Revision to Advisory
This is a revision from yesterday's Fruit Advisory. The Table on page two has been updated.
Click on the link to view the advisory newsletter. In this issue, Timing for codling moth has started in all of Southern Idaho. Other pests to watch for are aphids, mites, thrips, and fire blight.
cereal leaf beetle
Last week I found cereal leaf beetle larvae in winter wheat at the UI Parma R and E Center. There were not many, but they are out there. You may want to keep a look out for these pests, especially as spring grains begin to increase in foliage, since they are the preferred host.
colorado potato beetle
Colorado potato beetles were found in volunteer potatoes late last week in the Parma area. So far, only overwintered adults have been observed, and they will do little damage to potatoes. Scouting should begin soon for eggs and for larvae, which can cause considerable damage to commercial potatoes.
BYDV infection in wheat and barley
PNW Pest Alert. Prepared by Juliet M. Marshall, May 9, 2013.
Widespread incidence of Barley Yellow Dwarf Virus (BYDV) – infected winter wheat and winter barley is evident throughout the Magic Valley from Buhl to Murtaugh. Symptoms include yellowing of leaves, stunting of plants both above and below ground (look for small root systems), and irregular heading with small heads in affected plants. Often, the most severe symptoms will occur along field edges and the edges created along the tracks of pivot tires. (Please see pictures.) There may also be a yellowing to a very characteristic reddening of leaves of infected weedy grasses in nearby ditch banks (Fig. 3), which also host the virus and aphids. Additional symptoms may also include notching of the leaf margins, twisting, leaf tip scorch, and abnormal development of emerging leaves.
Yield losses increase with earlier infections, and can approach 100% in severely affected fields, especially in early-infected winter barley. Fall infection occurred in 2012 as large populations of aphids migrating from other crops to newly emerged wheat or barley. Aphids are attracted to lush growth that occurs under irrigation, often leaving plants in dryland corners alone. Those plants emerging earlier or planted earlier were more likely to attract viruliferous aphids. A mild fall led to increases in aphid populations into December before a hard frost reduced their impact and subsequent transmission of virus.
The species of aphids that can carry the BYDV viruses are many, but the most common culprits include Bird cherry-oat aphids and English grain aphids. Greenbug and corn leaf aphids can also transmit the BYDV virus.
The virus strain identified by molecular techniques (by Dr. Alex Karasev, UI virologist in Moscow) was the PAV strain of BYDV, which is efficiently transmitted by the Bird cherry oat aphid (Ropalosiphum padi) and the English grain aphid (Schizaphis avenae). Aphids can pick up the BYDV virus from infected wild and cultivated grasses, volunteer cereals, and corn. The virus spreads only in conjunction with the movement of the aphid vector, and transmission is greater at low temperatures. The virus is not seed-borne.
At this point, reducing crop stress will reduce the effect of the virus on the plant, but yield losses will occur both through reduced grain production as well as reduced test weight. The most effective control is through the use of resistant varieties, but insecticidal seed treatments may reduce the initial spread in fall wheat and barley. Viruliferous aphids will still transmit the virus in the fall before the insecticides kill the aphid, but as the insecticides wear off over time, new invading aphids will continue to transmit virus.
Current aphid populations are very low, and spring wheat and barley should escape early infection. Reducing infection in the fall-planted grain includes adjusted (later) planting dates to avoid peak aphid activity, however, many of the currently infected fields were not planted early, but were simply actively growing during a long fall that had no killing frosts until well into December.
Compendium of Wheat Diseases and Pests, 3rd Edition. APS Press. 2010.
Compendium of Barley Diseases, 2nd Edition. APS Press. 1997.
approaching sugar beet root maggot threshold in Rupert/Paul
The degree day calculator (hosted by the Integrated Plant Protection Center at Oregon State University) for the sugar beet root maggot fly shows that—depending on your location in the Magic Valley—we have accumulated more than 200 degree days since March 1, 2010. Peak flight of root maggot flies should occur after 360 accumulated degree days when the maximum high temperature exceeds 80 degrees F. In the Mini-Cassia area, this usually occurs around the 2nd of June, but with warm weather this year, peak flight in Rupert may occur by midweek next week.
Monitoring flies adjacent to your sugar beet fields using orange sticky stake traps will provide even more useful information regarding the local population densities of flies. The Amalgamated Sugar Company monitors flies with sticky stake traps throughout the Mini-Cassia area and posts the counts on their website: http://www.srcoop.com/ The economic threshold for application of granular insecticides against root maggots is an accumulative total of 40-50 sugar beet root maggot flies per sticky stake trap (the threshold varies depending on your contract price per ton). In the Mini-Cassia area, which historically has had high root maggot pressure, growers should consider an insecticide application 10 days before exceeding threshold captures on sticky stakes. Otherwise, insecticide applications should be made within 10 days before or after reaching the threshold (the closer to the threshold date, the better). Activation of granular insecticides should be accomplished by irrigation as soon after application as possible. See University of Idaho publication CIS 999, IPM Guide to Sugar Beet Root Maggot: http://www.uiweb.uidaho.edu/sugarbeet/insc/sbmaggot.htm
You can monitor degree day accumulation for sugar beet root maggots as follows:
1) Log onto: http://uspest.org/cgi-bin/ddmodel.pl?spp=srm
2) Select “Sugarbeet Root Maggot Bechinski et al. 1990” degree day model from the “Select degree day model….” drop down box at the top of the form
3) In the “Select location” box, select a location in the drop down box best describing your location (e.g. “RUPERT id agmet” in the “Washington, Idaho” box if you want information for a field near Rupert). Make sure to select “None” at the top of the lists in the other two location boxes.
4) Leave the “Or upload your own…” box blank
5) In the “Forecast:” area, enter your zip code or your city, state in the “NWS zipcode/city, state” box, or the location nearest your field from the “or weather.com site” drop down box to the right). This selection forecasts 7 days forward based on the local weather forecast (beyond 7 days the forecast is based on the historical average). The predicted date of peak fly flight will vary depending on the forecast location selected, so pick the one closest to your location. Select “none” to have the forecast based only on the historical average.
6) Select the location nearest your field in the “Select historical average forecast location” area. Your selection here should match, as close as possible, your selection in the “Select location” area above: there may not be an exact match. As above, select “none” in the other two boxes.
7) Make sure the “Table” and “graph” boxes are checked (and the “precipitation” if you want rainfall information) and click the “Calc” button. A table with the current degree day accumulations matching your selection should appear. There should also be a graph near the bottom showing the current year accumulation compared to the historical average for your selections.
Click on the link(s) below for more information about this pest:
- : http://uspest.org/cgi-bin/ddmodel.pl?spp=srm
Onion Thrips – A check of the onion fields at the Malheur Experiment Station and surrounding grower fields showed an average of almost 1 thrips per plant. Most thrips found were adults, but larvae were also observed on several plants. With the warm weather that is forecast for the next 7 - 10 days, thrips populations may build very rapidly. This would be a good time for growers to begin scouting fields for thrips activity.
U-Idaho 2013 potato psyllid and ZC recommendations
Click on the link below to see the 2013 Idaho recommendations for potato psyllids and zebra chip, a brief summary of 2012 findings, and the monitoring plans for 2013.
Recommendations were a collaborative effort of Erik Wenninger, Nora Olsen, Phil Nolte, and Mike Thornton of the University of Idaho; Jeff Miller of Miller Research; Andy Jensen of the Idaho, Washington, and Oregon Potato Commissions.
Click on the link(s) below for more information about this pest:
Scab and Fireblight
Apple scab infections also can occur when leaf wetness extends for as little as six hours in temperatures around 70 degrees. Southern Idaho has not had large outbreaks of scab over the past several years due to the reduction of overhead sprinkler use. If you have had a bad scab year in the past two or three years you might consider treating your trees this week and changing your irrigation system in the future.
Fire Blight infections occur when leaf wetness or high humidity accompany a temperature around 65 degrees or higher for a 24 hour period. The forecast of thunderstorms and moderate temperatures this coming weekend could prove dangerous for your trees. Forecasts rate the likelihood of infection as EXTREMELY HIGH. Have an antibiotic such as serenade or agri-mycin on hand. Homeowners can use blight ban or Mico-shield. If you do not choose to control fire blight at this time monitor very closely for new infections and prune them out. They usually show up within 7 to 14 days.
In both cases young trees are more susceptible than older trees. And young flowers are more susceptible than older flowers.