How to Control Powdery Mildew of Grape

Q. I have white powdery mildew on my green, table grapes.  This has not been a problem in the past.  What now? Is this related to the cool, moist weather?

Grapes should have air movement around them to prevent powdery mildew and bunch rots. In the hot desert we have to be careful about giving them full sun throughout the day because of sunburn to the fruit.

A. Yes, powdery mildew on grape is seldom seen here because of our very dry and hot weather. This very cool spring, higher humidity and recent rains has made powdery mildew, as well as early blight on tomatoes a problem. Powdery mildew will disappear when it gets hot and dry.

Horticultural oils can help reduce powdery mildew problems

One thing that really helps control powdery mildew forming on grape bunches is improved air movement around grape bunches as well as sunlight during the morning hours. Sunlight on grape bunches in the late afternoon can cause sunburn on the berries so be careful about giving the fruit too much sun late in the day.

We can usually prevent powdery mildew by removing the leaves around grape bunches for better air movement and keeping bunches dry. Once powdery mildew has started, you may have to apply a fungicide to keep it at bay or eradicate it.

One of the best organic controls of powdery mildew on grape are the horticultural oils. Horticultural oils are mixed with water and sprayed on grape bunches in the early morning hours. There is a precaution in using oil sprays and not to apply it when temperatures are high. However, I have had no problem applying oils during the cool early morning hours.

Insecticidal soaps labeled for disease control have also given some control as well as dusting dry bunches with sulfur dust.

Why Are My Boxwoods Dying?

Q. Can you tell me why my boxwood shrubs are showing signs of dying?

A. The usual reason for this kind of dieback in our climate is either a watering problem (keeping the soil too wet or not watering frequently enough which is drought) or wet mulch against the trunk of the plant.

Boxwoods dying back because soil is kept too wet, they were planted too deep or wet mulch is in contact with their stems.

Be sure you pull any mulch back away from the stems of the plants. Six or 8 inches is enough just so it does not touch the stem when it is wet.

Wet mulch can contribute to collar rot where the lower stem or trunk rots from too much moisture and the presence of disease organisms. The organisms are always there, they just need the right environment to develop. The right environment are wet conditions against the trunk and plant stress. Sometimes they don’t even need the stress.

Die back can also be because the soil is kept too wet. Roots need to dry out between irrigations. If they don’t, they will die back causing the stems to die back as well.

Keeping the soil too wet or too dry can look identical above ground. This is because root dieback or death is the same thing as drought. The roots die and can’t supply water to the top and the plant stems die back due to drought for different reasons; lack of water or too much in the soil causing roots to die.

Pull the mulch away and let it dry out before it gets too far along. It is most likely not a disease in the tops but in the stems or roots.

Black aphids on Chitalpa

Aphids on red Yucca flowers before they Bloom in February

Q. I live 40 miles east of Kingman, AZ and I'm having a bug problem this spring on our chitalpa and ocotillo. There are tiny black insects on every bloom and bud. I've started noticing them on the red-tipped yucca blooms as well. We've had all of these plants for years and they are well established. We would hate to loose them. Should we be concerned about these bugs? 

A. These are black aphids which are common on Chitalpa, its leaves and flowers as well as other plants. They suck plant juice out of the soft tissue of leaves and flower buds and petals, concentrate the sugars taken from the plant and drop it out of their rear as a high sugar, shiny and sticky concentrate.

Aphids and ants working together

 This sugary concentrate attracts ants and can foster the growth of sooty mold. Sooty mold is not sooty canker, a very bad disease of landscape trees. Sooty mold does not infect the plant but just grows along the surface of leaves and stems and is easy to remove.

 Ants herd and protect these aphids from other insects as well as move them around. Controlling the ants helps to control aphids and sooty mold. These insects will not kill the plants but they will affect your plants floral display. Spray these aphids off of your plants with a strong stream of water and control the ants.

Aphids and ants working together on red Yucca after they flowered

Alternatively, spray the flowers and leaves with insecticidal soap, neem oil, canola oil or horticultural oil. If you are still not satisfied with the results, then you can be more aggressive with a conventional insecticide with aphids and ornamental plants listed on the label.

Remember, conventional insecticides can be much more damaging to beneficial insects and honey bees.

Spray in the very early morning hours or at dusk when honeybees are no longer present. If you look at one of your pictures of the flower buds you will see a ladybird beetle immature (larva) feeding on them. It is grey compared to the black aphids.

They are voracious feeders of aphids but there are just too many for this solo beetle larva to handle. Spray them off with a strong stream of water or use insecticidal soap or horticultural oil to kill them.

Tomato Disease Causing the Leaves Happening Now

Early blight of tomato

There is an issue occurring now in home gardens that may need your attention called early blight of tomato. Early blight of tomato has been seen on the variety called ‘Big Boy’but is probably on others as well.

If left alone this disease will first cause leaf yellowing on older leaves, followed by grey or brown spotting, then dieback of the plant.

Once plant dieback occurs, the fruits are left exposed to intense sunlight where they sunburn.

This disease can be easy to control if you start early. The key to prevention and spread of the disease is sanitation and rotating your vegetables between garden spots.

Remove yellowing foliage at the stem by “snapping” off the leaves or by cutting with a scissors. It is important to remove the infected leaves and stems as early as possible and put them in the trash, not the compost pile.

Prevent the disease from spreading on new foliage by using a fungicide. Any commercial vegetable fungicide will work but those containing in the ingredients chlorothalonil, mancozeb and copper work the best. I talk about it more in depth on my blog.

Fertilize Lawns At Least Three Times Each Year

Q. What time of year should a lawn be fertilized?

A good  fertilizer for established lawns should be
high in nitrogen (first number),
low in phosphorus (the middle number)
and moderate to high in potassium (the third number).

A. For tall fescue lawns, this is 99% of our residential lawns, I recommend at least three times per year if you are using recycling mowers; Labor Day, Memorial Day and Thanksgiving.The Thanksgiving day application may arguably be the most important application of the year in keeping
a winter lawn green.

If you have bermudagrass I recommend Labor Day, Memorial Day and 4th of July. You don’t want to apply anything to Bermudagrass in the fall if you are planning to overseed your lawn to keep it green during the winter.

Most fertilizer bags recommend a rate of 1 pound of nitrogen per 1000 square feet of lawn area. I consider this to be excessive unless this is a very high-end fertilizer containing lots of slow release nitrogen. You can cut that rate in half and get very good results.

It is also very helpful if you can use a mulching mower that chops up the clippings find enough to return to the lawn as a fertilizer.

You can download a copy of my fact sheet on turfgrass maintenance from here

https://www.unce.unr.edu/publications/files/ho/2010/fs1070.pdf

Look for Plants Dying Because of Grubs

This is the time of year when grubs are feeding on the roots of plants. Many of these types of grubs are the same types that feed in compost piles. Some people refer to them as “compost worms”.

Grubs feeding on the roots of Lantana

The adults of these compost worms are frequently large beetles that we see flying in June and July.

Grub Guard is one of the products containing beneficial nematodes

The eggs of these larvae or worms were laid in March. If there are lots of them, their feeding in the months of March, April and May can cause plants like Lantana and agave to decline and even die.

There are organic options. I personally have not used them but I have received good reports on the use of both beneficial nematodes and bacteria specifically designed for grubs.The bacterium is usually referred to as "milky spore".The nematodes are usually referred to as "beneficial nematodes".These do not kill grubs immediately but do have a long-term effect in keeping the populations low over a long period of time. Look for the words Steinernema carpocapsae in the ingredients.

Control of these immature insects is usually accomplished with applications of chemicals as granules or a liquid diluted in water and poured around the roots of the plants. Sprays or dusts applied to the leaves or foliage will not control these types of pests.

This is the insecticide that contains imidacloprid.

One of the most effective chemicals has imidacloprid, as an active ingredient listed in its label and sold by any nursery, garden or box store. But any chemical listed for controlling “grubs” should work and is permitted as long as it includes the plant that your treating on its label.

One word of precautionon the use of imidacloprid; It has been implicated (but not proven) to possibly contribute to some environmental problems including colony collapse disorder of honey bees (CCD).

Research implicating imidacloprid in CCD

If you do use this product, I would not apply it to flowering plants and only apply it as a liquid, soil drench and not as a foliar spray.

If you have any further questions contact me through my email, Extremehort@aol.com, or on my blog Xtremehorticulture of the Desert.

My Zucchini Will Not Produce Any Fruit

Here is a zucchini plant with both male and female flowers. The male flowers are supported by a long thin stalk. The female flowers have a stalk supporting it which is swollen and resembles a small zucchini.

Q. My friends are giving me grief because I can't grow zucchini or other squashes. I get female squash flowers with the squash below the flower. I have male flowers, too. We seem to have insects around enough to pollinate other plants. Fruit withers at about large grape size.  I am thinking that the two flowers aren't opening at the same time for the insects. What can I do to become one of those zucchini and squash growers who have so much they can't even give it all away?

A. The weather right now has been very strange. Give it a chance to warm up a little bit. Summer squash likes warm temperatures.

Zucchini fruit falling off due to high temperatures.

Zucchini usually produce male flowers first followed by female flowers a little bit later. It is possible that they are not open at the same time and having more than one plant should solve that problem.

Bees are needed for pollination. If the plant is very dense, bees may have trouble getting inside the canopy where flowers are located. Try removing some of the leaves in the canopy to make it more open so bees can find the flowers more easily.

Some zucchini have a hard time setting fruit when temperatures are high. You might try hand pollinating. This requires a soft paint brush and transferring the pollen from the male flower to the female flower. This is a pretty good video on hand pollinating zucchini.

Video on hand pollinating zucchini

It is also possible that you have a variety that is just not do well in our climate. I have one right now that I did not select and it is absolutely a lousy producer.

It is not true that you can just pick any old variety and it will do well here because it does well in South Carolina or Ventura, California.

Why Is My Queen Palm Yellow?

This is not the queen palm mentioned in the question.
But this is a very common yellowing that occurs
to queen palm in our desert environment and our desert soils.

Q. I have a queen palm that is recently beginning to yellow. It's done well every year until this Spring. I Miracle-Gro the soil around it every two weeks from spring through Summer. I've given it Palm Food a few times a year. One nursery told me I am watering too much. I severely cut back the bushes on both sides of the tree that were overgrown and covering the base and trunk of the palm for the past couple years. Could that possibly have anything to do with it?

A. First of all, Queen palms are very difficult to grow in this desert climate and in these very difficult soils. They really have trouble because of our hot dry winds and hours alkaline soils that contain no organic material.

Now that we have that out of the way…

Yellowing of palm in our soils is usually related to a lack of iron reaching the foliage. You might try applying some EDDHA iron to the soil. This type of iron works at highly alkaline pH which other irons do not.However it should be applied to the soil in the very early spring before new growth occurs.

Applying iron to the soil this late in the season only corrects foliage produced after you apply it to the soil.  Older foliage, foliage that grew before this soil application, will not green up with a soil application. Yellow foliage must be sprayed with an iron solution to get it to green up. Applications to the foliage have to be done several times to be effective.

This is an example of an iron chelate
used for correcting yellow foliage on plants
with liquid sprays.You must adjust
the pH of the spray or use distilled water
for sprays like this to work.

Here is the proper way to mix and apply iron to the foliage:

1. Mix only enough that you will need for spraying. It will not keep after you mix the dry ingredients with water. You must use it up.
2. Use distilled water if possible. If you use tap water you will have to adjust the pH or alkalinity of the water for an iron application to the foliage to work.If you use tap water, add 1 tablespoon of white vinegar to each gallon of water to lower the pH.If you really want to be sure about the pH, use the pool test kits to get your pH between 6.0 and 7.0.
3. After you have adjusted the pH, add the iron fertilizer to the water. Do not add the fertilizer first and then add the vinegar. If you use distilled water you can skip the vinegar.
4. Add a good wetting agent such as EZ Wet. Why? This is not a gimmick. It is very important when spraying liquids, whether its fertilizer or a fungicide, on the leaves of plants. Follow the label directions but you usually add about 1/2 to 1 tablespoon for each gallon of spray. Add this at the very end and mix it into the spray mixture.
5. Apply this spray when temperatures are cool, such as the early morning or evening. Pump up your sprayer and spray it on the leaves with enough liquid to wet the surface of the leaves or when you see the spray liquid beginning to drip from the foliage. Spraying the foliage for longer than this is wasting your time, spray mixture and money.



This is a good wetting agent for applying liquid sprays.
It is made from an agave extract and cold pressed.

6. Repeat this spray in four or five applications several days apart. The normal way for iron to get inside the plant is from the roots. You are trying to get iron inside the plant in the opposite direction. This is much more difficult. You need multiple applications and a wetting agent such as EZ Wet to get it inside the plant.

I would agree that if you water too often or if you have poor drainage you would see yellowing like this from root damage because the soil is kept to wet. All palms should be watered infrequently but with quite a bit of water when you do apply it.

Other mineral deficiencies that can cause yellowing on palm include manganese, potassium and magnesium. The better palm fertilizers will contain these elements and you will see it in their label. I noticed this is not the case with some palm fertilizers.

I don't see why cutting back shrubs next to the queen palm would have any impact on it.

Queen palms look really pretty in San Diego. They are very questionable growing in the Mojave Desert unless you’ve got the perfect spot for them. Stick to more desert adapted Palms next time and you will have fewer problems.

Controlling Spider Mites in Italian Cypress

Q. I have three Italian Cypress trees that are 20 feet tall.  I have a problem with spider mites and want to know the best way to reduce their populations.  I started spraying them with high pressure water and it got rid of all the webs. Since the trees are so tall I cannot effectively apply a pesticide using my Ortho sprayer and garden hose.

Webbing in Italian Cypress does not always mean spider mites. You need to do the paper test explained below to see if mites are the problem or not.

A. How did you confirm that the problem is spider mites? They are easy to misdiagnose and there are problems that can appear like spider mite problems and they are not.

For instance, not all spider mites create webbing and not all webbing in Italian Cypress means it has spider mites. You can find webbing in Italian Cypress from spiders that are actually good guys and helping you out.

Spider mites normally occur during hot weather. We seldom see them during cooler weather.

An Italian Cypress which has spider mites will have the green needles or foliage beginning to die or turn color, usually grey first. If I look at these needles they will have a dusty appearance if spider mites are present.

Spider mites are extremely small. This one is highly magnified.
They are about the size of the dot at the end of this sentence .

This isn't dust but these are dead spider mites that litter the surface of the foliage. If I see Italian Cypress with dusty needles or foliage I begin to think they might have spider mites. The way I usually determine if spider mites are the problem is to take a white piece of paper and slap the branch of Italian Cypress against the paper pretty hard. This dislodges the spider mites from the foliage and onto the paper.

I then hold the white piece of paper in bright sunlight very still for 15 to 30 seconds. If mites are present, I will see tiny little dots the size of a large period crawling around on the paper. If I brush my fingers lightly across this moving dot on the paper, I will see red smears on the paper.

If the Italian Cypress appears damaged, the foliage or needles appear dusty and I get red smears on the white piece of paper I will conclude the damages from spider mites.

Soap and water sprays are somewhat effective if done on a regular basis (couple of times during hot weather or after a dust storm) as a preventive. Otherwise you would have to apply a miticide effective against spider mites for good control. You would apply two applications about ten days apart to control the hatching of young mites from eggs which are not controlled with the first spray.

Unfortunately this would require that you spray the entire tree if mites are a problem. It is really hard for homeowners to spray much above 10 feet. I do not know of any miticides that you can apply to the soil and get good control.

First, make sure the tree has spider mites and that is the problem. Insecticidal soaps are good first choice but they are not extremely effective in controlling this pest. If you do get it confirmed that it spider mites and they are out-of-control, you will have to spray miticide. Watering Italian Cypress too often causing root disease problems can give them a similar appearance as branches begin to die.

Spraying trees above 10 feet is difficult for homeowners. Pest control operators and arborists have equipment to do this.

We Have Holes in Our Tomatoes!

Q. I have Early Girl green tomatoes with round holes in three of them. Otherwise plant is in great shape. Other fruits on plant OK. .

A. That is feeding damage probably by the tomato fruitworm. Applications of Bt or spinosad should slow them down and are "organic" controls.This is basically the same "worm" that attacks the ears of corn by laying its eggs on the new silk coming from the forming ears.

The tomato fruitworm is probably the most damaging pest to tomato fruits. As the name implies, the damaging part of this insects lifecycle is the "worm" stage or more properly called "larva".

Click here to see the larva or immature form before it becomes a moth

They don't all come in one color so they can range in colors from pale yellow, to red, green or even brown with pale stripes down its length. They are about an inch and a half long when fully grown but they can be smaller than this if they are not yet mature.

Unlike hornworms which are pretty easy to spot during the day or at night  with a black light because they glow green,  fruitworms you wont see until you see damage to the tomato fruit. With your black light you can go scouting for hornworms and scorpions at the same time!

The adult of the fruitworm is a night-flying moths that ranges in color from tan to brown with orange in it. They are about 1 to 1 1/4 inch across their wingspan.

Click here to see the adult moth

Because they fly at night that's when the egg laying occurs.They like to lay their eggs on tomato leaves close to green fruit or they might lay them on the leaves on the outer edge of the plant if the plant is dense. They are flying now and have been flying for quite some time.

Click here to see a close-up of an egg

The eggs that they lay are very difficult to see because they are so small.The eggs are white when first laid and then develop a brown stripe or mark just before they're ready to hatch. First they begin to feed on leaves before they attack the fruit. They prefer to feed on green fruit and the damage that they create by tunneling into the fruit causes the tomatoes to ripen more quickly. The fruit is pretty well demolished once they enter and feed and move on to a new fruit.

Shining a white light or black light against a white sheet at night is an easy way to see if they are flying.  You can try it now and you will probably attract some but the best time is when tomatoes begin to flower so you can time your spraying.

You can also use pheremone traps.

Black light or even light traps serve as a good indicator when these guys are flying and will be a problem in the garden in the future. This is a cool way to look for them and great to show kids and grandkids.