Systemic insecticide affects entire tree, including fruit

Q: Several weeks ago I noticed whiteflies on my dwarf orange tree. I went to Lowe's where they recommended the following product: Bayer Advanced Tree & Shrub Protect and Feed. Upon reading the instructions it states: Do not use on plants grown for food. But it does not mention trees or shrubs. Can you please tell if this product is safe to use and, if not, what would you recommend?

A: I cannot tell you if it is safe to use on edible crops or not. I went back and looked at the product label online. For some formulations the manufacturer claims you can use the produce on edible crops including fruit trees.

The manufacturer also claims 12 months of control of some insect pests using this product. Some formulations say you can spread the granules under the tree. The tree takes up this product through its roots, where it spreads through the plant; poison then gives 12 months of control to pests listed on the label. This means that the poison has spread throughout the entire plant systemically to provide enough of the product to control the insects for 12 months. This means the poison should also be in other plant parts as well, such as fruit.

These products undergo extensive testing for so-called "safety" issues that must be done before receiving a label approved by Environmental Protection Agency. So our EPA is saying that this product has met its tolerances of "safety" (the agency does not like you to use the word "safe" in instances like this because it does not guarantee any pesticide is "safe") and has approved this label. The product is supposed to be at such low levels in the plant that the government considers it safe to eat.

In my opinion, I would never eat fruit from a tree that has been treated with a systemic insecticide, period - particularly when the manufacturer has claimed 12-month control of insects after its application. It does not make any sense to me to eat fruit from this tree in the same year it was treated with this type of pesticide. I hope this helps.

Q: I have a couple of vines of grapes. Should I cut them back so the stem is about 1 foot high? I've been doing that and have not gotten many grapes from my Thompson plant and none from my seedless Flame. These plants are about 5 years old.

A: If you continue to cut off all of last year's vine growth, you will never have grapes. Bunches of grapes produced in 2012 come from buds on growth that was produced in 2011, the previous year. The only thing you have to do now is decide how much of the growth produced in 2012 you will leave remaining after you have finished pruning.

I usually delay the final pruning of grapes until at least mid-February to avoid loss of fruit from late freezes.

Let me walk you through the steps for pruning table grapes. You can prune wine grapes this way, but wine grapes should be pruned slightly different. With wine grapes we want to be more careful to "balance" the load of fruit with the growth of the vine to get better quality grapes.

I like to prune grapes in either one step in mid-February or a two-step process with an initial pruning of the grapes at leaf fall and a final pruning on the February date. Some people are itching to cut those grapes early, and this will give them something to do. Otherwise just delay the pruning.

There are two things to know before you begin. First, the wood where the fruit is produced is on last year's growth, which is a different color from older, nonproductive wood. It is usually more reddish. I will post pictures on my blog so you and others can see what I am talking about.

Secondly, most grapes are pruned so that the amount of last year's wood, the reddish colored wood, is only an inch or two long. But there are two table grapes that are not pruned like this. These are Thompson seedless and Black Monukka. These are pruned so that the remaining reddish, last year's wood is about 12 to 18 inches long.

When you leave just a very short length of reddish wood after pruning it is called spur pruning and the short stub of red wood is called a spur. When you leave a long piece of this reddish wood, then it is called a cane and you are cane pruning.

Pruning your grapes early can result in no fruit production this next year in our climate. If there are some very low temperatures and strong, cold dry winds blowing across your vines after you prune, it is possible to freeze back the spurs or canes and lose your crop or severely reduce it. If you delay pruning until February, you reduce that risk.

Here is how to prune. Find the end of a stem or branch of a grapevine. Follow it until you see a place where there is a definite change in color from red to gray and the wood looks older. There is a clear separation between these two colors. This is where the 2012 growth began (red) and growth in 2011 (gray and older) ended.

You will see buds on either side on the outside of the reddish stem. Last year's red growth (on buds close to the separation of colors) is where the fruit will be produced for most grapes.

For those grapes that require spur pruning, you can cut the reddish stem back leaving only two buds remaining. Prune ¼ inch beyond the second bud from the gray wood with a straight cut.

For those grapes that should be cane pruned, like Thompson seedless, you should cut the red growth or cane so that there are 10 buds remaining. Essentially it is just a much longer spur. This will leave a reddish cane in length, something less than 18 inches.

Grapevines are notorious for bleeding after they have been cut. In other words you may see water coming from the cut ends. Don't worry about that. It is normal and will heal.

When the vine sets small, BB-sized fruit in bunches, it is time to remove bunches that are poorly formed or have not set berries very well or are too small.

The remaining bunches are then pinched at the bottom, removing about 1/3 of the bunch. This increases the size of the berries that are remaining in the bunch.

If your berries are small, then you did not remove enough bunches or you did not pinch the bottom of the bunch enough. Both are important.

Bob Morris is a horticulture expert living in Las Vegas; he is on special assignment in the Balkh Province, Afghanistan, for the University of California, Davis. Visit his blog at xtremehorticulture.blogspot.com.