Corn Information

Disease:  For many years, corn has been adversely affected by a variety of diseases. But in drier climates, such as here in the tri-state area, fungicides were almost never used on corn, since disease was not as common, and because the fungicides were not well known or were not considered to be economically viable.

Since 2005, several fungicide manufacturers have been testing and promoting the use of fungicides such as Headline (BASF) and Quilt (Syngenta) on corn, soybeans, and sunflowers, using them in areas where they were previously unknown, and at disease levels much lower than previously thought to be economic. In addition, the companies began to note a general "plant health" benefit which occurred after application of the fungicide in fields with low disease pressure. In 2007, we presented a summary of the data in our newsletter, which you can reread by clicking here.

In 2008, BASF has a Technical Bulletin which claims that in 2007, an additional $450,000,000 worth of grain was harvested because of Headline applications. They now have over 3,000 on-farm trials, and claim 12-16 bushel per acre increases. To read the 2008 BASF bulletin, click here. (PDF, 1.1 MB)

Syngenta has similar, but less extensive data, for Quilt. Both products are considered to be effective when timed properly. Quilt has two active ingredients: a dual action which Headline does not have. Products such as Tilt can be tank mixed with Headline to achieve a similar dual action.  It is interesting to note that Syngenta says that Quilt can increase silage corn tonnage, too: 3.2 more tons per acre is the 2008 figure.

There is no question that controlling disease in corn increases yield, but the argument that there are "plant health" benefits even at low levels of disease has not been confirmed by some universities. It is clear that in many instances, dramatic yield increases and significant plant response occur. Click on the link to the BASF bulletin (above) to see some impressive  photographs.      

Weeds: The are a large number of herbicides which can be used on corn, both as a preplant application and post-emerge.

In the last few years, there has been a major move toward using glyphosate-resistant ("Roundup Ready") corn varieties. The popularity of this technique is obvious: initial control was excellent, and the cost, even allowing for the increased seed cost, was less than the more expensive traditional herbicides.

In 2008, the price of glyphosate increased dramatically, and the issues of weed resistance from overuse of the product are becoming more serious each year. To read more about the resistance issue, click here. 

For more specific corn herbicide recommendations, please contact us. There are a large number of variables to consider, including expected yield, type of weed pressure, rotation cycles, and historic usage on the field. In addition, the KSU Guides shown below have a lot of good data.

Insects: Controlling insects in continuous corn requires both investment and planning. In some cases, GMO seed can be used, but the cost of the seed is often significant: if your crop requires pesticides every year, the GMO seed can be a good deal. If your crop does not always have high insect levels, using conventional insecticides might be less expensive, since in some years you will not have to treat the insect.

Corn rootworm larvae: These insects eat the roots of the corn plant and cause lodging if not treated. They hatch from the eggs of the adult, the corn rootworm beetle, which lays them in the prior growing season. This means that continuous corn is most likely to be affected. Seed treatments can help, and traditional planting time insecticides are normally effective. GMO (Bt) corn can be employed, but there are refuge requirements.  Furadan 4F applied later in the season and watered in is effective, since the timing of the insecticide occurs when the larvae are freshly hatched. Another program, which entails monitoring and then treating the adult beetles--typically with Penncap M--so that no eggs are laid, is also effective. (See below.)

Corn rootworm beetle: This is the adult stage of the larvae described above. The adults reduce yields by clipping silks, thereby reducing pollination. KSU says that you need 8-10 beetles per silk. If you are treating the adults to reduce egg laying, the gravid females are carefully scouted and typically treated with two applications of Penncap-M. .This program can be economical, since the adult beetles are commonly treated anyway, and often a miticide or other pesticide can be tank-mixed into the second adult beetle treatment.

To see an adult corn rootworm beetle, click here.    

Western Bean cutworm: This insect, while not common generally, does occasionally show up in our area.  Begin looking for egg masses on the upper side of upper leaves at first tassel, and keep checking until silks are brown. If four plants in 50 (8%) have egg masses, you should treat, based on $2.50 corn.

The egg masses are distinctive: small whitish spheres, which turn brown as the larvae get closer to hatching, finally resulting in the "blackhead stage."  The eggs  are not overlapped or shingle-like, as in the case of corn borer (see below).

Treat when the corn is 95% tasseled to protect the ear tips from the hatched larvae. Do not delay treatment, as escaped larvae will be more difficult to control. Some Bt corns have resistance, but not all.

To see a Western Bean cutworm egg mass in the blackhead stage (very close to hatching), click here.     

Corn borer: In this insect, both first and second generations can cause economic damage, There are two types, European corn borer and Southwestern corn borer, but our area only has the European corn borer. Yield losses from both generations included reduced ear and kernel size, dropped ears, and lodging at harvest. Much of the damage is caused by the larvae boring into the plant, although some kernel damage from feeding is possible with second generation insects.

The egg masses are flat, about 1/4" in diameter, and mostly laid on the underside of the leaves near the mid-rib, although they can be anywhere on the plant. The eggs are pale colored and overlap, resembling shingles. Moths lay the eggs on calm evenings.

To see a European corn borer egg mass, click here.

First generation corn borer occurs occasionally in our area, but not commonly. Scouting for live larvae and egg masses should begin when corn is 18 inches tall. After the larvae bore into the stalk, the unrollling leaves have a distinctive "shot holed" appearance--click here to see a pop up photo--which indicates that the borer is present. Borers which have already bored into th plant resist control, so if you see the first shot-holed leaves, and you have 50% infestation (live larvae on half the plants),  based on $2.50 corn, treat immediately. Some varieties of corn have natural resistance to the first generation larvae, called DIMBOA, which is why you should look for live larvae in the plant's whorl. Bt corn has some resistance to 1st generation ECB.

Second generation corn borer is very common in our area. The moths again lay eggs on the underside of leaves. The egg laying can occur over a long period, generally beginning at silking, so cumulative counts taken over successive scouting trips are used to trigger control measures.  Treatment, on $2.50 corn, is recommended when you have 10-20 egg masses per 100 plants. This is a rough approximation: to read an excellent and extensive article on corn borers, which has more refined economic threshold calculations, please click here. 

KSU also has publications which provide a lot of information: links are below.

Second generation corn borer treatments can often be combined with spider mite applications, saving the cost of one application.

Spider mites:  Mites are easy to scout, even though the insects are very small. Mites generally begin building colonies on the bottom side of the lower leaves of a corn plant, and the tissue destruction is seen from above as a yellowing, usually beginning in the midrib area. Closer inspection of the leaf underside will reveal mites, eggs, and webbing. The leaf is damaged by the piercing of the tissue and the sucking of the juices by the mites.

There are no GMO seeds to control mites: insecticides and natural predators are the only mechanisms available.

There are two varieties of mites in our corn: the two-spotted mite and the Banks grass mite. The TSM and BGM react slightly differently to insecticides, and the BGM usually occurs earlier in the season and is easier to control. There are many natural predators for the mites, and they can be effective in slowing an infestation. Since treating for other insects often reduces predator pressure, miticides are often tank-mixed into those applications in an effort to avoid the mites "flaring".

To see an illustration of the two varieties, click here.

If your corn has a long history of heavy mite pressure, an early application of an ovacide, such as propargite (Comite), can be quite effective. Applied to 3 foot tall corn, the eggs are controlled, and the natural predators are left undamaged, resulting in good control throughout the season. In some years, another application may be required to control late emerging adults, but propargite is generally quite effective and results in excellent yield benefits, due to the lowered mite pressure during the growing season. In our area, many fields do not have the persistent mite pressure to justify this technique, however. It is interesting to note that mite populations will continue to increase before they decrease, because only the eggs are controlled by propargite. If you have persistent mite pressure, this is an excellent option.

A new entry in the field is Oberon byBayer, a product which shows good efficacy. Oberon needs to applied early, not as a rescue treatment, due to its mode of action. It also reduces predator damage. Oberon is relatively expensive, and has not been used by many local growers, however.  To read more about it, click on this link to the Bayer website. 

In past years, early in the season when BGM were emerging, many growers added dimethoate to their other applications, or even used it alone to suppress emerging mite colonies. Dimethoate was inexpensive and did an acceptable job of suppressing mites. However, in 2008, bifenthrin's (Capture) price is only slightly higher than dimethoate, so it has become the product of choice.

As the season matures the TSM joins the BGM in the field, and overall mite pressure increases. This is when bifenthrin (Capture) has always been the best choice.  As a bonus, bifenthrin will also control corn borers.

The trick in mite control is not to wait too long to begin control, and to remember that other insect control measures might affect the beneficial populations, thereby flaring the mite populations. As the leaves yellow and move up the plant, greater damage is done. There is some disagreement as to when mite control should begin, but when leaves are as high as the ear, treatment is certainly required. Many growers treat much earlier than this, and with higher corn prices, earlier treatment is likely profitable. Nebraska has an excellent NebGuide which discusses economic levels: click here to read it. (PDF, 510 KB)

To download the 2008 KSU Corn Insect Management Guide, click here. (PDF, 587 Kb)

The September, 2007, KSU Corn Production Handbook can be downloaded here. (PDF, 1.2Mb)