Sorghum progressing well through many areas of the state but sugarcane aphids are looming

What does the crop look like?

Throughout the state, the crop could be considered average to above-average.  However, similar to wheat, canola, corn, soybean, and cotton crops this year, it is highly variable.  Certain areas that have received moisture have taken advantage of the warmer temperatures and look quite well.  The areas that have not receive rains or only portions of the overall rainfall have more evident stressed plants.

Sorghum_chickasha
Above average sorghum crop planted early near Chickasha.  This area has received numerous rains since planting.

What will happen to these stressed plants?

This will depend on what happens in the next several days to weeks.  Areas of the state that have failed to receive many of the recent rains, the crop is starting to struggle.  This has resulted in a majority of leaves beginning to roll earlier in the day.  Even under these stressful conditions, many earlier maturity sorghum hybrids are beginning to push reproductive growth.  Moisture stress during booting and early flowering stage quickly reduces yield be decreasing the total number of seeds set for each head and decreasing overall seed size.  If water stress continues, it will decrease seed weight in addition to the other factors.  This will result in many of these hybrids yield potential, that could be achieve later in the year, decreasing.  However, we cannot forget that the tillering nature of sorghum can allow the plant to recover from these conditions a lot better than most other crops, as long as adequate conditions return shortly.

Can these recover?

Yes, the crop can still recover, especially if the crop was planted into decent moisture and had any degree of moisture within the soil profile.  Yield have begun to become to be limiting.  However, this is only after moisture stress.  Grain sorghum leaves will inherently begin to roll when humidity is low and temperatures are high.  Growers should evaluate moisture stress between 9-10am.  If leaves are already rolled or have started to roll, the plant are under moisture stress.  If leaves do not begin to roll until later in the afternoon, this is a natural reaction to the environment around the plant.  If hot, dry conditions persist, moisture stress will get more severe and the physiological response will occur earlier in the day.

Droughty_sorghum
Moisture stressed sorghum.  Leaves were rolled by 10am

What about sugarcane aphids?

There has been increasing reports of sugarcane aphids being found throughout the state.  The best place to keep up to date with sugarcane aphid activity is the MyFields website (https://www.myfields.info/pests/sugarcane-aphid).  This will keep you up to date with where sugarcane aphids have been identified by sorghum specialists from around the state and nation.  It must be noted that this is done on a county by county basis and your county being on this list solely means sugarcane aphids have been found in your county on sorghum.  Furthermore, this does not indicate that sugarcane aphids have even been found at a treatable level in the county but they have just been found.  Seeing your county on this list should solely be an indication that extra care and scouting should be done and not that action is warranted.  This should be used as another tool at producer’s disposal to help with management of sugarcane aphids.

What will the temperature do with sugarcane aphid populations?

Overall, general thought is that hot and dry conditions cause an increase in population to sugarcane aphids.  The mechanism for this is a little less known.  Some have indicated that sugarcane aphids thrive in these environments and can quickly overwhelm the grain sorghum plants due to not only population increases but the added stress on the plants from the environmental conditions.  Other indicate that sugarcane aphid population growth is not directly influenced by hot and dry weather but rather beneficial insects that would typically help keep aphid populations in check and negative impacted by these conditions.  Decrease in beneficial populations allows the aphids to grow unchecked and result in a drastic increase in population.  Indifferent of the mechanism, under hot, dry conditions, aphid populations will likely continue to increase and extra scouting should be done in order to catch populations low prior to any needed application.

When should I make an application for aphids?

Target threshold for aphid applications is the same as it has been the last several years.  We are looking for 100 aphids per leaf.  However, the way we distinguish this threshold has changed from previous years.  This season, when scouting for aphids, we will need to evaluate a minimum of 20 plants.  It is better if 40-50 plants are evaluated but 20 gives a decent indication.  Once a plant has been identified, growers will need look at two leaves.  This will make a total of 40-100 leaves being evaluated depending on how many plants are selected.  If over 50% of these leaves surpass the 100 aphid per leaf threshold an application is warranted.  We have shifted to this newer evaluation method to ensure applications are being made when aphids are present throughout the field and not just in isolated hotspots.  If hotspots are identified, there may be a validity in spot spraying these areas, especially if they are areas of the field prone to aphid movement and buildup (i.e. edges of fields near ditches with Johnsongrass or tree lines).

 

Overall, similar to other crops in the state, this year’s crop will be plagued by spottiness, where some areas of the state will have a great to average crop while other portions will be meet with challenges.  However, most of this is due to challenges with Mother Nature.  As far as aphids are concerned with this year, we have had several reports of aphids; however, number have been low.  This does not mean the applications are imminent or that populations will crash, solely that growers in these regions should be more proactive in their scouting patterns and visit the site an addition time or two during a week to scout.

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