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Louisiana Rice Notes – May 26, 2020

Louisiana Rice Notes – May 26, 2020 published on No Comments on Louisiana Rice Notes – May 26, 2020
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The newest edition of Louisiana Rice Field Notes is now available. This edition covers hail damage, early heading, sheath blight, and fungicide recommendations. It can be accessed on AgCenter website as a PDF (bit.ly/2ZN2AA0) or web version (bit.ly/2AhZGIO).

Louisiana RIce Notes #2

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A new Louisiana Rice Field Notes is now available. This edition covers the Rice Station virtual field day, crop progress, DD50 heat units and expected harvest time, how to id GR and PD, smut control, and chinch bugs.

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Seedling Cotton Injury

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In the past week, I have looked at a few central Louisiana cotton fields that appeared to have severe thrips injury, yet no adult or immature thrips were present. Thrips are often one of the first factors people attribute to seedling cotton injury. However, several factors can contribute to early-season cotton injury. These include cold temperatures, insect feeding, preemergence herbicides, sand blasting, seedling disease and water stress. Fields planted in April often will experience some form of environmental stress that delays seedling growth and vigor. Severe issues often arise when these factors become additive, such as chilling injury coupled with use of preemergence herbicides. Much of this injury will look very similar to thrips and is easily mistaken as such. This type of injury can lead automatic thrips sprays when they are not warranted.

The key to making thrips rescue sprays is the presence of immatures. When immatures begin to appear, this means the seed treatment has broken and reproduction is occurring. Luckily, thrips numbers appear to be low thus far in 2020 and are primarily composed of tobacco thrips; however, this can quickly change and may differ across the state.  If a rescue spray is deemed necessary, the decision should be made based on the presence of immature thrips and not old thrips damage or other non-insect related damage.

Below are some considerations when deciding what foliar insecticide to use.

Dimethoate:

Positives: Relatively inexpensive, decent efficacy at high rates, less likely to flare spider mites and aphids than acephate.

Negatives: Less effective on western flower thrips, less effective than acephate or bidrin when applied at lower rates.

Acephate

Positives: Relatively inexpensive, effective towards western flower and tobacco thrips.

Negatives: May flare spider mites and aphids if present.

Bidrin

Positives: Effective, less likely to flare spider mites and aphids than acephate.

Negatives: More expensive, less flexibility with applications early season.

Intrepid Edge

Positives: Effective, unlikely to flare spider mites and aphids. Intrepid Edge is a mix of Radiant and Intrepid. Activity is similar to Radiant.

Negatives: Requires the application of two modes of action but only gets the benefit of one.

If you have any questions or concerns please contact your local county agent or AgCenter specialist.

True armyworm head capsule

True Armyworms in Field Crops and Pastures

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In the past two weeks, instances of true armyworms (TAW) in wheat, corn and pastures have increased across the state. TAW are similar in appearance and size to fall armyworm (FAW). TAW possess a mottled brown head capsule (Figure 1) while FAW have an inverted “Y” on their head capsule. TAW develop into six instars, with larval development taking roughly 20 days and generational turnover occurring in 30 days. This insect is not well adapted to hot temperatures, and survival decreases significantly when air temperature is above 86 degrees F. TAW prefer grass hosts but will feed on broadleaves. TAW primarily feed at night, making observation during the day difficult. Larva consume 80% of the total foliage required for development in the last three to five days as larva. Larva congregate at the base of plants and on the soil surface to avoid midday temperatures. There are several natural enemies of TAW in Louisiana field crops. Predacious insects, parasitoids and pathogens occasionally will control TAW populations before a foliar overspray is required

Fig 1. True armyworm head capsule
Fig 1. True armyworm head capsule

TAW infesting Bt corn rarely causes economic injury, and Bt proteins available in field corn work very well controlling TAW. Non-Bt corn can experience significant injury from TAW, and fields should be scouted regularly to avoid defoliation. TAW can graze non-Bt corn to the ground; however, if the growing point is still beneath the soil (up to roughly V5), corn seedlings will recover quickly.

TAW can significantly injure wheat if worms are allowed to defoliate the flag leaf before soft dough or clip wheat heads at any stage. The LSU AgCenter threshold for TAW in wheat is when five worms per square foot are found and foliage loss is occurring.

In hayfields and pastures, TAW can cause significant injury to grass crops if left uncontrolled. TAW injury is identical to FAW, and routine scouting in the spring is recommended. The LSU AgCenter threshold is one worm per sweep.

Pyrethroid insecticides control TAW very well in corn, wheat and pastures. As a general rule, large worms are harder to control than small worms.

If you have any questions or concerns, please contact your local AgCenter agent for more information.

 

 

 

Methods to control corn prior to replanting

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Many producers are having to replant corn due to poor stands. There are three main ways to remove a failed corn stand.

  1. Use tillage equipment to physically remove the existing corn.
  2. Apply 0.0469 lb clethodim/acre and wait six days before planting the second corn crop. That equals 6 ounces of a 1 lb/gal clethodim, 3 ounces of a 2 lb/gal clethodim or 2 ounces of a 3 lb/gal clethodim. Waiting six days before planting is critical to prevent injury.
  3. Apply 0.625 lb paraquat/acre plus atrazine at 1 pint/A or diuron at 1 pint/A or metribuzin at 3 oz/A. Good coverage is essential. Even then, don’t expect outstanding control with this choice.

 

Call 318-308-7225 with any questions.

Louisiana Rice Notes #1 – 2020

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The first edition of Louisiana Rice Notes is now available. This edition covers planting progress, effects of warmer than average March weather on current crop, young rice farmers helping out, and new AgCenter rice publications which are available online.

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Louisiana Rice Notes #3

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A new Louisiana Rice Notes newsletter is now available. This edition covers the recent heavy rainfall and pending storms, nitrogen fertilizer questions, conventional rice following Provisia, Louisiana variety and hybrid trends over the last 18 years.

2019 Louisiana RIce Notes #2

2019 Louisiana RIce Notes #2 published on No Comments on 2019 Louisiana RIce Notes #2

This editions covers the reasons for the poor rice germination and poor stands we are seeing, things to consider prior to fertilizing and flooding, and why fertilizing on dry ground is so important.