Disease prevention in the garden

How about those rain showers many of us have gotten during the past few weeks? I am definitely ready for some sustained sunshine. With the rain comes the potential for many disease problems in our gardens. This week, we explore some thoughts on preventing diseases in our vegetable gardens and landscapes.

I have received calls lately from gardeners whose squash plants have suddenly, they say, developed a rash of powdery mildew. This whitish fungal disease covers the squash leaves, reducing photosynthesis, thus severely weakening the plant. This is just one of many examples of disease problems that may occur in the average vegetable garden.

Plant diseases can be caused by bacteria, fungi or viruses. They manifest themselves in the form of leaf spots, stem rots, root rots, cankers, wilts, etc. These can enter your garden in a number of different ways. There are certain situations that are beyond our control when it comes to the incidence of plant diseases. However, there are many ways to prevent or at least reduce the chance of diseases affecting your plants.

The most basic method of disease control is to create the best growing environment possible for your plants. Keeping plants healthy is your plants’ best defense against diseases. This includes putting the right plants in the right place. The soil should be loose and loamy — well drained — without an excess of sand or clay and well amended with plenty of organic matter.

Just as location is the key to success in real estate, sanitation is the key to a healthy garden. Start by keeping diseased plants out of your garden. Do this by inspecting all plants you are thinking of buying to be sure you don’t see any obvious signs or problems, such as leaf spots, stem rots or root damage. Next, buy plants that are resistant to various diseases, as with hybrid tomato plants. Look for tomato varieties with at least a “VFN” on the label.

Always keep your garden as free of weeds as possible. Besides the obvious fact of being unsightly, weeds provide a haven for certain insect pests, which often are disease carriers. Once they begin feeding on other plants in your garden, they can spread disease to them as well.

People and tools commonly spread diseases from plant to plant. Keep tools like pruners disinfected. A solution of 1 part bleach with 9 parts water is simple and effective. Spray your tools often, especially pruners, and always after making a cut to a diseased plant.

Mulch your plants whenever possible. Mulch provides several benefits. One is to provide a protective barrier between the soil and foliage. Many plants fall victim to soil born diseases caused when water splashes up from the soil onto the foliage. It is always wise to mulch your tomato plants soon after setting them out.

When it comes to watering there are a few important rules to remember. Avoid wetting the foliage and water early in the day if possible. Watering early gives the foliage a chance to dry out by midday. The longer foliage stays wet, the greater the chances of disease taking hold. The use of drip irrigation is the best way to minimize the risk of water transferring disease onto your plants from the soil.

Leave plenty of distance between the rows in your garden. This will allow good air circulation. If one row is allowed to grow right into the next, the plants may never have a chance to dry out properly after a rain or irrigation. Constant moisture above ground level encourages disease organisms.

Place your garden in the sunniest spot possible. Ultraviolet rays kill many would-be harmful organisms, and keeping your garden on the dry side between waterings discourages many potentially harmful organisms.

Try to avoid cultivating, pulling weeds or thinning when the plants are wet. Disease pathogens (bacteria, fungi and viruses) cling to your clothes, hands and tools, and these can easily be transferred to the plants when they are damp.

Also, keep insects under control, since they are disease carriers. Do this by not allowing the area around the garden to grow up in weeds. I realize that this is easier said than done, especially this time of year when the weeds and grass seem to display a growth spurt.

Also, do a good job of monitoring the insect population inside the garden. Check your plants often – everyday if possible – for signs of insect damage and presence. Especially look on the undersides of leaves.

A prime example of insect vectoring is the spotted wilt virus that many of us are seeing these days on our tomatoes. This virus is actually carried by thrips, insects that typically damage small grain crops and then move on to other host plants.

Till under or compost all plant residues after your plants have stopped bearing fruit. Leaving them to wither untouched only provides a place for pathogenic organisms to multiply.

A word of caution is in order here, however. Till under only healthy, unaffected plants. The pathogens on diseased plants which are tilled under the soil will many times, under the right conditions, merely multiply and or overwinter in the soil and come back to haunt you in the spring.

Avoid watering your garden on muggy, overcast days. Watering sometimes splashes disease spores present on plant leaves and on the soil onto other plants’ leaves. In other words, don’t water when the garden doesn’t need watering!

In spite of our best efforts, gardens will still get diseased. However, if you’ll apply the above practices, you will greatly reduce the number of problems you’ll encounter. I hope these pointers will be helpful to you as you strive to produce healthy, fruitful gardens.

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