Even in the best-managed vegetable gardens-ones with soil rich in compost, and a diversity of plants to encourage natural predators-certain pests will occasionally get out of hand.
There is a nugget of truth in the old maxim that insects are most likely to gang up on plants that are already unhealthy because of a soil nutrient imbalance or drought. This is the case, for examply, with some aphid outbreaks. Unfortunately, the maxim doesn’t come close to explaining all our pest problems.
For instance, vegetables are bred largely for yield and flavor, often at the expense of natural resistance to pests. Furthermore, all vegetables are tender and nutritious, and this fact is not lost on a wide array of insects. With cabbageworms, hornworms, bean beetles, and Colorado potato beetles, the better you’ve made the soil, the more they like your vegetables.
If these or similar insects are in your neighborhood and you are growing their favorite crops, you are almost certain to have a pest outbreak. Given these realities, what should you do? Most likely you’ll consider using some kind of insecticide.
Here we summarize the latest experience and expert advice about the sprays and dusts used to control pests in vegetable gardens.
Integrated Pest Management
Vegetable garden pest control begins with basic good gardening common sense, such as choosing varieties that are resistant to pests in your region, preparing the soil well and providing regular irrigation.
It helps to have in your garden a diversity of plants and habitats. Water, even a very small pond, is attractive to many insects and other creatures. Likewise, an abundance of flowering, nectar-bearing plants will encourage and sustain parasitic and predatory insects.
The next step in a least-toxic pest control strategy is to employ barriers, such as row covers, to exclude pests altogether. Using a pesticide, any pesticide, is always the measure of last resort. You spray or dust late in the game, when the pest insect is clearly way out of control and an important crop is at risk.
When a pest first arrives, or when prior experience tells you it soon will, the best approach is to develop a strategy of control. Integrated pest management (IPM) is a pest problem-solving process that includes considerations such as pesticide resistance, natural biological controls and pollution, in addition to problems caused by the pest. IPM integrates many pest-control methods and minimizes insecticide use, particularly of the more toxic, broad-spectrum kinds.
When a problem does occur, it is essential to correctly identify the cause. The beetle you see near a hole in a leaf may be a predator. But if it is damaging your plants, simply pick it off. Also consider that doing nothing at all-letting nature take its course-is often the best approach. Always use simple, noninvasive remedies first.
Sensible Insecticides Used Responsibly
Sometimes pest problems are not adequately managed by natural, cultural or mechanical control methods. Insecticides are often the only control option that remains. The prime factors in determining pesticide safety are:
- How specific it is to particular insects?
- How toxic it is to humans and nontarget organisms?
- How quickly does it degrade.
Remember, in a vegetable garden it is virtually impossible to spray just the one thing you want to spray. Other crops (perhaps ready to pick) are always nearby, so you want to stay away from insecticides that don’t break down quickly.
Choose an insecticide that is as specific to the pest at hand as possible and then use as little as possible. If only one spray will do the job, use only one spray. For the long-term health of your garden, the less spray you use, the better.
Remember, too, that just because an insecticide has a botanical origin or is considered acceptable to organic gardeners, it still contains a toxin and is not automatically safe for humans.
Vegetable Pest Remedies
Gardeners today have at their disposal a handful of effective and safe pesticides. When you have to spray to save your crop, here are the insecticides to consider using, with their characteristics, positive and negative.
Bt. The bacterium Bacillus thuringiensis (Bt) was identified in 1911 by the biologist E. Berliner, who found it infecting pupae of the Mediterranean flour moth and other insect larvae living in grain warehouses in the German town of Thuringia. It wasn’t until the 1960s, however, that entomologists learned how to make it into a powerful and very pest-specific insecticide.
Advantages of Bt include safety-it is essentially nontoxic to humans, other mammals and birds. The label specifies no waiting period between application and harvest. It is also highly selective so is easily incorporated with existing natural controls. A limitation of Bt is its slow action. After pests consume it, their feeding slows down. But their death won’t occur for two to five days. Bt is also perishable. Most formulations are less effective after a few years of storage.
Bt exists naturally in most soils. Different strains of Bt occur that produce protein crystals toxic to certain insects. The strain for most caterpillars is B. t. kurstaki. Commercially prepared Bt spray or powder has no effect on adult butterflies or moths. Remember, however, that not all caterpillars are pests.