Aphid populations boom Numerous growers cornered me during the county fair and asked me for information about soybean aphids. This is a new insect so everyone, including Extension Educators, are scrambling to find as much information as we can for growers. We just don’t have enough solid data to accurately predict what triggers populations to either explode or crash. Soybean aphids were first identified in the United States in 2000. They are native to China and Japan and are found in other countries where soybeans are grown. We do know that soybean aphids have the ability to increase in number very rapidly. Most exotic species thrive in new environments if they have the right weather conditions and food. In nature, other plants and animals keep native populations in check. The soybean aphid may be a problem for several years until our native insects and diseases build up and help control these aphids. The last week of July conditions must have been favorable because growers were surprised by aphid populations in their fields. In such conditions, aphids can double their population in two-three days. Counting aphid populations is not fun, but growers need to carefully scout fields and spray if aphids exceed the economic threshold of 200-250 aphids per plant. It’s possible some fields will need to be sprayed a second time when aphids repopulate fields. This is why we have encouraged growers to delay spraying until aphids reach the economic threshold. Growers in the Fergus Falls area had high aphid populations last year all the way through leaf drop in September. The year before, in southeast Minnesota, aphid populations crashed in early August. What aphid populations will do this year is anybody’s guess. Rust in lawns As far as I know, rust can infect nearly any type of plant including pine (white pine blister rust), apple trees (cedar apple rust), roses and soybeans, which has midwest soybean growers worried. In rural Minnesota, small grains are notorious for having rust. It can be very destructive to barley, oats and wheat if infections occur early in the growing season. Plants develop rusty orange colored spots that gradually spread to other parts of the plant. Heavily infected fields have poor yields and test weight because the disease weakens and sometimes kills plants prematurely. Rust can also infect certain types of bluegrass in lawns. Merion and Touchdown are two varieties of bluegrass that are more susceptible to rust. Rust infections occur when the weather stays warm and humid for extended periods of time. To control rust in lawns, water in the early morning hours, maintain soil fertility, and mow grass frequently to remove grass clippings. This makes it hard for the disease to become established and spread in the lawn. Fungicides are not recommended. When seeding a new lawn, it is advisable to avoid these two varieties of bluegrass.
