Specialist Speaking

We can only hope recent cold reduced overwintering pests

DR. M.O. “MO” WAY

TEXAS Rice Research Entomologist moway@aesrg.tamu.edu

Southeast Texas experienced a severe cold snap lasting almost a week beginning about Valentine’s Day. The temperatures (both high and low) were well below freezing for several days. Some Texans were still without power and water the week of Feb. 22.

I don’t know how the weather affected our Texas rice farmers, but possibly storage facilities, stored rice and farm equipment may have been damaged. One benefit for stored rice is very cold outside air may have been circulated in storage bins to minimize stored insect pests.

Some of our rice farmers also raise crawfish and cattle, which may have been affected. Southeast Texas has not experienced weather this severe in over 100 years.

Since I am an entomologist, I will make some conjectures concerning the severe weather effects on rice arthropod pests. As you know, I am an applied entomologist — not an evolutionary biologist — so please don’t take my comments as gospel.

This lengthy cold snap may have adversely affected overwintering populations of certain insects that could impact population densities this coming season. The rice water weevil and rice stink bug are native to the southeastern United States. The weevil overwinters as an adult in perennial clump grasses like Paspalum spp., while the stink bug overwinters as an adult in duff on the ground or even under pine bark.

I know the weevil can enter a state of diapause, which can be triggered by day length and temperature. Diapause can cause physiological changes in the insect to allow it to survive adverse conditions.

Some diapausing insects increase the concentration of glycerol in their blood, which acts like an anti-freeze. I’m not sure if the rice stink bug enters diapause in preparation for the winter. In any event, native insects in Southeast Texas have evolved over eons to adapt to our climate.

Thus, I would think these insects may be less affected by the recent cold snap than invasive pests, like the rice planthopper, which hails from the tropics (Central and South America). Maybe this cold snap wiped out any surviving planthoppers in Texas — we can only hope! The same may be said for the channeled apple snail, which is native to Brazil.

Some of you Texas rice farmers also grow soybeans. As you know, the redbanded stink bug has become the major pest of Texas soybeans, and this stink bug originated in South America. Another invasive pest is the sugarcane aphid, which has become a big problem on sorghum in the South; however, this aphid is thought to originate in the African Tropics.

Another Texas rice pest is the Mexican rice borer, which overwinters as a late instar larvae or pupa in rice stubble and weedy grasses. Maybe overwintering populations this year will be reduced, since this stem borer originated in Mexico as its name implies. Only time will tell.

The view from Jeanie and Mo Way’s back porch in Fannett, Texas, Feb. 16, when the temperature was 16 degrees Fahrenheit. Their corgi, Sophie, enjoyed the cold.

That leads me to my last comment: I retire Feb. 26. It’s been a wonderful career working for all you good folks! And the best part of my job has been the farmers, crop consultants and colleagues I have met and cooperated with over 38 years. Thanks for the memories!

Follow these tips to maximize nitrogen fertilization

DR. RONNIE LEVY

LOUISIANA Extension Rice Specialist RLevy@agcenter.lsu.edu

In a water-seeded pinpoint flood system, one-third of the crop’s nitrogen (N) fertilizer needs should be applied during the brief drain period between planting and reflooding. If urea is the fertilizer source, it should be treated with a urease inhibitor product containing the active ingredient N-(n-butyl) thiophosphoric triamide (NBPT), N-(n-propyl) thiophosphoric triamide (NPPT) or Duromide.

The second third of the N fertilizer should be applied one to two weeks later, and the final third by internode elongation (green ring). In a drill-seeded, dry broadcast or water-seeded delayed flood system, two-thirds of the N should be applied immediately before permanent flood.

To maximize N use efficiency, the application should be made on dry ground, and the field should be flooded as soon as possible after the application.

The balance of the N should be applied at internode elongation (green ring) or earlier if deficiency symptoms occur. Furrow-irrigated or row rice may require multiple smaller applications to improve N efficiency due to wetting and drying of the soil. Pre-flood urea fertilizer applications should be applied on dry ground and then flooded immediately to minimize N losses and maximize fertilizer efficiency. When urea fertilizer breaks down, it has the potential to be converted into ammonia gas, which subsequently can be lost to the atmosphere through a process called ammonia volatilization. Ammonia volatilization losses can be significant.

Studies at the AgCenter’s H. Rouse Caffey Rice Research Station have shown that 30% or more of the applied N fertilizer can be lost in a mere 10 days. Typically, volatilization does not start for the first couple of days after application when urea is applied onto dry ground.

However, when urea is applied onto a moist soil or is applied into a standing flood, the urea is broken down quickly and volatilization can start immediately. This significantly increases the potential for larger N losses. Treating urea with one of the urease inhibitors listed above can temporarily protect N from volatility losses when urea is applied onto a dry or moist soil surface. But the protection lasts only half the time (approximately five days) when the urea is applied on a moist soil compared to when it is applied on a dry soil (approximately 10 days).

In a drill-seeded, dry broadcast or water-seeded delayed flood system, two-thirds of the N should be applied immediately before permanent flood.

A urease inhibitor will not provide any protection when the urea is applied into a standing flood. Applications of urea into a standing flood on larger rice having a healthy root system can utilize the urea quickly and prevent losses. Applications of urea into a standing flood on young seedling rice should be avoided.

Adjust seeding rates based on several factors

DR. JARROD HARDKE

ARKANSAS Assoc. Professor/Rice Extension Agronomist University of Arkansas Cooperative Extension Service jhardke@uada.edu

Rice seeding rate recommendations are always a great topic of discussion. We all want to spend the least amount of money on seed while maximizing our return on that investment. While we may not be too far away from being able to “precision plant” rice seed, we’re still very reliant on drills, which have variability in seed placement and spacing.

As a typical reminder, our seeding rate starting points are 30 seed/ft² for pureline varieties (64-80 lb seed/acre) and 10 seed/ft²for hybrids (21-24 lb seed/acre). These recommendations assume a silt loam soil, good seedbed at planting and an optimum planting date, plus the use of insecticide and fungicide seed treatments.

We recommend adjustment to seeding rates based on a number of factors, but one main one is a 20% increase on clay soils, which would be 36 seed/ft² and 12 seed/ft² for varieties and hybrids, respectively.

Ultimately, we’re trying to achieve final stands of 12-18 plants/ ft² for varieties and 5-8 plants/ft² for hybrids. These stands give us the best chance to maximize grain yield. It’s up to the individual to adjust seeding rates based on planting conditions to give the best chance to achieve these final plant stands. Nobody knows your fields and conditions better than you, but these recommendations are an excellent starting point.

Net return is another important way to look at seeding rate rec-

ommendations. Reviewing plot research data across many varieties over the past several years, a few things stand out.

The first thing I notice is that grain yield generally continues to increase as seeding rate increases, even above the standard rates recommended here. The second thing that stands out is that those yield increases above standard seeding rates rarely result in a positive net return — that is, the yield increase doesn’t make up for the added seed cost. So simply planting more seed to squeeze out a little more yield isn’t necessarily worth it.

Having said that, remember there are always situations and field conditions where increasing the seeding rate are going to be worth it. Rough field conditions, for example, easily justify bumping up the seeding rate to avoid low plant stands.

If the weather will cooperate this year, stale seedbed conditions and an optimal planting date will give us the best chance to succeed with efficient seeding rates. Adjusting seeding rates lower than recommended is generally not advised, as we lose any room for error on stand establishment and plant density. But again, individual situations differ. Check out https://riceadvisor.uaex.edu/ to access the Rice Seed Calculator.

Be on the lookout for marshweed

DR. WHITNEY BRIM-DEFOREST

CALIFORNIA University of California Cooperative Extension Rice Adviser Sutter, Yuba, Placer and Sacramento Counties wbrimdeforest@ucanr.edu

Marshweed (Limnophila x Ludoviciana Thieret) is a perennial aquatic weed first officially identified in California rice fields in 1977 in Yuba County. Twelve additional sightings, all in Butte County, were made from 1998 through 2013. The only other place it has been found in the United States is in Louisiana, also in or around rice fields. It is thought to be a hybrid of two common aquarium plants.

In 2019, there were two reports to the UC rice advisors from growers who had found it in their fields. One was in Glenn County, the other in Sutter County.

Although no yield decreases were reported, there was a slow dry-down of the field. We hypothesize that this may be due partially to the nature of this weed, which forms a mat over the soil as the plants die and dry out. There were also higher-than-normal moisture levels reported in the harvester, most likely due to parts of the weed itself being pulled into the combine.

Dr. Albert Fischer, UC Davis weed scientist emeritus, did preliminary work on control in 2011-2013, all under greenhouse conditions. He looked at two timings: young plants approximately 1 inch tall and established plants that had not yet emerged from the water.

The researchers tested field rates of all registered granular products available at the time: Londax (bensulfuron), Sandea (halosulfuron), Bolero (thiobencarb), League MVP (thiobencarb + imazosulfuron), Shark H2O (carfentrazone), Granite GR (penoxsulam) and Butte (benzobicyclon + imazosulfuron). Liquid herbicide formulations were not tested as the weed does not emerge sufficiently from the water to make them effective.

On the young, newly emerged plants, Bolero and League MVP showed 100% control by about four days after application. Butte appeared to provide full control by 18 days after application. Londax and Sandea were slow to act, but by 18 days after application, they were mostly controlling marshweed.

On the established plants, no herbicides controlled marshweed, but Londax and League MVP prevented it from emerging from the water 30 days after application and prevented it from flowering.

Although marshweed does not appear to be a significant problem at this time, it is important to be aware of how weeds are moving between fields. Remembering to clean equipment between fields (if possible), particularly when moving between different ranches or counties, is probably the most important practice.

LUIS ESPINO LUIS ESPINO PHOTOS: SHAUN WINTERTON, AQUARIUM AND POND PLANTS OF THE WORLD, EDITION 3, USDA APHIS PPQ, BUGWOOD.ORG

Figure 1. Marshweed (Limnophila x Ludoviciana) at harvest in a rice field. Note the dried flowers, which indicate that these plants likely went to seed Figure 2. Marshweed (Limnophila x Ludoviciana) at harvest in a rice field Figure 3. Marshweed (Limnophila x Ludoviciana) before flowering Figure 4. Marshweed (Limnophila x Ludoviciana) at flowering