Home gardeners in our area are no strangers to plant diseases. Each year, I review afflicted plants and their fruits. In the past couple of weeks, I’ve already found anthracnose on tomatoes, bacterial scab on potatoes, and tomato mosaic virus.  

Ever wonder why some years your tomatoes flourish and other years they struggle? Gardeners often experience plant diseases in their home gardens and orchards. Fruits and vegetables are always susceptible to several pathogens. Once a plant becomes infected, there is little to do other than pruning out the diseased part or removing the entire plant in the case of root rot or a viral infection. In light of this, preventing diseases is more effective than controlling them once they have begun. 

Effective disease prevention involves using an integrated pest management (IPM) approach. Disease prevention begins with cultural practices, supplemented by pesticides if necessary. 

Preventative practices often control the spread of disease-causing organisms. These practices should be followed on all fruit and nut crops to help ensure that the fruits and nuts are free of disease.  The basic steps include:  Remove dead and diseased tissue, maintain proper plant nutrition, apply water properly, and rotate vegetable’s locations each year in the garden.

All diseases that infect fruit and vegetables are caused by bacteria, fungi, viruses or nematodes. Though nematodes are a microscopic roundworm, they are studied as a pathogen rather than included in an entomologist’s studies.

 Several bacteria cause serious problems on fruit plants. Fire blight of pear and apple is seen annually in home fruit production. Bacterial leaf spot, bacterial wilt, bacterial rot, and bacterial canker are some of the more frequently observed diseases in the home garden. Bacterial diseases are found in all areas, but they are generally more severe in areas of high to moderate rainfall. Bacterial diseases are controlled by resistant varieties, antibiotics, and cultural practices.

Viruses can be spread by insects, nematodes, carried on seeds, and mechanical methods. Symptoms can often be confused with those of plant mutations, nutrient deficiencies, toxicities or other pathogens. Virus diseases are controlled with the use of resistant varieties, rotations, and weed and insect controls.

The fungal group of organisms is the most widespread and damaging. Fungi survive on diseased plant material or on alternate crops. Wilts, fruit rots, and leaf spots are all symptoms of fungal infection. Fungal problems are most severe during periods of high humidity or when the plant tissue is covered by a thin film of moisture. Temperatures between 70 and 85 F are favorable for most fungi. 

Many disease-causing organisms are blown by wind from diseased trees or plant parts to nearby healthy plants. Brown rot of peaches, for example, is spread by spores. Once plants become infected, rain or irrigation water splashing on diseased parts further spreads this fungus.

Too many times, it is our own activities as gardeners that spread problems. Disease-causing pathogens can be spread mechanically during pruning, thinning, irrigating, or cultivating. These injuries create wounds through which harmful pathogens can enter. And if you don’t clean your pruning shears you can be spreading disease worse than a doctor from the early 1800’s that didn’t know about germs! 

If you know you are going to prune out diseased tissue on plants, you can easily disinfect your garden tools with a variety of options. I like to use a weak bleach solution. A bucket with 1 part bleach and 9 parts water does the trick. 

In advanced cases, pesticidal treatments are required to supplement cultural practices to produce high-quality, disease-free, fruits and vegetables. Whether you use conventional or organic pesticides, they should be used according to the instructions on the label. 

Applications of fungicides should be sufficient to maintain control but not excessive. When applying any material for disease control, make sure the foliage, fruit or vegetables are covered with a protective fungicidal film. As with any product, always follow pre-harvest interval (the waiting period between spraying and harvesting) from the time of application to the time a crop can be harvested. 

With these preventive measures, your garden can thrive season after season, rewarding your efforts with healthy produce.