Spray grapevines to control pests

The skeletonizer is a bluish-black moth seen flying around grapevines during the day. They are strong flyers. If your grapevine has them and you don’t do anything, they will devastate grapevines by skeletonizing the leaves.

Their young feed on the bottom side of the leaves in a battalion formation, marching along as they devour it and leaving behind only the leaf veins. To get them, you should spray the undersides of leaves with a spray containing spinosad. Also, Bt will usually work as well.

But the grape flea beetles often rest on the top side of the leaves and don’t fly as far because they’re not strong flyers like the skeletonizer. I apply sprays to control the skeletonizer, but I usually leave the flea beetles alone and don’t spray.

The skeletonizer will come back over and over with each new generation, but the flea beetles do their damage over two to three weeks and they’re gone. You will probably have to spray several times with spinosad each time skeletonizers return. so watch for them.

Flea beetles can create a lot of damage by chewing holes in grape leaves, but the grapevine will grow new leaves and recover perfectly fine without spraying. If you choose to spray for the flea beetles, any common insecticide approved for spraying grapes will work on these critters.

By the way, spinosad also does a decent job of cleaning up young grape leafhoppers at the same time you’re spraying for the skeletonizer. Two-for-one. Spinosad also controls the scarring damage on nectarine fruit by western flower thrips if you start spraying when the fruit is first forming and repeat the spray on a regular basis.

Q: I planted grapes against my concrete wall two years ago. I got a decent crop of grapes last year, but the birds ate them. How do you protect the fruit from birds? How much and how often should I water grapevines, and what about fertilizers?

A: One way to protect grapes from birds is to net the vines. Cover the vines with bird netting, which you can buy online or locally. Thoroughly cover the vines with this netting when you start seeing birds in them or when the grapes are starting to turn color. The netting must be tacked tightly against the wall and the ground or birds will get inside the netting and have a feast.

Some people don’t like bird netting because it can tangle birds in it if the birds are clumsy. I have never tried it, but some people report that instead of netting they place paper bags around the grape clusters about two weeks before they are ready to harvest. The bag protects the berries from birds. This technique can be done on pomegranates and some other fruit damaged by critters.

Grapes can be deep-rooted, unlike fruit trees, with roots as much as 30 feet deep. Personally, I water them about as often as fruit trees, but they can be watered less often than that. It is important to keep the soil moist around the roots when the berries are developing. After harvesting the fruit, you can water the vine less often. Two emitters for each vine, about 12 to 18 inches on either side, is enough if growing them on a trellis or near a wall.

Fertilize the vines once in the spring, just like fruit trees, and with the same fertilizer only do it about a month later. Water them every 10 to 14 days during the winter and once a week when you start seeing new leaves forming. Give a mature vine about 15 to 20 gallons each time it’s watered.

Water them twice a week when temperatures hit the 90s. Bump it up to three times a week when temperatures are solidly in the 100s. If you are covering the soil around them with a thick layer of wood chips, they will do extremely well in our desert soil.

Q: We have had a bottlebrush for about two years. It has some yellow leaves We applied iron fertilizer in March, but it doesn’t seem to be doing any good. The leaves are still yellow. Should we remove it and start over with something else?

A: Leaf yellowing also can be caused by watering too often. Check to make sure the irrigation is not occurring daily and it has some time between water applications so the soil dries out. This means in the middle of summer this plant needs at least one day between irrigations, more days than that if it’s possible.

The only way to get yellow leaves green again is by spraying the leaves with an iron solution several times a day or so. Use distilled water and a small amount of liquid detergent in the spray solution when spraying yellow leaves with iron.

Applying iron fertilizer to the soil will not make yellow leaves green again. It only prevents yellow leaves from forming; it will not green up yellow leaves already present. For most plants, iron is applied to the soil before growth starts in very early spring.

If the plant is surrounded by rock, the iron you apply may not be working because the alkalinity of the soil is too high. Use EDDHA iron chelate when making your application to the soil. It works regardless of the alkalinity.

This is true only if the yellowing is due to an iron shortage. Reasons for leaf yellowing other than an iron shortage will require a different strategy to green the leaves. Then maybe replacement is warranted.

Q: Does creating shade help plants grow or hold them back? I’m confused over this point.

A: It depends on the plant. I realize you want a simple answer, but when it comes to living things, sometimes there is no such answer. How plants respond to shade is sometimes considered general knowledge, while other times it’s learned experientially. But all plants need light.

In the desert, sunlight is abundant, and many times it can damage plants. Unlike animals, plants don’t have legs and can’t voluntarily move to a more pleasant location if the sunlight is too strong. Landscape plants rely on us to place them in the best location for their growth, appearance and health.

All plants need some shade during times of stress, such as when plants are not healthy or have added stress because they were recently planted, moved or transplanted. Plants grown in coastal nurseries with mild climates need a period of adjustment before being plunged into a sun-rich desert environment. Plants should have a period of adjustment to stronger light if grown inside the home and then plunged outside.

Names like Japanese blueberry or Carolina cherry laurel should immediately tell you that these are not desert plants. They might grow here but they will need some adjustment to the harsh desert environment.

Where they are placed in the landscape and how they are grown is critical to their health, appearance and survival. Of course, placement of plants with names like these into hot, dry environments with intense sunlight should be a dead giveaway that they will struggle here.

Let’s talk shade cloth. Okra doesn’t like any shade cloth at all. It looks beautiful under 30 percent shade cloth, produces beautiful flowers but no fruit. Tomatoes, on the other hand, seem to like about 20 to 30 percent shade during the intensely sunlit summer months. Lettuce does extremely well growing under shade as much as 50 percent.

What does 50, 30 or 20 percent shade mean? It means that the plants and soil in this shade have sunlight reduced by 50, 30 or 20 percent.

Fifty years ago, we created shade by constructing a lathe house. One-hundred percent shade was created by covering the entire roof of the structure with lathe. Fifty percent shade was created by removing every other strip of lathe. Thirty-three percent shade was created by removing two strips of lathe and leaving one.

In our desert environment, knowing where shade exists or creating shade is one of the management tools we have as horticulturists to manipulate plants into better performers.

Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.