Managing Plant Pests and Diseases Naturally

By Skip Richter

Contributing Editor

ny gardener can tell you that there is a long road between planting a seed or transplant and enjoying the harvest. This road is lined with things that threaten to spoil our plans of beautiful flowers or tasty fruits and vegetables. It is not enough to have to deal with soil challenges, excess rainfall, drought, heat, cold and wind. Our garden plants are also the targets of pests and diseases that can prevent us reaching the bountiful ending we have in mind.

You might expect an article on managing pests and diseases naturally to begin with a listing of the organic control products for killing these would-be garden spoilers. Actually, that would amount to coming in through a back window. Natural products are the last thing we need to talk about. Effective organic pest and disease management involves a much more comprehensive approach. Think of it like this: If you were to talk about how to win a war, the type of bullets to use in the gun are not where to start. There is much more to planning and coordinating such an effort.

These distinctions may seem like a lot of fussing over philosophical approaches, but they are important. When we view pests and diseases as things to be killed, the spray approach makes sense, and we can count on spending our weekends mixing up stinky water to head into battle in search of the enemy. On the other hand, when we take a broader perspective we can usually avoid the need to spray altogether.

This approach begins with the recognition that pests are part of a large and complex web of insects and other arthropods that interact with each other and respond to constantly changing environmental conditions to create something we call the “balance of nature.” Nature, by the way, is seldom in balance and is constantly correcting imbalances like the pendulum of a grandfather clock frequently passing but seldom at the midpoint.

Diseases, likewise, are completely dependent on environmental factors, and the constantly changing environment results in major shifts in whether or not a particular plant disease is currently posing a threat to a particular plant.

A scientifically based natural or organic approach is one that simply recognizes these interactions and factors, and seeks to manage the garden in a way that makes success easier and, to use the martial analogy, less of a battle.

The key is to figure out how to put such a perspective to work in the home garden. What follows are some simple tips to help create an approach that works for you. This is certainly a simplification of a complex topic and the tips are the basics which need to be developed to fit each growing location, crop and garden. But I think that starting with this basic mindset helps us think effectively when we seek to manage our gardens and avoid losses to pests and diseases.

Good Plant Health

While sometimes overstated, it is true that plants in good health and vigor are often less susceptible to some pest and disease problems. There are many factors that go into ensuring that your plants are strong and healthy to begin with.

Selecting a site that is suitable to a plant is critical. Most plants need lots of sun and well drained soil. Others prefer wet sites and/or shade. When you break the rules you are asking for problems. I’ve seen, on many occasions, plants succumb to root rots that are primarily brought on by soggy soil conditions. Sun vs. shade can affect some disease conditions. Pavonia, or rock rose, for example, will grow in shady spots but powdery mildew problems will be much greater when you grow it in the shade.

Preparing the soil for the particular plant you want to grow is also important. Raised beds help with drainage and organic matter helps improve the physical properties and nutrient availability in both sand and clay soils.

Selecting adapted species and cultivars is very important to success. I know we gardeners love to try and grow things “that won’t grow here,” but the more we choose well-adapted, disease- or pest-resistant plants, the more problems we can avoid. Some examples of this principle include roses that naturally resist black spot or powdery mildew, crapemyrtles that are resistant to powdery mildew, tomatoes with natural resistance to wilt and foliage diseases.

Proper planting is another factor in promoting plant health. Before you plant. prepare the soil with additions of decomposed organic matter. Then dig a hole and set the plant at the proper depth. Space plants out to allow for good air circulation between them. Roses that are crowded, for example, are much more prone to foliage diseases. Time your plantings to ensure best results. Corn, for example, that is planted late is doomed to an even more severe attack from earworms than early corn. Marigolds can take summer heat but are not plagued by spider mites if planted in late summer for fall blooms.

Caring for plants properly includes proper watering and fertilizing. Whenever possible, water plants with drip irrigation. Sprinkler irrigation means frequent wetting of the foliage and increased incidence of diseases.

Beneficial Insects

I have good news. It is not just “us vs. the pests.” In fact, most pest control is taken care of for us by a complex web of beneficial insects that are constantly doing what they do to keep pests under control. They feed on pest eggs, parasitize pests and even chase them down and eat them!

When we kill beneficial insects we inherit their job. When we build a garden environment that invites and sustains them we get extra free labor in our gardens.

Learn about the beneficial insects that inhabit your Texas garden. Learn what they need to thrive in the way of water, plants for nectar or low levels of pests to maintain their own populations. I think it is a major hurdle for some folks to stop looking at pests alone and to start to see the many interrelated creatures that are part of the balancing act going on in our gardens.

More often than not, when I see a pest I also see beneficial insects that are working to keep the pest populations in check. This brings us to the next point.

Damage Tolerance

How many holes in a spinach leaf are too many? Is it okay to have a few aphids on a tomato plant if their numbers are not going to affect yields? Can we tolerate some low levels of a pest to encourage a buildup of beneficial insects that in turn will work to prevent a major outbreak?

While the average consumer would prefer perfect produce and would be repulsed at the thought of a “bug” on their food, experienced gardeners know such a mindset is silly. Whether we see them or not, “bugs” are everywhere and in our home gardens some give and take is part of the game.

Know too that there are times when a pest population gets out of hand and the crop needs to be pulled and something else planted. Trying to fix a problem when it is too late is a waste of time and money. Each spring when the winter weeds take off in our lawns much money is spent on weed controls that are not effective against weeds that are now ripening seeds and will be dying soon anyway. When the harlequin bugs arrive en masse I usually call that the end of the broccoli season rather than try to spray my way to a few more weeks.

Pest Control Tools

There are some handy tools that will help manage pests without sprays. One of my favorites is row cover fabric. This lightweight polyester fabric can be placed over growing plants with or without a support structure. It allows light, air and water to pass through but screens out insects. You can cover squash until the first female blooms appear to block out squash bugs, virus-carrying insects and vine borers. You can wrap a tomato cage with it to provide a little cold protection and to block out aphids until the plants get large. It is great for covering greens to allow for a spray-free harvest.

Strong blasts of water will dislodge small pests such as aphids and mites. There are water wands on the market that work great for this purpose. The key is low volume with a blast of small droplets. Most watering devices provide too much volume with too little velocity and too many droplets that are too large. They end up creating a swamp rather than just blasting off some pest with a fine blasting mist.

Some gardeners have devised their own water wands with the above goals in mind. Use them once every week or two as needed to keep mite and/or aphid populations low. Remember the goal is not eradication but simply prevention of outbreaks.

Low Impact Sprays

Okay, here’s the part all you “nozzle heads” have been waiting for! There are a number of low-impact sprays that can be helpful when all our efforts have not been enough and when pests or diseases threaten to destroy our prize plants or reduce yields to unacceptable levels.

While there are many products to choose from, I’ll mention a few that I would consider the most helpful and the least toxic. These are listed in the order of importance to have on the garden shed shelf, just in case:

Insecticidal soap: Works well against small, soft-bodied pests such as aphids and mites. Once it dries, it no longer kills pests. Follow label instructions carefully as it can burn sensitive plants especially if mixed too strong or applied in hot, sunny weather. Repeated applications will reduce yields of some vegetable plants, so don’t overuse it.

Horticultural oil: Works well on aphids, mites, scale, insect eggs and whiteflies. Follow label instructions and keep the spray mixed well as you apply it. Can also damage plants if not mixed and applied properly.

B.t. (Bacillus thuringiensis var. kurstaki): Kills caterpillars. This works best on young caterpillars, so don’t wait too long to make an application. Caterpillars must ingest the product to be killed. Be sure to use this product judiciously because it will kill those caterpillars that turn into beautiful butterflies.

Kaolin clay: A fine, clay powder used in food products, toothpaste and Kaopectate! When sprayed on plants it leaves a white residue that repels some types of insects and discourages egg laying. I put it on the list as research shows that it works to repel stink bugs if applied early on when the pests first arrive.

Potassium bicarbonate: Similar to baking soda (sodium bicarbonate) but more effective. Helps prevent some diseases of the foliage if applied prior to infection to protect foliage from disease spores. Repeat sprays are needed to maintain control. Not a panacea and results will vary with various foliage diseases.

Neem oil: Works well to prevent powdery mildew or to shut down an early infection of the disease. Also helps control some insects such as whiteflies, thrips, and squash bugs to name a few. Be patient as the product works as an anti-feedant (appetite suppressant) and disrupts the developmental stages of affected pests. So in most cases the results are not immediately apparent.

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