Dealing With Common Garden Pests and Diseases

It’s safe to say that every gardener will eventually encounter a pest problem. But there are many Earth-friendly strategies to minimize damage and keep your plants healthy.

Regular inspection and monitoring of crops is the first step toward prevention. Look for holed leaves, shriveled or mangled growth and spots on fruits to identify issues quickly and respond accordingly.

1. Aphids

While they might look like a nuisance, in small numbers aphids do little harm. These soft-bodied insects feed on a wide range of garden plants, using their long, needle-like mouthparts to pierce leaves and stems. As they feed, they secrete a sticky substance called honeydew, which encourages the growth of black sooty mold and spreads plant viruses.

Invasive aphid populations are best dealt with by a combination of methods. Regular monitoring of the garden is key – check for curled or wilted leaves and stems from week to week. Natural predators, including ladybug beetles, green lacewings and parasitic wasps, are good for keeping aphid populations in check.

2. Leafhoppers

Leafhoppers are a common problem with vegetables, fruit trees and ornamentals. Identifying them early can prevent an infestation.

Many species complete several generations in a year, and heavy numbers of these insects can quickly devastate crops. They puncture the leaves of susceptible plants to siphon off plant juices, causing stippling or distorted growth. They may also transmit organisms that cause disease.

A regular inspection of your garden can help you determine the level of damage and if it warrants action. Grow companion plants like flowering dill, chives and sweet alyssum that attract lacewings, damsel bugs and other natural predators that prey on leafhoppers.

3. Leafminers

When you see squiggly trails of white squibbling across leaves, or big blotches of no chlorophyll, you probably have leafminers, the larvae of moths, sawflies, beetles and flies. They feed by burrowing into leaves to eat the tissue inside.

They lay eggs that hatch in warm weather, then chew into the layer between upper and lower leaf surfaces, creating a “mine.” When they finish their life cycle, they drop to the ground to pupate. Five to ten generations can develop each year.

Regularly monitor your garden. Use a systemic insecticide such as spinosad (sold as Monterey) at green-up to control leafminers. Plant dill, fennel and yarrow to attract beneficial insects that prey on leaf miners.

4. Whiteflies

Whiteflies are a serious problem for both vegetable and ornamental gardens. They suck sap from plants, weakening them over time and leaving them vulnerable to disease. They also secrete a sticky substance that attracts ants and raises the risk of fungal diseases and sooty mold.

They are particularly troublesome for indoor plants and greenhouse grown vegetables. They’re also a problem on many outdoor vegetables such as beans, brassicas, cucumber, eggplant, pepper, squash, tomato, and okra. Ornamentals like hibiscus and poinsettia are susceptible as well.

Vigilant inspection and monitoring will detect early infestations, and yellow sticky traps (available commercially) can help monitor and reduce populations. Plants that naturally repel whiteflies include catnip, bee balm, and chives.

5. Beetles

These iridescent green beetles are a major threat to many garden plants, and they can also damage landscaping trees and shrubs. They chew away at the soft leaves, leaving behind a lacy skeleton. Look for signs of beetle problems, such as wilted or dying plants, spots on fruits, or holes in wood.

Frequent garden patrols can prevent beetles from gaining a foothold, but once established they’re difficult to eradicate completely. Avoid sprays or dusts, which can be toxic to honeybees and native pollinators. Instead, attract native parasitic wasps and flies that lay their eggs inside the beetles and kill them. Also, restrict irrigation to a minimum in July and August.

6. Fungus

Fungus is everywhere in gardens, yards and landscapes. While many types of fungus aren’t helpful to plants, others do important work in decomposing organic matter and nutrient cycling.

Fuchsia rot, downy mildew and powdery mildew are common fungal diseases that attack plants. Leaf spot, rust and stinkhorns are other fungal pathogens that are troublesome in the garden.

Fungus is opportunistic and strikes when a plant’s weakness becomes evident. Fortunately, savvy cultivation practices and an effective fungicide help prevent and control most fungal diseases. Fungicides are especially important for growing fruits and vegetables. They’re also a good choice for reducing the spread of plant diseases and insects, such as beetles.

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