and you will have to abandon the crop. Insecticides treat insects, while fungicides treat fungal diseases, and herbicides treat weeds. Without knowing what is afflicting your plant, you will not be able to choose the most economical, safest and most effective treatment. In many cases, some type of environment modification is all that is needed to control your pest.

Let’s talk more about sanitation. Good sanitation begins at planting. Be sure to use fresh seed from a reputable source, since some diseases carry over on seed. Use a disease-free potting mix if you are starting your own transplants. Sterilize trays or pots that you start seed in with a bleach solution before filling with soil. Some diseases can be transmitted on infected tools, so rinse these with a bleach or disinfectant prior to use in the spring.

As the growing season progresses, water in the morning and, if at all possible, near the roots to avoid wet foliage. Again, diseases need moisture to survive and will thrive on moist foliage.

If leaves or fruit on a mature plant show signs of disease, strip them off and dispose of them. As leaves or fruit fall from the plant, remove them. Diseased plant material that is allowed to stay near a host plant will reinfect the plant.

At the end of the season, clean up your garden. Remove plant material — you can compost healthy material, but be sure to dispose of any material that was diseased or had insects during the growing season. Plant material that is left over winter can provide a place for insects and diseases to reside until the next growing season.

Pesticides are just one tool in the toolbox of pest control. A pest control strategy should consist of cultural methods, pest identification and judicious pesticide use when necessary. For more information on disease prevention and control, contact our center.

Want more pertinent horticulture information delivered directly to your home computer? Subscribe to the Lee County home horticulture e-mail list. Simply send an e-mail to mj2@lists.ncsu.edu with subscribe leehomehort in the body of the message. You will then be a member of leehomehort@lists.ncsu.edu.