Today’s foray into soybean fields has shown that soybean aphid numbers are increasing.  Today I was able to find several areas where numbers easily reached into the 500-1000’s per plant.  In fact, some of these areas were already in the honey dew/sooty mold stage.  Interestingly though, outside of these few areas, nothing else can be found; even in the same fields as these heavily infested areas.

 

Normally, I would have expected current aphid levels to have shown up about three weeks ago.  And, normally, it would have taken a few weeks for them to progress to treatable levels.  Does that mean about three weeks will be the optimum time to spray?  I don’t know.  For certain, our current weather is affecting their growth and spread.  All we can do is keep watching.  The attached photo is one of those hot spots not far from Wood Lake.

What about treatment thresholds?  You all have heard that 250 aphids per plant over 80% of the field is the economic threshold.  The actual threshold is 6000 aphid days – this means plants with one aphid per plant for 6000 days, or 2 aphids per plant for 3000 days, or 50 aphids per plant for 50 days or 250/plant for 24 days or 3000/plant for 2 days or 6000/plant for 1 day. You get the point.  This is a very difficult threshold to monitor.  The 250/plant threshold is used because it has been found that by the time they reach that level, the 6000 aphid day threshold has been (or soon will be) reached.  This is important to know because low levels of aphids over an extended period of time can be damaging, especially when the plants are already under other stresses.  Also, it is an economic threshold.  Your tolerance for aphids is justifiably lower on $16 soybeans.

Here is a quick update on what I have found in soybean fields.  First, soybean aphids are still very scattered and light.  I was in fields from around Granite to Cottonwood, Wood Lake and Belview.  So far most everywhere levels are low, but some pockets around Granite (north of Granite actually) are starting to do some spraying.  In many fields, SBA are still very hard to find.

I've been noticing a lot of yellow flash from these late applications of glyphosate, but there is yellowing from soybean cyst nematodes and actually some yellowing from potassium deficiencies.  The K deficiency is not because of low K levels in the soil, but rather the plants inability to properly utilize it because of the droughty conditions.  Don't use this as an excuse to apply a foliar fertilizer though because it will do you no good.  Simply, if the plant is unable to use the available potassium now, adding more will not make it any better since it is not a deficiency, but rather a physiological inability to mobilize the potassium.  Given the conditions, I would expect to see other deficiency symptoms as well.

I also looked at some corn ears to see how pollination went.  For the most part I'm impressed with how well the ears are filled out.  There is some noticeable gaps in the ears but given the conditions, not bad.  The picture above is a typical ear that I found today.

Here are a few comments on some insect observations in soybeans:

Soybean Aphids-
    
Aphids are present, but as of today they are at very low levels.  Even the fields that have had a history of being the first infested are almost devoid of any significant numbers.  The weather conditions we have been experiencing has been hard on them, but rest assured, they will show up in numbers to control in at least part of the area.  Vigilance is paramount.
    Your control options are the same as in past years. Some companies do offer respray protection guarantees with their products, and of course, they will cost more per acre.  The product you choose should be based on the current environment though, not a manufacturer program.  With the dry, hot weather the pyrethroid insecticides will not work as well since they are more easily degraded by this weather.  They also are not effective on spider mites, which we may have to deal with as well.

Spider Mites-
    Every time it gets hot and dry it seems that industry gets on the spider mite bandwagon. It is a worry, but again, mites are not at levels that require control - yet. I did run across a field today that I believe will need to be sprayed for mites soon. Unfortunately this field did not have any aphids, so spraying now does not guarantee no aphids in the future.  This may be a case were relying on one of the manufacturer backed products may be beneficial.  Spaying a pyrethroid insecticide on this field will not control the mites and will probably flare them.  Choose wisely.
    What do mites look like?  Well, the mite itself is very small. A good magnifying glass or microscope is needed to see them. This picture above is one I took with a microscope with a 60x lens.  Leaf symptoms are a bit easier to see.  Generally you will first notice symptoms on the field edges (although the field today was not) and they look like the picture below.  Not the best picture, but it does show the stippling that is typical of mites.