Q: Our apple trees had a lot of fruit set this year. When is a good time to reduce all of the fruit clusters to a single fruit? I once heard that a rule of thumb is to have one fruit for the distance of a pop-can.

A: It is best to thin apples within six weeks of the time that the petals start to fall off the flowers, but later is better than never. The chemicals in the fruit tree, which are used to produce seeds in the fruits, prevent the next year's flower buds from growing. Therefore, the longer fruit stays on the tree, the fewer flowers will bloom the next year. If many apples are left on the tree for too long, the weight could break the branch. Even if the branch remains intact, most of the apples could be too small to use.

Apples can bear fruit on two types of branches, but each apple variety tends to reproduce on only one of the two kinds. They can be singly on the ends of one-year-old shoots or available in clusters on short spur branches. If they are growing singly, reduce the quantity to one apple for about every 6 inches on the length of the main branch.

Apples grouped into clusters usually have a single large one in the center of the cluster - the flower that bloomed first is referred to as the king apple, because it had a head-start on the other apples. You can keep one or two apples per cluster. Save only the king or other apples that have a large stem feeding them. If the king is deformed, keep one or two other apples in the cluster. Remove the smallest and the most misshapen ones.

Young and thin main branches should have fewer fruit kept, so they don't break under the weight as the apples become bigger. Old sturdy branches can safely bear more fruit.

Use scissors or small pruning shears to remove stems. Pulling will break off clusters and maybe whole spurs, which can reduce the number of fruit possible in the future.

Q: I have determined that I have a thorny shrub or vine that is called greenbrier. It is nasty and taking over an area of my wooded lot. I have cut it down, poured weedkiller on the surrounding ground and used gasoline on the base of the plant, but it is coming back again. I can't kill it, but I sure want to. How can I get rid of this plant?

A: I will agree with you that greenbrier is a nasty plant that spreads all over. The stems are covered in sharp needles, and the plant is resistant to weedkillers. There are several hundred species in the genus Smilax growing across the country - some are evergreen and some contain thorns. They do spread easily by birds eating the berries and leaving behind the single seed found in each one. By rhizomes, the plant reproduces into widespread thickets that shelter small animals and birds.

If you kill one plant, nearby rhizomes can send up new growth that appears to be from the original plant. The top can survive fire burns because the rhizomes survive. Pruning and chopping up the top will have the same effect, as the plant sprouts anew from rhizomes.

Weedkillers come in three major groups. Nonselective kill all plants, some chemicals kill only grassy plants and others kill only broad-leaved plants. Don't use the one designed for grassy weeds; the others should work fine.

Follow the label directions. Neither overdosing nor applying it to the roots, if it is designed to soak into the leaves, help destroy the plants. Usually, an overdose will just burn off the leaves, leaving the root to continue sending up more. Smaller doses over a period of time are more effective. Look at the label to see if Smilax or brier is listed on the label. Most weedkillers need to be applied to actively growing plant tissue. After cutting off all the stems, all new growth should be treated weekly until the roots stop reproducing. If you skip a week or two, you will be starting over again.

Don't use gasoline as a weedkiller. It can kill many plants, but as you have found out it fails sometimes. You could end up harming other plants and polluting the soil.

Q: While I was planting some new shrubs in my flower bed, I found some grubs. How concerned should I be? Do I need to treat them with something? Will they eat the roots of my new shrubs?

A: Unless you found hundreds of them, I wouldn't worry. Grubs are present in practically every square yard of topsoil in North America. They do eat some roots on plants, but won't cause harm unless they develop in large numbers. Applying insecticides at this time of year might stop some of them, but most are at a stage where insecticides don't really affect them.

E-mail questions to Jeff Rugg, Kendall County unit educator, University of Illinois Extension at jrugg@uiuc.edu.

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