Xtremehorticulture

Xtremehorticulture of the Desert

Keep Irrigation Water Off of Plant Leaves to Reduce Powdery Mildew

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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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Small Round Holes in Tomatoes is Tomato Fruitworm

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Q. I found about 4 to 5 tomatoes with holes in them. I have been getting ripe tomatoes for about 30 days and found these with holes in them during the last two days. I searched for bugs, eggs and leaf damage but did not find anything. Any ideas? Probably tomato fruitworm damage A. The 3/8-inch diameter and larger holes in your tomatoes look like damage from the tomato fruit worm. These are worms, or caterpillars, are about an inch and a half long and 3/8 of an inch wide. They eat holes mostly in tomato fruit, usually when they are green or when they turn red but are still hard or firm. Frequently the fruit becomes rotten from these holes. Organic sprays of Bt or Spinosad when the fruits are starting to form will prevent this.

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Saguaro Should “Rest” Between Irrigations

Leave a Comment / Watering saguaro cactus /

Q. We have a concern about our Saguaro planted in 1988. It now has three large arms and we recently noticed a crack on the outside of one arm at the bend of the “elbow”. Saguaro growing near Parker, Arizona A. Don’t water it too often. Watering about 10 or 15 gallons around the base of the plant in a 5 to 6 ft radius once a month is enough. Those plants expand like an expanding accordion when they swell up with water. Let them use this water before you give them another drink. The plants will shrink in size when they use their internal water supply. If they are given water too often they can swell up and split. The splitting may have happened during the rains this spring and early summer. Regardless, the crack should heal and give the plant a little bit of character.

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Watering Saquaro

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Q. I have a healthy Yucca tree (10 years old) in my desert landscaped yard (similar but smaller to what is pictured below). The homeowner before me watered it daily in summer and weekly in winter along with the rest of the drought-resistant plants in the yard and did so for many, many years. I have continued that practice but have read that Yuccas should not have daily watering. Since everything looks healthy and vibrant, would it be OK to continue daily watering in summer? Thanks. A. Exactly right. They are not supposed to be watered this way. However it appears the previous owner found a happy medium between watering frequently and not watering too much. My guess is the tree was getting very small amounts of water daily.  I would not worry about it if the plants are doing okay and I wouldn’t change anything. However, you should be aware that you are doing it entirely wrong but it’s working. Be careful if you change anything because these plants are now adjusted to that watering schedule.

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Forcing Bougainvillea to Be More Vigorous

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Q. I am concerned about one of my three Bougainvillea plants growing on the south side.  I removed some very old and scraggly oleanders from this spot and raked out all the oleander leaves before planting these Bougainvillea.  I feed them and they have good water supply, but the one in the center is scrappy looking while its brothers on either side are thriving.  Bougainvillea grown as a woody perennials shrub in Bullhead city, Arizona where it seldom freezes. A. Bougainvillea do very well here during our summer heat with a minimal amount of care as long as the soil is amended at the time of planting and they are fed regularly with low nitrogen fertilizers. They like to be pruned so if you see them struggling, prune them back, give them water and fertilize them lightly with a rose or tomato fertilizer. They also bloom better if they are struggling rather than if they are pampered too much. Going through a dry period may encourage blooming.

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Why Are My Oranges Mealy?

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Q. We also have an orange tree that gets oranges (Not a lot  but some) and they are mealy and not very tasty.  How can we solve that? I do give the orange tree lots of extra water. Oranges grown in the Philippines are not orange in color when they are harvested because it is in the tropics. To get oranges typically orange orange in color requires that they are put into the chamber with ethylene gas in a process called “degreening”.The red fruit above the oranges is rambutan. A. Mealy oranges is usually a sign of over maturity, leaving the fruit on the tree too long. Next time they are starting to ripen begin harvesting one of the time a week apart until you hit the right harvest time. Mark it on your calendar. It doesn’t change much from year to year. Unless they are ripening in the winter, you must harvest citrus when they are ripe. They cannot stay on the tree. Don’t wait for an orange to turn color completely.  Begin harvesting it when there is still some green in the rind. If you wait until it is fully orange it may be overripe. Oranges are placed in chambers with ethylene gas to turn them completely orange.

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Nice vine, bitter grapes

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Q. I have sent three pictures of our grape vines.  We have been getting a few bunches of grapes but they are small and bitter. How do we get them to get larger and sweeter? A. Many grapes do well in the Mojave desert climate. Some perform better than others. Some perform Much better than others. A problem we have with grapes is uneven ripening of the berries in a cluster. This means that some of the berries will be ripe earlier than others. We see the ripening of the berries as a change in its color. Technically this is called veraison.  Uneven ripening is still a problem with grapes in general but climates with high temperatures it is more of a problem. In cooler climates, particularly with cooler nights, berries mature much more evenly.  Make sure that you have a variety of grape that performs well here. I noticed you did not mention which variety you have which makes me a little suspicious. All of the grapes that will do well here will mature, turn color (green grapes turn a light green or yellowish green while red or black grapes turn their respective colors; the yellow green grapes in the second picture look ripe to me) in the correct season. This can range from June through August or September depending on the variety. Your vines look healthy but healthy vines do not necessarily deliver a delicious grape. Make sure you wait long enough so that the fruit fully matures. In our climate grapes perform better with aced surface mulch of wood chips covering our desert soils. My suspicion is either the wrong variety or you are not waiting long enough until they mature when you’re harvesting. The individual berries in the grape clusters do not all ripen at the same time. I usually have to harvest them when a few of the berries are actually overripe. Once grapes have been harvested, they will no longer improve in flavor or sweetness, unlike plums, peaches and even bananas.

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Early Grande Peach Leaf Scorch

Leave a Comment / Peach tree yellow leaves /

Q. I have a new ‘Early Grande’ peach which produced over eighty blossoms. I removed fifty of them and harvested the rest. The leaves are turning yellow and dropping off.  I am watering the tree for 40 minutes, three times a week, on alternate days right now, so the tree is getting 16 gallons a week. A. If you’re peach tree is getting yellow leaves and these are dropping and the canopy is sparse (thinning, not very many leaves) I am guessing it needs more water applied. If the soil is bare, watering every other day sounds about right for most soils. If the soil is covered with a surface mulch then you might be able to squeeze two days between irrigations. Use the same technique to make sure the water is wetting the soil 18 to 24 inches deep. Just like fig, peaches will improve with a surface mulch. Peach trees at the University Orchard in North Las Vegas that are 7 feet tall and 7 feet wide are receiving 90 gallons of water each week in a basin that collects the water around the trunk that is 6 feet in diameter during the hot summer. NOTE: The term “too much water” has a double meaning. Too much water can mean that too much water is applied at a single time. Too much water can also mean that the water is applied too often. It is much more damaging to plants when water is applied too often than it is if too much water is applied in a single application. Enough water should be applied to wet the depth needed. That is a given. That will never change. What will change during the seasons is when to water, i.e. how often. Plants will use 500 to 800% more water in July and August than they do in January.

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Figs Dropping Off

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Q. My fig tree is receiving 12 gallons of water a week in the middle of the summer. I water it for 40 minutes, three times a week right now while it is hot. Some of the leaves are brown on the edges. The fruit did not mature and they dropped off. Figs drying and dropping from the tree A.  12 gallons of water a week is not enough. Trees at the University Orchard in North Las Vegas that are 6 to 7 feet tall and about just as wide should get 30 gallons of water, three times per week or a total of 90 gallons. Fruit trees are moderate water users but the soil cannot become dry when they are producing fruit. If it does, it affects the fruit size and quality and it’s possible it may not develop at all. When figs are not given enough water (either the quantity is not enough or they are not receiving water often enough) the fruit becomes small, hard and often times drops from the tree. I don’t know how much of this water is actually getting to the roots. When watering, enough water should be applied in a single application to water roots to a depth of 18 inches, minimum, 24 inches is better. The water should be applied under the canopy so that at least half of the area under the canopy is wet. Take a piece of 3/8 inch rebar and push it into a wet area under the trees canopy. You should be able to push it easily to this depth. Pushing it into the soil easily means the soil is wet. It pushes with a lot of difficulty if the soil is dry. Applying a 4 inch layer of surface mulch helps keep the soil moist, reduces fruit drop and improves fruit quality. Both rock and wood surface mulch works but wood is better for fruit trees. I am guessing a tree that is 4 feet tall might require 15 to 20 gallons, three times per week right now.

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African Sumac Leaf Drop

5 Comments / leaf drop, leaf yellowing /

Q. My African sumac tree strips itself into a skeleton about the time it gets hot. It drops its leaves. This summer I tried to water earlier and it didn’t get as awful looking. But it is a real mess when it drops leaves. Yellowing leaves of African sumac just before leaf drop A. African sumac is not “dry deciduous”, which is true of plants such as the Australian bottle tree. But African sumac will drop its leaves if it does not get enough water. Either increase the frequency and amount of water during the summer months or put down a layer of water conserving mulch so the soil stays wetter when it’s hot. This should help reduce leaf drop.African sumac is a “messy” tree in the landscape.

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