- Author: Luis Espino
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)
2013 Rice Grower Meeting presentation: Winged Willow Primrose
UC Rice Blog posts: New weed identified in California rice, and Behavior of winged primrose willow and herbicide options for control
June 2012 Rice Briefs newsletter: Behavior of winged primrose willow and herbicide options for control
Red rice:
- Author: Luis Espino
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!
- Author: Luis Espino
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.
- Author: Luis Espino
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.
- Author: Luis Espino
- Author: Randall Mutters
The armyworm outbreak we experienced a few weeks ago seems to be over. Several fields in Glenn and Butte counties had very high populations and experienced severe defoliation. In some cases, the affected areas have recovered (see pictures below). However, there are reports that a few fields were defoliated to the water line. As we approach PI and topdressing, it is worth thinking about the likely consequences of the outbreak.
Above, severe armyworm defoliation. Below, same area, 20 days later
Rice has the capacity to recover from defoliation by producing new leaves and tillers. When the main tillers are affected, the plant will try to compensate for the loss in foliar area by producing additional lateral tillers. These tillers will mature later and will delay the maturity of affected areas of the field respect to less affected areas. In these fields, expect uneven grain maturity during harvest.
Nitrogen may help in the recovery of defoliated plants. In some cases, growers have applied nitrogen to the affected areas in an attempt to promote rapid regrowth. However, excess nitrogen can have several undesirable consequences. Excess nitrogen promotes stem rot and blast, diseases that can affect plants all the way until panicle maturity. Also, too much nitrogen can extend the plant's vegetative growth period, resulting in delayed development and uneven grain ripening. When topdressing in the next few weeks, avoid over-fertilizing armyworm affected areas.
In fields that have been severely affected, water management may also be complicated. Flooding periods may have to be extended, and with current water conditions, this will put extra demands on an already stressed water system. If possible, plan on turning off the irrigation and allowing the water to subside instead of draining the field. In fields with heavy clay soils, it is safe to not have standing water (soil still saturated) 24 days after 50% heading (when one-half of the panicles in a field have emerged) without risking yield loss and grain quality.
Be on the lookout for another armyworm infestation by early August. Most years, there is a second population peak during heading. Typical panicle injury consists of blank panicle branches, although sometimes the whole panicle can be blank. What happens is that the armyworm bites the rachis of the branch and the grains in that branch don't fill. Sometimes, armyworm injury can be confused with other causes, such as cold temperature blanking. However, if you look closely at the blanked panicle or branches, you will see a chewing mark where the blanked area begins.
Armyworm panicle injury during heading
Armyworm panicle injury later as seen during grain maturity
Inspect your fields as the panicles come out of the boot – I believe this is when most of the armyworm damage occurs. If after inspecting your field you find that 10% or more panicles are affected, and you can still find armyworms, a treatment might be needed. Monitor your fields constantly to catch those infestations as early as possible.
Small armyworm feeding on rice panicle