Watch For Two-Spotted Spider Mites Damaging Soybeans

Spider mites are a common pest during dry conditions. This pest prefers dry dusty conditions.  Under a severe drought, mite populations can double every 5 to 7 days.  Rains can cause the mite populations to decline but fields should continue to be scouted.

Spider mites are first found along field borders or waterways.  Mite damage first appears as speckling or spots on the soybean foliage. Later injured leaves turn yellow then brown and die.  Damage moves across the field as mites infest additional soybean plants. 

You may need a hand lens to see mites.  Also, a white sheet of paper to shake the mites on will help you see them.  The mites once shaken on the paper will crawl about.

Generally, spider mites occur later in season.  However with the dry conditions, damage can be found on small soybeans.  A general recommendation is to control this pest when the foliage yellowing reaches 20% before pod set and when foliage turns 10% after pod set.

Heavy infestations of this pest can cause severe damage.  In my experience in the 80’s, spider mites would begin as a small circle in the field.  Then the wind would catch them and move them across the field.  There would be small circles of damage from the pest, and then the circles would enlarge causing damage.  It is important to note that the yellowed areas are already damaged and the pests are moved onto undamaged plants to feed.

Scouting is critical.  Since wind picks up this pest, one should watch the entire field.  Plants may show damage symptoms for up to 7 to 10 days following control of spider mites.

Dr. Bailey reports spider mites found along the Iowa and Missouri borders.  At the time of printing of this news article, I have not had any local reports into the Extension office.  With dry weather, however, it is a matter of time before we have this problem.

For more information, contact Wayne Flanary at 660-446-3724 or Heather Benedict at 660-425-6434, Regional Agronomists, University of Missouri Extension.

Scouting Area Fields

This year, drier conditions have brought about a number of issues.  Rootless corn syndrome continues to be an issue.  However, in areas that received rainfall, many of the plants will root into the moist soil and recover.  Those plants that have wilted and lay over, will not recover.

 

Dry soils also caused early season nitrogen deficiency on many corn fields.  Soil moisture is needed so plants can take up nitrogen.  Corn plants with nitrogen deficiency will have light green color.

 

Insect pests being found in other areas of the state should also be scouted.  False cinch bugs can cause damage to emerging soybeans when numbers get large.  They are often found following herbicide control of Peppergrass and Shepherds Purse.

 

Brown stink bug damage has been found on corn.  The damage occurred early and the plants exhibit twisted and damaged tissue.  Brown stinkbug is generally found along the field borders however, can be found across the field.

 

Musk thistle head weevil is working on local musk thistles.  The weevils eat the seed of the bloom causing the seed to be sterile. The underside of the head will have eggs and will look like drops of mud.  If you split heads open, there will be feeding larvae.

 

If conditions continue to be dry, there is an increased risk of spider mites.  Spider mites would preferably feed on soybeans but also can feed on corn.  They are often found on the underside of leaves.  Use a white piece of paper and shake the leaf so they will spill onto the paper.  They will move when exposed to sunlight and also a hand lens is helpful in diagnosis.

 

For more information, contact Wayne Flanary at 660-446-3724 or Heather Benedict at 660-425-6434, Regional Agronomists, University of Missouri Extension.

Extension Area Crop Pest Report

Growers have been finding high levels of alfalfa weevil and aphids. Fields have been sprayed but please refer to the pre-harvest intervals for insecticide applications. As far as aphids, different aphids have different economic thresholds. Use alfalfa weevil levels as a priority to guide spraying decisions.
The use of cover crops has provided additional complexity to herbicide program especially when managing glyphosate resistant weeds. The recrop intervals as provided on the herbicide label will some information of potential injury to planting a fall cover crop.
Weeds have an early start this spring with warm temperatures. Early herbicide applications may not last as long as you would typically expect. The early herbicide application timing should be monitored carefully for potential escapes as the weather impacts planting date.
Corn planting depth that is most concerning is too shallow especially in no-till. Coulters must cut residue and not hairpin residue into the seed furrow. Deep running of trash whippers may cause heavy rains to cut through the track especially if not running with soil slopes.
Watch fields coming out of CRP for additional pests or especially any fields that have not had typical management in the past. Pests such as white grub can be found especially the second year after coming out of sod. Scout fields carefully for crop injury.
Black cutworm moth flights in northwest Missouri have been light. As of this date, one may find an occasional area within a field that may have damage.
For more information, contact Wayne Flanary at 660-446-3724 or Heather Benedict at 660-425-6434, Regional agronomists, University of Missouri Extension.

Crop Insect Pest Update

The Statewide Pest Monitoring Network uses traps to monitor crop insect pest activity. The trapping is conducted by the University of Missouri Extension Specialists. You can use this site to monitor the trap counts of various pests that you are interested in. The data can be found at http://ppp.missouri.edu/pestmonitoring.

At the website, you can examine different pests, location and dates that most interest you. The data listed indicates the location, the trap count and the amount of days for which the count represents.

Currently, our local traps indicated some earlier black cutworm moth flights but light in numbers. We had some additional moths move in with the high winds from the southwest. However, again, these are light in number. In these situations, we may have areas in a field that attract moths and cause localized cutting. Monitor corn fields for any cutting activity and spray only if needed. We are fortunate in Northwest Missouri as other areas of the state had significant moth flights.

Also, growers may have used insecticide seed treatments, but the use of these products will not provide adequate control of black cutworm. Be sure to scout your fields.

Other pests one should watch for include white grub and wireworm. These insects feed below the ground. Often the plant will wilt and die. Examine the crown area of the plant for feeding injury.

Now also, is the time to monitor winter wheat and tall fescue for True Armyworm. True armyworm can also cause considerable damage by cutting wheat heads and stripping leaves from fescue. We have caught moths in traps but again low in numbers. However, be sure to scout as these insects can attack a field and leave other fields alone. Once in a field, they will move as a group.

If you have any fields that experience insect damage, please give us a call. This will help us to determine the extent of insect pest activity.

For more information, contact Wayne Flanary at 660-446-3724 or Heather Benedict at 660-425-6434, Regional Agronomists, University of Missouri Extension.