Marin IJ Articles
April 17, 2009
You generally don't need a calendar to tell you that spring has arrived. The days are getting longer and warmer, trees are bursting with brilliant blossoms and luscious new growth, birds sing their tunes in the hopes of attracting a mate and tender new growth emerges from those tiny vegetable seeds you so carefully planted last month. And it's also when the bane of the garden season hit us in full force - bugs. A portion of a tree, suddenly denuded of its leaves, sports in its place a wriggling clump of fuzzy caterpillars; a pulsating mass of tiny pests cloak the new growth on your roses, elderberries or peach trees, or seedlings just beginning to develop, disappear overnight.
Who are these marauders and how does one deal with them?
A group of Master Gardeners working at the help desk recently identified some
of the major villains in the spring garden - aphids, caterpillars (particularly tent caterpillars), snails and slugs, thrips and scale. A few of these garden pests are easy to recognize and manage while others require more diligent monitoring and rigorous control measures.
One of the most prevalent and recognizable spring pests is the aphid. These small, pear-shaped, often green soft-bodied insects suck the juices out of a wide variety of landscape plants and agricultural crops.
Frequently seen in masses covering new growth on plants, they can weaken a plant, cause leaves to yellow, curl or drop early or distort plant stems or fruit. As they feed, they produce honeydew that attracts ants that in turn, protect the aphids from various predators. Any honeydew the ants don't consume can end up supporting the growth of black sooty mold.
The best method of control is prevention. Aphids love rapidly growing supple new growth on plants that get a lot of nitrogen fertilizer, so don't use any more than needed.
Aphids are the favored food of many natural enemies, including lady beetles, soldier beetles and lacewings, so encouraging beneficials into your garden can often keep aphid populations in check. A blast of water is usually enough to knock them off the plant, but if you need something more, try using an insecticidal soap, or a botanical insecticide containing neem oil.
The tent caterpillar, a rather furry-looking reddish brown with blue spots and tufts of orange to white hairs, is also easy to recognize. Generally seen in huge numbers within their silken webs, they feed on deciduous trees and shrubs including ash, birch, fruit and nut trees, madrone, oak, poplar, redbud, toyon and willow. Their damage can be slight to serious on individual trees depending on the level of infestation.
Inspect plants regularly, and if you see these voracious pests, prune out the infested branches and dispose of them.
Snails and slugs
You may not see snails and slugs, but you can sure see their damage. These slimy mollusks emerge from hiding at night and chew holes in leaves and flowers of many garden plants and fruit.
Slugs (they don't have an external shell) and snails move by gliding along on their muscular "foot" that constantly secretes mucus forming their trademark silvery trail. They're hermaphrodites - each snail is both male and female, hence their ability to reproduce so rapidly.
Check your plants early in the morning and you'll likely find them moving back to their daytime hiding places - ivy, weedy areas, debris, boards or other dark, moist, protected locations. An integrated management approach that includes reducing moisture and hiding places, trapping, barriers and handpicking is the most effective.
Baits can be helpful, but be careful when using around children and pets; products based on iron phosphate (available under many trade names including Sluggo and Escar-Go) are not toxic to plants or animals and break down to provide some additional iron for the soil.
Thrips are generally bad news for the gardener. Not visible to the naked eye, they often feed within buds and furled leaves or other enclosed parts of the plant. These extremely small insects cause unsightly, cosmetic damage to a wide range of plants. Western flower thrips, Frankliniella occidentalis, one of the most common thrips, favors many herbaceous ornamentals (impatiens, petunia), vegetables (cucurbits, pepper), fruits (grape, strawberry) and some shrubs and trees (rose, stone fruit).
Managing thrips can be a challenge and preventing an infestation is the best option. Along with good cultural practices, providing habitats that encourage beneficial predators such as green lacewings and minute pirate bugs can help keep populations in check.
Where appropriate, use barriers such as row covers to exclude them. In small gardens, a spray of water can knock them off the plant. Limit heavy applications of nitrogen fertilizers as these actually promote higher populations of the pests (along with aphids).
If preventive measures aren't adequate, prune out damaged or infested plant material and discard. Healthy, vigorous plants should outgrow the damage.
Scale looks like bumpy, crusty bark or fine ash on branches of trees and shrubs. They are another insect that sucks sap from the plant, weakening it and causing dieback of twigs and stems. They also produce sticky honeydew the ants love and that supports black sooty mold.
Your best bet is to prevent infection through good garden sanitation, monitoring susceptible plants and treating any visible signs immediately. Prune away and destroy infected canes. You can apply a horticultural oil spray after pruning in the winter that will smother the pest; repeat spraying may be necessary.
For more information on any of these springtime pests or garden problems, contact the Marin Master Gardener Help Desk, 1682 Novato Blvd., Suite 150B. It is open 9 a.m. to noon and 1 to 4 p.m. weekdays. You can also ask your questions by phone or e-mail, at 499-4204 or firstname.lastname@example.org.