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Weather change can stop disease from spreading

Q: I have some large dead areas in my lawn. I don’t think it’s an insect problem. Watering is at 2 a.m. and 7 a.m. This was my first lawn problem in 16 years.

A: I looked at the pictures you sent, but the last picture was the most telling to me. I think your lawn had a disease problem that is now finished. Don’t do anything now. Let me tell you why I came to that conclusion.

Insect problems here are not like those “rolling back like a carpet” problems described in books and online. Those descriptions apply to Kentucky bluegrass damaged by white grubs.

We have grubs, but we don’t have much bluegrass anymore. Our lawns are 95 percent tall fescue, and tall fescue reacts differently to insect damage. It pulls out like loose hair from an old animal skin. Plus, the pattern of dying grass does not resemble insect damage.

I first thought the brown spots were an irrigation problem, but the pattern doesn’t fit an irrigation problem. With irrigation problems, dead or damaged areas are in a pattern that relates to the location of sprinkler heads. I didn’t know where the sprinkler heads were, but the damage was irregular, so I ruled out irrigation.

The pattern does, however, resemble a chemical spill flowing downhill and damaging the grass in its path. It was a possibility, but the last picture looked like advanced stages of a disease problem. We used to call this disease fusarium blight or “frogeye.” This disease has since been renamed necrotic ring spot. I thought frogeye was much more descriptive.

What led me in the direction toward disease were the small patches of green grass still alive but surrounded by dead grass. These small green patches of grass are how frogeye, now necrotic ring spot, got its name.

From the pictures, it looks like the disease has run its course, and the grass that’s alive is healthy. I say this because the grass surrounding the dead areas appears healthy.

This is the way lawn diseases usually work. They have a window of opportunity when the weather is right for the disease to spread, and it takes off. The weather changes, and the disease stops.

You would be wasting your money to apply a fungicide now that it’s over. But don’t disturb the brown, dead grass. Leave it alone until fall. If you remove it now, it opens the soil to invasion by Bermuda grass.

Bermuda grass loves sunshine, bare soil and water. It hates shade. Wait until the weather cools in late September or October, remove the dead grass and either seed or sod these areas.

Q: Two creosote bushes in my landscape have distorted leaves and very thin foliage. Both bushes receive light, supplemental water and have for the past 10 years. Can you give me recommendations on bringing them back to health?

A: It may be impossible to tell exactly what caused these distorted leaves, but I put these types of problems into two categories: insects or environmental. I would rule out diseases.

Judging from the pictures, most of the leaf distortion seems to be cupping. I see a few leaves with brown tips. I also saw in one picture some very light webbing among the leaves. This, together with leaf tip dieback, makes me suspicious of spider mites.

It’s a common misconception that native plants such as creosote bush don’t have pest problems. They do. Many of our native plants have insects and other animals that coexist together. Some of them cause damage, and others feed on these bad guys. That — and limited new growth — keeps them in check. But seldom does it get out of control.

There are several native insects that already have a relationship with creosote bush and have the potential to cause leaf cupping: the creosote bush stink bug and the creosote bush plant bug. Feeding damage by these insects can cause this type of damage. These insects come and go.

If I follow the KISS principle, my best guess is the damage is caused by insects and their relatives because of their abundance in the plants’ native range. Also, check this plant for spider mites.

Spider mites are tiny and hard to see. Take the stem of a plant and slap it hard against white paper. Look for crawling dots the size of a period at the end of a sentence. If these tiny dots are moving, then it has them.

I think the extra succulence of this plant, growing in a landscape, was a magnet to plant feeders like spider mites and other bugs. Plants with extra succulence are like a smorgasbord to plant feeders.

What to use? Washing the plant with a stream of water helps to keep spider mites from getting established, but once established they are a continuous problem during hot weather. Soap and water sprays, if done two or three times a week, oftentimes get spider mites under control. Spray the top and bottom of leaves.

Soap sprays don’t do much about the insects that cause leaf cupping. These insects must be sprayed directly with soap and water to kill them, and it must be a direct hit.

Applying other pesticides would be a better choice if you want total control. Personally, I think they will perform better if given water less often.

Q: I have Mexican fan palm trees that were skinned a few years ago. I just had them trimmed. The trimmer climbed the trees with spikes. The spikes left holes in the trees. Will this harm them?

A: Most likely not, but using tree spikes or gaffs is not a good idea. The holes created by climbing gaffs create places for diseases to enter the tree.

One disease, a lethal disease for Canary Island and Mexican fan palms called fusarium wilt, can enter the tree through these wounds. This can be particularly true if the gaffs were used first to climb a tree that was infected.

This disease and others can also be transmitted from tree to tree on pruning equipment if this equipment is not cleaned and sanitized properly between trees. Several methods can be used to sanitize pruning equipment, including alcohol, Pine-Sol, TSP or trisodium phosphate, and even 30 seconds of direct heat from a butane lighter.

There isn’t a good reason to not clean and sanitize pruning equipment. It’s laziness. Would you go into surgery and let the doctor use a dirty scalpel? If climbing gaffs must be used, at least sharpen, clean and sanitize them before climbing.

I can understand why you might be upset having holes punched into skinned palms. Avoid putting holes in the trunk, whether it’s pounding nails, pruning with a chain saw or climbing with gaffs.

Climbing gear that creates holes is no longer recommended for pruning palms. Taking a gentler approach is preferred. Ladders, cherry pickers or scissor lifts are recommended.

Q: I planted a Mexican bird of paradise about three years ago. It has never flowered and has only grown a small amount in that period. Any ideas why? Could it be its location? It doesn’t get morning sun, only afternoon sun.

A: Watering too often and not giving the plant enough water can create similar results. Afternoon sun should be enough for this plant. Make sure it’s not near a wall that gets hot from the afternoon sun.

Notice how the plant has more foliage or leafy growth because of the suckers at the bottom? The stems growing above the suckers are nearly void of leaves. That is usually a sign the plant is not getting enough water at each irrigation. It can also indicate the plant doesn’t have much nitrogen fertilizer for growth.

I must be careful because we are considering two things: how much water the plant is getting and how often it gets it. I would recommend watering this plant with about 5 gallons or more at each watering. Water it three times a week during the summer. Use two drip emitters within 6 to 12 inches of the base on either side of the plant.

These are desert plants, but they also can grow in wet landscapes if there is drainage. They grow best in improved and amended soils.

If this was planted directly in your landscape soil without soil amendments such as compost, or an inferior amendment was used at planting, then it could struggle as well. Apply a good compost within about 12 inches of the plant in a circle and water it in. Use about a quarter of a bag for each plant.

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

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