Grubs feed on plants this time of year

This is the time of year when grubs are feeding on the roots of plants. Many of these types of grubs are the same types that feed in compost piles. Some people refer to them as “compost worms.”

The adults of these compost worms are frequently large beetles that we see flying in June and July. The eggs of these larvae or worms were laid in March. If there are lots of them, their feeding in the months of March, April and May can cause plants such as lantana and agave to decline and even die.

Control of these immature insects is usually accomplished by applying chemicals as granules or a liquid diluted in water and poured around the plants’ roots. Sprays or dusts applied to the leaves or foliage will not control these types of pests.

One of the most effective chemicals has imidacloprid as an active ingredient listed in its label and is sold by any nursery, garden or big-box store. But any chemical listed for controlling “grubs” should work and is permitted as long as it includes the plant that your treating on its label.

If you have any further questions, email me at extremehort@aol.com, or visit my blog, http://xtremehorticulture.blogspot.com.

Q: What time of year should a lawn be fertilized?

A: For tall fescue lawns, which make up 99 percent of our residential lawns, I recommend fertilizing at least three times per year if you are using recycling mowers: Labor Day, Memorial Day and Thanksgiving.

If you have Bermuda grass, I recommend Labor Day, Memorial Day and Fourth of July. You don’t want to apply anything to Bermuda grass in the fall if you are planning to overseed your lawn to keep it green during the winter.

Most fertilizer bags recommend a rate of 1 pound of nitrogen per 1,000 square feet of lawn area. I consider this excessive unless this is an ultrahigh-end fertilizer containing lots of slow release nitrogen. You can cut that rate in half and get very good results.

You can download a copy of my fact sheet on turfgrass maintenance from: https://www.unce.unr.edu/publications/files/ho/2010/fs1070.pdf.

Q: I have a queen palm that has recently begun to yellow. It’s done well every year until this spring. I apply Miracle-Gro to the soil around it every two weeks from spring through summer. I’ve given it palm food a few times a year.

One nursery told me I am overwatering. I severely cut back the bushes on both sides of the tree that were overgrown and covering the base and trunk of the palm for the past couple years. Could that have anything to do with it?

A: Yellowing of palm in our soils is usually related to a lack of iron reaching the foliage. You might try applying some EDDHA iron to the soil. This type of iron works at highly alkaline pH that other irons don’t.

However, applying iron to the soil this late in the season will only correct foliage produced now. Older foliage will not green up with a soil application of iron applied now. Yellow foliage must be sprayed with an iron solution to get it to green up.

I will post the proper procedures to use when mixing an iron spray solution on my blog. You need to adjust the pH of the spray solution because of our alkaline water. You also should use a wetting agent when applying iron to foliage.

I’d agree that if you water too often or have poor drainage, you would see yellowing like this from root damage because of overwatering. All palms should be watered infrequently but with quite a bit of water when you do apply it.

Other mineral deficiencies that can cause yellowing on palm include manganese, potassium and magnesium. The better palm fertilizers will contain these elements in their label. I noticed this is not the case with some palm fertilizers sold here.

I don’t see why cutting back shrubs next to the queen palm would affect it.

Queen palms look really pretty in San Diego. They are very questionable growing in the Mojave Desert unless you have the perfect spot for them. Stick to more desert-adapted palms next time and you’ll have fewer problems.

Q: I dug up some standard-sized oleanders from my neighbor’s yard. They were healthy for years and some were 8 to 9 feet tall. I transplanted them about six weeks ago and used transplanting fluid every six to seven days. I also watered them every few days.

The leaves are all dry and crinkled, so I pulled them off. They’re dead now and just look like sticks. But I see new growth coming from the base. My husband tells me to pull them out and buy new ones. Will these make it?

A: When you dig up plants that are this old you can get only about 10 percent of their roots. With a very small percentage of the root system, they will have considerable dieback. If they make it at all, they will do exactly what you’ve described — regrow from the base.

If you want to keep them, it is best to just cut them off with a few inches above the ground and let them regrow from the base. Keep the soil around the roots wet by watering about once a week now and twice a week when it gets really hot.

They will survive and I’d be surprised if anything grows from the stems that are tall. The transplanting fluid wasn’t necessary. They would’ve done what they’re doing now with or without it.

In the future, understand when you move plants that have been in the ground for more than two or three years, the success rate is pretty low unless you know what you are doing.

Q: I have three Italian cypress trees that are 20 feet tall. I have a problem with spider mites and want to know the best way to reduce their populations. I started spraying them with high-pressure water and it got rid of all the webs.

Because the trees are so tall I cannot effectively apply a pesticide using my Ortho sprayer and garden hose. I did use these tools when the trees were smaller.

The trees are yellowing and I apply iron 138 as you recommended in a past article.

A: How did you confirm that the problem is spider mites? They are easy to misdiagnose and there are problems that can appear to be spider mites but are not.

For instance, not all spider mites create webbing and not all webbing in Italian cypress means it has spider mites. You can find webbing in Italian cypress from spiders that are good guys, helping you out.

Spider mites normally occur during hot weather. We seldom see damage from them during cooler weather. I’ll show you a way to detect spider mites on Italian cypress on my blog at Xtremehorticulture of the Desert.

An Italian cypress with spider mites will have the green needles or foliage beginning to die or turn color, usually gray first. If I look at these needles, they will have a dusty appearance if spider mites are present.

This isn’t dust; these are dead spider mites that litter the surface of the foliage. The way I usually determine if spider mites are the problem is to take a white piece of paper and slap a branch of Italian cypress against the paper hard. This dislodges the spider mites from the foliage and onto the paper so I can see them crawling around.

Soap and water sprays are somewhat effective if applied regularly as a preventive. Also, horticultural oils applied during the winter can suffocate these overwintering pests.

Otherwise you have to apply a miticide (pesticide) effective against spider mites for good control. Apply two applications about 10 days apart to control the hatching of young mites from eggs that aren’t controlled with the first spray.

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.