Lawn Diseases Struggle When the Humidity is Higher than Normal

Q. I live in Henderson where we enjoy having a lawn as part of our yard. It was thick and beautiful when we moved in, but it soon withered after we made some changes to sprinkler layouts and had the water off for awhile. I laid fresh sod and it too struggled. I tried a fungicide and that seemed to help but it then died completely.  Now the rest of the lawn is headed in the same direction. I’m at the point of desperation and could use some sound advice in the midst of some differing opinions.

This is the lawn the reader talked about. It is dying in patches. The reader asked me to look at it (consult) but I think the disease problems we had (high humidity) earlier had a lot to do with it.

A. Outside of watering, some lawns experienced disease problems earlier in the season that lingered after we had high humidity due to the rain. That change in our weather encouraged plant diseases to occur. In the desert, it’s usually the higher humidity that’s the problem.

I will take a look at this lawn and see if the disease is advancing or has stayed put. That will tell me what his options are. Now he must stop the lawn disease (if advancing) and get the grass to come back.

The humidity is now below 15% (except directly above lawns) and lawns should not need a fungicide application to keep the disease from spreading if we allow the lawn to dry after we apply water, and it is in good health. When there was higher humidity, some lawns along with some other plants, may have needed a fungicide. A lot of it had to do with the lawns current health.

If you applied a lawn fungicide, it should have stopped needing the applications if the general humidity was above let’s say 25%. Plant disease susceptibility is sometimes compared to a three-legged stool. Plants are susceptible to fungal disease if: 1. the disease organism is present, 2. general health and susceptibility of the plant is good, and 3. the current weather. In this case, all diseases like moisture. A couple of months ago the weather (humidity) was the problem. The higher humidity is now over. The relative humidity is now in the “desert” range. I think you are seeing old lawn disease damage (unless the lawn grasses are in poor health).

Make sure you follow label directions when you apply any fungicide. Any traditional broad-spectrum fungicide should work, but generally the higher-priced fungicides for lawns are usually a better choice in that respect.

This fall we should be watering lawns about two to three times each week. No more than four times each week for sure! Water early in the morning (imperative) and wet the lawns from 8 to 10 inches deep in a single application when you water. Sloped areas, or hard soils, may need multiple starts, about 30 minutes to one hour apart, to keep the water from “puddling” into low spots.

            Your lawn may not need it but try “aerifying” your lawn with a gasoline driven core aerifier. Then “topdress” your lawn with a rich compost to fill the aerification holes. Irrigate your lawn immediately after this. This process of filling the aerification holes, followed by topdressing and irrigation, improves the rooting depth of the grass. This will improve a lawns (grass) health.

"Fluffy" Soil a Problem When Reseeding a Lawn?

Q. Preparing to reseed a few bad spots in my lawn. I was surprised to find the ground completely infested with a spidery web of roots. The soil itself seems to have been changed to a fluffy, powdery texture. I’m thinking I should remove and replace the soil before seeding these spots but am concerned these crazy roots will grow back. Any ideas as to what they are and what I should do about them?

When Bermudagrass has a chance to grow rampant it can produce a thick mat of roots, similar to a spiderweb, that can cause the soil to be "fluffy" or "puffy".

A. I am guessing this "fluffy soil" you're talking about may be the Bermudagrass rhizomes mixed with soil. That's what your picture looks like. To repair it requires removing all these rhizomes all the way down to solid bare soil. Once you have done that, the soil should be about at the right height for seeding. I don't think the soil will be lower than it needs to be. Since you are right next to a sidewalk, the soil should not be more than about 3/8 inch lower than the sidewalk. If it's lower than this, you can add some soil to the area but I kind of doubt you will need to.

What bothers me, and I'm right it is Bermudagrass, is why it's there in the first place. Bermudagrass invades spots in the lawn that are drier than other areas. It out competes fescue where its dry. Sidewalks and driveways are hotter than other areas, so the lawn uses more water in these areas. Adjust your lawn sprinklers so this area gets more water.  You may have to water the entire lawn more often or with more water just to compensate for this dry area unless you fix the irrigation problem.

Bermudagrass thrives where it's hot and dry. It will outcompete fescue in a lawn where it's dry. Putting one sprinkler to cover an area that's triangular-shaped will cause Bermuda grass to invade that dry area.

Bermudagrass is even more aggressive if the lawn is mown short. Make sure the lawn is mown as high as possible during the months of April through October when Bermudagrass is most aggressive and no bevel cuts when you edge the lawn!

Brown Spots in Lawn Probably "Frogeye" Disease

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

Unusual pattern for dead grass. Too random for irrigation I think.

This picture you start to see the "frogeye" disease pattern. Looks like it could be a chemical spill.

Here is where "frogeye" starts to make an impression. But its over. 

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% 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.

Rolls Back Like a Carpet

            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.

Irrigation problems are nearly always easy to see how they connect to the sprinklers.

            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.

Seldom will you see it this obvious but this is frogeye. See how it got its name? In advanced stages these dead areas can become one but you still look for little patches of green grass that would still be there. Sometimes its hard to see them.

            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 and leave it alone until fall. If you remove it now, it opens the soil to invasion by Bermudagrass. Bermudagrass 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.

When to Fertilize Lawns

Q. When is it time to start fertilizing lawns again?

Lawns can be beautiful but they need regular feeding. The light green color of this lawn is an indicator it needs an application of nitrogen fertilizer. That nitrogen fertilizer will turn that light green lawn into a dark green lawn in a matter of a couple days.

A. It depends on whether the lawn is fescue, only Bermudagrass or Bermudagrass overseeded in Fall to maintain green winter color. Fescue lawns and overseeded Bermudagrass lawns are fertilized the same during winter months.

Ammonium sulfate fertilizer contains only nitrogen that the plants need when their color is not dark enough. The sulfur in the sulfate is also important for plants but in the case of light green color, all that's lacking is nitrogen.3 to 5 pounds of this fertilizer spread evenly over 1000 ft.² of lawn and watered in will turn the color a deep green instead of light green.

            Fescue and overseeded Bermudagrass should have been fertilized last Thanksgiving to maintain dark green color through winter. If this fertilizer application was missed and temperatures get cold, the lawn can turn brown when it gets very cold or just light green if it does not.

            The next fertilizer application to fescue lawns would be when air temperatures enter the 60s. Fertilize Bermudagrass that was not overseeded when temperatures enter the 80s.

Once or twice a year add a better quality fertilizer to the lawn like this one. It has a little bit of phosphorus, the middle number. Lawns don't need a lot of phosphorus because we don't grow them for their flowers and fruit. I would like to see the potassium, the last number, higher than this but this is a good lawn fertilizer.

            Established lawns require fertilizers containing high nitrogen, and occasionally an application of iron, for dark green color. However, they will perform best if this fertilizer contains also low levels of phosphorus and moderate to high levels of potassium.

            For this reason, fertilizers similar to 21-7-14 or 10-5-10 are frequently recommended for lawns. Some people use only high nitrogen fertilizer such as 21-0-0 and omit phosphorus and potassium.

            I think this is a mistake and a good lawn fertilizer should be applied at least once during the growing season. Instead, experiment and try fertilizing with only half the amount of fertilizer recommended on the bag. This is all that is usually needed if you are not bagging lawn clippings but mulching them back into the lawn using the mower.

Organic Soil Amendments at Planting vs No Organic Amendments

Q.  I’m planting new fruit trees and landscape trees this year. I noticed there is a consensus out there that fruit trees, trees and shrubs should be backfilled with native soil without using any amendments. However, is there an exception in Las Vegas with the soil is exceptionally poor?

Typical "native" or "natural" desert soil in Las Vegas. Would you plant directly in this? I hope not.

Here is the SAME soil (25 feet away) ten years later after wood chips were spread on the soil surface and water was applied for fruit trees. Now which soil would plants be "happier" growing in?

A. You are right and my advice is bucking conventional advice from most places. For instance, using native soil for backfill in North Carolina will be fine in most cases. But it also depends on what is planted. Many urban landscapes have "fill" that was brought in by the developer or general contractor. Most fill...No, I take that back...ALL fill... used in urban desert settings is junk. Using soil amendments depends on the soil and also the plants. Let me explain why.

Desert Soils Vary in Organic Content

            Some desert soils are okay to plant into directly and you will have few problems. Others are not. Much of it depends on the organic matter content of the soil and the type of plants. If your soil contains at least 5% organic matter at the time of planting, the addition of organics to the soil as a soil amendment probably won't do much. If the plants going into the soil prefer growing in highly organic soils, you are probably going to see a problem if the organic content is only 5%.For instance, a soil with low organic content but suitable for lawn grasses or some trees and shrubs will not be suitable for annual flowers or vegetables.

 Soils are a Mixture of Sand, Silt, Clay AND Organics

            Soils are a mixture of minerals and organic content that results from dead plants and animals that decompose into the soil. Desert soils with very low rainfall like ours.

This is a jar test. I have students do this to their soils at home. First of all, the soil is darker in color which means it has organics in it unless it is a soil like a Latersol in the tropics. This is NOT a desert soil. I can tell from the color. The organic component has mixed in with the soil particles and colored it darker but the larger stuff either floats on the surface or is the very top layer on top of the clay layer.

            When planting without soil amendments such as compost, soil organic matter content should be at least 5% if you don't want the plants to be "unhealthy". If it is lower than this, add organic content to the soil such as a good quality compost. Mix it with the soil taken from the planting hole.

            Another option is to use a soil mix for filling the planting hole around the tree roots or container roots. Soil mixes are like Hamburger Helper; they contain organics and it is convenient and easier to use than mixing the soil yourself.

Soil color can tell you alot about a soil. This cark soil color tells me there is a good amount of organics in it and will not need to be amended for lawns and some trees and shrubs.

            Be careful of adding too much organic content to the soil. This can work against the establishment of the plant in the surrounding soil. This is the situation with research done in Oklahoma, Arizona and other states. These practices of “not adding organic matter” to the soil at planting is from their research with soils already high enough in organic matter to make little difference after platning.

This is the same desert soil you saw above. Organics are added to this desert soil AND the soil is covered in wood chips to add organics to the soil over time as long as there is rain or irrigation.

Many soils of the Mojave Desert with very low rainfall are extremely low in organics. Soils in the desert that are relatively high in rainfall or were previously farm land (under irrigation). These are usually already high enough in organics and adding more does little, if any, good. Using the deserts of the Southwest as an example (Sonoran, Mojave, Chihuhuan, Great Basin) they range in historical rainfall from 4 inches to over 10 inches of rainfall each year. This is a 250% difference depending on locale!!! Of course we will see different types of plants and a difference in plant density and canopy size when we compare desert environments with a difference in rainfall of 250%!!! This is reflected in soil differences there as well. We see differences in organic content, salts, pH, etc.

Map of the US showing organic content of soils and how it varies with rainfall. Desert soils are always lower in soil organics than soils in wetter climates unless they are amended.

How Do You Know the Organic Content of a Soil?

We can send it to a soil testing laboratory and spend maybe $75 to $100 and wait for three weeks for a reply or use our noggin and get a rough approximation. The soil testing lab will give you a precise amount in the sample sent to them. If the sample sent to them is representative of the soil that interests us, then it may be fairly accurate. But, garbage in, garbage out. If the sample is NOT a good representation of the soil that interests us then it is garbage.

Look at the soil

Soil color is a pretty good indicator of soil organic content. Rich soils, full of organics are brown to black. The lighter the color, the less organics in it. If the soil is moist and dark brown, you probably don’t have to add anything. If it is light tan or very light colored, even when moist, it probably needs organics added despite the recommendations from Oklahoma or Arizona.

Dig in the soil

If you need a pick to dig or a shovel barely scrapes the surface, AND it is light colored….ADD ORGANICS!!!! Add organics in a ratio of about 1:1 by volume or container. Add a five gallon bucket of compost to this cement-like soil. Adding organics/compost in a 1:1 ratio (v/v) will NOT result in 50% organic matter content but probably in about 3 to 5% content after watering, settling, and growing for one season. 

Next year add 25% by volume (v/v) if it is a garden soil or apply about one inch of compost to the soil surface around a plant and lightly scratch it into the soil surface, and water it in. Keep compost at least (approximately) 6 to 12 inches from the “trunk” or stem of the plant. Beginning the third year, add compost around the tree/plant at the beginning of its growth cycle primarily for nutrients and improved biological activity.

Las Vegas soils, most of them, are extremely low in organics. ADD compost to these soils at the time of planting. You have one time to do it and after that it is very hard to do if not done at planting.

Would You Like to Learn More?

Sign up for my half day class on the Basics of Desert Soils and Growing Horticultural Crops offered in early March 2018. Read all you want in books and the internet but this class focuses on growing plants in desert soils of the Mojave. Class size is limited. Enroll now using the link below.

https://www.eventbrite.com/e/desert-soils-and-successfully-growing-plants-in-the-desert-tickets-42010937846

Bermudagrass Lawn Change of Color May Be Drought

Q. We have lived in the same house in Las Vegas for the last 42 years and every June my lawn has the same problem. The lawn is a mix of common and hybrid Bermudagrass. First the grass turns grayish (in patches) and then it turns brown. It slowly comes back by September. I water according to local recommendations, use Scott's Turf builder 3 to 4 times a year and use Ortho Bug-B-Gone insect granules twice a year.
 

A. If this were tall fescue I might be tempted to say this is a disease problem. However, since it is a mixture of Bermudagrasses I think this is an irrigation problem. This will be particularly true if these problem areas are in the same locations every year.

Turfgrass or lawns will turn a smoky or grayish green when they are not getting enough water. This is because the leaf blade either folds in half or roles depending on the grass. This creates a different color; smoky or grayish green

            Bermudagrass in our climate doesn’t develop many insect or disease problems.

            The success of lawns in our desert climate is directly tied to the quality of an irrigation system. In technical terms we say the irrigation system should provide head to head coverage; water from a sprinkler head should be thrown far enough to reach the head to its right and it’s left. If we don’t provide this kind of uniformity in the design and installation of an irrigation system it can result in brown patches that don’t receive enough water.

A close-up of the grayish green color where the lawn is not getting enough water

            The water pressure in the sprinkler system should fall within a range recommended by the sprinkler manufacturer. If the water pressure is too high or too low it will affect the distribution of water and create browning of the lawn in the same areas year after year. Otherwise, there are sprinklers now that will lower the water pressure before the water is applied to the lawn.

Another indicator of drought or lack of water in a lawn are footprints. If you walk across grass that needs water, look behind you. If your footprints remain in the grass does not spring back quickly, the grass needs water.

            You can correct this problem in the short run by increasing the number of minutes that you apply water. This delivers more water to the dry areas. Unfortunately, it also delivers more water to the wet areas resulting in overwatering of the green areas.

            It is also a good idea to punch holes in the lawn with an aerating machine in the spring, particularly in the brown areas. This helps water to move into the soil and not run off into low spots if there are any.

            Bermudagrass is notorious for building up “thatch”. Thatch is a buildup of old grass stems and debris under the surface of the lawn but on top of the soil. Years ago this thatch was burned off of the lawn with fire. We can’t do that anymore. We must do it mechanically now.

A core aerifier for lawns pulls plugs or cores out of the lawn that are about 4 inches deep. This type of verification provides better drainage and water penetration for lawns suffering from drought

            It is important to dethatch Bermudagrass each year. This is usually done in the fall when overseeding it with a cool season grass like ryegrass to maintain a green winter lawn. If the lawn is not overseeded in the fall then thatch can be a huge problem in Bermudagrass.

D thatching machines, sometimes called vertical mowers, pull debris from a lawn which allows water to better penetrate the soil and reduces runoff.

            Making changes to the irrigation system will correct some of this problem and reduce the amount of water needed to keep the lawn green. Increasing the number of minutes you apply water during the heat of the summer should solve this problem in the short run.

            But I would combine this with lawn aerification every three or four years and dethatching every year to improve the amount of water entering the soil in the dry areas.