Grass Seed and Dormant Oil

The problem with reseeding in the spring is that the good grass seeds will need the same weather conditions as the new crabgrass seeds and so they both come up together. Elena Elisseeva/Shutterstock

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

Answer: 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, we need to diagnose what the dead clumps are. If they are annual grasses like 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. If they’re dormant perennial grasses like nimblewill, then we can dig them out now or wait until spring when they start to grow to spray them with an herbicide.

The problem with reseeding in the spring is that the good grass seeds will need the same weather conditions as the new crabgrass seeds, and so they both come up together. If the areas of dead grass 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) and then take good care of the existing good grass with water and fertilizer to cause the good grass to spread into the bare spots.

Question: We have several plants in our landscape that we read should be sprayed with dormant oil. What in the world is dormant oil and how does it work?

Answer: 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, and will be covered with the oil. Many insects spend the winter on a plant in the egg stage of life and hatch in the spring as the plant begins to grow.

In the past, oils sprayed on plants in the summer when the insects were active also 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. They smother the eggs of the insects, thus preventing the first batch of insects from damaging the plant.

Newer oils have come to the market. Year-Round Spray Oil from Summit Chemical and All Seasons Spray Oil from Bonide control pests on even the most sensitive plants such as roses, impatiens, philodendrons, and ferns. They can be used any time during the year because they won’t harm plant buds, shoots, and leaves. These oils are odorless, environmentally responsible insecticides that kill a wide variety of insect pests including aphids, whiteflies, spider mites, mealybugs, scale, thrips, fungus gnats, some caterpillars, leaf beetle larvae, lace bugs, and others. Because of their low toxicity, year-round oils can be used on garden plants and fruit trees right up to the day of harvest. They should be available from local garden stores.

As always, follow the label directions. For instance, many oils will list a temperature range that they should be applied in. The oils may damage flowers or harm bees if applied while the plant is in bloom. Some plants may be sensitive to the oil, so spray a small area and wait a day to see if any damage appears. Don’t apply too much at one time or during one season.