You should have used the most important bug spray of the year – dormant oil sprays – in winter.
Why then? Because then insects that are susceptible to these sprays are the most susceptible.
Then why didn’t you do it? Because there was no problem.
Dormant oil sprays (sometimes referred to as horticultural oils) are “insurance sprays”. Without insurance sprays, spray insecticides if you see problems. This will force you to root out the problem (and the error that is causing the problem) if it comes up.
Examples of insect pests you experience without dormant oil sprays include aphids, whiteflies, scale insects, and mites – collectively called the soft-bodied insects. Dormant oil sprays won’t touch the drill bits or the ugly leaf bugs.
Dormant oil sprays are applied to trees and shrubs on warm, windless days in winter after they have been pruned. The entire tree or shrub is sprayed from head to toe.
I usually give it one last shot of dormant oil right at the foot of those trees and shrubs where insects like to take shelter in winter. Also kill and remove any weeds that grow in the area. Wintering insects also like these places.
Maggots live underground in the ground and chew on plant roots and eventually transform into many different types of flight beetles such as the so-called June beetles and hornworms, which feed on the leaves of tomatoes, grapes, and other foods. Since many maggots live underground, they are only seen when plants like Lantana begin to die.
The most effective and long-term controls for many types of maggots are the insectivorous nematodes, which you can buy from online sources. Remember, these should be applied to damp floors and kept refrigerated until used.
Aphids come on the scene first as soon as new leaves and flowers appear. In preventing curled and sticky leaves, you will likely see the greatest impact from dormant oils used in winter. If not used, mother aphids will produce live juveniles within hours of arriving on leaves in spring.
I usually recommend checking ants nearby as they help spread these aphids on the leaves. Ants are subordinate to the problem, but it is worth checking whether they are present in large numbers.
An evergreen tree forgotten during the winter sprays of dormant oil is the Italian cypress. A common pest of the Italian cypress that causes a tan in the hot summer months is the spider mite. Spider mites are easy to control with an application of dormant oil in late winter rather than waiting for an infestation to occur.
Unfortunately, dormant oil sprays do nothing to combat bores or the ugly plant bugs with leaf feet. These guys are strong fliers and can come into your yard from your neighbors’ plants. Unless a collaborative effort is made to reduce these pests, other methods of control are available in addition to spraying insecticides.
Q: I see a large yellow bee flying around my newly planted oak. Do they sting?
A: Yes, they do. Even the gentlest of bees and wasps sting when they get worse. I can’t tell you which bee your tree has, but if it looks like a bee and is flying like a bee, then it’s probably a bee or a wasp. And most likely it can sting.
This bee is likely attracted to the sticky, sugary honeydew that aphids produce. These aphids inhabit soft, tender new growth as soon as it appears. If your tree is evergreen, like most oaks, then these aphids have likely spent the winter sheltered near this delicate source of spring forage.
Mother aphids keep their wings through the winter and fly to new growth when it appears to be starting a new colony of fledglings. These newborn aphids are wingless.
Dormant oil applications in winter would have significantly reduced or eliminated them in spring. Right now, several soap sprays aimed at the leaves will dissolve the sticky honeydew, reducing its attractiveness to bees as well as the number of aphids.
Do this until the temperatures get hot. As with any organic spray, soap sprays should be used more frequently to get the same results, and they’re indiscriminate in what they kill.
Q: You mention wood chip mulch instead of stone on the ground surface for plants, but I find that wood chips provide protection for cockroaches and other pests that cause other problems. For this reason I prefer rock.
A: The main value of wood chips added to the surface of the soil instead of rock is to bring organic matter back into the soil as it decomposes or decomposes. Stones will crumble, but end up mineralizing the soil instead of adding organic matter to it.
This mineralization can last three to five years after planting, but some plants turn yellow during this time while others don’t. Some plants grow best when organic matter is continuously added to the soil instead of minerals.
Insects like cockroaches and pillbugs are decomposers that help break down wood chips into smaller pieces. Earthworms are often next in this process, followed by microorganisms such as bacteria and fungi, which further break them down into plant nutrients.
If you’ve put lots of wood chips on your landscape, expect lots of decomposers too. These pesky animals must be handled in such a way that they are not a problem.
You are attracted to water, food, and warmth. Use your favorite insect spray in watering boxes and keep wood chips 2 to 3 feet from the foundation of the house.
Applied water shouldn’t be closer to the foundation anyway. Remember that plant roots follow where the water is applied. No water applied, no root growth.
Your home is inviting when the outside temperatures are not inviting. Apply a barrier spray in late spring and early fall to keep these insects out of your home.
Your preferred barrier spray, applied to the foundation of the house, will help ward off annoying animals when they need a temperature change. The same principle applies to strawberries and other berry fruits such as tomatoes that touch the ground.
Q: I have roses with sticky leaves from aphids that feed on them. I have to get them under control before they become a problem. I found some insect and disease control sprays in the nursery that have worked in the past. Any opinion on her?
A: They work, and if you’re not against insecticides, use them. If you look at the list of ingredients, the pesticides used to control insects and others used to control disease contain both an insecticide and a fungicide. You usually don’t need both ingredients.
In climates with high humidity, rose diseases such as black spot, powdery mildew and botrytis are widespread. In these climates, applying a multipurpose insecticide plus fungicide spray is likely a good idea.
In our climate, diseases are less of a problem due to the lower humidity. I would focus on one insect control chemical rather than a combination of two chemicals. Why use a fungicide when you don’t need it?
Q: One of my roses is wilting despite being watered regularly. It’s getting morning sun. My other roses don’t do that. What’s happening?
A: This sounds like western flowers are damaging the rose petals. Thrips are very small insects that tear rose petals and cut into pieces. You can only see them if you use a magnifying glass.
They will spend the winter waiting for new growth before attacking. As soon as the rose buds form, they attack the soft petals.
Thrips tear and chop up soft plant tissue, licking up the fluids released by the cracks like a dog licking water from a bowl. When these insects are present in large numbers, they will attack rose petals while they are still in their buds, leaving them closed but damaged. They also attack nectarine fruits when they are very small, causing scarring.
The usual remedy is to remove all of the flowers and rid the plant of this pest, then spray it with a dormant oil when it is early in the season. Spinosad sprays have been effective in keeping thrips at bay. They don’t kill them like other more toxic sprays but offer a safer alternative because spinosad is considered a natural product.
Bob Morris is a horticultural expert and professor emeritus at UNLV. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.
