4 of the Worst Garden Pests and Problems to Watch for This September

As summer turns into fall, enjoy the bounty of your efforts—cut flower bouquets, baskets of garden-fresh produce, and a lush lawn—but don’t let down your guard when it comes to garden pests and other issues. After months of diligently watering during dry conditions, monitoring for insect damage, and staying on top of weed growth, you might want to hang up your hoe and retreat to the porch. Resist the temptation.

Despite the weather getting cooler, some of the pesky garden assailants are ramping up their activity. Stay in the game when it comes to pest and weed control, and your garden will respond with more flowers and fruit now, as well as a healthier start next spring.

1. Aphids and Spider Mites

These tiny, sap-sucking insects become more active in the fall, infesting flowering and fruiting plants. While they cause distorted growth and have the potential to weaken plants, the climate conditions often change before they do lasting damage.

What to do: Get rid of pesky aphids and spider mites with a strong spray of water from a garden hose. The water will dislodge and kill most of them.

2. Nuisance Insects

More bothersome than harmful in the garden, wasps, Asian lady beetles, picnic beetles, and ants are more bothersome than harmful in the garden. "They are attracted to damaged fruits and vegetables and honeydew from sap-feeding insects like aphids and spotted lanternfly,” says Dr. Laura Iles, entomologist at Iowa State University. Large numbers of these insects appear in gardens in the fall, seeking out sugary foods as they prepare to hibernate or gather energy to migrate, explains Dr. Iles.

What to do: “Because these insects are primarily bothersome and are only attacking damaged fruit and vegetables, we don’t worry about treating them,” says Dr. Iles. Limit the population by limiting their food source. Instead of leaving damaged fruits and vegetables, such as apples or tomatoes, on the plant, harvest them and toss them in the compost pile. With a little luck, most of the wasp, beetle, and ant population will migrate to the compost pile, too.

3. Weeds

In the fall, weeds are often more troublesome than insect pests. Cool temperatures and more frequent rainfall in late summer and fall will wake up dormant weeds. Both grass-like and broadleaf weeds will sprout new stems and leaves. If time permits before winter, they will produce flowers and seed for another generation of plants.

What to do: Get ahead of weeding chores next spring by controlling weeds in the late summer and fall garden. Be vigilant about rooting them out until the first hard frost kills them. Take time to dig out vexing taproots, such as those of dandelions and mulberry seedlings. Sift through the soil to get rid of weeds such as chickweed that spread wherever their roots touch the soil.

If weed pressure is more than you can handle, fall is a good time to apply a broadleaf herbicide on perennial herbaceous weeds, as well as vines such as bittersweet. Wait to apply until temperatures are between 65 and 85°F and there is a stretch of dry weather.

The best protection from a weed invasion is prevention. Spread a 2-inch-thick layer of organic mulch over your garden in early spring and refresh it as it breaks down during the season. Use a locally sourced mulch product, such as shredded bark from a local arborist or grass clippings from your lawn, to boost soil fertility.

4. Fungal Diseases

Late summer and fall bring cooler temperatures, more rainfall, and limited air circulation due to dense plant growth during the summer months. These factors combine to form the perfect ecosystem for fungal pests to take hold. Powdery mildew is a common issue. It causes white, powdery spots on leaves and stems. Brown or black leaf spot, along with rust, is also prolific when cool, moist conditions prevail in fall. Annuals, perennials, and turfgrass are all susceptible to fungal disease damage.

What to do: Good air circulation between plants limits fungal pests from growing on stems and leaves. Take time to thin overgrown plants in late summer, cutting select stems off at ground level to allow air to move freely around plants. Remove and destroy infected plant material to prevent diseases from spreading.