This is a question I have gotten recently. Should a N topdress be planned or can it be avoided? Research conducted by Bruce Linquist, UCCE Rice Specialist, has shown that a N topdress is unnecessary if an adequate amount of N is applied at planting. Here's part of an article he wrote earlier this year for Rice Farming Magazine:
Top-dressing N is expensive as it requires an airplane, and the fertilizer is expensive relative to aqua-ammonia. Top-dress N applications are absolutely needed if the plant is N stressed, which typically shows up as yellowing of lower leaves.
That said, I suggest planning so a top-dress N application is unnecessary. Research conducted on-station and on-farm has shown that if an adequate amount of N is applied at planting, a top-dress is not needed to achieve maximum yields.
If you find yourself constantly needing a top-dress N application at PI, you might want to increase your preplant N rate. I don't want you to necessarily take my word on this, but I encourage you to do your own testing to see if this is really necessary. A simple test involves three treatments across a field: (1) standard preplant N rate with no top-dress; (2) standard preplant N rate with top-dress and (3) increased preplant N rate with no top-dress.
The total amount of N in treatments 2 and 3 should be the same, and this will tell you if yield improved with a split. Having treatment 1 in the field lets you know if a top-dress or increased N rate was necessary to begin with. At harvest, use a combine with a yield monitor to test for differences within the treatments.
In addition to the well-known rice weeds we deal with every year, there are a couple of weeds I want to bring to your attention this year. One is an invasive and the other has been with us for a while.
The winged primrose willow was identified in 2011 in several rice fields near Richvale in Butte County. Since then it has spread to several other fields, up to 3.5 miles south of Richvale. Winged primrose willow was recently given an “A” pest rating by CDFA. What this means is that this weed is now considered to be of economic importance and may trigger an enforcement action by the state. Currently, no actions are being considered, but its presence will disqualify a seed field. The rice industry is implementing an outreach, monitoring and control program for winged primrose willow to stop its spread and reduce infestations.
Red rice has been found in a few locations in California over the years. In 2003, its presence was confirmed in six fields. In some of these fields, growers were able to eradicate it. However, since then, red rice has been found in other locations. The exact number of locations currently affected is unknown, but estimates are around 15. At this moment, red rice does not represent a threat to the industry. But if this weed spreads, it can severely impact the rice industry, affecting yields, quality and production costs. To get an idea of its potential impact, just ask any southern rice grower about red rice and you'll get an earful.
UCCE will be collaborating with other organizations and agencies to get information on identification and management of these weeds. We will be sending information out through our newsletters and websites, so make sure to be subscribed. In the meantime, here's a list of links with relevant information on these two weeds.
Winged primrose willow:
UC IPM Website (under Emerging Pests in California)
June 2012 Rice Briefs newsletter: Behavior of winged primrose willow and herbicide options for control
Last month I contributed a small article for Rice Farming Magazine. I used data generated by the UC Weed Project to illustrate the point of how difficult, complicated and expensive weed control can be once herbicide-resistant weeds are established in a field. Well, a very observant PCA noticed that there was a mistake in my example. Here it is: "However, if dealing with ALS-resistant watergrass and propanil-resistant sedges, this program would be a failure. In this case, a more appropriate program may consist of application of a tankmix of Granite GR and Shark at the 2.5 leaf stage of rice, followed by application of a tankmix of Abolish and Regiment at the 5 leaf stage of rice." Obviously, you can't tankmix Granite GR and Shark! What I meant to say was, a same day application of Granite GR and Shark at the 2.5 leaf stage. This base application gave very good control of umbrellasedge and broadleaves, good control of bulrush, but mediocre control of late watergrass. The follow up application of Abolish and Regiment resulted in excellent control of all weeds.
Apologies for the confusion!
Are you looking for continuing education units (CEUs) to complete your renewal application this year for the Department of Pesticide Regulation (DPR)? The UC Statewide IPM Program has several online courses available that can help you get those last few needed credits.
DPR license and certificate holders with last names beginning with M – Z renew this year. Renewal packets must be submitted to DPR before November 19th to ensure that licenses are renewed by January 1, 2016. After that, applications may take up to 45 calendar days to process.
The online courses available from UC IPM that offer units for DPR license renewal include:
- Providing Integrated Pest Management Services in Schools and Child Care Settings (1 unit Laws and Regulations and 1 unit Other)
- Pesticide Resistance (2 units Other)
- Pesticide Application Equipment and Calibration (1.5 units Other)
- IPM – A Solution for Reducing Pesticides/Water Quality: Pesticide Properties (1 unit Other)
- The Impact of Pesticides on Water Quality/Mitigating Urban Pesticide Runoff (1 unit Other)
- Water Quality and Mitigation: Bifenthrin and Fipronil (1 unit Other)
- Herbicides and Water Quality (1 unit Other)
CEUs from the Structural Pest Control Board are also available for most of these courses.
For a list of other approved online or in-person courses, visit the DPR website. UC IPM plans to add additional online courses for 2016, including those available for Laws and Regulations units. For more information about the courses UC IPM offers as well as additional training opportunities and pest management information, see the UC IPM web site.
It is difficult to accurately estimate yield losses due to armyworm damage. Early infestations that injure only foliage can reduce tillering, delay the crop, and cause uneven maturity. Infestations during heading and grain filling injure the panicle, causing blanks and broken panicle branches.
If defoliation was severe, try to estimate the percentage defoliation and what proportion of the field was affected. Many of the affected fields I saw had small areas where defoliation was almost complete, and some areas where defoliation was small. For example, such a field would have 80% defoliation on 90% of the area of the field, and 10% defoliation on the remaining 10% of the area of the field.
For panicle injury, observe the panicles before harvest. Broken branches are relatively easy to spot (see picture below). Grab 10 to 20 panicles and count how many have broken branches. Repeat this in three or four areas of the field, and then transform it to % injured panicles. If more than 10% of the panicles were injured, the action threshold was exceeded and there may be a yield reduction. The higher the % injured panicles, the higher the yield reduction. Research has shown that for every 1% increase in injured panicles, there may be a 0.07% reduction in yield. So, in a field with 10% injured panicles, yield could be lowered by 0.7%.
It's important to keep these estimates, together with any records of insecticide applications and yield, so that if we are in a similar situation next year, the industry can justify a section 18 for the insecticide Intrepid again.