Arkansas Rice: Disappointing Year for Weed Control

Crop Progress

“I ain’t cut out to be no Jesse James; don’t go writin’ hot checks down in Mississippi; and there ain’t no good chain gang.”  There’s also apparently no good weed control in 2018.  This one has been a year for the weeds.  We’ll get in to that discussion a little more in a minute.

Tables 1 and 2 give a current overview of the outlook for the rice crop development.  Generally speaking, around half of the rice in the state should be to green ring and beyond.  Many midseason applications are currently going out – just remember the 21 days post N incorporation AND green ring rule.  These two conditions are the minimums – don’t get in a hurry.  I feel better even better about 28 days after flood and you have a nice long window after green ring to apply midseason and still get the full benefit.

Perhaps more interesting, and hopefully it plays out this way, is the window of heading.  Hopefully we stay on track for this where most of the rice pollinates before the last two weeks of July.  That and the first two weeks of August are consistently the hottest of the year (Fig. 1).  Avoiding this period will help to ensure heat doesn’t affect pollination.

Our rapid crop development is no stranger to anyone out walking fields.  DD50 unit accumulation (Fig. 2) backs that up as we continue to stay ahead of previous years.  The long-term forecast is for above average temps through August, but maybe we beat the heat.

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Table 1. Percent of acres to reach 1/2″ internode elongation by week. Click Image to Enlarge

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Table 2. Percent of acres to reach 50% heading by week. Click Image to Enlarge

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Fig. 1. Average high and low temperature by week of year, 2008-2017. Click Image to Enlarge

Loyant Injury to Rice

More on Loyant was posted earlier this week here.  To add some clarification to the article, it is NOT recommending a hard dry-up.  But, reducing water levels to a shallow or “soupy” state may aid in rice recovery.

Disappointing Year for Weed Control

“Is everyone else’s rice as grassy as ours?”  If I had a nickel for every time I heard that, I’d have a lot of nickels.  The answer is yes.  The hot and extremely dry conditions through all of May got us where we are now.

Residual herbicides were often not activated due to lack of rainfall or flushing or inability to flush.  Relying strictly on a post-emergence herbicide program in rice is the fast track to poor weed control.  Often when it’s that dry our post-emergence herbicides don’t work well either.

Put it this way – if the weeds are hot and dry then they aren’t growing normally or taking up herbicides as they normally would.  That alone accounts for a lot of control failures.  There are certainly some other issues in there, but that alone explains a lot of it.

Our weed control bill is pretty hefty, especially for a crop that looks like we didn’t spend much.  However, a number of fields I’ve looked at with misses still achieved good control aside from field areas with intense pressure or along edges where coverage is poor anyway.

2,4-D in Rice

The cutoff for 2,4-D applications in rice is ½” internode elongation (IE).  After this, rice plants can be injured by the applications, most often in the form of boots blowing out the side of the stem.

The further past ½” IE you go, the risk and severity of injury increases.  The label has a ½” IE cutoff and a 60-day pre-harvest interval.

Rice Blast Update

Between June 6 and June 21, rice blast has been reported from 5 counties in Arkansas – Lonoke, Randolph, Poinsett, Pulaski, and Lawrence on Titan, Jupiter, and Diamond.  Blast appears to be predominately in blast-prone fields to date.

Fields considered to be blast-prone include fields over-fertilized with nitrogen, low in fertility particularly potassium, with soil types that are difficult to maintain a deep permanent flood, surrounded by thick tree lines more on the east side, and low lying ground in river bottoms or valleys.  Prolonged leaf wetness for more than 9 hours are favorable for sporulation and further blast disease development.  Therefore, dew, fog, shade (tree lines), frequent light rains and overcast conditions are included in the list of favorable conditions for blast disease development.

Scouting for leaf blast in blast-prone fields is highly recommended.  Initial symptoms may not be clear as in Fig. 2.  Look for the diamond-shaped lesions on lower leaves for confirmation (Fig. 3).  When scouting, blast can easily be detected on levees, tree lines more on east side, drier spots in the field, densely or double-drilled field edges, and spots with excessive nitrogen.  It can also be easily detected in open fields with sandier soils that cannot maintain permanent flood.

Planting resistant cultivars being the best management option, leaf blast at earlier stages of rice development can be suppressed by raising the flood depth to at least 4 inches.  Chemical products have been important and effective if applied to protect against neck and panicle blast (Fig. 4).

Neck and panicle blast that may include flag leaf collar blast appear after heading and can cause close to 100% grain yield loss under extreme conditions.  Therefore, the protective fungicides need to be applied at the right recommended timing and frequency.  Fields need to be well managed and a deep permanent flood should be maintained throughout the season to benefit from fungicide applications.

To read more on cultivars, tips to manage blast, and timings and frequency of fungicides go HERE.

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Fig. 2. Initial symptoms of leaf blast.

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Fig. 3. Typical diamond-shaped lesion from leaf blast.

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Fig. 4. Late season neck, panicle, and collar blast with total grain losses.

 

Rice Field Day Scheduled for Friday, August 3

The Rice Field Day at the UofA Division of Agriculture Rice Research & Extension Center is scheduled for Friday, August 3, 2018.  More details will follow.


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