Corn Silks, Stink Bugs, and Foliar Diseases: a Bad Combination

Early planted corn in South Georgia is near tasseling or in a few cases in the early silking stage. This is a time when corn is extremely vulnerable to any stink bug infestation and also to some foliar diseases. First, I strongly encourage all corn growers to thoroughly scout your fields or have your crop consultant scout your fields for stink bug presence and diseases such as southern corn leaf blight (SCLB), northern corn leaf blight (NCLB) and southern rust. In the case of stink bugs, check the perimeter first, then go into the field to check the intensity of an infestation that you may see on the perimeter.

While stink bugs are difficult to control, it is imperative that after scouting the fields, you consider an insecticide application particularly if you plan an aerial fungicide application. The table below (at the end of this entry) was developed by Dr. David Buntin, UGA Entomologist that conducts corn insect research.  He lists the many insecticides available for use against stink bugs.  I’ve also included the few that have some action against spider mites.  Do not inject an insecticide through the irrigation system and expect any control. Use aerial applications during the late stages of growth.  Our current threshold is 1 bug per 4 plants pre-silking and 1 bug per 2 plants at R1 and R2.

Dr. Bob Kemerait sent out a note earlier this week regarding his thoughts on foliar diseases.  He wrote the following: “Some of our earliest corn is rapidly approaching tassel.  My advice to corn growers with top yield expectations is to ask themselves, “Do I need to apply a fungicide as I get to tassel?”  The reason for this is that “tasseling” is a key timing when an application of a fungicide MAY be beneficial to fight disease and protect yield.  Such an application is generally appropriate if the grower is already fighting northern or southern corn leaf blight, if southern corn rust has been detected in the county or in neighboring counties, if weather is especially favorable for development and spread of disease, or if the corn is “late planted”.  Since most of these conditions don’t apply to most of our corn growers at this time, it is not an automatic need to spray a fungicide at tasseling now, UNLESS the grower simply wants to be proactive and to “put out some insurance”.  I can’t argue with that logic, as long as the grower makes an informed decision.  Typically, we don’t find southern corn rust in Georgia, at the earliest, until the first week of June.  We are looking now.  If you or your consultants find what appears to be rust, please let me know ASAP.”

I agree with Dr. Kemerait. If you believe you see southern rust or have a heavy infection of SCLB or NCLB, then let your county agent know. It helps inform others that the weather is favorable for an outbreak.  I do know that over the last week, NCLB has been found in Seminole Co. in a few fields.  If you verify that you have a disease infection taking place, now is the best time to begin that control.  Stay a head of the yield curve by protecting your yield potential.

I will update you a little more regarding fungicide applications.  I encourage you to be diligent in your scouting to stay ahead of any insect or disease problem to protect the yield potential of your crop.

Oh by the way,,,, with all the rain that has occurred, consider taking more tissue analyses to make sure you have sufficient available amounts of nitrogen and sulfur supporting your crop.  It is easy for those and other nutrients to leach and leave you short as you near tasseling and ear development.  Injecting nutrients through your pivot (if you can) is an efficient and effective way to remedy a problem before it becomes a problem.  If you are uncertain as to the nutrient sufficiency levels, the following url will take you to the online UGA Plant Analysis Handbook publication: http://aesl.ces.uga.edu/publications/plant/  .  This is a great publication to check your tissue analysis profile.  If you are low or suspect a problem, contact your local county extension agent to discuss  whether or not you should inject nutrients through your pivot or make an adjustment through an aerial application.

 

 

 

Insecticide

Green or Southern Green

stink bug

 

 

Brown

stink bug

 

 

Spider mites

Asana XL nl nl nl
Baythroid XL 1-2 3 (high rate) nl
Tombstone 1-2 3 (high rate) nl
Fastac 0.83 1-2 3 (high rate) nl
Brigade 2EC (bifenthrin) 1-2 3 (high rate) 3
Delta Gold 1.5EC 1-2

 

4 (high rate) nl
Declare 1-2 3-4 (high rate) nl
Warrior II (Karate) Zeon 1-2 3-4 (high rate) nl
Pounce 25 WP nl nl nl
Mustang Maxx 1-2 4 (high rate) nl
Sevin XLR Plus nl nl nl
Lorsban 4E nl nl nl
Lannate LV nl nl nl
Intrepid 2F nl nl nl
Prevathon 0.43 nl nl nl
Radiant 1SC nl nl nl
Tracer 4SC nl nl nl
Oberon nl nl 1-3
Onager (1.0) nl nl 2-3
Zeal 72WSP nl nl 2-3
Besiege 1-2 3-4 (high rate) nl
Consero 2 3-4 (high rate) 3-4
Cobalt advanced 1-2 3 (high rate) nl
Intrepid Edge nl nl nl
Hero / Steed 1-2 4 (high rate) 3
Stallion 1-2 4 (high rate) nl

Ratings range from 1-5: 1 = Very Effective and 5 = Not Effective; 1 = Standard; 3 = Fair; 5 = Poor; (2 = very good – fair, and 4 = fair to not effective).  ‘nl’ indicates an insect pest is not listed on the product label.  ‘?’ indicates efficacy not determined.

*Insecticide must be able to reach the target pests.  Ratings relate to applications made to the target pest before it enters the stalk or ear.

 

 

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