June 9, 1993

Flowering of Conifers

Some people find it hard to believe that plants must flower in order to set seed. In many woody plants the flower isn't very attractive. For some, the flowers are barely distinguishable from the leaves. Flowers of the conifers (pine, spruce, fir, and other cone-bearing woody plants) are called strobili, which means small cones. They do not have a calyx, corolla, stamens, or pistils as many flowers do. The strobili consist of a central axis with distinctively shaped scales and bracts. Male and female cones are separate and, in most cases, both are present on the same tree.

Hand Thinning of Fruit Trees

Many fruit trees bloomed heavily this spring and have set a large crop. Unfortunately, some fruit trees are bearing too many fruit. Trees loaded with fruit should be thinned to:

obtain large, high quality fruit at harvest allow development of flower buds for next year's crop, thus overcoming the tendency for some fruit trees to bear fruit in alternate years prevent limb breakage.

IPM Update--Apples and Strawberries


Plant Disease Clinic--Highlights

Peach Leaf Curl

Peach leaf curl is caused by the fungus aphrina deformans. This disease of peach and nectarines is easy to identify. Young leaves appear thickened and puckered and are often a pink or red color. The entire leaf may be affected or only small areas. As the disease progresses, leaves turn a gray color and fall prematurely from the tree. Trees that are severely defoliated may not yield well and are predisposed to winter injury.

Pesticide Poisoning Exposures

The American association of Poison Control Centers publishes an annual summary of telephone calls received by participating poison control centers. Data in the report for 1991 were derived from 73 poison control centers which served a population of 200.7 million people. These centers received a total of 1,837,939 calls on human exposure to poisons.

There's Still Time to Plant the Vegetable Garden

The rainy weather this spring has prevented some Iowans from planting their vegetable gardens. Fortunately, there is still time to plant many vegetable crops. The last practical dates to plant specific crops in central Iowa are listed below. The last practical planting dates are one week earlier in northern Iowa. The dates for southern Iowa would be one week later.

June 20---tomatoes, peppers, eggplants, muskmelons*, watermelons*
July 1---lima beans, sweet corn*
July 20---cucumbers, summer squash
August 1---beets, carrots, snap beans, Swiss chard

Pine Wilt Transmission by Wood Chips?

Pine wilt is a serious disease of pines, especially Scots pine, in the Midwest, including Iowa. Infected trees wilt and die within a matter of weeks to a few months. Although a nematode is the primary disease agent that blocks water flow in affected trees, pine sawyer beetles are the vectors that carry the nematodes from infected to helathy trees. The major recommendation to help control spread of the disease is to remove infected pines promptly and burn, chip, or bury them.