Delay nitrogen, delay yield

Jarrod Hardke, University of Arkansas

DR. JARROD HARDKE
ARKANSAS
Asst. Professor/Rice Extension Agronomist
University of Arkansas Cooperative Extension Service
jhardke@uaex.edu

The hot, dry conditions of 2018 were the poster child for difficulty establishing a timely flood to incorporate nitrogen (N) fertilizer. To achieve consistently high yields, timely application and incorporation of preflood N is the most critical input in rice. Luck always helps, of course.

The DD50 Rice Management Program (http://DD50.uaex.edu) is critical for timing preflood N. Originally developed to time midseason N applications, the importance has shifted to the preflood timing as we move more toward heavy preflood N rates.

Under high heat conditions, rice can progress through the optimum preflood N window (three- to five-leaf rice) very quickly (350-550 DD50 units). Depending on the specific cultivar, the final preflood N date ranges from around 600 up to 900 DD50 units. Keep in mind, the final preflood N date is the date by which preflood N should be incorporated. That means the fertilizer has been spread and the field has been flooded.

Be on time

As with everything in rice production, that’s what we’re aiming for, but it doesn’t always work out that way. When we encounter adverse weather that prevents us from applying urea to dry soil prior to flood establishment, the recommendation is to wait for that dry soil condition. However, as we approach the final recommended time to apply preflood N, we need to consider which cultivar we’re growing and the upcoming weather forecast.

aerial fertilizer applicatioin

The final preflood N date — roughly 600-900 DD50 units, depending on cultivar — is the date by which preflood N should be incorporated. That means the fertilizer has been spread and the field has been flooded — photo courtesy Mississippi State University

Generally speaking, all cultivars begin to have reduced yield potential as we pass the final N date. However, the hybrids do not experience as dramatic a drop-off as pureline varieties. So we can technically make competitive yields for longer past the final N date with hybrids while varieties drop off faster – meaning we need to be more timely with preflood N for varieties to maximize yield potential.

As we reach the final N date under adverse conditions, we need to have a plan of action. Recent research has shown that for varieties, a single preflood N approach or a traditional two-way split approach where the preflood applications are made to dry soil are the most efficient.

However, when wet or muddy soil conditions are present, the best management approach for varieties is to use a two-way split application and elevate the preflood N rate by 20-30 pounds N per acre. Under the worst-case scenario where rains put a flood on the field, a spoon-fed approach is less N efficient but can produce similar yields if we make four to five weekly applications of 100 pounds urea per acre. It’s worth repeating that we should never apply the preflood N into a standing flood in a single application.

Nitrogen is one of the greatest expenses in rice production, but it’s also the most directly rewarding. Let’s pay off on that investment by getting the N applied and incorporated on time and under the best conditions possible.

Keep eyes peeled this season for rice planthopper

Dr. Mo Way

DR. M.O. “MO” WAY
TEXAS
Rice Research Entomologist
moway@aesrg.tamu.edu

This month’s topic is right up my alley—BUGS! But first, I want to commend Vicky on last month’s editorial about the great things our U.S. rice industry has done and continues to do in terms of sustainability. This back-burner issue is moving to the front burner as competition for resources and environmental concerns heat-up. To read Vicky’s editorial, visit the Rice Farming website at https://bit.ly/2HCPbS9.

It’s been too wet to work much ground in Texas, but temperatures are becoming more spring-like and Indian paintbrush is beginning to bloom (a long-time rice farmer told me he plants around the time these showy roadside flowers bloom).

Regardless of rice variety, make sure you plant seed treated with an insecticide for rice water weevil (RWW) control. Last year was a bad one for this root-feeding pest. In some of my research plots, RWW caused up to 2,000 pounds-per-acre total yield losses on main and ratoon crops. If you control RWW on the main crop, you will get a yield benefit on both main and ratoon crops.

NipsIt Inside and CruiserMaxx Rice seed treatments will control chinch bugs that normally feed on seedling rice. These insects with piercing-sucking mouthparts can reduce stands. Dermacor X-100, the other labeled insecticidal seed treatment, controls armyworms and stem borers while all three seed treatments control RWW.

Be on the lookout for the rice delphacid or rice planthopper, which is an exotic pest from Latin America. We found it last year in Texas attacking ratoon rice.

My gut feeling is that it will be here again this year and possibly in subsequent years. In 2018, in cooperation with crop consultants and private industry scientists, we found Endigo ZC provided good control of the rice delphacid. We and the Texas Department of Agriculture (thanks to Kevin Haack) submitted a request to the U.S. Environmental Protection Agency for use of Endigo ZC under a Section 18 Emergency Exemption.

planthopper nymphs

Rice delphacid nymphs — photo by Weldon Nansen

EPA recently granted our request, so Texas rice farmers can use this product in 2019 and 2020 to control the rice delphacid if it is found again and is problematic. Many thanks to EPA and TDA for their work/approval.

Endigo ZC is toxic to bees, so we must be mindful of these pollinators if and when this insecticide is applied. The area around rice fields to be sprayed should not harbor any bee-attractive flowers.

EPA has requested farmers mow surrounding areas to remove flowers that are attractive to bees. Don’t worry about flowering grasses, because they are not attractive to bees. Also, bees’ peak foraging activities occur usually during the heat of the day, so spraying early or late can reduce exposure.

We are cooperating with scientists in South America (CIAT/FLAR) to evaluate selected southern rice varieties for resistance/tolerance to the delphacid. In Latin America, the main method of control is resistant varieties.

We also have plans to import seed of resistant varieties from CIAT/FLAR to try to incorporate resistance genes into southern U.S.-adapted varieties. Scientists from the U.S. Department of Agriculture, Louisiana State University and Texas A&M are collaborating in this effort.

Rethinking N management in furrow-irrigated rice

Dustin Harrell, LSU AgCenter rice specialist

DR. DUSTIN HARRELL
LOUISIANA
Extension Rice Specialist
dharrell@agcenter.lsu.edu

The amount of furrow-irrigated or row rice has increased significantly over the past two years. In Louisiana, approximately 2,500 acres of furrow-irrigated rice were grown in 2017. The acres in Louisiana doubled in 2018 to 5,000, and acreage in Louisiana is expected to double again or even triple in 2019.

Acres of furrow-irrigated rice in the Mid-South as a whole could exceed 150,000 in 2019. However, there are still many unanswered questions when it comes to the practice. Nitrogen fertilizer management is probably one of the biggest areas of concern.

Water management of furrow-irrigated rice directly affects N fertilizer efficiency. Soil moisture changes from wet to dry and back to wet again, negatively affecting fertilizer efficiency due to changes in soil N forms and an increased potential for N loss.

Because of this, most furrow-irrigated fields will typically need more N fertilizer than normal flooded rice fields. Research at the H. Rouse Caffey Rice Research Station in 2018 on a silt loam soil compared hybrid and conventional rice grown using furrow irrigation with rice grown using flood irrigation.

The results indicated that furrow-irrigated rice needed approximately 100 pounds more urea than rice grown under a permanent flood. A second research trial found that spoon-feeding 100 pounds of urea three times using seven-day intervals beginning at the four-leaf stage of development was the best application scenario.

row rice louisiana

Photo by Bruce Schultz/LSU AgCenter

A mid-season application (green ring to half-inch internode) would still be applied depending on in-season crop management decisions just like flooded rice. I should point out that this is only one year of data on one soil and by no means is it enough data to establish a best management practice for N use in furrow-irrigated rice.

However, it is a good start and it does confirm, without a doubt, that N fertilizer management is different between the two water management systems. It should also be pointed out that this research was done without holding water at the bottom of the field.

Commercial furrow-irrigated rice where water is held at the bottom of the field and is backed up as the rice gets bigger throughout the year will create different zones in the field.

The flooded zone at the bottom of the field will act like normal flooded rice, the middle of the field may behave more like an AWD (alternate wetting and drying) field, while the top would act like the furrow-irrigated scenario similar to our research described above.

We still have a lot to learn about furrow-irrigated rice and will continue to do research in this area.

Get ready for armyworms

Luis Espino

DR. LUIS ESPINO
UNIVERSITY OF CALIFORNIA
Rice Systems Adviser
laespino@ucanr.edu

Armyworm problems in 2018 were not as severe as in 2015 or 2017. A pheromone trap network was set up to monitor the flight of adult armyworm moths.

The traps give us an idea of when the high populations will occur, but they are not a direct way to measure the infestation level in a field. Last year, armyworm moth catches started to increase in late May, peaked in late June and then reached another peak in mid-August.

In general, the timing is similar every year, but the peak in 2018 was reached approximately 10 days later than the peak we saw in 2017. This may be why problems were not as bad last year; a later peak means plants will be larger when most of the worms reach damaging size, and so plants can withstand more injury.

I did see more armyworms feeding on panicles last year than in 2017, but in most cases, an insecticide application was not needed. The trap monitoring network will be set up again this year.

The key to successful worm management is monitoring. The most efficient way to check for worms is to look for signs of their feeding. As the numbers in the moth traps start increasing, inspect your fields more frequently.

armyworms

Photo by Luis Espino, UCCE Colusa County

Armyworms grow quickly and can defoliate rice in a couple of days. I have heard several stories of growers that were gone for the Fourth of July weekend and came back to severely defoliated fields. Once defoliation is noted, check for worms. If they are present, pull the trigger if the defoliation is more than 25 percent of the plant’s foliage.

Severe defoliation will result in shorter plants that mature faster, potentially reducing yield. During heading, look for blanked panicle branches. In many cases, by the time this injury is noticed, the worms are gone. But if you still find worms and close to 10 percent of the panicles are injured, a treatment is needed.

Insecticide trials conducted last year showed that Intrepid and Dimilin can provide good control, while control with pyrethroids is deficient. Intrepid was used in 2018 because a Section 18 registration was obtained. Hopefully, we can get another Section 18 registration in 2019 to be prepared for outbreaks. Remember that Dimilin has a pre-harvest interval of 80 days, so it can only be used during a June-July infestation.

We may need to vary water weevil control under alternate water strategies

Bobby Golden, MSU

DR. BOBBY GOLDEN
MISSISSIPPI
Extension Rice Specialist
bgolden@drec.msstate.edu

As I write this article (March 20), we are finally seeing sunshine and drying conditions that we have all desperately been wanting. Here in Mississippi, rice planters will more than likely begin to roll Friday or Monday of next week on stale ground.

Despite all the wet weather, we look to be in for an on-time start to 2019.

There’s been a lot of recent interest in rice production systems using water management strategies that do not maintain a continuous flood, such as furrow-irrigated rice or AWD (alternate wetting and drying). So I felt it appropriate to highlight

Read Kelly’s master’s degree work in this article. Read studied under Jeff Gore, Mississippi State University Extension entomologist, evaluating the effects of alternate water management strategies on rice water weevil density and control.

Experiments were conducted in 2017 and 2018 throughout the Mississippi Delta on production fields and in small plots at the Delta Research and Extension Center.

In production fields, Read’s data showed rice water weevil larval densities were greatest in the bottom of the field where standing water was present throughout the growing season.

The uppermost portion of the field that remained relatively dry (never flooded) resulted in the lowest water weevil densities counts. This research suggests rice water weevil control strategies may need to vary with the field grade to maximize net returns based on insect control measures.

rice water weevil

Photo courtesy Mississippi State University

Read’s small-plot research revisited draining of fields for rice water weevil control. Observations from these experiments suggested that draining a field is not an economically beneficial strategy to control rice water weevil larvae. Economic returns were greater in a continuous-flood system compared to that of a drained and reflooded field during years where rice water weevil populations were high.

At low water weevil populations, there was no difference in profitability between continuous flooded and drained plots. This may seem counterintuitive; however, we feel the amount of root pruning from water weevil larvae levels in excess of 20 per core increased the likelihood of drought stress once the field was drained.

Currently, the use of an insecticide seed treatment is recommended to provide effective control of rice water weevil populations and has proven to be the backbone for economical control and protecting rice yields for this important insect pest.