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Friday, December 2, 2016

Lemon, Freezing, Light Bulb and Bedsheet

Q. It has gotten down to 30 degrees overnight here in Boulder City, NV. I'm worried about my little 6-foot lemon tree (in a 5-gallon pot on the porch). So I placed a queen-sized bed sheet over the tree, and hung a 100 watt incandescent lamp from a branch last night. I'm hoping that small amount of heat will raise the temps above freezing. Is this necessary?

A. There are some different reasons and different temperatures that will affect citrus in different ways. Remember that low or freezing temperatures have two components; the low temperature you reported of 30F and its duration or how long that freezing temperature lasts. The longer a damaging temperature lasts the more damage it will do. Meyers Lemon is more tolerant of freezing temperatures than other lemons.

Hanging a light bulb that gives off heat will help a tree if there is no wind or the wind is blocked. If there is wind present then heat from the bulb helping is questionable. Covering a tree with a sheet or burlap helps keep the wind off of the tree and may trap some warm air under it for a short time. If the cold lasts a long time, then eventually the air under the sheet will get to the same temperature. Again, it’s a matter of duration. The more insulating properties this cover has, the better it will be at keeping that temperature from dropping.

Open flowers, young fruit and new growth are the most sensitive parts of any fruit tree. Open flowers of any fruit tree, whether the fruit tree itself can withstand -20F or 32F will always be damaged if not outright killed when temperatures hit 32F for very short periods of time. If your tree had flowers that were open AND the temperature around those flowers hit 31F for 30 minutes, the flower and any fruit it could have produced are dead and gone. 

Unopened flowers and young fruit are slightly more tolerant of freezing temperatures but not much. If the temperature dropped to 28F for 30 minutes, very young fruit will be killed and these will drop from the tree. Larger fruit require lower temperatures but still can be damaged depending on the “antifreeze” (sugar content) of the fruit. 

New growth will be damaged just below freezing as well. This is why I tell people NOT to fertilize winter tender plants during the second half of the summer.

Established trees are a bit different. Each type of fruit tree has its own special tolerance to freezing weather. All citrus is generally tender to winter freezing temperatures. They are considered "semi-tropical". This is why growing citrus in the Las Vegas Valley is generally considered risky. Young citrus are damaged more extensively at the same freezing temperatures than mature citrus. Mature citrus has more “mass” and so it can withstand the same freezing temperatures that might kill a young tree of the same kind. Instead, larger trees will get some damage but they will grow back from that damage.

So to answer your question, yes, the light bulb helps. Keep the bulb from burning leaves and stems. But ultimately it will depend on how windy it is, the duration of the freeze and how insulated the cover is. It is best if the cover reaches the ground so that as much warm surfaces can radiate heat back to the tree as possible.

Wednesday, November 23, 2016

Stay With Hot Weather Wine Grapes in Las Vegas

Q. I'm getting ready to place an order for wine grape plants. Currently I have 25 plants that are 3+ years old. These consist of mainly Zinfandels and Cabernets with a few Merlots. Can you give me any info on nurseries to deal with and type of plants I may need?

A. You can wait a bit to make a wine grape order unless you tell them not to ship until late February or March. I want to avoid freezes after planting.

Basically stick with the so-called hot climate grapes. Summer Muscat is a good one for you. Others to look at include Syrah (Shiraz), Petit Syrah, Barberra, Grenache, Sangiovese, Malbec, Tempranillo,
Zinfandel growing in Las Vegas in trials 2007-2011
Pinot Noir growing in Las Vegas. Not a grape I would normally recommend here but I wanted it so I grew it and it did surprisingly well
Sauvignion Blanc growing in Las Vegas trials
Alicante Bouschet in veraison growing in Las Vegas trials. Another problem with hot weather is uneven ripening of the grapes due to hot weather and warm nights
Viognier to get you started. Look closely at Malbec if you like Malbec wines. Syrah is always a good one for blending as well as Barberra, Grenache, Merlot, Petit Syrah, Zinfandel and Primativo which some claim is a Zinfandel.

Should I Put a Sheet on my Veggies This Winter?

Q. I have vegetable garden. Do I have to cover with a sheet if it freezes?
A. It depends on the vegetables and the site. Vegetable gardens located in warm areas of the yard with reflected heat and very little wind are much warmer. They may not need to be covered or covered less often than those that are exposed. Vegetables growing in these locations are not as likely to freeze during the winter.
Freeze damage to tomato plant
Freeze damage to tomato fruit
     Of course any of the warm season vegetables like tomatoes, peppers, eggplant, squash, etc. are going to freeze as soon as temperatures drop below freezing. In fact, they can suffer some damage when temperatures drop to the temperature of your refrigerator.
            Some warm season vegetables like beans may freeze to the ground at the hint of a freeze while others like peas, spinach and radishes may sail through the winter with no problems. Sorry that I can't give you a definite answer on that because there are so many variables.
Bush bean collar rot due to cold soils
            To be on the safe side get yourself a 1 ounce or more frost blanket and cover your growing area when temperatures are predicted to drop below freezing. Depending on the frost blanket, it can allow 50% or more of the light to reach the vegetables and it also breathes while it can raise the temperature under the blanket five or 6° F. It also keeps the wind off of the vegetables.
Crop cover (frost blanket) on raised bed for improved germination during cold weather
            Follow the direction and tack it down tightly so the wind doesn't get under it. Or put some weighted objects along the perimeter of the blanket. Don't use burlap or plastic sheeting. Spend the money, buy the 1 ounce or heavier frost blankets and they will last for three or four seasons or more.

De Witt makes a good one. So does Agfabric.

Sometimes Low Chill Apples and Hot Desert Clinate Don't Mix

Q. I heard the Israelis established a low desert apple tree. A few orchards have been established in the Phoenix area. I would like to learn more with the intent to purchase.
A. There are a couple of apples suitable for the low desert developed in Israel but the quality of the apple is typically not the best, in my opinion, unless you are a big fan of ‘Yellow (Golden) Delicious’. Both “Anna’ and “Ein Shemer’ apples were bred in Israel as a “low chill” apple for warm climates, not necessarily hot desert climates.

Anna grown in Las Vegas, Nevada in the Eastern Mojave Desert

            “Low chill” refers to the chilling requirement required by some fruit trees to flower and produce fruit the next growing season. A chilling requirement is a specific number of hours below a threshold temperature, usually around 45° F, so they “recognize” winter has passed.
            Just because a fruit tree has a low chilling requirement does not necessarily mean it produces good fruit in a hot desert climate. Hot desert climates are not the best places for apples. It doesn’t mean necessarily that an apple tree won’t grow but may have trouble producing fruit and decent yields and the flavor, texture and keeping qualities may be inferior. Apple fruit frequently sunburn in our hot summer climate and develop thick skins and high sugars but lower acidity. These climates are more suitable for stone fruit such as apricots and peaches.
Immature apple in the early stages of sunburn
Apple fruit with severe sunburn from lack of protection from late afternoon sun (West)
Hot deserts without cool nights close to harvest don’t develop a good balance of acids and sugars for flavor development. Cool nights are important for this. A 4000 foot elevation adds cooler nights which is very important for flavor development.
            The orchards in Arizona that I know of such as those near Wilcox, Arizona, are at a 4000 foot elevation or higher. Compare that with Phoenix at an elevation of around 1000 feet. These higher elevations and can handle some popular apples like Granny Smith, Fuji, Fuji, Gala and Pink Lady.
            Some lower chill apple varieties to try in hot desert climates include Dorsett Golden, Anna, Ein Shemer, Mutsu, Pink Lady and Sundowner. From my experience, try but proceed with caution with Fuji, Granny Smith, Gala, White Winter Pearmain, Winter Banana, Gordon, Yellow Bellflower and Pettingill. All of the apples do better with protection from late afternoon sun.

Sap From Plum May or May Not Be Borers

Q. I have a fruit bearing plum tree approximately 2 years old. I noticed an amber hard substance on the trunk. I think it’s borers. If it is, what can I do to save it and still be able to eat the fruit? 

A. The most effective way to kill borers is to apply a systemic pesticide and let the tree distribute this pesticide everywhere inside it. There is a very popular systemic insecticide available nearly 100% effective at killing borers if they are present.

            This insecticide is distributed everywhere (systemic) inside the tree and lasts for nearly 12 months. And yes, it is labeled for fruit trees that are bearing fruit as well as vegetables. This pesticide applied to food bearing crops makes me nervous for obvious reasons.
            Let me present to you an idea that does not require pesticides but a little work on your part. I have observed it to be about 80% effective. This requires a sharp knife and a method to sanitize it such as alcohol, butane lighter or even Pine-Sol.

Plum sap from a pruning cut in the spring
Sap oozing from the trunk of a fruit tree due to overwatering
            Plums are very sappy trees. Any injury to living parts of the tree cause sap to be produced. The production of sap is a defense mechanism against “intruders”. The tree does not differentiate between damage from boring insects and damage caused by pruning, invading diseases or environmental damage.
Extensive damage to the trunk of plum and bark is peeling from the west side
            To a plum tree, it’s all the same. It reacts by producing sap. If it is an intruding insect like a borer, sap engulfs and frequently suffocates it. If the damage by boring insects is extensive, loose bark easily lifts away from the damaged area because that area is dead. 

Borer damage under the bark leaving behind "debris" in the tunnels just under the bark from eating
            Damage from boring insects most first appears on the west or south facing sides of the trunk and limbs or on their upper surfaces. A tree may have damage for one or two seasons before you see parts of it suffering outwardly. On plums, sap is a good indicator something is going on.
            The only way to find out if a boring insect is involved is to inspect the wood under the sap for damage. It is easiest to do this after the leaves drop in December. You can wait. It’s cold now and they are not active.
            When you are ready, take a very sharp, sanitized knife and remove the sap along with the bark just under it. Look for damage to the trunk or limbs in the exposed wood. Boring insects leave debris from feeding, in tunnels, just under the bark.
Borer damage removal using a sharp knife removing all the damaged bark to fresh wood
            If you do not see damage to the wood under the sap, then this damage is not due to borers. Leave it alone if the limb appears otherwise healthy. If you see insect damage in the wood under the bark, cut and remove ALL bark from the damaged area with your sharp knife and let it heal on its own. If the damage is extensive and the limb is weak, remove it.
            There is no pesticide you can apply to the tree that will kill the borers AND leave the fruit safe to eat in my opinion even if it’s on the label and you can use it for that purpose.