Greetings everyone. This time of the year you can almost bet to see worm pressure in soybeans, peanuts and cotton. So far pressure has been sporadic dependent on rainfall. Never the less worms will come later this month and I want you to be prepared to help your clients. Call me with any questions.

Please see emails below with some more valuable information from Mac Malloy, Agriculture Agent – Field Crops

Sincerely,

Rick Morris – Harvey’s Agronomist

 

Greetings,

I have received reports of Podworm/Corn Earworm (CEW) in maturity group V soybeans at R2 growth stage above threshold levels in parts of South Carolina.  Current moth flight numbers are picking up in black light monitoring traps across the area in NC.  Trap data can be found by clicking here.    (Be sure to select the pest on the left side of screen to see corresponding numbers).  It may be time to pull out the sweep nets (7″-21″”spacing) or beat cloths (> 30″spacing).  Keep an eye out over the coming days for worm activity to pick up in soybean and cotton fields as pressure has been heavy earlier in the season in corn.  Growers are encouraged to use an Integrated Pest Management approach and make applications based on exceeding economic thresholds.   As mentioned in an earlier email, growers may need to be aware of this heavy pressure in Bt cotton as well.  Click here for recommendations on cotton.  It is important to note that recommendations on thresholds for Bt cotton have changed from previous years.  Treatment decisions should be based off of egg counts rather than larvae counts such as in years past.

In flowering soybeans – remember that a soybean plant produces many more flowers than it can convert into pods and seeds.  Recent studies conducted in NC have shown that corn earworm larvae can eat and injure flowers, but that the soybean plant compensates for this loss.  Yield losses were not recorded even with corn earworm levels three times higher than the economic threshold for podding stage soybeans.  There are very few cases when corn earworm larvae should be sprayed in flowering soybeans.

Pyrethroid insecticides are most commonly used to reduce corn earworm numbers below the economic threshold, although several newer chemistries are gaining in popularity (chlorantraniliprole, flubendiamide, indoxacarb and spinosad). Ideally, treatment should be directed to mid-size larvae since control of small larvae is sometimes difficult (they are within flower clusters, terminals, etc) and large larvae may have already caused economic loss. Use the economic threshold calculator found by clicking here to determine if a treatment is needed.

Recently NCSU entomologists have encouraged growers to avoid using pyrethroid insecticides for corn earworm control in soybean. During recent seasons this insect has shown signs of becoming resistant to pyrethroids in the state and across the Southeast. Furthermore, some populations of “corn earworm” in soybeans have recently been found to be composed of mixed populations of corn earworm and tobacco budworm (Heliothis virescens Fabricius). Tobacco budworm has long been resistant to pyrethroids and corn earworm  are showing increase in survival rates in certain populations. Remember, tobacco budworm and corn earworm can not be distinguished apart except by close inspection under a microscope.  Soybeans can be used as a resistance management refuge by using insecticides other than pyrethroids. Thus, growers may help increase the useful life of pyrethroids for use in cotton, where their value for bollworm (corn earworm) is greatest.  However, pyrethroids may be needed if other pest such as stink bug or kudzu bug are present.

Information on other pest in soybeans can be found by clicking here. 

You can familiarize yourself with soybean growth stages by clicking here.

Sincerely,

Mac Malloy

 

A follow-up to the previous email with some clarification.

Defoliators
There are two thresholds for defoliators in soybeans.
1. Early season until two weeks prior to bloom, the threshold is 30% defoliation throughout the entire canopy.
2. Two weeks prior to bloom and throughout the reproductive stages, the threshold is 15% defoliation throughout the entire canopy. 

See photo below for examples of defoliation thresholds.  It is easy to overestimate leaf defoliation. 

DefoliationThresholds

 

 

 

 

 

 

 

 

Common defoliators are armyworms, soybean looper, bean leaf beetle, green cloverworm, velvetbean catepillar, mexican bean beetle, spotted cucumber beetle, blister beetle and others. Loopers tend to feed in the bottom of the canopy.  Corn earworm (CEW) can also cause defoliation in addition to pod feeding. Often times fields will have a mix of pest so use the above thresholds.

Pod and Stems Feeders (CEW and Stink bugs)

Use the available Economic Threshold Calculators.

Corn earworm Economic Threshold Calculator can be found by clicking here


Stink Bug Economic Threshold Calculator can be found by clicking 
here. 

Kudzu Bug Threshold: 1 nymph stage kudzu bug / sweep (i.e. 15 nymphs /15 sweep sample)

Additional notes for proper sampling:
Beat cloth: sample two rows, 3 feet on each side, for a 6 row-foot sample
Sweep net: each sweep should cover 5, 3, or 2 rows of 7 inch, 14 inch, or 21 inch rows, respectively
Rigid beat cloth: sample two 7″ rows simultaneously (side by side rows) or one row if at, or above, 14 inch row width

 

The stink bug calculator can be simplified into the following:

Sweep net (7-21″ rows): Seed production – 2.5 stink bug/ 15 sweeps

                                         Grain production -5 stink bug/ 15 sweeps

Beat Cloth (30-40″ rows): Seed production- 3 stink bug / 6 feet of row

                                         Grain production – 6 stink bug/ 6 feet of row