- Editor: Laurie Askew
- Author: Rob Wilson
This year is turning out to be a terrible year for insect problems in the Klamath Basin. The mild winter and warm spring temperatures are perfect for supporting insect pest development. Over the last week I've observed cereal leaf beetle larvae and Russian wheat aphid in winter and spring wheat and barley fields. Most fields have low populations that do not warrant insecticide treatment, but insect populations appear to be building in a few fields. I ran the degree day model for Cereal Leaf Beetle using Tulelake weather data today. Peak egg hatch occurred on May 23rd 2015 and peak larvae emergence is predicted to be June 14th 2015. Almost all eggs from the overwintering generation should hatch by June 25th. Below are pictures of a Cereal Leaf Beetle adult, larvae, and feeding symptoms.
The following link discusses Cereal Leaf Beetle monitoring and control from the Pacific Northwest Insect Management Handbook http://insect.pnwhandbooks.org/agronomic/small-grain/small-grain-cereal-leaf-beetle
CDFA and IREC are cooperating to rear the biological control agent T. Julis this year. Hopefully we will be able to collect enough parasitized Cereal Leaf Beetle to release in Tulelake grower fields this year. If you find parasitized larvae in your fields please notify UC IREC staff so we can obtain a better understanding of the presence of T. Julis in the Tulelake Basin. Contact the Siskiyou County or Modoc County Department of Agriculture for information on transporting hay and grain if you suspect live cereal leaf beetle may be present in the commodity. Also make sure to clean equipment after driving in infested fields.
Russian wheat aphid has been found in a few fields in low numbers. Russian wheat aphid injects a toxin in the plant. This toxin is responsible for the characteristic white longitudinal streaks on leaves shown in picture below. Infested leaves often curl up like a soda straw; curled flag leaf can cause grain heads to be distorted. The following two links describe small grain aphid identification, monitoring, and control. UC-IPM Guidelines for Russian Wheat Aphid http://www.ipm.ucdavis.edu/PMG/r730300211.html Small Grain Aphids- Pacific Northwest Insect Management Handbook http://insect.pnwhandbooks.org/agronomic/small-grain/small-grain-aphid
- Author: Rob Wilson
- Author: Steve Orloff
With the much needed recent rain, we had some time this morning to provide a short update on some of the observations we've made in the crop fields around Tulelake this spring.
Onions
2015 appears to be a terrible year for seed corn maggot damage. The high amounts of organic matter in several fields and warm weather were favorable to high maggot populations. It appears maggots have caused significant damage to many fields, including fields treated with Lorsban. I estimate we lost over 10% of the onion stand at IREC even though the field was treated with the maximum rate of liquid Lorsban applied in-furrow. With this being said, we had a few onion plots that were not treated with an insecticide this spring, and we lost over 90% of the onion stand.
I ran the degree day models for seedcorn maggot and onion maggot today. Seedcorn maggot is nearing the end of the first generation and second generation flies are emerging. Peak onion maggot fly emergence occurred last week, so most fields are susceptible to onion maggot damage this year. This trend stresses the importance of using a preventive insecticide treatment at planting.
On another note, the recent rainy weather and overcast conditions make onions more susceptible to Goal herbicide injury. Growers should keep this in mind when applying postemergence herbicide to seedling onions this week. Delaying applications until sunny weather conditions return is best approach to avoid injury.
Alfalfa
Alfalfa was off to a great start this year with the mild winter, but it wasn't long until many fields went backward. The blue alfalfa aphid, which injects a toxin into the alfalfa plant, is widespread throughout the Basin. Pressure has been especially intense around Tulelake.
Preliminary research trials suggest that the insecticide Sivanto, and the unregistered insecticides Endigo and Transform, were highly effective. Lannate and another experimental insecticide killed the beneficial insects and eventually increased the blue alfalfa aphid, resulting in far more alfalfa damage than even the untreated control plots.
In addition to the blue alfalfa aphid, alfalfa weevil populations have climbed to levels warranting treatment in many fields. The aphid damage, coupled with weevil feed, on top of some hard frosts a couple of weeks ago, have left many fields much worse off than normal, rather than ahead of schedule like one would expect with the mild winter and warm spring. Hopefully, after this cloudy weather clears out we will return to warm sunny days and the alfalfa will get back on track. This sure has been a strange year so far. "Normal" sure sounds nice.
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- Author: Steve Orloff
- Author: Larry Godfrey
- Author: Rob Wilson
As mentioned in a previous posting, the blue alfalfa aphid (BAA) situation in the Klamath Basin this year is unprecedented. To my knowledge, we have never before experienced such high aphid populations on such young alfalfa. There is a lot we don't know about this “new aphid” that invaded last year and has intensified this year. Aphids have been a periodic problem in the past in Tulelake but I believe those aphids were primarily pea aphids rather than this BAA, which injects a toxin into the plant (Figure 1). This BAA in our area and other parts of the state has been extremely difficult to control and perhaps more tolerant of high temperatures. The earliness of the problem this year is probably a reflection of the extremely mild winter weather allowing the aphids to overwinter in the fields, which enabled populations to surge early.
Regardless for the reason for this year's extremely high BAA populations, growers are left scrambling to come up with effective control measures. The combination of high BAA populations and freezing temperatures have left some fields looking scorched and they appear to be going backwards rather than actively growing. Fortunately, the insecticide Sivanto received California registration just in time for our use but regrettably supplies are extremely low due to unexpectedly high BAA populations in the Low Desert areas of Arizona and California and high populations of sugarcane aphids in sorghum in Texas creating a high demand for the product. Effective insecticide options are few and many treatments are only providing approximately 50 – 70 percent control. The concern is that with partial control, the aphid population may rapidly rebound—especially if insecticide treatments kill beneficial insects that ordinarily suppress aphid populations.
Some interesting ideas are being tossed around, and some even tried, to help reduce aphid numbers and damage. We are breaking new ground with this aphid situation and there are a lot of unknowns, but it might be good to discuss the potential effectiveness of these practices based on what has been learned about this aphid and alfalfa growth. We definitely don't have all the answers when it comes to this aphids behavior and the damage it may cause in the intermountain area. You are encouraged to post comments on your experiences (both successes and failures) if you are interested. Just Leave a comment below at the end of this article.
Harrowing: Some have noted that fields that were harrowed a month or two ago appear to have less aphid damage now. If that is the case, it was most likely due to harrowing in the dormant season disrupting aphids that were overwintering in the field or harrowing covering alfalfa with soil and making the plants less attractive to aphids that were flying in. However, harrowing the alfalfa now is likely not to have much of an effect on the high aphid population currently present in fields. In addition, harrowing is likely to damage the alfalfa.
Rolling: Rolling fields now may kill more aphids than harrowing but it is questionable how thorough a job it would do because the roller will likely raise up over the crowns protecting many aphids from the crushing action. However, smashing the new alfalfa growth will damage the plants depleting carbohydrate root reserves, as stored reserves will be used to generate new alfalfa growth.
Sheeping: Grazing alfalfa with sheep can help reduce weevil populations. Weevil eggs are laid in the stems thus grazing has a place for managing this pest. Grazing sheep will obviously consume some aphids as well. However, they do not graze close enough to the ground to provide complete control. Aphids are likely to rebound from grazing, and like crushing the alfalfa with a roller, grazing alfalfa after it has broken dormancy will deplete root reserves and reduce alfalfa vigor. I have heard a report that fields that were grazed over the winter though have significantly lower aphid populations than those that were not. This is most likely due to the hoof action disrupting aphids that were overwintering in the field and consumption of alfalfa foliage with aphids.
Burning: Flaming alfalfa fields in late winter can suppress some weeds and reduce weevil populations. It is likely it would also significantly reduce aphid populations. However, is flaming now recommended? Flaming alfalfa at this stage would kill the aphids but would require large amounts of propane and would similarly deplete alfalfa root reserves needed for vigorous new growth. Flaming may be an option in organic fields—especially to control aphids in “hot spots” (pun intended) to help reduce their spread. Most aphids currently in fields are wingless. They develop wings when populations on plants are very high or when the condition of the alfalfa host plant declines. The winged forms then take flight and move to other areas. Burning around a field to prevent the entry of aphids from adjacent fields would not be effective, as aphids migrate to new fields by flying and would simply fly over burned areas.
Flood Irrigation. Central Valley alfalfa fields are flood irrigated and it does very little there to control the aphids. However, their alfalfa varieties are classified as nondormant and there is alfalfa foliage above the level of the flood irrigation water. However, with our dormant varieties and the severely stunted alfalfa in some fields, flood irrigation water will likely overtop the alfalfa. So flooding may control some of the aphids but will also kill some of the beneficial insects that do not have wings. Some aphids may also become dislodged from the alfalfa, float and survive to re-infest the plants. So flood irrigation may help on some fields and may be worth a try especially if an irrigation is needed soon anyway. Take care not to over-irrigate, which can bring on other problems (water-logged conditions and Phytophthora root rot). Monitor soil moisture carefully and you may want to delay the next irrigation after an early flood irrigation for aphid suppression.
Some fields are being flood irrigated to reduce aphid populations. This will not eliminate the aphids but may help reduce the population depending on the height of the alfalfa and the duration of the flooding. (Photos: Skyler Peterson)
Introducing Lady Bugs. Beneficial insects are extremely important to keep aphid numbers in check. However, releasing ladybird beetles into a field is not likely to have much of an impact. Imported ladybird beetles oftentimes just leave the field where they are released and exceedingly high ladybird beetle populations would be needed to provide measurable control in the highly infested fields we are now observing.
There are no simple silver bullet solutions for controlling the aphid populations now encountered in many Klamath Basin alfalfa fields. Wise use of the most effective insecticides and trying to preserve beneficial insects are the key, but this is not easy to achieve. The cultural practices mentioned above may be partially effective but come at a price of depleting the root reserves. It is a difficult tradeoff—a partial reduction in aphid population and the toxin they inject versus a reduction in vigor from depleting root reserves. It looks like it is going to be a difficult spring and losses will be unavoidable.
There is a lot about the BAA aphid and its recent behavior that we still don't understand. Central Valley alfalfa growers experienced extensive losses the previous two years and Low Desert growers had high BAA levels the last 3 years (including this year); in all cases they had an extremely difficult time controlling the aphid. Some fields were treated as many as three to five times and in some cases growers were forced to use three-way insecticide tank mixes to get acceptable control. Why the aphids are now so difficult to manage is not known. It is not believed to be insecticide resistance because many insecticides that used to control aphids are not working well—it's not the case of just a single mode of action or insecticide that is giving poor control (which is usually the case with insecticide resistance). Many people think that it is just a “numbers game”. The aphid populations are so high that the percentage control that is usually enough with more moderate populations is not adequate for the populations we are dealing with now. Others think we could possibly be dealing with a different biotype of BAA.
Similarly, it is not completely understood why some fields are so heavily infested and neighboring fields are not. This same pattern was observed in the Central Valley. There is no simple explanation like just a difference in varietal resistance. Unfortunately, the dormant varieties we produce here do not have strong BAA resistance. BAA is typically not a problem in dormant alfalfa areas so the varieties are typically not bred for resistance. Also, it is not known why aphid populations are so high in the Klamath Basin and are not in alfalfa fields in central Siskiyou County (Butte, Shasta and Scott Valleys). It is likely due to wind patterns and aphid flights, but no one knows for sure.
We are currently evaluating different insecticides and insecticide combinations at the Intermountain Research and Extension Center. We have only done one initial evaluation so far but it appears there are some new insecticides that show promise. One is registered in another state and will hopefully have California registration next year.
It is difficult to predict what awaits alfalfa growers the rest of this season. BAA are not well adapted to high temperatures and their population typically falls when temperatures reach the mid to high 80's. This BAA does appear to be more tolerant to high temperatures though. Who knows how soon we will get sufficiently high temperatures to suppress the BAA and how much more damage to the alfalfa may occur before those temperatures are reached. Looking forward, I think BAA are likely to be a more common occurrence in the Intermountain area in the future but I think that the devastation we have observed this year is not likely to be repeated anytime soon and is probably the result of the extremely mild temperatures we had this winter. Let's hope so anyway…
Other blogs have been written on this BAA aphid problem in other areas of the state in the Alfalfa and Forage Blog. The links are below. We have learned more about the aphid since these blogs were first written. For example, the BAA is more heat tolerant than was thought.
Aphids Flourishing and Causing Problems in Southern CA Alfalfa
Blue Alfalfa Aphid Continue to be Found in High Populations in Some Locations
They're Back! Be On the Lookout for Early Aphids in Alfalfa and Share Your Observations!
The Blue Alfalfa Aphid: A continuing problem
- Author: Rob Wilson
The 2015 Crop Water Use Table is updated and available on-line on the IREC website. This table is a useful tool to track daily water use for crops grown in the Klamath Basin. Keep in mind values shown in the table are estimates of crop water use and do not reflect soil moisture levels. Growers should regularly check soil moisture by digging or installing soil moisture monitors to determine when fields need irrigation.
As of April 14th, alfalfa, fall planted winter grain, and grass pasture used 2 to 2.5 inches of water since breaking dormancy. Taking into account rainfall for the same period, alfalfa has depleted 1.7 inches of water from the soil and winter grain and pasture have depleted 2 inches of water from the soil. Alfalfa should not require irrigation yet due its' deep root system, but winter grain and pasture are likely running low on soil moisture. I dug in winter grain trials at IREC today and all fields need irrigation ASAP.
Feel free to stop by the IREC office if you need additional information on crop water use, soil moisture monitoring, or irrigation practices.
Use this link to access the web page: Weather, Physical & Biological Data, then click on 2015 Weather at the bottom of the page.
Click on the file below to view the table.
2015 Crop Water Use Table
- Author: Steve Orloff
Tuesday afternoon (3/31) Nick Macy from Macy's Flying Service and IREC Director Rob Wilson looked at some alfalfa fields in the Tulelake area that exhibited poor growth this spring. The severe stunting looked similar to stem nematode—a common occurrence seen in the spring in the intermountain area when alfalfa is just breaking dormancy. Stem nematode damage has been observed in several fields in the intermountain area this spring, but this damage was not stem nematode. Upon closer inspection, the young alfalfa shoots were absolutely covered with aphids. Samples were collected and we examined them under a microscope at IREC and they definitely appeared to be the blue alfalfa aphid rather than pea aphid (Figure 1A & B). Distinguishing between blue alfalfa aphid and pea aphid is important because blue alfalfa aphid actually injects a toxin into the alfalfa stunting plant growth, whereas, pea aphid does not. Therefore, the economic threshold (the aphid population level at which treatment is advised) for blue alfalfa aphid is lower.
The easiest way to differentiate blue alfalfa aphid and pea aphid is to examine the antennae. The antennae of the pea aphid has narrow dark bands at the end of each segment (Fig. 1A), whereas the blue alfalfa aphid has uniformly brown antennae without dark bands (Fig. 1B).
Blue alfalfa aphid has been a HUGE problem in the Central Valley and Low Desert areas of California the previous two years but not this year. This year was wetter so it is believed that a beneficial fungus that is favored by moist conditions that attacks aphids kept the population more in check or beneficial insects were more effective this year for some reason.
Why we have such high aphid populations so early on such young alfalfa is not known. Aphids do overwinter in alfalfa fields in the warmer areas of California but our winters are typically too cold. Perhaps this winter was so mild that the aphids were able to survive in the fields and overwinter and that is why they are back with a vengeance at such high numbers this year. The graph below shows average temperature for the months of November 2014 through March of this year compared with the 30-year average temperatures for the same months (Figure 2).
Every month was significantly warmer than the 30-year average (over the 5 month time period temperatures were 4 degrees warmer). Most people don't recall ever experiencing a winter this warm in this area before. Whether this was mild enough to allow the aphids to overwinter in the alfalfa fields or not is not known, but I'm confident it contributed to the high aphid populations we are observing in alfalfa fields now.
We have had some aphid outbreaks in Tulelake and areas of Lassen County last year but nothing anywhere near this early and probably not this infestation level either. Populations vary considerably among fields. So what should a grower do? I'd recommend scouting fields often to monitor the population. There is no economic threshold for fields this short. The decision whether to treat will have to be somewhat subjective. With the population level observed in many fields we saw yesterday, treatment is clearly needed. You could easily see the damage in many fields without even getting out of the pickup (though getting out on your hands and knees to inspect the plants is imperative). In the heavily infested fields, the knees area on your pants will turn green from all the squished aphids. There are a fair number of beneficial insects in some fields already (lady bird beetle adults and larvae primarily) but they will likely not be able to keep up with this aphid population, which is obviously already holding back alfalfa growth. Remember, this blue alfalfa aphid injects a toxin in the plant that stunts alfalfa growth. So fields with high populations will require treatment soon or the aphids will continue to hold back the growth. Symptoms may be worse in fields recently treated with an herbicide because aphid damage is oftentimes exacerbated on stressed plants.
A difficult question is which insecticide to use. Blue alfalfa aphids have been extremely difficult to control in recent years in other areas and the wrong approach has resulted in fields needing to be treated several times. There are two approaches most likely to be effective.
1) Use an insecticide that is safer and less disruptive to the population of beneficial insects so that although it may not control all the aphids, many beneficial insects survive and their population builds keeping the aphids below damaging levels.
2) Use a combination of insecticides that together are highly effective on aphids providing an excellent initial kill. Although the insecticide combination is lethal to most of the beneficials, the control is hopefully great enough that if the population does eventually resurge, enough time will have lapsed for the beneficials to have recovered.
In other areas, serious problems have arisen when a partially effective insecticide has been used alone that knocks back the aphids but kills most of the beneficials. In this situation, the aphid population has resurged largely unchecked by beneficials and significant alfalfa yield reductions have resulted and/or multiple insecticide treatments were needed.
The best insecticide for Approach 1 above would be to use the newly registered insecticide Beleaf. It has not been widely used on alfalfa yet because its registration is so new and because of a 62 day pre-harvest interval (PHI). Because of its mechanism of action it is safer to beneficials. The drawback is that it is more costly than many alternatives and it does not control weevils if they are present in the field at the same time. The 62 day PHI has been an issue in other areas but there will likely be sufficient time in our area if fields are treated real soon.
A treatment combination that has been effective for Approach 2 above is a tank mix of a high rate of dimethoate with Baythroid or Warrior (or their generic versions). The main drawback of this approach is the possibility of the aphids resurging after treatment and requiring an additional treatment.
There are still a lot of unknowns about these new blue alfalfa aphid infestations in the intermountain area and in other parts of California. Why has this aphid become so difficult to control and why have population levels been so much higher than normal? Since we are finding aphids so early this year does that mean it will be a problem throughout much of the season this year? We don't have a lot of answers yet, but this promises to be an interesting year with the moderate temperatures we have had this winter and we will learn more about the behavior of this aphid under our climatic conditions.
Fortunately, there is interest in new insecticide registrations in alfalfa that look very promising for aphid control. The one that is closest to registration in California is Sivanto by Bayer. This product just completed the 30-day public comment period and is likely to be registered by the middle of this month. Initial results with this product look promising.
While we clearly don't know all the answers about this blue alfalfa aphid infestation, the intent of this blog is to inform you of the problem so it doesn't catch you by surprise and you can take appropriate action (monitor population levels in your field and treat if necessary) to avoid the potential level of damage blue alfalfa aphid can cause.