Insecticides kill borers on trees but may make fruit inedible

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 borer damage. If it is, what can I do to save it and still 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 percent effective at killing borers if they are present. This pesticide applied to food-bearing crops makes me nervous for some obvious reasons.

Let me present an idea that does not require pesticides but a little work on your part. This requires a sharp knife and a method to sanitize it such as alcohol, butane lighter or even Pine-Sol.

Plums are very sappy trees. Any injury to living parts of the tree causes sap to be produced. This includes damage from disease, heat and people. The production of sap is a defense mechanism against intruders. To the tree, disease, heat and people damage are intruders. It doesn’t know the difference.

If it is an intruding insect such as 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 and no longer clings to the bark.

Damage from boring insects first appears on the west or south facing sides of the trunk and limbs or on their upper surfaces. The only way to find out if a boring insect is involved is to inspect the wood under the sap for damage.

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.

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 a sharp, sanitized knife and let it heal on its own. If the damage is extensive and the limb is weak, remove it.

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. Both Anna and Ein Shemer apples were bred as a “low-chill” apple for warm climates, not necessarily hot desert climates. Anna, the most successful of the two, was released back in 1959.

“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 the hot desert. Hot desert climates are not the best place to produce apples. It doesn’t mean that an apple tree won’t grow but may have trouble producing fruit, decent yields, marketable fruit and the flavor, texture and keeping qualities may be inferior.

Apple fruit frequently burns in our hot summer climate and develops thick skins and high sugars but lower acidity. These climates are more suitable for stone fruit such as apricots and peaches.

Hot deserts without cool nights at harvest typically don’t develop a good balance of acids and sugars. This is important for good flavor development.

Orchards in Arizona that I know of, such as those near Wilcox, Arizona, are at a 4,000-foot elevation or higher. Compare that with Phoenix at an elevation of around 1,000 feet. Higher elevations can produce decent quality popular apples such as 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, proceed with caution when growing lower-chill varieties such as Fuji, Granny Smith, Gala, White Winter Pearmain, Winter Banana, Gordon, Yellow Bellflower and Pettingill. All apples perform better in hot desert climates with protection from late afternoon sun.

Q: I have a 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 get damaged during the winter and are better quality.

Some vegetables like beans freeze to the ground during freezing temperatures, while others such as peas, spinach and radishes may sail through the winter with no problems. If you don’t want to cover them, make sure your garden is growing cold season vegetables that are tolerant of freezing temperatures. These include vegetables such as radish, spinach, Swiss chard, broccoli, cauliflower, cabbage, lettuce and many kinds of greens.

There are other types of damage that reduce the quality of winter vegetables if they are not covered. This includes leaf tip burn on lettuce, spinach and chard. Their quality improves if covered with something that reduces wind and intense sunlight.

To be on the safe side, get a 1 ounce or better frost blanket and cover your growing area when temperatures are predicted to drop below freezing or during windy weather. Depending on the frost blanket, it can allow 50 percent or more of the sunlight to reach the vegetables. It also breathes while at the same time raising the temperature under the blanket 5 or 6 F.

Follow supplied directions and tack it to the soil so the wind doesn’t get under it. Don’t use burlap or plastic sheeting. They will not perform as well. Spend the money. Buy the 1 ounce or heavier frost blankets and they will last for three, four seasons or more.

Q: I’m getting ready to place an order for wine grape plants. Currently, I have 25 plants that are 3 years or older. These consist of mainly zinfandels and cabernets with a few merlots. Can you give me any information on nurseries and type of plants I may need?

A: A good selection of wine grapes from nurseries are going to be hard to find for the serious wine lover and gardener in the hot desert. Retail nurseries carry the basic European vinifera varieties, as you mentioned: merlot, zinfandel, cabernet.

It could be argued that both merlot and cabernet sauvignon should probably not be grown here unless you are just having some fun and not serious about the quality of your wine grapes. It’s too hot for them.

Other vinifera types that perform best in cooler climates include chardonnay, pinot noir, riesling and many of the “white” wine grapes so stay away from them.

Basically, stick with the so-called warm climate grapes. Summer muscat is a good one for our climate if you like that foxy flavor of muscats. Others include syrah (shiraz), petit syrah, barbera, grenache, sangiovese, malbec, tempranillo and viognier. Syrah is always a good one for blending as well as barbera, grenache, merlot, petit syrah, zinfandel and primitivo, which some claim is a zinfandel.

Many wine grapes come grafted onto a rootstock, just like fruit trees. This is a must in California due to pest problems that decimate wine grapes there. In our more isolated desert climate, it is probably not necessary. Grapes growing on their own roots will work or grow your own from cuttings and propagated in March.

If you are faced with buying grafted wine grapes, look for rootstocks such as 1103P, 110R or 5C, which are arguably better for our desert soils than some others.

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