Master Gardener: Aphids and spider mites and grasshoppers, oh my
For Steamboat Pilot & Today
With our recent hot weather and watering restrictions, your plants can get stressed and that is when we often see summertime pests in our Steamboat Springs gardens. You may remember basic plant pathology from your high school biology class. If not, here are the basics:
The roots of the plant gather nutrients and water from the soil, which travels up the xylem and allows the shoot to grow and develop foliage. The leaves gather sunlight turning it into sugar molecules, a process called photosynthesis, which feeds the plant via the phloem. This sugary liquid is called plant sap.
Aphids are tiny insects that love plant sap. Typically, 2mm in length with a soft, pear-shaped body, long antennae and two short cornicles protruding from their hind end, they are often found in groups on the underside of leaves. They can range greatly in color as there are over 350 different species. They eat the plant sap, which can result in leaf curling, yellowing or stunting.
Most aphids like new plant growth and excrete a sticky liquid called “honeydew” onto the leaves, which attracts ants and sometimes bees, wasps and other insects and also encourages mold growth. Aphids multiply quickly so it is important to get them under control before reproduction starts. To get rid of these pests:
• Introduce some of their natural predators: lady bugs, lacewings or parasitic wasps
• Spray the plant with a cold water stream physically removing them and their sap
• Try using soapy water, an insecticidal soap, Neem oil or a horticultural oil. As a last resort, insecticides containing the active ingredients acephate, bifenthrin, and imidacloprid can be effective — follow all label instructions.
Spider mites also eat plant sap. Smaller than the size of a pin head, they have eight legs and can be red, brown, yellow or green. They also gather in groups on the underside of leaves in a web-like silk spun to protect themselves from predators and their eggs. They have mouth parts that eat the plant sap leaving speckled leaves, leaf discoloration or leaf scorching.
Hot, dry and dusty conditions attract mites. Some of the same procedures used to get rid of aphids also applies to spider mites, such as spraying to physically remove and washing with soapy water, an insecticidal soap, Neem oil or horticultural oil. Natural predators of spider mites include lady bugs, predatory mites, minute pirate bugs, big-eyed bugs and predatory thrips.
Chemical control of spider mites generally involves pesticides that are developed specifically for spider mites (miticides or acaricides). The use of pesticides can increase the presence of spider mites, killing off their natural predators. A second application is usually required to kill the eggs.
Grasshoppers are easily recognized insects and can be the most damaging insects and difficult to control due to their mobility. There are over 100 species of grasshoppers in Colorado alone. They lay their eggs in dry, undisturbed soil encouraged by a hot dry spring. They are 1 to 2 inches long and feed voraciously with their mouthparts on grasses and foliage. They leave jagged and tattered holes in leaves.
To control these pests:
• Introduce natural predators of grasshoppers such as preying mantis, chickens, ducks or cats. Other natural predators are garter snakes. birds and coyotes.
• Leave a tall grass area nearby with a short grass border. Grasshoppers are reluctant to enter the short grass where they are not protected from predators.
• Roto-till your garden in the spring to kill overwintering eggs.
Use row covers, use Neem Oil, use Nolo Bait, an organic bait that kills grasshoppers and passes the infection on to others, and as a last resort, spray an insecticide such as carbaryl (Sevin).
Spraying insecticide is most effective in early June but can be costly for large areas. Additionally, these sprays are broad spectrum, meaning they will kill pests including beneficial insects such as bees, lady bugs and mantises.
The best way to prevent pests in the garden is to keep your garden well watered to encourage healthy plants.
Penney Adams moved to Steamboat Springs last June from Hilton Head, South Carolina, and recently completed the Master Gardener program.
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