Xtremehorticulture

Xtremehorticulture of the Desert

Keep Irrigation Water Off of Plant Leaves to Reduce Powdery Mildew

Leave a Comment / powdery mildew /

Q. I have powdery mildew on lower branches on my shrubs. Should I remove the dying leaves? Since the temperature will be 114 tomorrow, should I wait until Fall? Powdery mildew on Japanese euonymous. These plants are famous for mildew. A. Powdery mildew on these plants is probably left over from this wet spring. Powdery mildew disease does not require high humidity. As far as diseases go, it probably has the lowest requirement for humidity or moisture.             The usual reasons for powdery mildew besides cloudy, rainy weather is shade, poor air circulation and poor plant health. If you can reduce the shade with some light pruning that may help. Make sure there is no splashing water from an irrigation system. This will spread the disease from leaf to leaf or plant to plant. Sulfur dusts as well as neem oil have been known to work as preventive sprays. Otherwise use traditional fungicides that list powdery mildew control on the label. But with these high temperatures the disease should subside. It is a cool temperature disease. If the leaves look pretty bad, then go ahead and remove them. At least then you are removing disease inoculum. But consider some light pruning instead. You won’t hurt anything with light pruning this time of year and you may give the lower parts of the canopy more sunlight.

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Pick the Right Variety of Roses for the Desert

1 Comment / growing roses in the shade, leaf drop, powdery mildew, Rose selection, which roses best for the desert /

Q. I have some of these roses that are the kind that they said are ground cover type but they did very poorly in the Summer, when it was hot. Now I have planted them in the shade and they leaves are turning white then falling off. Could it be that these expensive roses from the Cal coast will not do well here? My other roses are looking great now and getting higher and higher.  These ground cover roses have never looked or done well. A. Some of the best roses available to us are from Weeks Roses http://www.weeksroses.com/ out of Ontario, California.  Actually this is a very good climate for roses. The very worst time of the year for them is Midsummer. When planting roses they need full sun and lots of soil amendment at the time of planting. They benefit from 2 to 3 inches of wood chip mulch on the surface of the soil surrounding the plants.  They don’t have a lot of pest problems like they would in wetter parts of the country but in the shade you might expect powdery mildew. Powdery mildew will cause the upper surface of the leaves to turn white and fall from the plant. Powdery mildew seldom occurs if roses are growing in full sun and if they are irrigated through drip irrigation, not overhead irrigation. Overhead irrigation encourages the development of powdery mildew on rose leaves and flowers.   Powdery mildew of roses When selecting roses stay with recommended varieties for the desert. This list of roses can be found on the weeks roses website at http://www.weeksroses.com/_RoseInfo/climate.html

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Euonymus Plants Have White Spots and Dying

Leave a Comment / powdery mildew, sunburn, why do the leaves of my Japanese euonymus have white spots /

Q.My euonymus plants are dying. These are all plants that have been in the ground 8-10 years. Now, they are getting a white spot on their leaves and shortly afterwards the plants die. The plants in my backyard did this last year, and now plants in the front have the same symptoms. Some people said they needed more water. That didn’t do anything for the white spot. I tried cutting off the spotted leaves. That might help, but I am not sure. Is there anything I can spray or dust the plants with to stop the fungus? Powdery mildew and leaf death. Powdery mildew is deeper inside the canopy were it is shady. A. I am not sure what you mean by a white spot, whether this white spot can be rubbed off or whether it is permanent. These plants do get powdery mildew which looks like leaves have been dusted with white flour in some locations.This disease occurs on plants in shady locations. If it is powdery mildew it usually means they are not getting enough sun or the canopy of the plant is not open enough for air movement. Powdery mildew, unlike other fungal diseases, requires very little humidity to become a problem. It is spread by splashing water from overhead irrigation hitting the leaves and splashing on others carrying the disease to these leaves and so it spreads. You can buy a dust or spray to control powdery mildew but that just circumvents the problem and it will come back. The long term way to control it is to get more sun on the plants (move or prune them to open the canopy up), improve their health with fertilizers and appropriate watering. If the plant is under watered the canopy will be very open and I doubt you would have powdery mildew unless it is in shade or partial shade. A white spot can also mean scorching of the leaves due to direct intense sunlight. This type of damage cannot be rubbed off with your fingers. It is permanent damage to the leaf. If this is the case then the plant may be in the wrong spot (intense sunlight or lots of reflected heat and/or light from windows and a west or southwest exposure and planted in rock.  If this is the case then you need to move it away from this intense location into one that is more cooling with less intense sunlight. This is not a desert plant and cannot handle this kind of exposure. It does not like rock mulch very much so put it in organic mulch on the soil surface. If it has only one drip emitter, put two or three depending on its size. If you are watering every day then water deeply every other day or every third day now. Make sure you fertilize this plant in the spring with a good tree shrub fertilizer. If you want to move this plant, you can move it to a new location in October, moving as much of the soil with it as possible, and mulch it. Predig the hole and move it and plant it in less than 30 seconds once the roots are exposed. Euonymus does much better with a wood surface mulch.Neem oil is a pretty good organic control for powdery mildew.

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Powdery Mildew on Tomato… what to do?

Leave a Comment / powdery mildew, tomato, vegetable disease, white spots /

Q. I have a problem with my heirloom tomatoes  the leaves on top have mildew on them what is causing this? I have never had this problem before. The plant is producing tomatoes and the leaves on top are still green.  I am baffled! This is not tomato but it gives you an idea what powdery mildew looks like. It looks like someone sprinkled the plants with wheat flour A. I would be very interested if what you are seeing is actually mildew and if you mean the disease powdery mildew. Powdery mildew is a disease that is very specific to certain plants. For instance the powdery mildew on roses cannot attack tomatoes. Powdery mildews can attack numerous plants but each type of powdery mildew is specific to that plant. Powdery mildew is a common disease in desert environments because it can be very active under very low humidities. The environment for this disease to occur is usually the same; somewhat shady areas frequently irrigated with overhead sprinkler type irrigations. This causes water to splash when it hits surfaces. This splashing water can carry the disease from one plant of the same type to a neighboring plant. Nonchemical control of powdery mildew is the same for all types; reduce or eliminate the shade problem and the splashing water problem. Use drip irrigation. Improve air circulation among the plants by not planting too close together and don’t let them shade each other. Give them some space and dont over fertilize them so they get real bushy and have alot of internal shading. Thin out the canopies of the plants to improve air circulation. Go to a different type of growing. Dont let them sprawl but stake them and tie them to stakes to get them more vertical and improve air circulation. Usually if you can do all this you will not need a fungicide. Otherwise there are fungicides you can apply to keep it from spreading.

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