This is the time of year we see a rise in humidity along with a threat from afternoon rains. This rise in humidity and high nighttime temperatures can also bring plant disease problems. You can do something now to prevent diseases before they occur. Clouds building during summer monsoon in Las Vegas             The potential for disease on plants is always present. But when the environment favors disease development, their potential becomes a reality. Two plants prone to summer diseases include lawns and tomatoes.             Three methods used to combat summer diseases are to strengthen the plants natural defenses, improve the environment where they are growing so disease is less likely or use chemicals when “all else fails”.   Top picture is summer patch disesae on tall fescue. The bottom is summer patch disease on perennial ryegrass. This disease used to be called “frogeye” for obvious reasons in the bottom picture. This disease loves the heat and loves it more when it is humid and the grass is weak.             Lawns. Tall fescue is prone to summer diseases if they are not healthy or watered between 6 PM and 2 AM. Summer diseases favor warm temperatures and humid conditions. If your lawn is watered and still wet when night approaches, disease is more likely. Water your lawn between the hours of 2 AM and 5 AM.             If your lawn has not been fertilized for 2 or 3 months, apply a half rate of fertilizer early in the morning when temperatures are cooler and make sure it is immediately followed with an irrigation.  One of the “blight” diseases on tomato. But you get the picture. These diseases love the humidity. Open the canopy, keep vines off the ground and wet the leaves ONLY early in the morning.             Tomatoes. It may feel dry to you but inside that tangle of tomato leaves is a hot, humid jungle. Growing tomatoes upright rather than letting them sprawl on the ground reduces disease problems. Also, thinning the foliage improves air movement, reduces humidity inside that tangled mess, and reduces disease potential.             Lightly fertilize tomato plants once a month. If you plant them in the ground and never fertilize them, chances of disease problems increase because of poor health.             Never overdo it. A light application is all they need. Applying too much nitrogen can be just as bad as not having enough.             Some people like to hand water their vegetables by spraying with a hose. Some people apply liquid fertilizer to the leaves. Do this early in the morning so that “tangled mess” has plenty of time to dry before nightfall.             When all else fails, then turn to chemical protection. Fungicides for lawns and vegetables can be found at the nurseries and box stores. Make sure to read and follow the directions on the label. Applying more than recommended on the label is not better.

Q. I have two multi-trunk Palm trees in my backyard, same size. One has had brown fronds in the middle of the  main trunk  ever since it was planted 5 years age while the one on the right one has always had green fronds.  Looks like the brown fronds are now moving up the main truck.  I  fertilize each of these trees in June, July and August and each gets the same amount of water.   Looks like I am going to lose the palm. A. The browning is a combination of water, soil nutrient and management issues. Water. The Palm is either not getting enough water or getting watered too often. Do not water every day. If you are not watering every day but watering a few days apart or longer, then increase the number and/or the size of the drip emitters irrigating the palms.  This is a better solution than bumping up the minutes since everything else on this valve will get an increase in water. If you find that water is running out of this area under the palm tree, then break your irrigation into 2 or 3 separate waterings within our separation between. Soil nutrients. Either these palm trees are not getting the fertilizer they need or they have been fertilized but you’re not getting much of a good response. Put about 2 cubic feet of compost under the tree and water it in with a hose. Putting some iron chelate under the compost before you water it in.  These palms will do much better if the soil surrounding their roots is covered with 3 to 4 inches of wood chip mulch. This is not bark mulch but woodchip mulch. The woodchip mulch will begin to dissolve into the soil and add organics. So will the compost. If you want a faster response from the compost, dig about 6 vertical holes in the soil with a post hole digger about 18 inches deep. Backfill these holes with compost and water it in thoroughly.   Woodchips laid on the soil surface and decomposing and improving the soil beneath it Management. Notice how the fronds are not bad looking at the top but they get pretty brown and ugly closer to the ground. These palms should be pruned. Remove any fronds that are lower than horizontal.  Remove these fronds as close to the trunk as you can. Consider skinning the palm with a linoleum knife or box cutter. This removes the base of the frond, exposes the trunk, and makes it look very sophisticated. Cutting off the bottom fronds will improve the look of these palms by exposing the trunk.

Q. Would you please tell me what to do to keep leaves on my Sago Palms from yellowing?    This is not the readers sago palm but is representative of the kind of problem I am frequently asked about regarding this plant growing in the Mojave Desert. A. The usual problems with sago palm in our climate and soils are very poor soils, hot exposures, irrigation problems and using the wrong kind of surface mulch around them. Cycad or sago palm can look like this if planted in the right kind of soil and put in the right location. Landscape exposure. Sago palms should not be planted in southern or Western exposures unless they are placed in filtered shade from large trees. They grow best in Eastern and Northern exposures. The northern exposure should not receive intense sunlight late in the afternoon. In southern and Western exposures in intense sunlight the fronds will scorch on the edges, may turn yellow, but will not grow to their full length. If this is their exposure, I would move them to a new location in mid-to-late October. Soil improvement. Sago palm grows poorly and the fronds yellow when soils don’t have any organic matter. A one half bag of compost spread around the base of the plant each year helps. If this has not been done in previous years then you might want to add compost to the soil in vertical holes placed about a foot to a foot and a half away from the Sago palm about 2 feet apart. You can use a post hole digger to dig the holes about 18 inches deep and back fill them with compost. Irrigation. Sago palms can handle a lot of water if the soil drains easily. If the soils are slow to drain, Sago palm will get root rot and begin to yellow and the fronds will begin to scorch on the edges. Adding compost to the soil and putting in vertical holes for drainage as explained above usually takes care of the problem. Surface mulch. Some people plant sago palm with rock applied to the surface as in a desert landscape. Sago palms do not belong in desert landscapes. They should be used in high water use landscapes with lots of organics in the soil. They are not a cactus or succulent. They should never be surrounded with rock mulch. If it is then rake away the rock from the sago palm 3 to 4 feet from the trunk and apply a layer of wood chip mulch on top of an application of compost to the soil surface. Adding compost to the soil, vertical drain holes, woodchip surface mulch and moving the plant to a new location that is not in full sun will help this plant a lot.

Q.  Here are the rest of the photos of our African sumacs with leaf drop.  Our yard is too small for me to get far enough away to get an entire tree in the photo.  Please let me know if that would help and I’ll go outside the neighborhood wall and see if I can get a photo of the entire top of the trees.  Thank you for any advice you can give us! Readers African sumac yellowing and dropping leaves A. The usual problem with African sumac yellowing and leaf drop this time of year is a lack of water. When these trees are planted by landscapers they frequently do not use enough drip emitters. Or when they plant them small, they use just a few emitters and no one adds more emitters as these trees get larger. During hot weather the amount of water larger trees require is considerably more than when it was growing during 90° weather. It is now 115 to 117F. And it has been very windy. Another possibility could be watering too often. If the tree roots are in soil that is watered daily and it’s not draining, the roots could suffocate. If they begin to suffocate and die they can also have yellow leaves and leaf drop. I think this possibility is less likely in your case. There is a 3rd possibility. It is possible to water these trees daily and still not give them enough water. If the total volume of water applied is not enough to satisfy the trees demand for water, they can actually be under watered even when they are watered daily. I would add more emitters instead of increasing the number of minutes on the controller. Yes, I know it’s more work but you won’t be over watering everything else on that valve. There is one way to find out. See if the soil around the tree is wet or dry. Take a steel probe that is at least 18 inches long. This can be a very long but skinny screwdriver or it can be a piece of 3/8 inch steel rebar 3 feet long.    This screwdriver might work if it is long enough. Push it into the soil in several locations under the canopy of the tree. If it pushes into the soil with a great deal of difficulty, then the soil is too dry. If this is the case, flood the soil under the tree with a hose or sprinkler with a good soaking that goes down at least 18 inches deep. You have the probe so you can measure how deep the water penetrates by pushing the probe in the soil. If the water is running off of the area, turn the sprinkler or hose on multiple times 30 minutes or an hour apart. I use a mechanical water timer and an inexpensive sprinkler on the end of a hose. You should see a response by the tree if the soil is dry in 7 to 14 days. It would be like this but there would be no grass. If the soil is too wet under the tree then of course you have to wait longer between waterings. But I tend to think it’s probably not getting enough water. Covering the area of the soil under the canopy of the tree with woodchip mulch 4 inches deep helps keep the soil wet tremendously.

Q. Can you give some tips to on how to survive this latest bout of heat? Is it simply too hot right now for plants? Is shade cloth the answer? A. It has been hot these past few weeks and very stressful for many landscape plants. There has been a combination of high temperatures, intense sunlight, very low humidity and windy conditions. Just like us, healthy plants have the best tolerance to the extremes of heat and cold. But water and fertilizer can be a killer if too much is applied.             Shade cloth is helpful in some situations but it is usually for vegetables. Use shade cloth to manage the intensity of sunlight and reduce sunburn on tender vegetables. Shade cloth providing somewhere between 30 to 50% shade is used with these plants. Otherwise, rely on leaves of plants to provide their own filtered light. Avoid watering trees, shrubs or any plants that are woody every day. Try to give these plants at least one day of rest, without irrigation, between waterings. Some landscape plants have roots that suffocate easily if the soil contains too much water. These plants seem to “die overnight” when watered daily or the soil remains wet. Mulch helps. Mulch of any kind, whether it is rock or wood chips, applied to the surface of the soil helps cool it, preserves soil moisture and helps battle weeds. Rock mulch applied to the surface of the soil is best for desert species of plants. Woodchip mulch is best for non-desert species of plants. A surface layer of mulch can add one or two extra days between irrigations. A wet sponge drips water because it can hold no more.A sponge is moist after it has been squeezed. Water just before the heat. Make sure plants enter the heat of the day with their roots surrounded by moist soil. There is a difference between “wet” and “moist”. This is particularly true of plants grown in containers. These soils dry out faster than soils in the landscape. Plus containers warm their soils faster compared to landscape soils. Wet or moist soils warm up slower than drier soils.               Water lawns early in the morning. Apply lawn irrigations as close to sunup as possible but when still dark. Windspeed is usually slowest at these times. Never put a lawn “to bed” wet. Give the leaves a chance to dry off before it gets dark. This helps avoid lawn diseases.              Fertilizer can be applied now. You can apply fertilizers this time year but use half the recommended rate and apply it when temperatures are cool, during the mornings or evenings. Make sure dry fertilizers are rinsed into the soil immediately after they are applied. Lifertilizers can be sprayed on leaves but only during morning when temperatures are cool.               Some pruning can be done now. Light pruning can be done anytime during the growing season. Never use anything bigger than a hand pruner this time of year. Use saws and loppers only during late fall winter and early spring. Don’t remove too much. Always leave some growth to shade the trunk, stems and branches.

Q. When laying hybrid Bermudagrass sod, does it make sense to water two or three times on hot days?   A. Freshly laid bermudagrass sod should be watered once a day. Make sure the soil beneath the sod is wet and not just the sod itself. Bermudagrass is a very fast grower and loves the heat when it’s roots are in wet soil and there is plenty of nitrogen fertilizer.. Avoid sprinkling the sod just enough to wet it. It needs more water than that. This was tall fescue sod laid in the middle of summer on very hot, dry soil. The hot dry soil burned the roots of the sod causing dead patches like a disease. Fescue sod is hard to establish during the heat. Bermudagrass and other warm season grasses like St. Augustine or zoysia should be laid during the early heat of summer..             Water and nitrogen. Bermudagrass sod needs water and nitrogen fertilizer so that its roots can “knit” into the soil beneath it. When watering, make sure enough is applied to wet the soil several inches beneath it. As you begin mowing, increase the amount of water applied and try to water every other day during the heat. This forces its roots to grow deeper and the grass will become more drought tolerant.             Hopefully a phosphorus fertilizer was applied to the soil before laying the sod. If not, then apply one now. Use a single application of 16-20-0 at a rate of 2 to 3 lbs of fertilizer per 1000 square feet and water it in immediately after application.              Applying nitrogen fertilizer frequently. Apply nitrogen fertilizers once a month during establishment. Apply 21-0-0 at 3 lbs per 1000 square feet. Once the lawn is established in about 3 months, reduce fertilizer applications to three or four times per growing season.

Q. Our Acacia and other trees in our neighborhood in Mesquite, Nevada, have leaves that are turning yellow. Is this from all the heat we’ve had or too much watering?  This is citrus but leaf yellowing accompanied by scorching of the edges is usually a good indicator the plant is not getting enough water. The solution is not to water more often but to give it more water when you do water.Scorching and yellowing of the leaves can also mean some salt problems. Salt problems can happen when plants aren’t getting enough water. Flush the soil around the plant with high volumes of water a couple of times. A. This extended heat wave requires you to water more often. But water long enough to wet the soil deeply. Avoid watering daily, particularly trees and shrubs. It is not needed if you water deeply. It is better for the plants if you don’t. Instead, increase the number of minutes so that you can avoid watering every day.             Healthy plants can handle the heat. Leaf yellowing is not because of heat but because of either dry soils or soils that are continually wet. Continually wet soils can occur from daily watering. Watering desert adapted plants every day may cause their roots to “suffocate” from too much water.             Watering less often, but with larger amounts of water, forces roots to grow deeper and harvest water from greater soil depths.             Plants are lazy. Plants require more energy to harvest water from deep in the soil than from the surface of a soil. If water is applied to the surface every day, these lazy plant roots “slurp” up the surface water and hardly touch the deeper water, if there is any.             If water can be found deep in the soil and the surface of the soil begins dry, tree roots will be forced to grow and harvest water from these deeper, wet soils. This deeper growth improves anchoring of the tree and reduces “blow over” during high winds.             If you are going to make a mistake when overwatering, make the mistake of giving the plant too much water rather than watering daily.

Q. What is the optimal watering and fertilizer schedule for desert pines? I started taking care of a large horse property two months ago. Many of the trees were in distress from lack of water and fertilizer. I’ve been watering about 5 gallons per tree per day and the trees have responded with new growth and color. A. Five gallons of water per tree per day is not much. Watering this way forces tree roots to grow along the surface of the soil. It does nothing to encourage deeper growth. Deeper root growth is important to  prevent them from blowing over during high winds. It is also important for their tolerance to dry conditions.             I understand they were in bad shape but with the amount of water you are giving them they will never become lush and dense. The density of most trees increases with increasing amounts of water. Tree density decreases with lesser amounts of water.             Larger trees require more water. Smaller trees require less water. You can decrease their water use through selective pruning to control their size if their water use is a problem.             It is difficult to estimate how much water they need. But the amount of water they will need in one year is roughly equivalent to the volume of water 4 feet deep under their canopies.               Let’s do some math. Estimate the cubic feet, 4 feet deep, under the canopy.First calculate the area under the canopy. Use 3.14 x half of the diameter squared. If the diameter of the canopy is 20 feet, multiply 3.14 x 100 which is 314 square feet. Now multiply 314 x 4 to get the cubic feet of the area 4 feet deep. The cubic feet of water needed by EACH pine is 1256 cubic feet. Multiply the cubic feet by 7.48 to estimate gallons of water. This will be about 9320 gallons of water consumed by each tree this size each year. About 2/3 of this water, or about 6100 gallons, will be used from May through October. The remaining 1/3, about 3100 gallons, will be used from November until May.  Water less often but with more water. Depending on the soil you have, water once or twice each week during the summer months. Water less often than this during the fall, winter and spring months.Give each tree enough water so the water will drain at least 2 feet deep around the tree. It is very important to give these trees the same amount of water each time you irrigate them. A surface mulch of wood chips in these basins, at least 4 inches deep, would help these trees considerably.   You can’t see it very well but there is a basin around this pine tree. I would make this basin deeper so that it will hold at least 2 to 3 inches of water. Large basins may require 2 bubblers or 2 rings of drip emitters around the tree.             Trees of this size might be best irrigated using a basin around each tree trunk. The trees are watered by filling this basin. The basin should be constructed at least half the size of the trees canopy.It does not have to be round but should be located where you want most of the roots to grow. If these trees are close together, you could group 2 or 3 trees with a shared basin. Just make sure each of the basins are level. The basin is also a convenient place to apply fertilizer or horse manure, in your case, once or twice a year.

Q. One of the pine trees in my backyard has developed a split in the bark and is oozing some sap. The trees were planted about 10 -12 years ago and are now 12 -14 “in diameter. Is this something we should be concerned about? None of these pictures are from the reader but it is easy to see that pine trees, when they are injured, produce an abundance of sap. A. If the trees appear otherwise healthy, most likely not. When pine trees have wounds, it is normal for them to “leak” sap. It is their way of healing from wounds.When you do see sap from pine trees it is an indication that there was damage done.             Make sure the tree is getting enough water. Also, make sure it is not watered too often.Having adequate water speeds the recovery from wounds. The trees canopy is a quick way to know if your pine tree is receiving enough water. Dense canopies with lots of new growth is a good indicator enough water is being applied.             Water these trees deeply but infrequently. In other words, give them big drinks of water and then hold off as long as you can before the next irrigation. Deep irrigations 2 or 3 times a week should be enough.