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The Plant Lady: Spray trees now to get rid of pesky infections and pests

Here’s when and how to spray your fruit tree to avoid leaf curl

‘Plant Lady’ Marlene Simon, a horticulturalist at UC Davis, demonstrates the best way to spray your fruit tree to protect it from fungus.
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‘Plant Lady’ Marlene Simon, a horticulturalist at UC Davis, demonstrates the best way to spray your fruit tree to protect it from fungus.

This is the perfect time of year to be thinking about spraying trees during their dormant season. I’ll give two examples of conditions which warrant spraying: fungal infection and pest infestation.

First, let’s look at a common fungal infection. A question I get asked in spring is “why are my peach or nectarine leaves curling?” Leaf curl is caused by the fungus Taphrina deformans. The spores, spread by air or rain, thrive in wet conditions. When they germinate in spring, they infect the plant’s leaf tissue, causing leaves to turn red, curl and pucker.

If the infection is severe enough, the tree will defoliate and fruit production will be decreased. If the leaves fall off, a new set will immediately grow back with no symptoms. However, the spores will lay dormant on the tree surface during the dry heat of summer. The following spring the spores will germinate, causing the symptoms to re-emerge. If peach leaf curl is not controlled and allowed to manifest year after year, it can lead to an unhealthy, unproductive tree.

The dormant season is the time to prevent this fungal infection from attacking your trees, or treat ones with a prior outbreak. Unfortunately, I have to tell people there is no immediate action to take by the time symptoms of peach leaf curl manifest on peaches/nectarines in spring.

The good news is that depending on the severity, current year fruit production may not be impacted. However, even if current year production is ample, it is critical to treat the affected tree the following winter. So how to treat this problem? Liquid copper sprayed on the trees can prevent or minimize this infection. Here’s how:

Liquid copper is a generic term for CME (Copper Metallic Equivalent). The brands sold at nurseries are a copper ammonium complex with 8% CME.

Best practice is three sprays done before the buds break in mid to late February, particularly if it’s a wet winter.

Thanksgiving, Christmas and Valentine’s Day are good target dates to spray.

Spray on a dry day with at least one dry day following.

Apply using a hose-end-sprayer — I like the Ortho Dial N Spray (sold at most nurseries). No measuring is needed. Simply pour the copper into the container, attach the hose and set the sprayer dial to recommended rate on the copper label and spray.

Spray the copper onto the tree until all limbs are coated and it is dripping off the tree.

Any unused copper can be poured back into original container.

Spraying a petroleum-based horticultural oil onto the tree directly after copper application will help the copper “stick” to the tree. This oil is commonly found at nurseries, and is applied using the same hose-end sprayer.

Although the example above is about peach leaf curl, liquid copper can also be used to control other fungal infections on fruit trees, roses, grapes and ornamentals. These include brown rot on apricots, powdery mildew on roses and grapes and various leaf spots on many ornamental plants.

Next, let’s look at a few examples of pest infestation that can be treated by winter/spring spraying. Mealybugs, aphids, scale, whiteflies and thrips are phloem sucking insects that can be controlled using oils. These insects pierce into the plant’s sugar transport system (phloem) and suck out the tree’s carbohydrates. When their numbers are high, their sugary excrement can coat a plant or tree and drip down onto surfaces below (often mistaken for the plant dripping sap). Most of these insects either overwinter as adults, eggs or larvae on a plant.

The dormant season is the ideal time to spray a horticultural oil to control these various pests. During winter/spring these sprays can be applied to evergreen and dormant plants, but avoid applying when a frost or rain is expected. It is crucial to read the product label carefully to see if any side effects may occur on specific plants.

Application/timing — adhere to the same guidelines as stated above for liquid copper.

For winter/spring spraying, I prefer a petroleum-based horticultural oil.

Some oils will be labeled and marketed as “dormant” or “all-season.” Regardless, due to our high temperatures starting early in the year, it is ideal to limit spraying plants to the winter season to prevent oil-induced burning.

I set an upper temperature limit of 85 degrees Fahrenheit for spraying of any oil.

The horticultural oil will smother the pests, killing them.

The oil is short-acting ,so there is less chance of beneficial insects (such as ladybugs and lacewings) coming in contact with it.

Ask The Plant Lady

Q: My Ficus lost its leaves when I moved it [from one location inside my house to another]. Is it dead?

A: The common houseplant Ficus benjamina is very finicky when moved. Even with slightly different light exposure and/or temperature, it will drop its leaves and put on a new set more suited to its current environment. This can take upwards of a few weeks, so avoid moving it during this period. Reduce watering until new leaves emerge — the Ficus has reduced hydration needs without leaves. If you are concerned if the plant has died, lightly scrape the bark. If green underneath, then it is still alive and just needs more time to acclimate and put new leaves on. Ficus require moderate to bright light inside and prefer to be slightly potbound, meaning you only transplant to a larger pot if the roots are literally bursting out of the original.

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