Soybean aphids arrive Fairly high populations of soybean aphids are appearing in area soybean fields. We expected the aphid to cause problems last year but only a handful of fields were sprayed. This year aphids seem to be quite common in eastern counties in the state. Populations are significantly less in counties farther west. Scout fields through mid-August, and watch for aphids on the underside of the leaf concentrated near the last emerging trifoliate. The economic threshold is 200-250 aphids per plant. Whole fields should be scouted because aphid populations will vary widely in a field. Often they are concentrated near the field borders. A number of insecticides are available including Lorsban and Warrior. They can be applied by ground sprayer or applied aerially. If applied with a ground sprayer, use at least 15 gallons of water with high pressure to improve coverage. Where’s the fruit? You’ve done everything right. You planted your new tree at the right depth. You’ve nurtured it, watered it, talked to it; and yet it fails to bear the fruit promised in that glossy garden catalog. What happened? Fruit trees need several things in order to bear fruit and often something prevents it from happening. The likely causes may be any of the following: o The tree is too immature and has not yet reached bearing age. o Some cultural practice is lacking. o It’s planted in an area that does not receive enough sunlight. o Stress from improper soil conditions (too wet or dry), or from insects or disease. o Lack of insect pollination. Most standard-sized fruit trees require five to seven years after planting before they will bear fruit. Dwarf trees usually fruit sooner, within two or three years after planting. A fruit tree requires at least eight hours of direct sun daily to grow, flower and set fruit well. In addition, fruit trees require annual pruning and pest management to maintain optimum health. That does not mean that you have to spray “willy-nilly” every time you see an insect. Rather, pay attention and learn to identify the insects present. The insect world is much like our human world; most are beneficial or harmless and pose no harm to your tree. Excessive applications of pesticides kill the beneficial insects which generally keep the pests in check. Even with good cultural practices, a particularly harsh winter or a hard freeze in early spring can damage the flower buds – which means no fruit this year. This is especially true for fruit trees that bloom very early in spring, like tart cherries and plums, and species that lack hardiness in our region like peaches and sweet cherries. Even rainy weather during bloom can reduce or eliminate a crop by hindering the insects that pollinate the flowers. This actually may happen more often that we think. Finally, apples, apricots and hybrid plums require that two different varieties be located within 100 feet of each other for pollination to occur. Tart cherries and European plums, however, can self-pollinate. For more information on this or other topics, contact Jim Stordahl at stordahl@umn. edu or call (800) 450-2465.
