Signs of spring are everywhere we look: trees and shrubs are full of blossoms, flowers are bursting into bloom, bees are buzzing all around, and aphids are stacking up on rose buds. What to do?
Aphids are a common occurrence in the spring. They rapidly appear in large numbers when the weather starts to warm and are most prevalent between 65 and 80 degrees. Look closely at many plants and you'll notice that aphids come in a variety of colors, especially green, yellow, brown, red and black. They are small, soft-bodied insects with mouths like skinny straws that pierce leaves and green stems then suck out the plant's fluid.
Plants can tolerate some aphid feeding with no apparent damage. However, aphids also have the ability to carry some plant viruses from an infected plant to a non-infected plant. In ornamental plants, most plant viruses are cosmetic, but in vegetables like squash and tomatoes these viruses damage the produce.
Well, all of that plant juice has to go somewhere and since aphids don't swell up to the size of a balloon, they excrete the sugary sweet plant sap right back on to plant leaves. This digested substance is called "honeydew" and it is easily seen glistening on plant leaves. Honeydew is sticky and attracts sooty mold spores from the air. Sooty mold is a fungus that lives off of the honeydew and as it grows it becomes black, hence the name. Besides blackening the leaves and creating a mess, it deprives the leaf from maximum light for photosynthesis and when sooty mold is abundant, the plant can be weakened.
Ants climbing up and around your plants are another sign that honeydew is around. Ants also feed on honeydew for nourishment and will protect the aphids from natural predation. There are several beneficial insects that prey on aphids including ladybugs, lacewings, damsel bugs, and hover fly larvae, which can all significantly reduce an aphid population. When ants succeed in warding off beneficial insects, the good bugs can't do their job of keeping aphids under control. Controlling the ant population will help control the aphid population.
Roses are particularly susceptible to springtime aphids, and it is very common to see them in late March and throughout April when the bushes have started to leaf out and send up the first blooms for the season. A question heard over and over again in the spring. "My rose buds are covered with aphids, what should I do"?
With aphid control, timing is everything. Different aphid species feed on different plants, but identification is not needed when it comes to trying to control them in your garden.
Reaching for a broad spectrum insecticide is the last choice and can do more harm than good when applied in the spring because beneficial insect populations are knocked down to zero. It is better to suffer a little aphid damage in the spring and let the beneficial populations build up by preying on the aphids. This will keep more insect pests under natural control (also called biological control) throughout the summer.
Does that mean you don't do anything in the springtime? Not at all. First thing to do is check the plants daily during this time of rapid new growth. As aphids build up, spray the plant with a strong spray of water to knock off the insects from the buds and leaves. For heavy infestations I hold clusters of buds in one hand and the spray nozzle in the other.
Certain measures will help with prevention. Don't over fertilize in the spring, since aphids love that new lush growth. When you do fertilize, use a slow release or organic fertilizer or compost. Prune out heavily infested leaves and stems. Ladybugs and lacewings will naturally appear in your garden and will gradually reduce the aphid populations.
If you are unable to control the problem by hosing off the plants and beneficial insects, then try the least toxic insecticides. Insecticidal soaps, soap pyrethrum mixtures, and neem oils are a safe alternative that work by smothering the insect. Make sure you have complete coverage by spraying with a high volume of water and target the underside of the leaves, as well as the tops. These products only kill what is present and do not have residual activity. Always follow the directions on the container and use when the temperature is below 90 degrees. They are readily available in nurseries and garden departments.
Systemic products are a final control possibility, particularly for rose bushes. They should never be used on garden vegetables or fruit trees. This should be your last resort choice, since they are toxic to almost all insects. Most systemic products are actually 3 products in 1 container: a fertilizer, a broad spectrum insecticide, and a fungicide for some disease control. Never use more often than every 6 weeks and it is of utmost importance to strictly follow the application amounts detailed on the product label. These products are available in a liquid form to be sprayed on the plant or as a granular form that is applied at the base of the plant and watered in to the soil.
So remember when considering different control tactics for aphids, choose the methods that moderate aphid populations and do not disrupt the natural population of beneficial insects. You're in for a constant battle with bugs, if you do.
The Master Gardeners will be available to answer your questions at a few select locations in the next few months!
Ace Hardware, Visalia - first Sat./every month
Luis Nursery, Visalia - second Sat./every month
At this time, we are not in the office to answer phone calls, but if you send us an email or leave a message on our phone lines, someone will call you back!
Master Gardeners in Tulare County: (559) 684-3325; Kings County at (559) 852-2736
Visit our website to search past articles, find links to UC gardening information, or to email us with your questions: http://ucanr.edu/sites/UC_Master_Gardeners/
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