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University of Illinois Extension serving Fulton, Mason, Peoria and Tazewell Counties

Main Office (Tazewell County)
1505 Valle Vista
Pekin, IL 61554
Phone: 309-347-6614
FAX: 309-347-5472
Email:uie-fmpt@illinois.edu
Hours: Monday-Friday 8:00am to 4:30pm (Closed 12 - 1pm)

Branch Office (Fulton County)
15411 N IL 100 Highway
Lewistown, IL 61542
Phone: 309-547-3711
FAX: 309-547-3713
Hours: Monday-Friday 8:00am to 4:30pm (Closed 12 - 1pm)

Branch Office (Mason County)
133 S High, Box 170
Havana, IL 62644
Phone: 309-543-3308
FAX: 309-543-6239
Hours: Monday-Friday 8:00am to 4:30pm (Closed 12 - 1pm)

Branch Office (Peoria County)
4810 North Sheridan
Peoria, IL 61614
Phone: 309-685-3140
FAX: 309-685-3397
Hours: Monday-Friday 8:00am to 4:30pm (Closed 12 - 1pm)

News Release

Sticky Crops

July 9, 2012

During intense periods of drought-like conditions, producers sometimes begin to notice that alfalfa and corn are being covered with a sticky substance that clings to the leaves. Closer examination shows massive amounts of small insects to be present. Many diamond-shaped blue-green insects may be present in corn, and many diamond-shaped tan or green insects may be observable in alfalfa. In both cases, the insects appear to be the cause of the problem. The bad news is that the mass of diamond-shaped insects are damaging the crop in question, and these insects are in the process of excreting the "sticky material" that covers leaves.

Further examination of leaf undersides or tassels in combination with a good insect book in hand, will show these 1/8 inch-long blue, green, or tan insects to be aphids.

The aphid is an unusual insect in that it requires no mating to reproduce. Instead, the aphid can use a process called parthenogenisis to increase its number. In effect, one aphid is needed to begin a vast infection, and each one of its offspring are born already pregnant. In a short time a plant can become covered with these insects.

How do they cause their damage? Aphids are plant suckers. In other words, they inject a needle-like mouth part into the plant and begin to devour plant sap. So much sap is taken in that the aphid doesn't know what to do with it and releases the rest as a sticky substance referred to as honeydew. This honeydew, with enough production, sometimes runs on the leaves causing them to look glossy in appearance and falls off the affected area covering lower leaves.

In corn fields, we usually do not get too concerned with aphid infestations until about half of the tassels are infested and pollination is being disrupted. In alfalfa fields, aphids should be controlled when more than one hundred are detected per each sweep taken with a fifteen-inch sweep net.

Hot weather increases these insect populations and increases their ability to impact yields as they feed. If rainfall is needed in an area, problems with this type of insect will become further widespread with time.

The good news is that one may occasionally find "exclamation point" shaped, black insects along with the aphids. In actuality these insects are part nature's solution to the "aphid problem." These insects are actually the larval stage of the lady beetle, often referred to by youngsters as lady bugs, and become nearly as prevalent as the pests in order to feed on them. One can often use their presence as a diagnostic tool for insects such as aphids. Further examination of leaves may also show that the pupal stages of the lady beetle are also present as immobile, lady beetle sized, orange objects with no apparent legs, wings, or head. As the different stages of lady beetle develop, they can provide some aid in controlling aphids, as well as other minor insect infestations in the field.

Source: Matt Montgomery, Extension Educator, Local Food Systems and Small Farms, mpmontgo@illinois.edu