Crabgrass and Dormant Oil

If the areas are smaller than a dinner plate, it would be better to apply crabgrass preventer to stop all grass seeds from growing. Christian Delbert/Shutterstock

Q: Does dead crabgrass look like white dead clumps dotted around the lawn? If so, should one dig each one up and fill in with fescue seed, fertilizer, and dirt?

A: At this time of year, all dead annual and many dormant perennial grasses look like white dead clumps. If the good grass in your lawn has some signs of green and there are scattered dead grass plants, then you could reseed those spots. If the dead grasses are annual grasses, such as crabgrass, they died with the frosts in the fall and, at this time, are acting as mulch on the bare spots and don’t need to be removed. The problem with reseeding is that the good grass seeds will need the same weather conditions as the new crabgrass seeds, so they may both come up at the same time. If the dead areas are large, using sod may be better. If the areas are smaller than a dinner plate, it would be better to apply crabgrass preventer to stop all grass seeds from growing (including any seeds you plant). Then, take good care of the existing good grass with water and fertilizer to cause the good grass to spread into the bare spots.

Q: We have several plants in our landscape that we forgot to spray with dormant oil over the winter. Do you think it is too late to apply now?

A: There are very refined oils known as horticultural oils. They almost have the consistency of water. They are sprayed on plants to smother some kinds of insects or their eggs. Some insects don’t move quickly, such as scale insects, mealybugs, and spider mites, so they will be covered with the oil. Many kinds of insects spend the winter on a plant in the egg stage of life and hatch in the spring as the plant begins to grow. The oil smothers the eggs of the insects, thus preventing the first batch of insects from damaging the plant.

In the past, oils sprayed on plants with leaves smothered the leaves and caused as much damage to the plants as the insects. Dormant oils are used when the plant is dormant to prevent much of the damage. But many times, we didn’t know there were insects on the plant until the spring, when it was too late to apply the dormant oil.

Newer oils have come onto the market. Year-Round Spray Oil is a lightweight horticultural oil manufactured by Summit Chemical that effectively controls pests on even the most sensitive plants, such as roses, impatiens, philodendrons, and ferns. It can be used any time during the year because it won’t harm plant buds, shoots, or leaves. It is an odorless, environmentally responsible insecticide that kills a wide variety of insect pests, including aphids, whiteflies, spider mites, mealybugs, scale, thrips, fungus gnats, certain caterpillars, leaf beetle larvae, lace bugs, and others. Because of its low toxicity, Year-Round Spray Oil can be used on garden plants and fruit trees right up to the day of harvest. It should be available from local garden stores.

Courtesy of Jeff Rugg

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